INFLUENCE OF WELDING AND HEAT TREATMENT ON ALUMINUM ALLOYS A Thesis Presented
Transcript of INFLUENCE OF WELDING AND HEAT TREATMENT ON ALUMINUM ALLOYS A Thesis Presented
INFLUENCE OF WELDING AND HEAT TREATMENT ON
ALUMINUM ALLOYS
A Thesis
Presented to
The Graduate Faculty of The University of Akron
In Partial Fulfillment
Of the Requirements for the Degree
Masters of Science
Eric B. Hilty
May, 2014
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Eric B. Hilty
Thesis
_______________________________ ______________________________ Co-Advisor Dean of the Graduate School Dr. T.S. Srivatsan Dr. George Newkome
_______________________________ Department Chair Dr. Weislaw K. Binienda
_______________________________ ______________________________ Advisor Dean of the CollegeDr. Craig C. Menzemer Dr. George Haritos
Approved: Accepted:
_______________________________ ______________________________ Committee Member Date Dr. Anil K. Patnaik
INFLUENCE OF WELDING AND HEAT TREATMENT ON
ALUMINUM ALLOYS
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ABSTRACT
The welding of structural materials, such as aluminum alloys 6063, 6061 and
6005A, does have an adverse influence on the microstructure and mechanical properties
at locations immediately adjacent to the weld. The influence of heat input, due to
welding and artificial aging, was investigated on aluminum alloy extrusions of 6063,
6061 and 6005A. Uniaxial tensile tests, in conjunction with scanning electron microscopy
observations, were done on the: (i) as-provided alloy in the natural temper, (ii) the as-
provided alloy artificially aged, (iii) the as-welded alloy in the natural temper, and (iv)
the as-welded alloy subject to heat treatment. The welding process used was gas metal
arc (GMAW) with spray transfer at approximately 140 - 220 amps of current at 22-26
volts. The artificial aging used was a precipitation heat treatment for 6 hours at 360oF.
The aluminum alloys of the 6XXX series contain magnesium (Mg) and silicone
(Si) and are responsive to temperature. Optical microscopy observations revealed the
influence of artificial aging to cause change in both size and shape of the second-phase
particles present and distributed through the microstructure. The temperature and time of
exposure to heat treatment did cause the second-phase particles to both precipitate and
migrate through the microstructure resulting in an observable change in strength of the
material.
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Uniaxial tensile tests were conducted for desired specimen thicknesses for sake of
comparison. Section 6.4.2-2 of the 2010 Aluminum Design manual discusses provisions
for mechanical properties of welded and artificially aged aluminum light poles, fabricated
from aluminum alloy 6063 and 6005A. A basis for these provisions was the result of
older round – robin testing programs [2, 3]. However, results of the studies were never
placed in the open literature. Hence, the focus of this study was to determine the
expected mechanical properties of welded and artificially aged 6063, 6061 and 6005A
aluminum alloys and publish the results. Tensile tests revealed the welded aluminum
alloy to have lower strength, both yield and ultimate tensile strength, when compared to
the as-received un-welded counterpart. The impact of post-weld heat treatment on tensile
properties and resultant fracture behavior is presented and briefly discussed in light of
intrinsic microstructural effects and nature of loading.
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ACKNOWLEDGEMENTS
I would like extend abundance of thanks and appreciation to Mr. Stephen Gerbetz
(Engineering Technician Sr., Department of Mechanical Engineering) for his
understanding and timely assistance with resolution heat treatment, and to Mr. David
McVaney (Engineering Technician Sr., Department of Civil Engineering) for much
needed help in using the infrastructure (test machine) for purpose of mechanical testing.
The aluminum alloy used in this research study was provided by Hapco, Inc. I would like
to thank Hapco for providing me with the materials and opportunity to carry out this
research experiment.
The support provided by my advisor Dr. Craig Menzemer (Associate Dean,
Engineering Deans Office) has been a tremendous help throughout my graduate
experience. With his advice and guidance, I have learned a tremendous amount of
engineering and life skills that will help me throughout my career. In addition I would
like to express my gratitude to my co-advisor Dr. T. S. Srivatsan (Professor, Department
of Mechanical Engineering) for his resources and guidance in furthering my research
study to a higher level of success.
With guidance from my parents Roger and Linda Hilty and all the faculty and
professors it has been a great experience obtaining my graduate degree, and I would like
to express my thanks and appreciation in return.
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TABLE OF CONTENTS Page
LIST OF TABLES..…………………………………………………………………….viii LIST OF FIGURES………………………………………………………………………ix CHAPTER I. INTRODUCTION…...............................................................................................1
1.1 Background………………………………….…………………………….1
1.2 Research Significance……………………………………………………..1
1.3 Research Objective.…………...…………………………………………..3
II. LITERATURE REVIEW…………………………………………………………5
2.1 Background of Aluminum Alloys….……………………………………..5
2.2 6XXX Series Aluminum Alloys…………………………………………..6
2.3 Welding and Heat Treatments……...……………………………………..7
III. MATERIALS AND PROCEDURES ……………………………………………..9
3.1 Test Specimen Preparation………………………………………………..9
3.2 Heat Treatment…………………………………………………………...10
3.3 Mechanical Testing…………………………………………………...….11
3.4 Microstructure Characterization…………………………………………11
3.5 Failure-Fracture-Damage Analysis………………………………………12
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IV. RESULTS AND DISCUSSION…………………………………………………13
4.1 Microstructure Analysis………………………………………………….13
4.2 Tensile Response and Properties………………………………………...25
4.2.1 Stress vs Strain: as-provided alloy……………………………….28
4.2.2 Stress vs Strain: as-welded alloy…………………………………31
4.2.3 Stress vs Strain: Solution Heat Treatment Comparison………….34
4.2.4 Unusual Tensile Strength Values………………………………...35
4.3 Tensile Fracture Behavior………………………………………………..38
4.3.1 As-Received Parent Metal……………………………………….38
4.3.2 As-Welded……………………………………………………….48
4.3.3 Mechanisms Governing Tensile Fracture………………………..58
4.3.4 Kinetics Governing Stress-Material Response…………………..60
V. SUMMARY OF CONLUSIONS………………………………………………..62
5.1 Conclusions………………………………………………………………62
REFERENCES…………………………………………………………………………..65
APPENDIX………………………………………………………………………………67
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LIST OF TABLES
Table Page
1. Nominal Chemical Composition of 6XXX Series Aluminum Alloys [4]………...6
2. Aluminum Alloy 6005A Tensile Strength………………………….……………36
3. Aluminum Alloy 6061 Tensile Strength……………………………...….………37
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LIST OF FIGURES
Figure Page
1. Weld Removal……………………………………………………………….……9
2. Final Tensile Shape……………………………………………………………..…9
3. Light optical micrographs of the as-welded aluminum alloy 6063-T4: (a) Base metal, (b) Region of the weld pool, and (c) At the boundary between the base metal and weld pool……………….….………………......…………………..….15
4. Light optical micrographs of the post weld heat treated aluminum alloy 6063 (a) Distribution of both coarse and intermediate size second-phase particles in the base metal, (b) Distribution of second-phase particles in the region of the heat affected zone, (c) Fine recrystallized grains in the weld pool, and (d) Microstructure at the weld-pool-base metal interface………………………..….16
5. Light optical micrographs of the post weld heat treated aluminum alloy 6063: (a) Fine recrystallized grains at the region of the weld, (b) High magnification observation of (a) showing both size and morphology of the fine grains………..17
6. Light optical micrographs of the post weld heat treated aluminum alloy 6063: (a) boundary of the weld, and (b) at the toe of the weld pool……………………17
7. Light optical micrographs of aluminum alloy 6005A-T4 showing microstructure of the following: (a) Coarse and intermediate second phase particles in the base metal of the as-received or as-provided metal (b) High magnification observation of (a) (c) Distribution of intermetallic particles in the heat treated sample. (d) High magnification observation of (c)………………………………...…………19
8. Light optical micrograph of the base metal 6061 showing fine grains of varying size and shape: (a) Grain size and morphology in the weld pool in the as-received metal (b) High magnification observation of (a) (c) Weld pool in the as-received plus heat treated metal (d) High magnification observation of ( c)……….……..20
9. Light optical micrographs of AA6061 showing the following: (a) Microstructure at the weld-base metal interface of the as-received Aluminum alloy 6061-T4, (b) High magnification observation of (a), (c) Microstructure of the weld-base metal interface in the as-received plus heat treated aluminum alloy 6061, (d) High magnification observation of ( c)………………………………………….……..21
10. Light optical micrographs of AA6061 showing the following: (a) Distribution of intermetallic particles in the base metal adjacent to the weld bead, and (b) Microstructure of the weld pool of the heat treated alloy……………………......22
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11. Light optical micrographs of aluminum alloy 6061 showing: (a) Weld bead-base metal interface of the as-received alloy, (b) High magnification observation of (a)………………………………………………………………………......…….22
12. Light optical micrographs of aluminum alloy 6005A-T4 showing: (a) Coarse and intermediate second phase particles in the base metal of the as-received or as-provided metal (b) Region or location of the weld bead in the as-welded aluminum alloy 6005A-T4 (c) Microstructure at the interface of the weld bead and base metal, in as-welded metal. (d) Microstructure showing second phase particle distribution in the as-received metal that was subject to heat treatment………………………………………………….…………………...…24
13. Light optical micrograph of the base metal showing fine grains of varying size and shape of the heat treated aluminum alloy 6005A………………………....…25
14. AA6063 1/4” thick specimen, as-received vs as-received heat treated……..…...28
15. AA6063 3/8” thick specimen, as-received vs as-received heat treated……....….28
16. AA6061 1/4” thick specimen, as-received vs as-received heat treated………….29
17. AA6061 3/8” thick specimen, as-received vs as-received heat treated………….29
18. AA6005A 1/4” thick specimen, as-received vs as-received heat treated………..30
19. AA6005A 1/8” thick specimen, as-received vs as-received heat treated………..30
20. AA6063 1/4” thick specimen, as-welded vs post weld heat treated……………..31
21. AA6063 3/8” thick specimen, as-welded vs post weld heat treated……………..31
22. AA6061 1/4” thick specimen, as-welded vs post weld heat treated……………..32
23. AA6061 3/8” thick specimen, as-welded vs post weld heat treated……………..32
24. AA6005A 1/4” thick specimen, as-welded vs post weld heat treated…………...33
25. AA6005A 1/8” thick specimen, as-welded vs post weld heat treated………...…33
26. AA6005A 1/8” thick specimen, as-received vs ARHT vs solution heat treatment with PHT………………………………………………………………………....34
27. AA6005A 1/8” thick specimen, as-welded vs PWHT vs solution heat treatment with PWHT………………………………………………………………………34
28. Scanning electron micrographs of the tensile fracture surface of as-received aluminum alloy 6063 in the T4 temper, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing non-linear nature of macroscopic cracks, (c) Isolated pockets of striations on the transgranular fracture
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surface, (d) Observable population of voids of varying size intermingled with dimples…………………………………………………………………..……….39
29. Scanning electron micrographs of the tensile fracture surface of the heat treated aluminum alloy 6063-T4, showing: (a) Overall morphology of failure normal to far field stress axis, (b) High magnification observation of (a) showing population of voids of varying size intermingled with isolated microscopic cracks, (c) High magnification observation of (b) showing the nature and morphology of voids covering the transgranular fracture region and void coalescence to form microscopic crack, (d) Voids of varying size intermingled with dimples on overload fracture surface…………………………………………………………40
30. Scanning electron micrographs of the tensile fracture surface of as-received aluminum alloy 6061-T4, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by observable population of voids and dimples, (c) High magnification observation of (a) showing size and morphology of the voids, (d) The overload fracture surface, features give no indication of likely micro failure mechanism…………………………………………………………………...…..42
31. Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6061-T6, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction……………………………………………………….…43
32. Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6061-T6, showing elongated dimples indicative of shear and locally occurring ductile failure………………………………….……44
33. Scanning electron micrographs of the tensile fracture surface of as-received aluminum alloy 6005A in the T4 temper, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing nonlinear nature of macroscopic crack surrounded by observable population of voids and dimples, (c) High magnification observation of (a) showing size and morphology of the voids, (d) The overload fracture surface, features give no indication of likely micro failure mechanism………………………………………………………………..46
34. Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6005A in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with
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highly shallow dimples, (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction…………………………...….47
35. Scanning electron micrographs of the tensile fracture surface of the as-welded aluminum alloy 6063-T4, showing: (a) Healthy population of voids of varying size on tensile fracture surface, (b) High magnification observation of (a) showing nature and morphology of the voids, (c) Healthy population of voids and dimples, (d) Microvoid growth during far field loading and coalescence to form a fine microscopic crack………………………………………………………………..49
36. Scanning electron micrographs of the tensile fracture surface of the as-welded and heat treated aluminum alloy 6063, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing the nature, morphology and distribution of voids covering the transgranular fracture regions, (c) Voids and shallow dimples covering the overload fracture surface…………………………50
37. Scanning electron micrographs of the tensile fracture surface of as -welded aluminum alloy 6061 in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, ( c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction……………………………………….….52
38. Scanning electron micrographs of the tensile fracture surface of post weld heat treated aluminum alloy 6061, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing a healthy and observable population of voids and shallow dimples adjacent to the intergranular crack, (c) High magnification observation of (b) showing size, morphology and distribution of the voids, both macroscopic and fine microscopic, (d) The presence of voids and void coalescence to form macroscopic crack in the region immediately prior to overload……………………………………………………………………….53
39. Scanning electron micrographs of the tensile fracture surface of post weld heat treated aluminum alloy 6061, showing fine ripples or striations- like featuring reminiscent of locally occurring micro plastic deformation……………………..54
40. Scanning electron micrographs of the tensile fracture surface of as-welded plus heat treated aluminum alloy 6005A in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction…………………………………………..56
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41. Scanning electron micrographs of the tensile fracture surface of aluminum alloy 6005A in the T4 temper and as-welded condition, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing a healthy and observable population of voids and shallow dimples adjacent to the intergranular crack, (c) High magnification observation of (b) showing size, morphology and distribution of the voids, both macroscopic and fine microscopic, (d) The presence of voids and void coalescence to form macroscopic crack in the region immediately prior to overload……………………………………………57
42. Schematic showing the formation of void sheets between expanding or growing voids leading to void-void interactions and eventual coalescence………………60
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CHAPTER I
INTRODUCTION
1.1 Background
Structural aluminum alloys have been used in more applications in recent years
because these materials are strong, lightweight and cost efficient. Many products are
being fabricated from 6XXX series aluminum alloys due to their ability to be extruded,
welded, and possess a natural resistance to corrosion [2, 7-10]. The use of these
aluminum alloys does bring an aspect to engineering. This is because they are sensitive
to temperature when subject to welding and heat treatment, and the resultant change in
mechanical properties must be accounted for in engineering design. Understanding the
weldability of these materials is important in order to make the most efficient use of the
materials. It is uncommon for a material to be welded and have no effect on its
microstructure and strength [1]. However, precipitation heat treatment can reduce the
effects of welding on the parent metal.
1.2 Research Significance
One particular product of interest is welded aluminum light poles. Section 6.4.2-2
of the 2010 Aluminum Design manual discusses mechanical properties of welded and
artificially aged aluminum light poles [1]
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1) For lighting poles fabricated from 6005 aluminum that are less than or equal
to 0.25 in thick, welded in the T1 temper with 4043 filler and subsequently
artificially aged to the T5 temper after welding, mechanical properties of the
base metal within 1.0 in of the weld shall be taken as 85% of the un-welded
6005-T5.
2) For lighting poles fabricated from 6063 aluminum that are less than or equal
to 0.375 in thick, welded in the T4 temper and subsequently artificially aged
to the T6 temper after welding, mechanical properties of the base metal within
1.0 in of the weld shall be taken as 85% of the un-welded 6063-T6.
Basis for these provisions was the result of older round – robin testing programs [2, 3].
However, results of the studies were never placed in the open literature. Aluminum
alloys 6063, 6061, and 6005A will be referred to throughout this manuscript as AA6063,
AA6061, and AA6005A.
The use of an appropriate precipitation heat treatment for extrusions of AA6063,
AA6061, and AA6005A will enable the alloys to achieve an optimum combination of
mechanical properties. The precipitation heat treatment used was similar to that
presented for MgSi-containing aluminum alloys; as specified in ASTM B918-01, which
was 6 hours at 360o F [5]. The precipitation heat treatment process is especially
important for welded aluminum alloys in an attempt to reduce or minimize residual
stresses that tend to form during cooling of the weld while concurrently improving
properties. Materials that are heated to the molten temperature experience changes in
their microstructure. The subsequent rate at which the material cools has a direct
influence on its microstructure and resultant mechanical properties, particularly strength
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and ductility. An example of this is when steel is heated to its molten temperature of
approximately 2550° F. When the steel is cooled fast, the micro carbon structure creates
a microstructure that is hard, brittle and easily susceptible to cracking by hydrogen during
solidification. When this occurs, the steel tends to become brittle and contains many
points of “local” stress concentration that tend to promote fracture during loading.
Arc welding does require a great deal of heat input in an attempt to get the
materials to fuse together. After the chosen material is welded, it gradually cools
depending on the temperature of the room and/or the immediate surroundings. Welding
of these alloys often causes an adverse effect on overall mechanical response of the
material due to intrinsic metallurgical changes in the zones that are heat affected. The
AA6063 and AA6061 are commonly welded in the T4 temper, i.e. 6063-T4 and 6061-T4,
and AA6005A is commonly welded in the T1 temper, i.e. 6005A-T1. Subsequent to
welding these alloys are precipitation heat treated to get an alloy whose temper is
comparable to the T5 and T6 temper, i.e. 6063-T6, 6061-T6, and 6005A-T5 [6].
1.3 Research Objective
Investigation of specific influence of heat treatment on the welded aluminum
alloys is needed in order to have a better understanding of their structural behavior when
subject to loading. The focus of this study was to determine the expected mechanical
properties of welded and artificially aged AA6063, AA6061 and AA6005A and publish
the results. Each alloy was tested in different thicknesses, with the prime objective of
determining the results of post weld heat treatment (PWHT) tensile strength. AA6063,
AA6061 and AA6005A were tested in conjunction with light optical microscopy
observations for the following:
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(i) The as-provided alloy, i.e., 6063-T4, 6061-T4, and 6005A-T1
(ii) The as-provided alloy artificially aged, i.e., 6063-T6, 6061-T6, and 6005A-T5
(iii) The as-welded alloy welded in the natural temper, and
(iv) The welded alloy that was subject to post weld precipitation heat treatment.
Multiple tensile tests on each specimen were conducted in order to provide both
substantial and valuable evidence of material behavior. The values of strength are
compared with the typical values documented in the published literature in order to
establish differences, if any, in both material and structural behavior. The main objective
is to increase understanding of process-property relationship of welded and heat treated
6XXX series aluminum alloys.
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CHAPTER II
LITERATURE REVIEW
2.1 The Background of Aluminum Alloys
Pure aluminum itself is not very strong, soft and ductile, and light in weight.
Mechanical and physical properties of pure aluminum can be changed by the addition of
other elements such as copper, magnesium, and silicon. The addition of other elements is
typically less than a few percent of the total solution. The benefit of producing these
aluminum alloys is to enhance their properties and provide alloys with different
properties useful for various products and applications.
The use of aluminum alloys in structural applications has primarily been to
decrease weight and improve corrosion resistance [9]. The aerospace industry has used
aluminum alloys in an attempt to design aircrafts that are faster and more fuel efficient.
The first use of aluminum alloys in airplanes was in the early 1900’s. At this time copper
was being used to strengthen the alloy. The use of copper led to the development of the
commonly used 2XXX series aluminum alloys (Al-Cu-Mg). However the weldability of
these alloys was insufficient at the time and the alloys could not be used with confidence
in structurally welded applications. The addition of magnesium and silicon led to the
formation of 6XXX series aluminum alloys (Al-Si-Mg) [20]. Zinc was added to spark the
creation of 7XXX series alloys (Al-Zn-Mg-Cu). All of these alloys are
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precipitation heat treatable as a means to strengthen. Different heat treatments are used
to change the alloy temper depending on the desired material properties needed.
2.2 6XXX Series Aluminum Alloys
Compared to pure aluminum, aluminum alloys contain solute additions that effect
grain structures and the microstructures within the grains (Table 1). The occurrence of
this allows the alloys to respond differently to working and heat treating. The properties
of 6xxx Al-Mg-Si alloys have been known to be influenced by the precursor phases to the
equilibrium Mg2Si (β) [19]. With copper in many 6xxx series alloys additional hardening
phases appear [20]. The appearance of these phases makes the alloys temperature and
time sensitive when aging. This can make predicting strength and material properties
difficult. The 6XXX series alloys have better corrosion resistance and slightly higher
strength compared to 2XXX series alloys. A major benefit to the 6xxx series alloys is the
extrudability due to the addition of silicon.
6063 6005A 6061% % %
Al Max 97.5 96.65 - 98.95 95.8 - 98.6Cr Max 0.1 0.0 - 0.3 0.04 - 0.35Cu Max 0.1 0.0 - 0.3 0.15 - 0.4Fe Max 0.35 0.0 - 0.35 Max 0.7Mg 0.45 - 0.9 0.4 - 0.7 0.8 - 1.2Mn Max 0.1 0.0 - 0.5 Max 0.15Si 0.2 - 0.6 0.5 - 0.9 0.4 - 0.8Ti Max 0.1 0.0 - 0.1 Max 0.15Zn Max 0.1 0.0 - 0.2 Max 0.25
Other, each Max 0.05 Max 0.05 Max 0.05Other, total Max 0.15 Max 0.15 Max 0.15
Table 1: Nominal Chemical Composition of 6xxx's Series Aluminum Alloy [4]
Element
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2.3 Welding and Heat Treatment
Welding of aluminum alloys has been known to be difficult and result in a
decrease in strength near weld heat affected zones (HAZ). The most common process for
welding aluminum alloys is gas metal arc welding (GMAW) with spray transfer. Spray
transfer allows many small drops of filler metal to spray across the arc from the electrode
wire to the base metal. This results in a larger weld puddle therefor limiting the possible
weld positions to only lap joint and fillet welds. Shielding gas used for GMAW of
aluminum is commonly argon and argon/helium mixture.
When welding metals it is important to prepare the base metal removing any
contaminants before welding. Oxide layers on metals can contain many contaminates,
that if not removed will result in poor weld quality and decreased material strength.
Aluminum oxide layers are often strong and must be removed using an abrasive
technique such as a wire brush. The melting point of aluminum oxide is 3700o F, while
the melting point of the base material underneath the oxide layer is 1200o F. If the
material is not properly prepared before welding, particles from the oxide layer that have
not melted will be deposited within the weld causing discontinuities in the material
microstructure. Weld cracking may occur when welding aluminum due to the fact that
aluminum dissipates heat quickly. Preheating can be used to prevent cracking and cold
welds.
Aluminum alloys start as constituents in solution. Quenching is used in order to
keep the elements in the solution from migrating to fast through the microstructure. After
quenching, aging occurs over a period of a few days at room temperature until the alloy is
in its natural temper. Following the natural aging of the alloy artificial aging is used to
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obtain different temper designations, often referred to as precipitation heat treating. The
material tempers are sensitive to time and temperature of artificial aging. The process of
precipitation heat treating allows second phase particles to precipitate from the material
matrix [18]. In most metals this process is a means of stress relieving and strengthening.
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CHAPTER III
MATERIALS AND PROCEDURES
3.1 Test Specimen Preparation
The tensile test specimens were prepared consistent with ASTM standards for
sheet tensile samples [5]. Each of the aluminum alloys tested were cut from extruded
sections for sake of testing the alloys. The samples were first cut into one inch wide strips
with the extrusion direction perpendicular to the width. Once all samples were cut, some
were selected to be welded in order to obtain heat affected samples. After the welds were
placed, the weld joint was machined off of the sample leaving only the parent metal with
a heat affected zone. (See Figure 1) The machine used to remove the welds from the
samples was a Bridgeport vertical hand mill. After welds were removed, each sample
was then cut into its final tensile test shape using a Haas CNC router for accuracy. A
desired quantity of welded and un-welded samples was then selected to be heat treated
prior to testing.
Figure 1: Weld Removal Figure 2: Final Tensile Shape
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3.2 Heat Treatment
The heat treatment process was selected from ASTM B918-01 [5]. This
precipitation heat treatment is often referred to as artificial aging (PHT or PWHT - Post
Weld Heat Treatment), and the treatment consisted of soaking the material at
approximately 360° F for 6 hours and subsequently allowed to cool in the oven.
Aluminum alloys start with constituents in solution before aging. Artificial aging can
then be used to precipitate second phase particles (Mg2Si) to change the aluminum alloy
from a natural temper (i.e. 6063-T4) with a typical ultimate strength of 25.0 ksi, to a
higher temper, such as 6063-T6 with a typical ultimate strength of 35 ksi. The un-welded
materials used were artificially aged to a T6 temper for 6063 and 6061 parent metal tests
and a T5 temper for the 6005A parent metal tests. The welded materials were artificially
aged (PWHT) to obtain post weld heat treated samples with expected properties to be
similar to that of 6063-T6, 6061-T6, and 6005A-T5.
A few selected samples of 6005A were re-solution heat treated prior to the
precipitation heat treatment. The re-solution heat treatment (SHT – Solution Heat
Treatment) was selected from ASM Handbook, Volume 4, Heat Treating [6]. This
treatment process was at 985o F for 1 hour and rapidly quenched in 60/40 (water/glycol)
mixture. The purpose of this heat treatment was to obtain the aluminum alloy in solution
and allow the second phase particles to precipitate naturally for the welded and un-
welded samples. Following the solution heat treatment, the same samples were
precipitation heat treated to obtain 6005A-T5. The benefit of this test was to compare
strength properties of welded 6005A re-solution and precipitation heat treated samples to
that of PWHT 6005A samples.
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3.3 Mechanical Testing
Each test specimen was placed in a mechanical test machine (Model: Baldwin
Materials Testing Equipment: Warner & Swasey 300 HV-300.000 lb) and deformed to
failure in uniaxial tension. A Class B extensometer was fixed at the gage section of each
test specimen to obtain the axial strain during loading. The data from each tensile test
was recorded on a PC-based Data Acquisition System and used to create the stress versus
strain curve for the specific test specimen. The stress versus strain curves were used to
both understand and compare the strength values and behavior of the aluminum alloy
specimens. Multiple tensile tests were conducted on each specimen type, i.e. as-provided
AA6063-T4 (AR), as-provided artificially aged AA6063-T6 (ARHT), as-welded
AA6063-T4 (AW), and the welded AA6063-T4 subject to post weld heat treatment
(PWHT) with the objective of obtaining valuable physical evidence pertaining to
behavior of the chosen alloy 6063, 6061 or 6005A. The values of strength were
compared with the typical values in order to highlight any differences in material and
structural behavior.
3.4 Microstructure Characterization
Light optical microscopy was used to examine the microstructure of each alloy-
temper combination studied. Samples of 6063, 6061 and 6005A in the following
conditions, i.e., as-provided AA6063-T4 (AR), as-provided artificially aged AA6063-T6
(ARHT), as-welded AA6063-T4 (AW), and the welded AA6063-T4 subject to post weld
heat treatment (PWHT), were prepared very much in conformance with procedures
followed for metallographic preparation of samples for purpose of observation in a light
optical microscope. The ground and polished samples were etched using Keller’s reagent
12
(a solution mixture of hydrofluoric acid, concentrated nitric acid and distilled water).
The etched surface of each sample containing the weld region was observed in an optical
microscope and photographed using a bright field illumination technique.
3.5 Failure-Fracture-Damage Analysis
Fracture surfaces of the deformed and failed test specimens were examined in a
scanning electron microscope (SEM) so as to determine the macroscopic fracture mode,
and to concurrently characterize the fine-scale features and topography of the fracture
surface and thereby establish microscopic mechanisms governing fracture. The
distinction between the macroscopic mode and microscopic fracture mechanisms is based
entirely on the magnification level at which the observations are made. The macroscopic
mode refers to the overall nature of failure, while the microscopic mechanism refers to
the failure processes occurring at the ‘local’ level, such as: (i) microscopic void
formation, (ii) their gradual growth under the influence of far-field stress and eventual
coalescence, coupled with (iii) cracking. Samples, for observation in the scanning
electron microscope (SEM), were obtained from the failed specimens by sectioning
parallel to the fracture surface
13
CHAPTER IV
RESULTS AND DISCUSSION
4.1 Microstructure Analysis
Light optical micrographs taken over a range of low magnifications reveal the
initial microstructure of the chosen alloy in the different conditions it was tested in this
research study. This is shown in Figures 3-13. The microstructure of the as-welded
AA6063 in the T4 condition is shown in Figure 3. The base metal revealed a non-
uniform dispersion of both large and intermediate-size intermetallic particles randomly
distributed through the microstructure. No attempt was made in this research study to
determine the actual chemical composition of these intermetallic particles, which
primarily result from the presence of impurity elements iron and silicon. The result is the
formation of a variety of Al-Fe and Al-Fe-Si intermetallic particles during solidification.
Any silicon, which is not incorporated in the alpha-aluminum matrix or the Al-Fe-Si
intermetallic phases, combines with magnesium to form Mg2Si during the later stages of
the solidification process. The nature of intermetallic particles present in the final
microstructure will thus be determined by not only the as-cast state, but also by the
subsequent homogenization and thermo-mechanical processing given to the alloy [11].
The region of the weld revealed a fully recrystallized fine grain structure (Figure 3b).
14
A noticeable difference in microstructure was evident in the base metal and weld pool as
evident on crossing the weld pool-base metal interface (Figure 3c).
The optical microstructure of the post weld heat treated AA6063 to the T6 temper
is shown in Figure 4. The base metal revealed a random dispersion of both the coarse
and intermediate size intermetallic particles, which result from the presence of the
impurity elements iron and silicon (Figure 4a). At the region of the weld the
microstructure was fully recrystallized with very fine recrystallized grains (Figure 4b).
A noticeable difference in microstructure of the two regions, i.e., base metal and weld
pool is seen and is shown in Figure 4c and Figure 4d. The microstructure at the region of
the weld is shown in Figure 5 at two different magnifications. The grains were fine in
size and fully recrystallized (Figure 5a). Higher magnification reveals the random
orientation of fine grains having well-defined grain boundaries. Microstructure of the
post weld heat treated AA6063 did reveal observable differences at the boundary between
the base metal and the weld pool (Figure 6a). In the base metal, i.e., AA6063, it was
evident a healthy population of both the coarse and intermediate size intermetallic
particles dispersed randomly through the microstructure. At the region of the interface
between the base metal AA6063 and the weld pool isolated microscopic cracks were
evident as shown in Figure 6b.
15
Figure 3: Light optical micrographs of the as-welded aluminum alloy 6063-T4 showing: (a) base metal, (b) Region of the weld pool, and (c) At the boundary between the base metal and weld pool.
20μm
(b)
20μm
(a)
(c)
20μm
16
Figure 4: Light optical micrographs of the post weld heat treated aluminum alloy, i.e.6063, showing: (a) Distribution of both coarse and intermediate size second-phase particles in the base metal, (b) Distribution of second-phase particles in the region of the heat affected zone, (c) Fine recrystallized grains in the weld pool, and (d) Microstructure at the weld-pool-base metal interface.
20μm 20μm
50μm 50μm
(b)
(d)
(a)
(c)
17
Figure 5: Light optical micrographs of the post weld heat treated aluminum alloy, i.e., 6063, showing: (a) Fine recrystallized grains at the region of the weld, and (b) High magnification observation of (a) showing both size and morphology of the fine grains.
Figure 6: Light optical micrographs of the post weld heat treated aluminum alloy, i.e., 6063, showing: (a) boundary of the weld, and (b) at the toe of the weld pool.
(b)
(b)c)
40μm 20μm
25μm 20μm
(a)
(a)c)
18
The as-provided, i.e., as-received, AA6061-T4 revealed a random distribution of
both coarse and intermediate-size intermetallic particles (Figure 7a and Figure 7c).
Similar to AA6063, these intermetallic particles result from the presence of the residual
elements, such as, iron and silicon. In an earlier study these particles have been identified
to be the Al12Fe3Si and Al15 (FeMn) 3 Si and Al5FeSi [17, 18]. The iron-rich intermetallic
particles range in size from 1 to 10 microns and are clearly responsible for the initiation
of damage during plastic deformation [12, 13]. The dispersoids, which are manganese-
rich particles in this alloy (Al9Mn3Si), help in controlling both grain size and grain
growth during solidification. The as-provided AA6061 in the as-welded condition
revealed very fine recrystallized grains at the region of the weld bead (Figure 8 b). A
noticeable difference in microstructure between the two regions, i.e., weld bead and base
metal, was clearly evident at the interface between the two regions (Figure 9). The as-
provided alloy, i.e., AA6061-T4, that was artificially aged, or precipitation heat treated,
to get the T6 temper revealed an observable volume fraction of both coarse and
intermediate-size second-phase particles in the base metal as shown in Figure 10a. These
particles were distributed randomly through the microstructure. The as-welded AA6061
that was subject to post-weld heat treatment revealed very well-defined grains that were
(a) small in size and of varying shape, and (b) distributed randomly through the
microstructure of the base metal (Figure 10b). The microstructure at the interface of the
weld bead and the base metal AA6061 is shown in Figure 11. Fine microscopic cracks
initiated at the interface and propagated into the base metal.
19
Figure 7: Light optical micrographs of aluminum alloy 6061-T4 showing microstructure of the following: (a) Coarse and intermediate second phase particles in the base metal of the as-received or as-provided metal, (b) High magnification observation of (a), (c) Distribution of intermetallic particles in the heat treated sample, and (d) High magnification observation of (c)
(b)
(d)
(a)
200 μm
200 μm
(c)
500 μm
500 μm
20
Figure 8: Light optical micrograph of the weld pool showing fine grains of varying size and shape: (a) Grain size and morphology in the weld pool in the as-received metal (b) High magnification observation of (a), (c) Weld pool in the as-received plus heat treated metal, and (d) High magnification observation of (c)
(b)
(d)
(a)
200 μm
200 μm
(c)
500 μm
500 μm
21
Figure 9: Light optical micrographs showing the following:(a) Microstructure at the weld-base metal interface of the as-received Aluminum alloy 6061-T4, (b) High magnification observation of (a), (c) Microstructure of the weld-base metal interface in the as-received plus heat treated aluminum alloy 6061, and (d) High magnification observation of ( c)
(b)
(d)
(a)
200 μm
200 μm
(c)
500 μm
500 μm
22
Figure 10: Light optical micrographs of AA6061 showing the following: (a) Distribution of intermetallic particles in the base metal adjacent to the
weld bead, and (b) Microstructure of the weld pool of the heat treated alloy
Figure 11: Light optical micrographs of aluminum alloy 6061 showing: (a) Weld bead-base metal interface of the as-received alloy, and (b) High magnification observation of (a)
(b)
(b)
(a)
200 μm 200 μm
500 μm 200 μm
(a)
23
The as-provided AA6005A revealed a random distribution of both coarse and
intermediate-size intermetallic particles similar to AA6063 and AA6061 (Figure 12a).
Residual elements iron and silicon cause the formation of these particles. The dispersoids,
which are manganese-rich particles in this alloy, help in controlling both grain size and
grain growth during solidification. The as-provided alloy in the as-welded condition
revealed recrystallized grains having a very fine grain size at the region of the weld bead
(Figure 12-b). A noticeable difference in microstructure between the two regions, i.e.,
weld bead and base metal, was clearly evident at the interface between the two regions
(Figure 12-c). The as-provided alloy, i.e., AA6005A-T1, that was artificially aged, or
precipitation heat treated, to get the T5 temper revealed an observable volume fraction of
both coarse and intermediate-size second-phase particles in the base metal as shown in
Figure 12-d. These particles were distributed randomly through the microstructure. The
as-welded alloy that was subject to post-weld heat treatment revealed very well-defined
grains, small in size and of varying shape, distributed randomly through the
microstructure of the base metal (Figure 13).
24
Figure 12: Light optical micrographs of aluminum alloy 6005A-T4 showing:(a) Coarse and intermediate second phase particles in the base metal of the as-received or as-provided metal, (b) Region or location of the weld bead in the as-welded aluminum alloy 6005A-T4, (c) Microstructure at the interface of the weld bead and base metal, in as-welded metal, and (d) Microstructure showing second phase particle distribution in the as-received metal that was subject to heat treatment
(c)
50μm
(d)
50μm
50μm 50μm
(a) (b)
25
Figure 13: Light optical micrograph of the base metal showing fine grains of varying size and shape of the heat treated aluminum alloy 6005A.
4.2 Tensile Response and Properties
It is important to understand that welding does exert an influence on mechanical
properties of 6XXX series aluminum alloys. The influence differs depending on the alloy
as well as the welding process used coupled with overall quality of the weld. The type of
weld joint and thickness of the starting material influences the heat input and resultant
strength. The results of an investigation on welded 6063, 6061 and 6005A aluminum
alloys revealed precipitation heat treatment tends to increase strength of the materials.
Further, it was found that when these aluminum alloys were welded and not heat treated
they experienced an actual decrease in strength as a consequence of welding. The reason
for the observed decrease can be ascribed to changes in microstructure of the material as
a direct consequence of heat input during welding. When the materials were welded, the
rate of cooling depended upon the prevailing temperature in the room, approximately
72°F. The majority of the “as welded” samples broke at the region of the weld; usually
on the side of the weld to which more heat was provided during welding. This is a
20μm
26
common occurrence in welded products primarily because the weld itself is stronger than
the parent metal. However, the heat-affected zone (HAZ) immediately adjacent the weld
bead tends to be lower strength.
A statistical analysis using the guidelines establish in the 2010 Aluminum Design
Manual [1] coupled with guaranteed minimum strengths was used to determine
reasonable design minimum strength values for the post weld heat treated samples. The
mechanical properties of the base metal, within 1.0 in of the weld for those test
specimens welded in the as-received temper (6063-T4, 6063-T4, 6005A-T1) and
subsequently subjected to post-weld heat treatment should be taken as a percentage of the
guaranteed minimum un-welded strengths: (6063-T6, 6061-T6, 6005A-T5).
1/4” 6063 – 93.4% ultimate and 95.7% yield
3/8” 6063 – 95.0% ultimate and 79.7% yield
1/4” 6061 – 97.9% ultimate and 98.5% yield
3/8” 6061 – 74.5% ultimate and 60.1% yield
1/8” 6005A – 92.6% ultimate and 82.5% yield
Using the results from tensile tests of post weld heat treated AA6063, AA6061,
and AA6005A, recommendations for Section 6.4.2-2 of the Aluminum Design manual
regarding mechanical properties of welded and artificially aged aluminum light poles
would be as follows:
1) For lighting poles fabricated from 6005A aluminum that are less than or
equal to 0.125 in thick, welded in the T1 temper with 4043 filler and
subsequently artificially aged to the T5 temper after welding, mechanical
27
properties of the base metal within 1.0 in of the weld shall be taken as
80% of the un-welded 6005-T5.
2) For lighting poles fabricated from 6063 aluminum that are less than or
equal to 0.25 in thick, welded in the T4 temper and subsequently
artificially aged to the T6 temper after welding, mechanical properties of
the base metal within 1.0 in of the weld shall be taken as 90% of the un-
welded 6063-T6.
3) For lighting poles fabricated from 6063 aluminum that are 0.25 in thick
up to .375 in. thick, welded in the T4 temper with 4043 filler and
subsequently artificially aged to the T5 temper after welding, mechanical
properties of the base metal within 1.0 in of the weld shall be taken as
80% of the un-welded 6063-T6.
4) For lighting poles fabricated from 6061 aluminum that are less than or
equal to 0.25 in. thick, welded in the T4 temper and subsequently
artificially aged to the T6 temper after welding, mechanical properties of
the base metal within 1.0 in of the weld shall be taken as 95% of the un-
welded 6061-T6.
28
4.2.1 Stress vs Strain: as-provided alloy
Figure 14: AA6063 1/4” thick specimen, as-received vs as-received heat treated
Figure 15: AA6063 3/8” thick specimen, as-received vs as-received heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AR
ARHT
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AR
ARHT
29
Figure 16: AA6061 1/4” thick specimen, as-received vs as-received heat treated
Figure 17: AA6061 3/8” thick specimen, as-received vs as-received heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AR
ARHT
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30
Stre
ss (
ksi)
Strain (%)
AR
ARHT
30
Figure 18: AA6005A 1/4” thick specimen, as-received vs as-received heat treated
Figure 19: AA6005A 1/8” thick specimen, as-received vs as-received heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AR
ARHT
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30
Stre
ss (
ksi)
Strain (%)
AR
ARHT
31
4.2.2 Stress vs Strain: as-welded alloy
Figure 20: AA6063 1/4” thick specimen, as-welded vs post weld heat treated
Figure 21: AA6063 3/8” thick specimen, as-welded vs post weld heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AW
PWHT
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AW
PWHT
32
Figure 22: AA6061 1/4” thick specimen, as-welded vs post weld heat treated
Figure 23: AA6061 3/8” thick specimen, as-welded vs post weld heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AW
PWHT
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16 18
Stre
ss (
ksi)
Strain (%)
AW
PWHT
33
Figure 24: AA6005A 1/4” thick specimen, as-welded vs post weld heat treated
Figure 25: AA6005A 1/8” thick specimen, as-welded vs post weld heat treated
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AW
PWHT
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14 16
Stre
ss (
ksi)
Strain (%)
AW
PWHT
34
4.2.3 Stress vs Strain: Solution Heat Treatment Comparison
Figure 26: AA6005A 1/8” thick specimen, as-received vs ARHT vs solution heat treatment with PHT
Figure 27: AA6005A 1/8” thick specimen, as-welded vs PWHT vs solution heat treatment with PWHT
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30
Stre
ss (
ksi)
Strain (%)
AR
ARHT
SHT+PHT
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30
Stre
ss (
ksi)
Strain (%)
AW
PWHT
AW+SHT+PHT
35
4.2.4 Unusual Tensile Strength Values
During the testing of AA6061 and AA6005A, it was found that the tensile
strengths of some samples were lower than the standard values for the as-received, as-
received heat treated, as-welded, and post weld heat treated tests. There was no attempt to
determine the exact chemical composition of the extruded alloys prior to testing. There
was no evidence to explain the reason for the decreased material strength. Figures 28 and
29 show tensile yield and ultimate strengths for all the samples tested from AA6061 and
AA6005A.
36
Table 2: Aluminum Alloy 6005A Tensile Strength
Ultimate,
ksi
Yield,
ksi
Ultimate,
ksiYield, ksi
Ultimate,
ksi
Yield,
ksi
Ultimate,
ksiYield, ksi
Ultimate,
ksi
Yield,
ksi
25.1 14.3 32.1 27.1 24.3 12.8 31.9 26.4
25.5 14.1 32.5 27.4 22.9 12.9 33.6 28.2
25.5 14.6 32.4 27.3 25.2 13.2 31.3 26.4
25.4 14.8 33.5 28.2 23.0 11.0 34.1 28.7
26.9 11.5 34.6 31.5 27.2 12.5 35.0 29.9
26.5 11.1 34.5 29.1 26.3 12.8 35.2 30.0
27.2 11.0 34.4 29.0 26.2 11.9 32.6 27.4
27.3 11.1 34.5 29.4 24.2 11.2 34.5 29.2
25.1 11.2 34.1 28.8
24.2 10.0 29.9 24.1
29.8 24.4
30.8 25.9
39.9 32.1
37.8 31.9
39.2 34.5
40.7 34.3
38.5 32.5
38.9 31.9
39.6 33.4
41.8 34.3
39.7 32.0
39.6 33.2
38.5 32.9
38.4 31.5
26.2 12.8 33.6 28.6 24.9 12.0 36.1 30.2
NA NA
6005A-T5
42.0 38.0
Showing Material Strength values cut from
two different alloy extrusions
Parent Metal
(AR+PHT)
6005A-T1
Aluminum Alloy 6005A, 1/8" Tensile Strength
Parent Metal (AR) As Welded (AW)Post Weld Heat Treat
(PWHT)Typical Values
37
Table 3: Aluminum Alloy 6061 Tensile Strength
Ultimate,
ksi
Yield,
ksi
Ultimate,
ksiYield, ksi
Ultimate,
ksi
Yield,
ksi
Ultimate,
ksiYield, ksi
Ultimate,
ksi
Yield,
ksi
33.4 18.2 43.8 39.7 29.5 16.8 41.6 38.5
33.3 17.9 43.0 39.7 29.8 16.8 40.2 37.3
33.0 18.2 42.0 39.1 29.0 15.6 40.1 37.2
25.2 12.9 33.3 27.2 29.5 16.9 42.0 38.5
25.3 12.5 33.2 27.8 29.5 16.8 40.1 37.3
25.2 12.7 33.8 28.6 29.0 15.6 40.1 37.3
23.0 11.3 42.6 40.0
23.2 11.8 42.4 39.0
22.8 11.0 41.8 39.0
22.9 10.9 40.5 37.5
22.4 10.7 40.2 37.5
22.0 10.5 39.2 36.5
22.4 11.0 41.0 38.4
23.3 11.9 40.5 37.0
40.0 37.2
32.3 26.2
31.2 25.2
31.0 24.8
30.6 24.1
28.8 23.9
29.0 24.0
31.9 25.7
33.3 27.1
34.5 29.3
32.3 26.5
29.2 15.4 38.2 33.7 25.6 13.4 37.1 33.0
Aluminum Alloy 6061 - T4, 1/4" Tensile Strength
Parent Metal (AR)Parent Metal
(AR+PHT)As Welded (AW)
Post Weld Heat Treat
(PWHT)Typical Values
6061-T4
35.0 21.0
6061-T6
45.0 40.0
Showing Material Strength values cut from
two different alloy extrusions
38
4.3 Tensile Fracture Behavior
The fracture features on the surface of the deformed and failed test specimens are
shown in Figures 28-41. Aluminum alloys 6063, 6061 and 6005A are tough alloys
making linear elastic fracture mechanics little value in describing fracture conditions.
4.3.1 As-Received Parent Metal
Tensile fracture of the AA6063 in the as-received or as-provided condition, i.e.,
temper T4 (6063-T4), was essentially flat and normal to the far-field stress axis. At the
higher magnifications the fracture surface was microscopically rough and revealed an
array of macroscopic cracks running perpendicular to the far-field stress axis (Figure
28a). The highly non-linear nature of the macroscopic crack (Figure 28b) was
interdispersed with pockets of transgranular regions. In the region immediately prior to
overload the fracture surface revealed regions containing pockets of striations adjacent to
the macroscopic cracks indicative of localized micro plastic deformation (Figure 28c).
The region of overload was covered with a noticeable population of voids of varying size
intermingled with dimples, features that are clearly indicative of the “locally” occurring
ductile failure mechanisms (Figure 28d).
Tensile fracture of the as-received AA6063 heat treated to the T6 temper is shown
in Figure 29. Macroscopic fracture was normal to the far-field tensile stress axis and
essentially flat (Figure 29a). Careful high magnification observation revealed an
observable combination of microscopic cracks, voids of varying size intermingled with
dimples (Figure 29b). These features are indicative of the occurrence of predominantly
ductile and isolated brittle failure mechanisms at the fine microscopic level. The non-
linear nature of the fine microscopic crack surrounded by a healthy dispersion of voids
39
and dimples is shown in Figure 29c. The region of overload revealed a healthy
population of voids of varying size intermingled with pockets of shallow dimples
indicative of “locally” occurring ductile failure mechanisms (Figure 29d).
Figure 28: Scanning electron micrographs of the tensile fracture surface of as-received aluminum alloy 6063 in the T4 temper, showing: (a) Overall morphology of failure (b) High magnification observation of (a) showing non-linear nature of macroscopic cracks (c) Isolated pockets of striations on the transgranular fracture surface (d) Observable population of voids of varying size intermingled with dimples
(a)
100μm
(b)
20μm
(c)
10μm
(d)
10μm
40
Figure 29: Scanning electron micrographs of the tensile fracture surface of the heat treated aluminum alloy 6063-T4, showing: (a) Overall morphology of failure normal to far field stress axis (b) High magnification observation of (a) showing population of voids of varying size intermingled with isolated microscopic cracks (c) High magnification observation of (b) showing the nature and morphology of voids covering the transgranular fracture region and void coalescence to form microscopic crack (d) Voids of varying size intermingled with dimples on overload fracture surface.
(a)
100μm
(b)
(c)
20μm
(d)
10μm 10μm
41
On a macroscopic scale tensile fracture of the test sample taken from the as-
received AA6061 was essentially normal to the far-field stress axis (Figure 30a). Overall
morphology of fracture was rough at the fine microscopic level with the surface
comprising of ductile voids and dimples and brittle macroscopic cracks. The
macroscopic cracks were running parallel to the major stress axis (Figure 30b). Fine
dimples of varying size and shape and intermingled with voids was found immediately
adjacent to the intergranular fracture region (Figure 30c). The voids were microscopic in
nature with little evidence of their growth and eventual coalescence during far-field
loading. The overload fracture region was rough and devoid of features that would be
indicative of purely ductile or brittle failure mechanisms (Figure 30d).
The overall morphology and features of the as-received AA6061 that was
precipitation heat treated and then deformed to failure are shown in Figure 31. Overall
morphology was also normal to the far-field stress axis with an array of macroscopic
cracks, essentially co-planar in nature, and intermingled with fine microscopic cracks
(Figure 31a). High magnification observation of (a) revealed the non-linear nature of
the macroscopic and fine microscopic cracks surrounded by pockets of voids and
dimples; features reminiscent of locally occurring brittle and ductile failure mechanisms
(Figure 31b). Adjacent to the intergranular cracks was evident pockets containing
shallow dimples of varying size (Figure 31c). This region of the fracture surface when
observed at higher magnification revealed voids of varying size intermingled with
shallow dimples (Figure 31d). A sizeable number of dimples on the fracture surface were
elongated in shear providing concrete evidence of ductile failure processes occurring at
the ‘local’ level (Figure 32).
42
Figure 30: Scanning electron micrographs of the tensile fracture surface of as-
received aluminum alloy 6061-T4, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by observable population of voids and dimples, (c) High magnification observation of (a) showing size and morphology of the voids, and (d) The overload fracture surface, features give no indication of likely micro failure mechanism.
(c)
20μm
(d)
10μm
(a)
200μm
(b)
100μm
43
Figure 31: Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6061-T6, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, and (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction
(a)
200μm
(c)
5 μm
(d)
4 μm
(b)
10μm
44
Figure 32: Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6061-T6, showing elongated dimples indicative of shear and locally occurring ductile failure.
On a macroscopic scale tensile fracture of the test sample taken from the as-
provided AA6005A was essentially normal to the far-field stress axis similar to AA6063
and AA6061 (Figure 33a). Overall morphology of fracture was rough at the fine
microscopic level with the surface comprising of both ductile voids and dimples and
brittle macroscopic cracks. The macroscopic cracks were running parallel to the major
stress axis (Figure 33b). Fine dimples of varying size and shape and intermingled with
voids was found immediately adjacent to the intergranular fracture region (Figure 33c).
The voids were microscopic in nature with little evidence of their growth and eventual
coalescence during far-field loading. The overload fracture region was rough and devoid
of features that would be indicative of purely ductile or brittle failure mechanisms (Figure
33d).
Samples of the as-received AA6005A that were precipitation heat treated and then
deformed to failure the overall morphology and features are shown in Figure 34. Overall
(a)
2 μm
45
morphology was normal to the far-field stress axis with an array of macroscopic cracks,
essentially co-planar in nature, and intermingled with fine microscopic cracks (Figure
34a). High magnification observation of (a) reveals the non-linear nature of the
macroscopic and fine microscopic cracks surrounded by pockets of voids and dimples;
features reminiscent of locally occurring brittle and ductile failure mechanisms (Figure
34b). Adjacent to the intergranular cracks was evident pockets containing shallow
dimples of varying size (Figure 34c). This region of the fracture surface when observed
at higher magnification revealed voids of varying size intermingled with shallow dimples
(Figure 34d).
46
Figure 33: Scanning electron micrographs of the tensile fracture surface of as-received aluminum alloy 6005 in the T4 temper, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing nonlinear nature of macroscopic crack surrounded by observable population of voids and dimples, (c) High magnification observation of (a) showing size and morphology of the voids, and (d) The overload fracture surface, features give no indication of likely micro failure mechanism.
(c)
10µm 20μm
(b)
(d)
5 µm 20μm
(a)
20µm 20μm
20µm 20μm
47
Figure 34: Scanning electron micrographs of the tensile fracture surface of as-received plus heat treated aluminum alloy 6005 in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with highly shallow dimples., and (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction.
(a)
50µm μm
(b)
10µm
μm
(c)
10µm 20μm
(d)
5 µm 20μm
48
4.3.2 As-Welded
Tensile fracture surface features of the AA6063 sample in the as-welded
condition are shown in Figure 35. Overall fracture was at a slight inclination to the far-
field stress axis and predominantly transgranular (Figure 35a). High magnification
observation of (a) revealed a healthy dispersion of voids of varying size intermingled
with dimples indicative of locally occurring ductile failure mechanisms (Figure 35b). At
higher allowable magnifications of the SEM this region revealed an observable
population of voids of varying size intermingled with dimples (Figure 35c). In the
region of tensile overload were evident voids of varying size, void growth and eventual
coalescence to form fine microscopic cracks surrounded by isolated pockets of shallow
dimples (Figure 35d). These features are clearly indicative of the occurrence of both
ductile and brittle failure mechanisms at the fine microscopic level.
Fracture features on the tensile sample of AA6063 that was heat treated following
welding are shown in Figure 36. Overall morphology at low magnification revealed
predominantly transgranular failure (Figure 36a) with the fracture surface covered with a
healthy dispersion of voids of varying size and shallow dimples (Figure 36b). There was
a distinct absence of macroscopic cracks and isolated fine microscopic cracks as a
consequence of void growth and coalescence. In the region of overload was an
observable dispersion of dimples, which were overall very shallow in nature (Figure 36c).
49
Figure 35: Scanning electron micrographs of the tensile fracture surface of the as-
welded aluminum alloy 6063-T4, showing: (a) Healthy population of voids of varying size on tensile fracture surface, (b) High magnification observation of (a) showing nature and morphology of the voids, (c) Healthy population of voids and dimples, and (d) Microvoid growth during far field loading and coalescence to form a fine microscopic crack.
(b)
20μm
(a)
100μm
(c)
10μm
(d)
10μm
50
Figure 36: Scanning electron micrographs of the tensile fracture surface of the as-welded and heat treated aluminum alloy 6063, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing the nature, morphology and distribution of voids covering the transgranular fracture regions, and (c) Voids and shallow dimples covering the overload fracture surface
(a)
20μm
(b)
10μm
(c)
5μm
51
Scanning electron microscopic observation of the as-welded sample of AA6061 is
shown in Figure 37. Overall morphology was essentially flat and rough at the fine
microscopic level (Figure 37a). At higher magnification the surface revealed a healthy
dispersion of voids intermingled with dimples (Figure 37b). The exact morphology of
the dimples and the nature of the voids are shown in Figure 37c. These fine features
observed at the microscopic level are clearly indicative of the locally occurring ductile
failure mechanisms. In the region approaching overload the fracture surface revealed
features when observed at the higher allowable magnification of the SEM. Presence of a
healthy population of voids of varying size intermingled with dimples along with fine
microscopic cracks is indicative of both ductile and brittle failure mechanisms occurring
at the fine microscopic level (Figure 37d).
Fracture behavior of the tensile sample of this aluminum alloy that was subject to
heat treatment subsequent to welding is shown in Figure 38. Overall morphology was
normal to the far-field stress axis and contained an array of both macroscopic cracks
intermingled with fine microscopic cracks (Figure 38a). High magnification observation
of the fracture surface revealed cracking along the grain boundaries with pockets of voids
intermingled with dimples adjacent to the intergranular fracture regions (Figure 38b and
Figure 38c). At higher magnification the voids were observed to be of varying size and
shape and inter-dispersed with shallow dimples (Figure 38d), features reminiscent of the
locally occurring ductile failure mechanisms. The cracks propagated with ease along the
grain boundary triple junctions. Coalescence of the fine microscopic voids initiated at
both the coarse and intermediate-size second-phase particles dispersed through the
microstructure results in dimples and fine microscopic cracks. At very high
magnification the region on the fracture surface immediately prior to overload revealed
fine striation-like features reminiscent of ‘locally’ occurring microplastic deformation
(Figure 39).
52
Figure 37: Scanning electron micrographs of the tensile fracture surface of as-welded aluminum alloy 6061 in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of (a) showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, ( c) High magnification observation of (b) nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, and (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction.
(b)
10μm
(d)
5 μm
(c)
5 μm
(a)
200μm
53
Figure 38: Scanning electron micrographs of the tensile fracture surface of post weld heat treated aluminum alloy 6061, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing a healthy and observable population of voids and shallow dimples adjacent to the intergranular crack, (c) High magnification observation of (b) showing size, morphology and distribution of the voids, both macroscopic and fine microscopic, and (d) The presence of voids and void coalescence to form macroscopic crack in the region immediately prior to overload.
(a)
200μm
(d)
5 μm
(c)
5 μm
(b)
10μm
54
Figure 39: Scanning electron micrographs of the tensile fracture surface of post weld heat treated aluminum alloy 6061, showing fine ripples or striations- like featuring reminiscent of locally occurring micro plastic deformation.
Scanning electron microscopic observation of the as-welded sample of AA6005A
is shown in Figure 40. Overall morphology was essentially flat and rough at the fine
microscopic level (Figure 40a). At higher magnification the surface revealed a healthy
dispersion of voids intermingled with dimples (Figure 40b). The exact morphology of
the dimples and the nature of the voids are shown in Figure 40c. These fine features
observed at the microscopic level are clearly indicative of the locally occurring ductile
failure mechanisms. In the region approaching overload the fracture surface revealed
observable features when observed at the higher allowable magnification of the SEM.
Presence of a healthy population of voids of varying size intermingled with dimples
along with fine microscopic cracks is indicative of both ductile and brittle failure
mechanisms occurring at the fine microscopic level (Figure 40d).
(a)
1 μm
55
Fracture behavior of the tensile sample of this aluminum alloy that was subject to
heat treatment subsequent to welding is shown in Figure 41. Overall morphology was
normal to the far-field stress axis and contained an array of both macroscopic cracks
intermingled with fine microscopic cracks (Figure 41a). High magnification observation
of the fracture surface revealed cracking along the grain boundaries with pockets of voids
intermingled with dimples adjacent to the intergranular fracture regions (Figure 41b and
Figure 41c). At higher magnification the voids were observed to be of varying size and
shape and inter-dispersed with shallow dimples (Figure 41d), features reminiscent of the
locally occurring ductile failure mechanisms. The cracks propagated with ease along the
grain boundary triple junctions. Coalescence of the fine microscopic voids initiated at
both the coarse and intermediate-size second-phase particles dispersed through the
microstructure results in dimples.
The coarse iron-rich and silicon-rich intermetallics along with other insoluble
particles present coupled with the a microstructure that favors ‘localized’ inhomogeneous
deformation due essentially to the presence of easily shearable matrix strengthening
precipitates facilitates in the nucleation and coalescence of the voids, of varying size, to
occur at low to moderate stress levels. In fact void nucleation at a coarse-second phase
particle is favored to occur easily when the elastic energy in the particle exceeds the
surface energy of the newly formed void surfaces.
56
Figure 40: Scanning electron micrographs of the tensile fracture surface of as -welded plus heat treated aluminum alloy 6005A in the T4 temper, showing: (a) Overall morphology of failure showing an array of macroscopic and microscopic cracks, (b) High magnification observation of showing non-linear nature of macroscopic crack surrounded by pockets of voids and dimples, reminiscent of highly localized ductile failure mechanism, (c) High magnification observation of nature, morphology and overall distribution of the voids intermingled with highly shallow dimples, and (d) A mixture of voids of varying size, shallow dimples adjacent to cracked grain boundary triple junction.
(b)
50µm 20μm
(a)
100µm
(c)
20µm 20μm
(d)
10µm 20μm
57
Figure 41: Scanning electron micrographs of the tensile fracture surface of aluminum alloy 6005A in the T4 temper and as-welded condition, showing: (a) Overall morphology of failure, (b) High magnification observation of (a) showing a healthy and observable population of voids and shallow dimples adjacent to the intergranular crack, (c) High magnification observation of (b) showing size, morphology and distribution of the voids, both macroscopic and fine microscopic, and (d) The presence of voids and void coalescence to form macroscopic crack in the region immediately prior to overload.
(a)
50µm 20μm
(b)
20µm 20μm
(c)
10µm 20μm
(d)
5 µm 20μm
58
4.3.3 Mechanisms Governing Tensile Fracture
Formation of the macroscopic voids is favored to occur because of failure of the
coarse second-phase particles dispersed through the microstructure by cracking.
Coalescence of the macroscopic voids occurred by the formation of void sheets and
exacerbated by the intense localization of strain between the expanding and growing
voids. This is shown in Figure 42. The highly localized deformation favors the
formation of microscopic voids at the intermediate-size second phase particles upon
reaching a critical value of strain. The presence of both coarse and intermediate-size
second phase particles in the microstructure of AA6063, AA6061 and AA6005A may
have little to no influence on strength but on account of their intrinsic brittleness they
tend to either easily fracture by cracking during deformation thereby reducing the total
energy that is required for rupture, or segregate from the aluminum alloy matrix when the
local strain exceeds a critical value.
The transgranular regions did reveal pockets of highly deformed matrix
reminiscent of localized plastic deformation, referred to as ‘microplasticity’, of the
aluminum alloy matrix. The highly localized microplasticity is predominantly distributed
through the microstructure of this alloy, presumably within the favorably oriented grains.
The observed distribution of microplastic deformation in the microstructure of AA6063,
AA6061 and AA6005A is dependent on the mutually interactive influences of the
following [14, 15]:
(i) The orientation of grains (texture),
(ii) Elastic anisotropy and the concomitant stress concentration arising due to
contributions from both grain size and grain shape,
59
(iii) Presence and role of grain boundary triple junctions, and
(iv) The overall nature of loading.
The formation and presence of an observable population of voids, of varying size and
shape, transforms this polycrystalline aluminum alloy, in the conditions it was tested or
deformed in uniaxial tension, into a “composite:” with two populations of particles.
These can be considered to be the (a) grains, and (b) the void [a void being considered as
a particle having essentially zero stiffness]. Since the voids, regardless of their size, are
intrinsically softer than the grains in the aluminum alloy metal matrix, the local strain is
exacerbated for the voids causing as a result an increase in their volume fraction. The
presence of an observable population of voids, of varying size and shape, transforms the
macroscopic mechanical response of the polycrystalline 6XXX series alloy through
significant degradation in ductility. The presence of an observable amount of both coarse
and intermediate size intermetallic particles coupled with an alloy microstructure that
favors inhomogeneous deformation during loading facilitates the nucleation and
coalescence of voids to occur at fairly low to moderate stress levels. In fact void
nucleation at the second-phase particle is favored to occur when the elastic energy in the
particle exceeds the surface energy of the newly formed void surfaces [16].
60
Figure 42: Schematic showing the formation of void sheets between expanding or growing voids leading to void-void interactions and eventual coalescence.
4.3.4 Kinetics Governing Stress-Material Response
It is important to understand the extrinsic influence of the heat that is both
supplied and generated during the welding process on the mechanical properties of
aluminum alloys belonging to the 6XXX series. Further, the extrinsic influence of heat,
that is both supplied and generated during welding, can differ depending upon the
exposure to the welding process and resultant quality of the weld. Also, the type of weld
joint coupled with material thickness will tend to influence: (i) the heat input, (ii) heat
build-up, and (iii) resultant strength of the weld.
Results of this investigation on welded 6xxx aluminum alloys showed heat
treatment to increase strength of the chosen material. Also, it was found that when the
welded aluminum alloy was not heat treated it experienced a decrease in strength as a
consequence of welding. This has the tendency to favor premature failure during high
rate of loading. Overall, it is important to understand the extent to which welding can
affect the strength and ductility properties of the chosen aluminum alloy and the proper
61
loading that the welded aluminum alloy, and post-weld heat treated aluminum alloys can
carry through the heat-affected zone (HAZ).
Strength, ductility, and overall fracture behavior are the three key properties
which govern or determine the tensile response of a material. The grain size and
distribution in the microstructure of these aluminum alloys did change as a consequence
of the heat input during welding. The heat treatment enables the grains to return closer to
their normal size and distribution. When the chosen aluminum alloy, is welded and not
subject to post weld heat treatment, then the values of strength obtained are noticeably
less than expected for the non-heat treated alloys. When comparing the strength values
obtained from the tensile tests with the aluminum standards, the values for both the heat
treated aluminum alloy and the welded counterpart were marginally higher than the
standard values.
62
CHAPTER V
SUMMARY OF CONCLUSIONS
5.1 Conclusions A study aimed at investigating the conjoint influence of welding and artificial
aging on microstructural development, tensile behavior and fracture behavior of
aluminum alloys 6063, 6061 and 6005A, provides the following findings:
1. Lap joint welds were deposited across some of the samples in order to examine
the effect of localized heating on the material. This welding process of gas metal
arc was chosen since it is one of the most commonly used in the industry for
aluminum alloy-related applications.
2. The base metal of each alloy revealed a non-uniform dispersion of both large and
intermediate-size intermetallic particles randomly distributed through the
microstructure. Presence of impurity elements iron and silicon result is the
formation of a variety of iron-rich and iron-silicon rich intermetallic particles
during solidification. Any silicon which is not incorporated in the alpha-
aluminum matrix or the Al-Fe-Si intermetallic phases combines with magnesium
to form Mg2Si during the later stages of the solidification process. The region of
the weld revealed a fully recrystallized fine grain structure.
63
3. Microstructure of the post weld heat treated alloys did reveal observable
differences at the boundary between the base metal and the weld pool. In the
base metal, it was evident that a healthy population of both the coarse and
intermediate size intermetallic particles dispersed randomly through the
microstructure. At the region of the interface between the base metal and the
weld pool observable microscopic cracks were evident.
4. The ultimate strength and yield strength of the post weld heat treated (PWHT)
samples increased when compared with the samples prepared from the as welded
aluminum alloy.
The ¼ inch AA6063 PWHT samples showed a 66% (yield) and 36% (ultimate)
increase in strength over the as-welded condition.
The 3/8 inch AA6063 PWHT samples showed a 17% (yield) and 9% (ultimate)
increase in strength over the as-welded condition.
The ¼ inch AA6061 PWHT samples showed a 57% (yield) and 28% (ultimate)
increase in strength over the as-welded condition.
The 3/8 inch AA6061 PWHT samples showed a 48% (yield) and 24% (ultimate)
increase in strength over the as-welded condition.
The 1/8 inch AA6005A PWHT samples showed a 65% (yield) and 35% (ultimate)
increase in strength over the as-welded condition.
5. The re-solution heat treatment of AA6005A provided strength results comparable
to typical values of 6005A-T5. Tensile strength values of 38.7 ksi yield and 42.9
ksi ultimate were obtained from welded SHT + PHT tests. Typical values of
6005A-T5 are 38.0 ksi yield and 42.0 ksi ultimate.
64
6. (i) Tensile fracture of the 6063, 6061 and 6005A alloy in the as-received or as-
provided condition, was essentially flat and normal to the far-field stress axis.
(ii) The fracture surface of the three alloys was microscopically rough and
revealed an array of macroscopic cracks running perpendicular to the far-field
stress axis.
(iii) The highly non-linear nature of the macroscopic crack was interdispersed
with pockets of transgranular regions.
(iv) In the region immediately prior to overload the fracture surface revealed
regions containing pockets of ripples or striation-like features adjacent to the
macroscopic cracks indicative of localized microplastic deformation.
65
REFERENCES
[1] 2010 Aluminum Design Manual, The Aluminum Association, Washington, D.C., 2010
[2] Willard, J.P., ALCOA Green Letter: Four Extrusion Alloys 6061, 6063, 6351,
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D.C., 2009 [5] ASTM B918-01 Standard Practice for Heat Treatment of Wrought Aluminum
Alloys, DOI: 10.1520/B0918-01 [6] ASM Materials Handbook, Vol. 4 and Vol. 6, ASM International, Materials Park,
Ohio, USA, 1991. [7] Ding Xian-fei, Sun Jing, Ying Jia, Zhang Wei-dong, Ma Ji-jun, Wang Li-chen.
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[13] D. Lassance, D. Fabregue, F. Delannay, T. Pardoen: Progress in Materials Science, Vol. 52, 2007, pp. 62-129.
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67
APPENDIX
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ss (
psi
)
Strain
6063-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
76
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stre
ss (
psi
)
Strain
6063-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stre
ss (
psi
)
Strain
6063-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
77
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stre
ss (
psi
)
Strain
6063-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Stre
ss (
psi
)
Strain
6061-T6, As Received0.25" Thick, 0.5" Width
78
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Stre
ss (
psi
)
Strain
6061-T6, As Received0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
79
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
Series1
Series2
Series3
Series4
80
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
81
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
0 0.05 0.1 0.15 0.2
Stre
ss (
psi
)
Strain
6061-T6, As Received0.375" Thick, 0.5" Width
82
0
5000
10000
15000
20000
25000
30000
0 0.05 0.1 0.15
Stre
ss (
psi
)
Strain
6061-T6, As Received0.375" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1
Stre
ss (
psi
)
Strain
6061-T6, As Received0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
83
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Received0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
84
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
85
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
86
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
87
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
88
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
89
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
90
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Stre
ss (
psi
)
Strain
6061-T6, As Welded0.375" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
91
0
5000
10000
15000
20000
25000
30000
0 0.05 0.1 0.15
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
0 0.05 0.1 0.15
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
92
0
5000
10000
15000
20000
25000
30000
0 0.05 0.1 0.15
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
93
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
94
0
5000
10000
15000
20000
25000
30000
35000
0 0.02 0.04 0.06 0.08 0.1
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
95
0
5000
10000
15000
20000
25000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
96
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
97
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
98
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
99
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
100
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.25" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
101
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08 0.1 0.12
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
102
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
103
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.02 0.04 0.06 0.08
Stre
ss (
psi
)
Strain
6005A-T6, As Received0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
104
0
5000
10000
15000
20000
25000
30000
0 0.02 0.04 0.06 0.08
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
105
0
5000
10000
15000
20000
25000
30000
0 0.01 0.02 0.03 0.04 0.05 0.06
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
0
5000
10000
15000
20000
25000
0 0.01 0.02 0.03 0.04 0.05 0.06
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
106
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
107
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
108
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
109
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
110
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
111
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)
0
5000
10000
15000
20000
25000
30000
35000
40000
0 0.01 0.02 0.03 0.04 0.05
Stre
ss (
psi
)
Strain
6005A-T6, As Welded0.125" Thick, 0.5" Width
Precipitation Heat Treat (6 Hrs, 360o F)