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EFFECT OF HOLDING TIME ON THE PHYSICAL AND
MECHANICAL PROPERTIES OF DISSIMILAR METAL
DIFFUSION WELDED BETWEEN ALUMINUM AND STEEL
THESIS
Organized to Meet a Part of the Requirements to Achievethe Master Degree of Mechanical Engineering Department / Specialization of Material supporting
for Renewable Energy
BY
ALI JEBRIL SAAD JEBRIL
NIM: S951208008
POSTGRADUATE PROGRAM
SEBELAS MARET UNIVERSITY
SURAKARTA
2014
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ALI JEBRIL SAAD JEBRIL, Student Number: S951208008 EFFECT OF HOLDING TIME ON THE PHYSICAL AND MECHANICAL PROPERTIES OF DISSIMILAR METAL DIFFUSION WELDED BETWEEN ALUMINUM AND STEEL Supervisor I: Dr.Triyono, ST, MT. Supervisor II: Dr. Agus Supriyanto, S.Si M.Si. Thesis: Mechanical Engineering Department, Graduate School, Sebelas Maret University.
ABSTRACT
Holding time is used for optimizing the bond diffusion between aluminum Al and Carbon steel SS400. The objective of this research was to investigate the effects of holding time on the mechanical and physical properties at interface reactions of diffusion welding between aluminum and carbon steel. Holding time variations of 10, 15, 30 and 45 minutes were applied at 950°C using mixture of Cu and Fe powder as elements promoter. Single lap joint configuration was performed in vacuum furnace to join the dissimilar materials which allowed bonding diffusion. Microstructure was examined on the same test piece. It was found that during diffusion process at 950°C, the interfacial zone between aluminum and carbon steel substrate features intermetallic layers. The intermetallic thickness increased with increasing the holding time. Crack or incomplete bonding appeared on the specimens with holding time up to 30 minutes and didn’t appear on the specimens with holding time of 45 minutes. Cu rich-element promoter made diffusion penetrated deeper than Fe rich-element promoter in the same holding time. Macrostructure, microstructure and SEM examinations revealed that Al-steel joint had the best result with element promoter content of 60/40 % at 45 minutes holding time. There was no interlayer gap at this specimen. Additionally, from mapping view it can be suggested that in terms of poor interface bonding, Cu molecules were located just around the interface area, on the other hand, in case of strong interface bonding, Cu molecules are scattered throughout the specimen. The highest shear strength value of specimen with filler composition Fe 80% Cu 20% using 45 minutes holding time is 8.2 MPa. The lowest shear strength values are specimen with filler composition Fe 60% Cu 40%, Fe 80% Cu 20% and Without Filler at 30 minutes holding time. The highest hardness value is 681.1 HV on without filler at 10 and 45 holding time minutes. In fact, the position of Cu molecules can be used as a promising marker for the detection of quality of diffusion joint.
Keywords: aluminum, diffusion bounding, interface, steel, holding time.
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ABSTRAK
Holding time (waktu simpan) digunakan untuk mengoptimalkan difusi ikatan antara aluminium Al dengan Carbon Steel SS400. Tujuan dari penelitian ini adalah untuk meneliti pengaruh holding time terhadap sifat-sifat fisika pada reaksi interface diffusion welding (antar muka patri difusi) antara aluminium dengan baja karbon. Variasi holding time antara 10, 15, 30 dan 45 menit diterapkan pada suhu 950o C dengan menggunakan campuran serbuk Cu dan Fe sebagai promoter unsur. Konfigurasi sendi satu putaran dilakukan didalam tungku vacuum untuk menggabungkan bahan-bahan yang tidak serupa yang menghasilkan difusi (penyebaran) ikatan. Struktur mikro diuji pada bidang tes yang sama. Diketahui bahwa selama proses difusi pada suhu 950o C, zona interfacial antara aluminium dengan substrat baja karbon memperlihatkan lapisan-lapisan antar logam. Ketebalan antar logam naik dengan bertambahnya holding time. Ikatan yang retak atau tidak sempurna muncul pada spesimen-spesimen dengan holding time hingga 30 menit dan tidak muncul pada spesimen-spesimen dengan holding time 45 menit. Promoter unsur yang kaya akan Cu membuat difusi menembus lebih dalam daripada promotor yang kaya akan FE pada holding time yang sama. Pengujan struktur makro, struktur mikro dan SEM memperlihatkan bahwa sendi (sambungan) Al-baja memiliki hasil terbaik dengan kandungan promotor unsure 60/40% pada holding time 45. Tidak ada kesenjangan antar lapisan pada spesimen ini. Selain itu, dari tinjauan pemetaan, dapat dikatakan bahwa dalam kaitannya dengan ikatan interface yang buruk, molekul-molekul Cu ditempatkan tepat disekitar daerah interface, di lain pihak, pada kasus ikatan interface yang kuat, molekul Cu disebarkan keseluruh specimen. Nilai kekuatan shear specimen tertinggi dengan komposisi filler (pengisi) Fe 80% Cu 20% dengan menggunakan holding time 45 menit adalah 8,2 MPa. Nilai-nilai kekuatan shear terendah adalah spesimen dengan komposisi Fe 60% Cu 40%, Fe 80% Cu 20% dan Tanpa Filler pada holding time 30 menit. Nilai kekerasan tertinggi adalah 681,1 HV pada tanpa filler pada holding time 10 dan 45 menit. Pada kenyataannya, posisi molekul Cu dapat digunakan sebagai penanda yang menjanjikan untuk pendeteksian kualitas sendi difusi. Kata Kunci: aluminium, ikatan difusi, interface, baja, holding time.
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ORIGINALITY AND PUBLICATION STATEMENT
We Declare that: 1. Thesis entitled: “ THE EFFECT OF HOLDING TIME ON THE PHYSICAL
AND MECHANICAL PROPERTIES OF DISSIMILAR METAL DIFFUSION
WELDED BETWEEN aLUMINUM AND sTEEL” is my work and free of
plagiarism, and there is no scientific papers that have been asked by others to
obtain academic degrees and there is no work or opinion ever written or published
by another person except in writing used as a reference in this text and a reference
source as well as mentioned in the bibliography. If at a later proved there is
plagiarism in scientific papers, then I am willing to accept sanctions in accordance
with the provisions of the legislation (Permendiknas No 17, tahun 2010)
2. Publication of some or all of the contents of the thesis or other scientific forums
and permission must include the author and the team as a supervisor. The
program in Mechanical Engineering of UNS has the right to publish in a scientific
journal published by Study Program in Mechanical Engineering of UNS. If I
violate of the provisions of this publication, then I am willing to get an academic
sanction.
Surakarta, October 2014
ALI JEBRIL SAAD JEBRIL
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PREFACE
Foremost, I would like to express my gratitude to my supervisors,
Dr.Triyono, MT for his continuous support during my master study and research, I
am extremely grateful for his patience, motivation and enthusiasm to convey his
immense knowledge. He was very helpful for me in the all time of my research and
writing of this thesis. The authors would like to express their sincere gratitude for
ministry of education and culture of Indonesia republic through MP3EI 2013 grant.
Besides to the head of mechanical engineering department Dr. Techn Suyitno, ST.
MT, I would also like to thank the rest of my thesis committee. Dr.Agus Supriyanto,
S.Si, M. Si for her encouragement, teaching and insightful comments. My sincere
thanks also go to my classmates in UNS University for their stimulating discussions
and helping. And last but not least, I would also like to dedicate this work to my
beloved parents, my mother, my family and my wife for their moral and financial
supports, I am totally convinced that I would never come to exist and have succeeded
without them. Thank you all. Sincerely.
Surakarta, October 2014
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TABLE OF CONTENTS
Page TITLE .............................................................................................................................................. i
APPROVAL PAGE ................................................................................................................... ii
ABSTRACT ..................................................................................................................................... iii
FOREWORD ................................................................................................................................... iv
TABLE OF CONTENTS ................................................................................................................. v
CHAPTER I INTRODUCTION...................................................................................... 1
1.1 . Background ................................................................................................................. 1
1.2 . Problem statement ....................................................................................................... 3
1.3 . Problem Limitation of the study ................................................................................. 3
1.4 . Objective ..................................................................................................................... 3
1.5 . Significance of the study ............................................................................................. 4
CHAPTER II BASIC THEORY & LITERATURE REVIEW ................................... 5
2.1. Basic Theory ................................................................................................................ 5
2.2. Properties of Almuinum ............................................................................................... 6
2.3. Properties of Steel ........................................................................................................ 7
2.4. Literature Review ......................................................................................................... 8
2.5. Diffusion welding with interlayer ................................................................................ 9
2.6. Variable Diffusion Welding ......................................................................................... 10
2.7. Advantages and Disadvantages of Diffusion Welding ................................................ 11
2.8. 6061 Aluminium .......................................................................................................... 11
2.9. SS 400 Steel ................................................................................................................. 12
2.10. Phase Digram Fe–Al ................................................................................................. 13
2.11 Phase Diagram Fe – Cu ............................................................................................... 15
2.12 Phase Diagram Al – Cu ............................................................................................... 15
2.13 Hypothesis of Research ............................................................................................... 16
CHAPTER III RESEARCH METHODOLOGY ......................................................... 17
3.1. The place of study ........................................................................................................ 17
3.2. The material used is Al 6061 with SS 400 ................................................................... 17
3.3. Research tools .............................................................................................................. 19
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3.4. Research flow chart ...................................................................................................... 21
CHAPTER IV RESULT AND DISCUSSION ......................................................... 22
4.1. Macro and Microstructure Investigations .................................................................... 22
4.2. Scanning Electron Microscope (SEM EDX) ............................................................... 24
4.3. Analysis of the Hardness Test Data ............................................................................. 27
4.4. Analysis the Shear Strength Test Data ......................................................................... 29
CHAPTER V CONCLUSIONS AND RECOMMENDATIONS ............................. 33
5.1. Conclusion ................................................................................................................... 33
5.2. Suggestion .................................................................................................................... 33
REFERENCES ................................................................................................................... 34
APPENDIX
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LISTS OF PICTURE
Page
Figure 2.1 Microstructure of furnace brazed joints ........................................... 10
Figure 2.2 Microstructure of furnace brazed joints ........................................... 10
Figure 2.3 Microstructure of 6061 Aluminium ................................................. 12
Figure 2.4 Microstructure of SS400 Steel ......................................................... 13
Figure 2.5 Fe-Al equilibrium phase diagram .................................................... 14
Figure 2.6 Fe-Cu equilibrium phase diagram .................................................... 15
Figure 2.7 Al-Cu equilibrium phase diagram .................................................... 16
Figure 3.1 Dimensions of test specimen ........................................................... 18
Figure 3.2 Specimen size mm ........................................................................... 20
Figure 4.1 Macro structure of diffusion joint depending on holding time and
filler composition ............................................................................. 23
Figure 4.2 Macro structure of diffusion joint depending on holding time and
filler composition ............................................................................. 24
Figure 4.3 SEM images of Al / Fe interface ..................................................... 25
Figure 4.4. Hardness of interface area without filler .......................................... 28
Figure 4.5. Hardness of interface area Fe 60% -Cu 40% ................................... 28
Figure 4.6. Hardness of interface area Fe 80% - Cu 20% .................................. 29
Figure 4.7. Shear Strength test with variable holding time and composition .... 30
Figure 4.8. Graph of Shear Strength test with variable holding time and
composition ...................................................................................... 31
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LISTS OF TABLE
Page
Table 2.1 Crystal structure, stability range and hardness Fe-Al ...................... 14
Table 3.1 Chemical Composition of Al 6061 .................................................. 17
Table 3.2 Chemical composition of SS400 ...................................................... 17
Table 3.3 Mechanical Properties of Aluminum and Steel (SS400) ................. 17
Table 3.4 Research parameters variations ....................................................... 19
Table 4.1 Hardness of intermetallic components in Al-Fe system .................. 27
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CHAPTER I
INTRODUCTION
1.1. Background
Aluminum is the most enormous metal and the third most abundant element in
the earth's hard surface, after oxygen and silicon. It covers near to 8% by weight of
the earth’s solid surface. On the basis of its chemical nature, Aluminum is also
reactive to occur innately as free metal (Kobayashi and Yakou, 2002). There are
many applications of Aluminum in our daily life, such as construction machinery,
aircraft construction, ship construction, home furnishing and electronics component.
For the vehicle industry, Aluminum has set up a worldwide position because of its
obvious convenience utilities over the other competitive materials. Aluminum
facilitates exceptional unit strengths (strength/density ratio), extensive corrosion
resistance, small maintenance costs, considerable temperature resistance, flexibility
which is an idiosyncratic ability of a material to undergo a certain amount of plastic
deformation without the occurrence of macroscopic cracks due to its lightweight
(Maea et al., 2008). It can be easily utilized by all commercial processes such as
welding, brazing, or soldering. Aluminum can be effortlessly formed by all general
processes, including extrusion (a major advantage) and can be recycled. Apart from
advantages, there are some negative aspect of Aluminum. First, Aluminums is
comparatively more expensive than steel. Secondly, Aluminum sheets are more
distressful to stamp into car body parts. Thirdly, Aluminum is ponderous to weld than
steel. Lastly, Aluminum doesn't have the strengths levels as steel (Abhiyan et al.,
2013).
The effectiveness of Aluminum choice depends on the nature of the aluminum
type used. Nature of poor work indurating alloy Al 6061–T 6511, a very extensive
work tightening annealed material 1100 Al, and both Al alloys (Al6061-T6511 and
annealed 1100 Al) were experimented and reported in subsequent researches (Khan et
al., 2009; 2010a; 2010b). It was mentioned that the subsequent expansion and
positive cross-effect was seen in the a high work hardening alloy annealed 1100 Al as
compared to poor quality hardening alloy Al 6061–T 6511 where corrugation and
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incompatible cross-effect with finite deformation yield surfaces was demonstrated.
According to Khan et al., (2010a), the subsequent yield surfaces for annealed Al
1100, the rate of kinematic hardening, Young’s and shears moduli reduced and
isotropic hardening went up with finite plastic deformation, which exhibited positive
cross-effect for linear, bilinear and non-linear uploading.
Steel is a sort of alloy of iron and a small quantity of carbon. Carbon is the
primary alloy element, which accounts between 0.002% and 2.1% by weight in steel.
There is no obvious advantage in using aluminum over steel. Basically, strength
denotes to the highest load that a material can be tamed to without yielding, while
hardness refers to how much a material bends when a load is applied (Ajit et al.,
2013). Stiffness is quantified by a parameter called Modulus of Elasticity. Steel’s
modulus is around 3 times mightier than Aluminum but steel’s weight is about 3
times heavier than aluminum.
Aluminum is very difficult to join with steel because there are problems like
different melting points, physical natures and other intermetallic differences. Kim et
al. (2006) presented that intermetallic diffusion in interface Al and steel is formed.
The Intermetallic Compound For motion (IMC) is rapidly developed and grows
between the steel and the molten aluminum. Only aluminum diffuses into the steel
substrate without the dissolution of iron at the interface of the steel-intermetallic
compound. This result was supported by Qiu et al. (2009).
According to Kim et al. (2006) the primary diffusing species of the hot dip
aluminizing process in their study was aluminum. Al coating on the steel and the
short dipping time prevent the iron from dissolving into the aluminum melt. The IMC
is confirmed to be Fe2SiAl8 with a hexagonal unit cell (space group P63/mmc). Sun
and khalel (2007) showed that the intermetallic phases FeAl2 and Fe2Al5 were the
most dominant phases that could be observed, that they were formed sequentially, in
contrast to intermetallic, which formed synchronously in bulk materials. A good
diffusion inter-countenance cannot be made up if the heating temperature is
extremely low, since extent of diffusion is not enough even though the holding time is
longer and the pressure is higher. However, if the heating temperature is too high, the
grains will grow up heavily and the diffusion transition zone can become wider,
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which will negatively affect the performance of the diffusion bonding joint (Yajiang
et al., 2005).
Furthermore, the usage of filler material such as Cu- Mg enhance the hardness
of interface bonding between two dissimilar metal following by perfect holding time
(Mahendran et al., 2009). Therefore, this paper aims to determine the effect of
holding time on the diffusion characteristics of the joint with the 6061 aluminum and
Carbon steel filler using Cu and Fe.
The focus of this research is on optimizing the holding time required for
diffusion welding of Aluminum and Steel. In this research, the variation of holding
time will be 10, 15, 30, and 45 minutes. After the specimen processed by the variation
of holding time, it will be tested by shear tests and macrostructure tests using optical
microstructure and SEM. The completion of the work will be a further strengthening
input to the field of science and dissimilar materials welding industry.
1.2. Problem statement
The explanation above shows that it is possible to joint Aluminum and steel
using diffusion bonding. Aluminum diffuses into the steel substrate without the
dissolution of iron at the interface of steel-intermetallic compound. Diffusion will
perform in certain time.
1.3. Problem Limitation of the study
In this study, the problems can be limited as follows:
1. Surface treatment is similar for every specimen.
2. Variations in composition of filler will be (80% Fe - 20% Cu), (60% Fe - 40%
Cu), Without Filler).
3. Holding time variation are 10, 15, 30 and 45 minutes.
1.4. Objective
The objective of this research is to investigate the effects of holding time on
the physical properties, shear strength and the hardness of dissimilar metal diffusion
welded between Aluminum-Steel.
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1.3. Significance of the study
Up on its completion, this research is believed to provide benefits:
1. Comprehensive understanding about of aluminium 6061 welded with steel SS
400.
2. As a reference for education field and further research by any other students in the
future.
3. This research can be used on industrial field especially on the field of welding.
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CHAPTER II
THEORY AND LITERATURE REVIEW
2.1. Basic Theory
Diffusion is the discursive system within a container where particles are able
to distribute themselves. According to the definition of Medical Dictionary, it can be
mentioned that it is a process of continuous motion of liquids, gases particles, or
solids interlace, caused by thermal restlessness and in dissolved substances shift from
a region of higher to one of lower concentration). The rate of diffusion speed, mass,
and resistance to movement are the most influencing factors within a disorganized
medium. A function of temperature indicates the average speed of a particle. With
the increasing of temperature, particles travel more quickly. A faster movement of
particles is achieved from a higher velocity and gained a more even distribution
sooner. For gases, the root mean square velocity is used for the estimation of average
speed. Measured as the square root of (3·R·T / N·m) where R is the gas constant
(8.3145 J/K·mol), T is temperature in Kelvin, N is Avogadro’s number, and m is mass
of the particle in kilograms. Gases at low pressure are the simplest case, as they are
proficiently running through open space. It is considered that the mass of the particle
also influences its speed. As intuition conceives, more weighty particles run more
slowly and diffuse more slowly as a result (Zumdahl, 2007).
Diffusion welding is the process of switching between the two materials by
means of heating and pressure, without melting the material. Splicing that occurs due
to the lack of diffusion of atoms across the material. Emphasis is to provide contacts
in the interatomic distance between the atoms so that the diffusion of material can
occur more easily.
Characteristics of connection with the diffusion process are as follows:
1. Connection occurs at temperatures below the melting point of the material is 0.5
to 0.8 of melting temperature.
2. The unification between the contact surfaces generated by giving a small load so
that no excessive plastic deformation.
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3. Between the layers can be provided to help increase the activity of the
establishment of the connection in the process of switching (Dunkerton, 1995).
2.2. Properties of aluminum
The features could carry a new material so rapidly from nowhere to a top
position with a diverse range of usage. (Aluminum holds the chemical symbol Al,
atomic number 13 and atomic weight 26.98. The isotope with mass number 27 is the
only stable isotope)
1. Lightness: On the basis of volume, aluminum is merely around thirty three
percent in case of counting the weight of steel at hundred percent. Moreover, from
the aspect of savings of weight substantially, that can be achieved in every sector
mechanical usage because of lightness property.
2. Longevity or Durability: One of the great natures of aluminum is to create an
impervious layer of oxide quickly on opened surface. Consequently, it is gained
the property of high resistant against environmental corrosion, even in marine
atmosphere and no need to coloring for protection from environmental hazards.
3. Conductivity: It is a very common question that why aluminum is inevitable in
the electronic industry. The key answer is because of its spectacular and specific
electrical conductivity. As for instance, compare to copper at the same weight
aluminum carry twice times. Moreover, from the aspect of using for heating and
cooling purpose, it can be utilized due to its remarkable thermal conductivity
feature.
4. Feasibility or Workability: All the common metal-working techniques can be
capitalized for the formation of aluminum, more comprehensively than most. As
it carries some advantageous property if it is considered from the feasibility point
of view such as casting simplicity, transforming ability of die- cast to complicated
forms precisely. Additionally, some more benevolent characters of aluminum are
easiness and quickness materials to machine, fabricating capability, rolling to a
superfine coil as well as it can be thrown into intricate sections, or compressed.
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5. Versatility: Being occupied the properties of hardness or flexibility, corrosion-
resistant, it can be used to tailor the metal easily by the application of heat
treatment and alloying, to fulfill a wide range of demands.
6. Attractiveness: Aluminum is well- known as a translucent element or material. It
looks becoming luster without providing further finishing, but holds enough
glitteriest that can be used to a great number of applied coatings, from paints to
cultured anodizing.
7. Recyclability: Another one of the key features of aluminum is reusability. Only
consuming the 5% of the energy required for initial smelting, it can be easily
reprocessed. The statistical report reveals that the considerable quantity, likely
almost one third in terms of total usage of aluminum today is derived from scrap,
reusable materials (Jones et al., 1949).
2.3. Properties of steel
(Steel doesn't have an atomic weight because it is not an element but rather an
alloy of iron and carbon).
1. Tensile Strength: It can be denoted as the ability of an object or substance to
tolerate the pressure up to certain extent before becoming structurally crippled.
One of the key issues in its application in infrastructure building is to higher
tensile strength compare to others, letting it heavily reverberating to crack or
fracture.
2. Ductility: Without fracture, switching the shape followed by the application of
force is another benevolent mechanical property of steel. In case of delicate wires,
or big automotive parts and panels, the flexibility nature of steel is highly
demanded for different shapes and constitution.
3. Malleability: There is another nature of steel called malleability, which is likely to
be closely affiliated with flexibility, allowing it to be disfiguring under pressure.
By following different force devices such as hammering or rolling on the
malleability nature of steel, sheets of variable density is achieved.
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4. Durability: The property of steel which is used to ascertain its capability to
tolerate strain once conformed is high durability or hardness, lasting for a long
time and heavily resistant to external wear and tear.
5. Conductivity: On the basis of conductance property, steel is considered as a fair
conductor of heat and electricity, making it benevolent in the generating of
cookware for domestic usage, as well as electrical wiring.
6. Luster: The fascinating external appearance, silvery in color with a shiny outer
surface, is one of the key physical features of steel.
7. Rust Resistance: One approach like the conjugation of certain elements lets some
sorts of steel obstructive to rust. There are certain elements, which promotes its
ability to tolerant against rust, such as nickel, molybdenum and chromium form
the composition of Stainless steel (Tilottama, 2010).
2.4. Literature Review
Aluminum joining method by welding process is still studied a lot up to now
because there haven’t been many products of both aluminum joined with aluminum
and aluminum joining with other metals. There are still a lot of possible inventions of
aluminum joining process from the existing researches that is by making use of
various available factors. The factors which can influence the success of any research
on joining aluminum by welding is to convert the variants on one of the elements
suitable with the applied welding type and additional material called filler. MIG and
TIG welding for instance, these two processes need gas protector called argon as the
variants for welding on aluminum (Wiryosumarto et al., 2004). FSW welding by
using probe from HSS material with diameter variant of shoulder for joining
aluminum 5083 (Megantoro et al., 2012). RSW welding by adding argon gas on
joining aluminum mixture with the variants within the welding process (Khaleel et
al., 2012). Changing variants on one of the elements on welding type for joining
aluminum can also be done on joining other metals such as steel. Change of variants
on steel is easier to improve the characteristic of the welding result.
The welding of aluminum with steel is very complicated to do, because both
have different nature and characteristic. Adding filler on welding aluminum with steel
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using covered welding point with the change of variants on both metals, it is possible
to join two dissimilar metals and minimize material cost is one of the methods which
can be developed.
2.5. Diffusion welding with interlayer
In the process of diffusion welding can be done by adding between the layers
(inter layer) on the contact surface of the material to be spliced.The addition of
interlayer aims to help increase the activity of the diffusion process on the material to
be joined .In this case usually chosen interlayer of a material that has good solubility
in the materials to be joined. Interlayer can also be selected from a material that can
catch dirt on the interface elements and produce a clean surface. For that purpose the
selected material is a material that has a high solubility containing elements of
interstitials. At interlayer can also use soft materials with the goal of maximizing the
contact area during the first phase of the connection. The material which often used as
an interlayer is copper, silver, and nickel. The thickness of the interlayer layer will
affect the mechanical strength of the connection. To obtain the mechanical strength of
welded joints for maximum diffusion, the layer must be a thin interlayer, or a
relatively thin interlayer. The tensile strength of connections increases, because the
matrix material stretched on plastic flow in the contact interface that interacts with the
parent metal. Experimental studies which have shown that to obtain the maximum
power of the interface, the recommended interlayer thickness is approximately 0.025
mm (Mahoney et al., 1995).
There is a space between the filler metal alloy and the stainless steel. The
growth of the first interconnected intermetallic layer is observed that gap. It
commences to form during the heating cycle before the braze melts. It is found that
the thickness of the layer is increased with the rising of holding time. The holding
time is a key indicator for the detection of second intermetallic layer. It is generated
between the first intermetallic layer and the stainless steel substrate, and its holding
times longer than 10 min. A intermittent layer made of isolated particles belong to the
second intermetallic, possess a holding time of 10 min and becomes incessant for
longer times (Mortensen et al., 1999)
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Fig 2.1. A. Microstructure of furnace brazed joints (LUSTER et al.,1999)
Fig 2.2. B. Microstructure of furnace brazed joints (LUSTER et al.,1999)(((((((((((
Fig: 2.1. A. An illustrated view of the progress of the first (Fe-Si-AI) layer
along with the micrographic view of specimen at 40-min holding time, conjunction
and development of the second (Fe-AI). A distinct view of the hardness of both
interfacial reaction layers compared with both substrates regarding the cracks,
generating through the second (Fe-AI) layer (fracture were at times also found in the
first layer) and hardness indentations.
Fig 2.2. B. An illustrated view of the constitutional arrangement of the first
(Fe-Si-AI) layer and the two-phase composition of the second (Fe-AL) layer along
with the micrographic view of specimen a 60- min retention time, figuring out the
more growth of both layers. The consolidated brazing alloy exhibits large (dark)
intermetallic precipitates above the two intermetallic layers (Altschuller et al., 1999).
2.6. Variable Diffusion Welding
Many variables affect the outcome of diffusion welding. These variables
include environmental conditions, process, material surface conditions, the pressure
connection, and duration of heating. Diffusion welding can be done in an
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environment that is protected with a protective gas such as argon gas, better done in a
vacuum environment pressure 10¹- 10² Pa. (Kazakov, 1985)
2.7. Advantages and Disadvantages of Diffusion Welding
a. Advantages
1. The resulting connection has the properties and microstructure similar to the
parent metal
2. Components which are connected distorted minimum and do not require
machining or forming again.
3. Can connect two different materials.
4. Multiple connections to a structure can be done simultaneously.
5. Can connect to the place or the hard part.
6. Can connect large components without preheating process.
b. Disadvantages
1. It generally requires longer cycle duration, the cost of expensive equipment
that affect its economic value.
2. Require a special environment that is protected from oxidation process,
because the diffusion process is very sensitive to oxidation.
3. Interlayer corresponding structures have not been developed for all the alloys.
4. Spliced or repaired surfaces require more elaborate preparation.
5. The application of heat and high compressive force simultaneously in a
vacuum environment is a matter of switching diffusion (Sirod et al., 2005).
2.8. 6061 Aluminum
Magnesium aluminum silicon alloy (AlMgSi) is an aluminum alloy that can
be hardened by heat treatment (heat treatable) and included in the 6061 series. Al
6061 alloy is widely used in industry, such as automobile industries, construction of
houses, bridges and even can be used for the nuclear industry. In the nuclear industry,
for example for the 6061 Al alloy materials research reactor structural elements and
components of the reactor tank.
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The selection of material from the tank caused the Al 6061 alloy has a
hardness that is high enough to be able to withstand the load for use in the reactor .
Because of the nature of the violence of Al 6061 Al 6061 alloy is suitable for
development as a new fuel cladding as U3Si2 - Al, UMO and U - Zr. ( Masrukan et
al., 2009 )
6061 Al alloy is included in the group of silicon magnesium aluminum alloy
(AlMgSi) which has good strength, able to weld, and corrosion resistance is quite
good. The microstructure of 6061 AL alloy is shown in Fig.2. AlMgSi alloys can be
classified into three groups. The first group, include alloys with a balance of
elemental Si with Mg between 0.8 % and 1.2 % by weight. This group can be
extruded. The second group, containing Mg and Si more than 1.4 %. These alloys can
quickly cooled (quench) to improve powerful the strength after the extrusion process.
The third group is a group that popular in North America and has more Si
composition with the purpose to increase hardness.
Fig 2.3. Microstructure of 6061 Aluminium (Cedrix Xia et al., (2004)
2.9. SS 400 Steel
The SS 400 Steel is a kind of low carbon steel due to the amount of 0.2%
carbon content. These steels are widely used for sheet metal forming process, for
example to the body and frame of the vehicle and other automotive components. This
type of steel is made and applied by exploiting the properties of ferrite. Ferrite is one
important phase in the steel which soft and ductile. Low carbon steel has carbon
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content generally below the eutectoid composition and has almost entirely ferrite
microstructure. In sheet steel, carbon content is very low or ultra-low the
microstructure of SS400 is shown in Fig 3. The even number of carbon atoms is well
within its solubility in solid solution so that the micro structure is entirely ferrite.
Fig 2.4. Microstructure of SS400 Steel (Hua Ding et al. (2005)
2.10. Phase diagram Fe - Al
The key role for bonding two intermetallic layers is characterized by the two
factors likely thermal conductivity and disparity in the melting points and solubility’s
of the materials with each other for the industrial applications the association or
composition of Al and Fe and Al and Ti are highly importance. A great problem is
occurred during joining with conventional welding technologies such as MIG and
TIG, because of the substantial difference between melting points and thermal
conductivities of the specific metal properties. This problem is interconnected with
other problems on the sub-sequential basis. Consequently, the emergence of IMPs
and crack formation within the joint zone are generated with subsequent failure of the
joining.
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.
Fig 2.5. Fe-Al equilibrium phase diagram (Schimek et al., 2012).
A depicted figure of Fe-Al equilibrium phase diagram following by the IMP
with allowable mechanical properties in case of welding’s marked is shown above.
An iron-derived solid solution and six non-stoichiometric intermetallic compounds of
Fe3Al, FeAl (α2), FeAl2, Fe2Al3 (ε), Fe2Al5 and FeAl3 is applied for the
characterization of the (Antrekowitsch et al., 2006)
Table 2.1 Composition of crystal, range of fixity and stiffness of the phases formed in
Fe-Al binary System at room temperature. (Rathod et al., 2004)
Phases Crystal structure Stability range (at. %) Vickers Hardness (9.8N)
Fe solid solution BCC 0-45 Not investigated
y-Fe FCC 0-1.3 Not investigated
Fe Al BCC (Order) 23-55 470 (3) (491 -667) (4)
Fe3Al DO3 23-34 330 (3) (344 -368) (4)
Fe2Al3 Cubic (complex) 58-65 Not investigated
FeAl2 Triclinic 66-66.9 Unknown (3) (1058-1070)(4)
Fe2Al5 Orthorhombic 70-73 1013(3) (1000-1158)(4)
FeAl3 Monoclinic 74.5-76.5 892(3) (772-1017)(4)
Al solid solution FCC 99.998-100 Not investigated
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2.11 Phase Diagram Fe - Cu
A binary system based on Cu-Fe and its phase diagrammatic view is shown in
Fig. 2.6. The liquid phase this diagram shows a calculated metastable miscibility gap
for the liquid phase. Several studies on this miscibility gap of the liquid phase in Cu-
Fe base system have been carried. Phase equilibria in the Cu-Fe base ternary systems
have been investigated by the present group both experimentally and
thermodynamically. C.P. Wang et al,. ( 2004 )
Fig 2.6. Fe-Cu equilibrium phase diagram (ASM International, (1992)
2.12. Phase Diagram Al - Cu
The phase diagram of the Al - Cu binary system is viewed in Figure .2. 7. It is
a matter of concern at the part of the line furthest away from the liquid region,
achieving the part of the alloy which holds a liquid state. Naturally, a following value
of percentage is 81.6%.
From the aspect of complexity the estimation of the constitution of the 18.4%
α, in cases of copper and aluminum is relatively easier. By seeing insight view it can
be said that the α-region, likely position at Cα = 2.5%., is the closest one with
vertical, where the composition of the α is therefore 2.5% copper and 97.5%
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aluminum. If the same method is considered by an identical way it can be found that
the composition of Liquid is CL = 21.5% copper and 78.5% aluminum. ASM
International, (1994)
The checking of the addition of estimated percentages with the original
concentration of copper in the mixture is always worth. 2.5% copper is present in
18.4% of the solution, and 21.5% copper is available other 81.6%. Now follow the
multiplication: 0.025 · 0.184 + 0.215 · 0.816., which should be equal to 18%, the
concentration of copper in the solution. However, if it is not found which indicates
that something is wrong with the estimation. A diverse types of horizontal axes is
seen in the phase diagram.
Fig 2.7. Al-Cu equilibrium phase diagram (ASM International, (1994)
2.13. Hypothesis of Research
Alternative hypothesis (Ha): Holding time holds a great effect on the
properties of diffusion welding between aluminum and steel.
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CHAPTER III
RESEARCH METHODOLOGY
3.1. The place of study
The study was conducted at the Laboratory of Production Process Mechanical
Engineering Department, Faculty of Engineering, University of Sebelas Maret
Surakarta.
3.2. Method
a. Material
The used material in this research are aluminum AL 6061 and carbon steel
SS400. The chemical composition of the base metals is shown in table 3.1 and
3.3.
Table 3.1. Chemical Composition of Al 6061 (Dinaharan et al., 2012).
Mg Si Fe Mn Cu Cr Zn Ni Ti Al
0.95 0.54 0.22 0.13 0.17 0.09 0.08 0.02 0.01 Bal.
Table 3.2. Chemical composition of SS400 (Triyono et al (2013).
C Mn Si P Cr Mo Ni Cu Fe
0,05 0,225 0,15 0,094 0,04 0,05 0,07 0,16 bal
The used material in this research are aluminum AL 6061 and carbon steel
SS400. The Mechanical properties of the base metals are shown in table 3.4.
Table 3.3. Mechanical Properties of Aluminum and Steel (SS400) (Aizawa et al,
2007), Triyono et al (2013)
Material
Melting
Point (oC)
Specific Heat
(J/kg.oC)
Density
(kg/m3)
Thermal
Conductivity
(W/mK)
Electrical
Resistivity
(µΩ.cm)
Al 6061 660 900 2.7 g/cc 167 W/m-K 3.99
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Material
Melting
Point (oC)
Thermal
Conductivity
(W/mK)
Coefficient of
Thermal Expansion
(µm/m/oC)
Tensile
Strenght
(Mpa)
Electrical
Resistivity
(µΩ.cm)
SS 400 1495-1525 12,6 13,0 240 2,65
b. Diffusion welding process
Diffusion welding of aluminum to steel in the process is the use of a
vacuum furnace. In these conditions, diffusion welding can occur with either.
This diffusion process occurs in two different material surfaces between Al 6061
with SS 400. This aims that both atoms diffused each other resulting in a material
strong bond interface these metals. Material Al 6061 and SS 400 carbon steel is
cut to the size of 32.5 mm x 20 mm, then the carbon steel SS 400 square made use
traditional milling machines up to size 10 x 10 mm with a depth of 1 mm. At the
center of the composition of the powder is given, and then introduced into the
furnace machine. For filler composition Fe-Cu mixing powder by lathe machine
used about 30 minutes with 120 RPM used joining in single lap joint they are
mixture of Al-Fe powder. With composition are using in this research namely Fe
80% - Cu 20%, Fe 60% - Cu 40% and without filler table 3.4 shows the schedule
of diffusion process Machine specification furnace with 400 volt, 1200 watt, 3
phase, 50 Hz and a maximum temperature of 1200 ° C is used for diffusion
welding process. More inserted into the machine until the temperature 950oc
furnace with holding time are 10, 15, 30 and 45minutes.
Fig 3.1. Dimensions of test specimen size in mm
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Table 3.4. Research parameters variations.
Run No. Mixture of Eements Promoter Holding time (Minuets)
1 60%Fe ‐ 40%Cu 80%Fe ‐ 20%Cu Without Filler 10
2 60%Fe ‐ 40%Cu 80%Fe ‐ 20%Cu Without Filler 15
3 60%Fe ‐ 40%Cu 80%Fe ‐ 20%Cu Without Filler 30
4 60%Fe ‐ 40%Cu 80%Fe ‐ 20%Cu Without Filler 45
3.3. Research Tools
Hardness Tester 1. Loading method. Lever method by electric automatic loading system 2. Periods of loading, 5, 10, 15, 30 and ace. 3. Loading weight, 15, 25, 50, 100, 200, 300, 500 and 100g 4. Indenter, Vickers 5. Magnifications of microscopes observing microscope 100 time 6. Objectives observing 10 times and measuring objective 40 times 7. Micrometer ocular maximum measuring scale 200 m
8. Area of stage 120*120 mm 9. Height of specimen inside the stage 60 mm and outside the stage 180 mm 10. Weight of machine and approximately 30 Kg 11. Power supply 120 or 230 V, 50 or 60 Hz, 50 VA and fuse 0.5A type T
Optical Microsturcer
The test sample is a cylindrical or rectangular and there are positions sample surface can be flattened. Identification and specification of macro and micro test equipment as shown in figure 3.3 as follows: a. Brand: Olympus / SZ 1145 TR
Specifications: Zoom ratio 6.1; maximum work piece height of 7.3 mm; magnification from 1.8 to 11 x
b. Brand: Euronext Holland Specifications: Magnification 10x ocular lens, objective lens magnification 4x, 10x, 20x, 40
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Shear strength test. Specimen Preparation The specimens in this process is made in accordance journal reference
standard size 32.5 x 20 mm for Al 6061 carbon steel and carbon steel SS 400. SS 400 in milling in this part of monarch filler powder size of 15 x 13 x 1 mm. Specimens of Al 6061 and SS 400 carbon steel surface is smoothed using sandpaper. Filler in the form of powder mixed according to the composition, then the contents of section 400 SS carbon steel that has been in the milling beforehand.
Shear strength is calculated used . (1).
Where F = force (N). A = area (mm2). = shear strength (MPa)
15
6 2,3
20 50
Fig 3.2. Specimen size in mm.
Scanning Electron Microscope (SEM EDX) Testing Procedure SEM 1. Samples to be observed cleaned, dirty and rusty when ultrasonic cleaning can be
done. Ultrasonic cleaning using acetone solution given by the frequency of ultrasonic vibration.
2. Placed. In sample holder contained in the chamber 3. To attach the mounting is not connected to the base. Holder, usually using double-
sided conductive tape that connects the sample holder base. 4. When running the engine SEM, chamber must always be kept in a vacuum by
turning on the vacuum pump.
Fe
Al
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3.4. Research flow chart:
TESTING
START
MAKING PREPARATION TOOLS: • SS400 2.3 mm thick, length 32.5 mm, width 2 cm
• AL6061 thickness 6 mm, length 32.5 cm, width 2 cm
SAMPLE PREPARATION
MAKING METAL PLATE (FILLER) WITH VARIATIONS COMPOSITION (80% Fe - 20% Cu ), (60% Fe -40% Cu), (Without Filler)
• The focus on the affect of holding time`s 45, 30, 15 and 10 minutes • The temperature`s 950 °C
Testing • Microscope • Microstructure • Scanning Electron Microscopy
(SEM) • Shear strength test • Hardness test
Data Processing and Analysis
Result
End
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CHAPTER IV
RESULT AND DISCUSSION
Research was conducted to determine the effect of holding time on the physical
and mechanical properties of dissimilar metal diffusion welded between Aluminum
and Steel. Mechanical properties of joints were obtained by performing several tests
including shear strength test, hardness test, macro and micro structure investigations
and Scanning Electron Microscope (SEM EDX). The test data were analyzed to
generate a discussion and conclusions which were consistent with the objectives of
the study.
4.1 Macro and Microstructure Investigations
Study of holding time effect on the diffusion behavior at interface of dissimilar
metals joint between Aluminum and Carbon Steel joint using element promoter
showed that Diffusion occurred at the interface of steel-aluminum joint on all of
variations. Aluminum atoms diffused into steel and steel atom diffused into
aluminum for mainly joint. Holding time gave different behavior of diffusion as seen
in Fig. 4.1. The longer holding time, the better bond behavior.
At holding time range of 10-30 minutes, it was found that there are
incomplete bonding and cracks in interface of aluminum-steel as shown in Figure 4.2.
There were visible cracks on the surface area with small interface layer in specimens
at holding time of 10 minutes in all the joints with element promoter composition of
60% Fe - 40% Cu, 80% Fe - 20% Cu and without filler. It means that diffusion of
aluminum into steel did not happen significantly with 10 minutes holding time. At 15
and 30 minutes holding time, however, the interface layer thickness increases with
smaller gap and cracks. It was very clear as shown in the figure that the solubility of
aluminum increased with increasing of holding time where more aluminum dissolved
into steel. The best results were found in specimens with composition of 60% Fe -
40% Cu at 45 minutes holding time. In this case, diffused surface area increases
because the diffusion occurs between aluminum and steel which bond each other
resulting in thick interface area and negligible cracking. Additionally, continuous
intermetallic layer appeared in that specimen, which didn’t appear in other specimens.
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Similar studies have also been carried out for the welding of aluminum and
steel friction stir welding by Watanabe et al. (2006) and Rafeng et al. (2009). The
results obtained from the studies on the microscopic structure, the strength of steel
with aluminum, welding resistance indicated that the maximum tensile strength of the
joint was about 86% of that of the aluminum alloy base metal. Additionally, a small
amount of intermetallic compounds were formed at the upper part of the
steel/aluminum interface, while no intermetallic compounds were observed in the
middle and bottom parts of the interface.
Filler
Fe 80% Cu 20% Fe 60% Cu 40% Without Filler
10 M
inutes
15 M
inutes
30 M
inutes
45 M
inutes
Fig 4.1 Macro structure of diffusion joint depending on holding time and filler composition
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Filler
Fe 80% Cu 20% Fe 60% Cu 40% Without Filler
10 M
inutes
15 M
inutes
30 M
inutes
45 M
inutes
Fig 4.2 Microstructure of diffusion joint depending on holding time and filler composition.
4.2 Scanning Electron Microscope (SEM EDX)
Apart from micro and macrostructure photo analysis, SEM study was
conducted to investigate the details of interface layer and diffusion. Diffusion of
aluminum atom to steel and faro atom to aluminum generally occurred at interface of
aluminum-steel during diffusion process. Holding time significantly affect the quality
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of Al-Fe diffusion. Holding time of 10, 15, 30 and 45 minutes gave different result of
the diffusion as seen in Figure 4.3.
Holding
time
Fe (80%), Cu (20%) Fe (60%), Cu (40%)
10
minutes
15
minutes
30
minutes
45
minutes
Fig 4. 3 SEM images of Al / Fe interface
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Figure 4.3 shows the influence of holding time on intermetallic layer
thickness at interface between aluminum and carbon steel by two different Fe-Cu
compositions at holding time 45 minutes intermetallic layer was formed having a
thickness of 1.2 and 0.53 µm for 60% Fe- 40% Cu and 80% Fe-20% Cu specimen
combinations, respectively. The minimum crack between aluminum and carbon steel
was found at composition 60% Fe/40% Cu. At holding time 30 minutes Intermetallic
layers are formed with thickness of 2.30 and 2.47 µm for 60% Fe- 40% Cu and 80%
Fe-20% Cu combinations, respectively. At holding time 15 minutes Intermetallic
layers are formed with thickness of 1.07 µm and 3.08 µm for 60% Fe- 40% Cu and
80% Fe-20% Cu combinations, respectively. Significant gap between aluminum and
carbon steel was obtained both at 80% Fe-20% Cu and 60% Fe- 40% Cu specimen
combinations at holding time 10 minutes, with intermetallic layer thickness of 2.19
µm and 2 µm, respectively. Additionally, from the mapping point of view at 20 µm it
can be observed that Cu molecules are confined only to the interface area and slightly
scattered outside the inter-confront area in specimens with holding time up to 30
minutes both at 80%Fe-20%Cu and 60%Fe-40% Cu compositions. On the other hand,
Cu molecules were scattered throughout the specimen at holding time 45 minutes,
having Intermetallic layer thickness of 0.53 µm. It means that Cu molecules play a
vital role of identifying best Al-Fe interface condition i.e. if the Cu molecules are
located just around the interface area it can be considered as a bad interface, whereas
if the Cu molecules were scattered throughout interface zone that can be considered
as a good interface. The diffusion and expansion of iron and copper powder into
Aluminum during welding occurred due to the fact that aluminum is more anodes as
compared to those materials. Due to this reason two main compounds were formed in
the intermetallic layers which are Fe Al3 and Fe2 Al5. The result showed that
aluminum was attacked by the diffusing materials. This result is similar to research
done earlier by Kengkla and Tareelap (2012) that revealed that heat from welding
caused formation and expansion of intermetallic compound, Fe Al3 and Fe2 Al5, along
Al/Fe interface.
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4.3 Analysis of the Hardness Test Data
The hardness test shows that the average of hardness value in diffusion zone is
higher than the base plate of aluminum and steel. The welding process make
aluminum dissolved into steel, but the different filler compositions and variations of
holding time make the different result in the thickness of intermetallic layer and
solubility of aluminum into the steel. The increase of interface thickness cause
increasing hardness in diffusion zone depends on cracks and gap. The Vickers
hardness test data shows that there is no directly proportional between the hardness
level and variations of holding time. This is proved by Mahendran et al. (2010) which
found that there is no significant correlation between the hardness level and variations
of holding time
Table 4.1. Data of Hardness diffusion bonding at interface layer.
Holding time Fe-Cu composition Hardness (VH) Intermetallic compound
layers (minutes) 60% - 40% 80% - 20% Without filler
10
420.5 383.1 681.1
FeAl (110), Fe3 Al (220) 441.3 487.7 641.7
420.5 420.5 641.7
15
463.6 572.3 641.7
FeAl (200), Fe3 Al (400) 463.6 641.7 605.5
441.3 605.5 641.7
30
541.8 441.3 605.5
FeAl (211), Fe3 Al (422) 541.8 463.6 641.7
513.7 441.3 463.6
45
681.1 661.0 641.7
(600-900), Fe2 Al5 641.7 641.7 681.1
641.7 641.7 641.7
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Fig 4.4 Hardness of interface area Without Filler
Fig 4.5 Hardness of interface area Fe 60%, Cu 40%
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Fig 4.6 Hardness of interface area Fe 80%, Cu 20%
4.4 Analysis the Shear Strength Test Data
The results of tensile shear tests are shown visually in Fig 4.7 to get an idea of
the structure of the metal surface which occurred after performing tensile shear test.
Detection of the symptoms of what was happening in both these material can be
conveyed. This study clearly reveals the phenomenon of welding metals which are
not similar. This phenomenon reveals the influence of holding time on the diffusion
characteristics of the welded joints between 6061 aluminum with SS 400, Barometers
used to answer these phenomena on diffusion welding are the variation of holding
time and composition of the filler. Data were obtained by measuring diffusion
bonding zone and then processed to provide an answer about the extent of diffusion.
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Filler
Fe 80% Cu 20% Fe 60% Cu 40% Without
Minutes10
a b
a b
a b
15 M
inutes
a b
a b
a b
30 M
inutes
a b
a b
a b
45 M
inutes
a b
a b
a b
Fig 4.7 Shear Strength test with variable holding time and composition
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Fig 4.8 Graph of Shear Strength test with variable holding time and composition
Fe and Al diffuse easily and a thick and brittle intermetallic compound is
produced. The intermetallic layer thickness varied according to different holding
time. However, the thickness is not uniformly proportional to time variations.
Holding time has an effect on the quantity of atomic diffusion thereby making
variations in the intermetallic layer. Thicker intermetallic compound caused weaker
shear strength. Since the formation of diffusion layer at the interface influences the
strength of the bond, it is necessary to analyze the role of diffusion layer on bonding
characteristics according to holding time. IMC at 10 minutes holding time was
thinner than 15 minutes holding time. The thickest IMC observed was at 30 minutes
holding time because of large accumulation of diffused materials. Thicker
intermetallic compound is usually associated with weaker shear strength. However, as
the holding time is further increased to 45 minutes the thickness of IMC decreased
this is because of the reason that in order to obtain high strength a longer and
optimum holding time is required which helps to reduce the thick IMC formed during
the initial processes. The possible reason for this may be due to the contribution of
the filler Cu that facilitates diffusion of IMC when the copper scatters.
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Another phenomenon that occurs is the increasing levels of Cu in the filler
which is a promoter of switching diffusion impact on decreasing the tensile strength.
This is caused by an impact because of porosity (Tatsuro and MikioYamanaka,
2013).
As shown in Fig 4.8, in contrast with the increasing of Cu content contained
on any filler, the shear strength decreased. This is in order to show the influence of
the parameters used in this study more clearly. The shear strength of the bonds peaks
at 8.2 MPa after 45 minutes holding time at the brazing temperature. This peak is
generated by the growth of the second intermetallic layer, which can be seen as atom
fragile that joint perfectly.
Additionally, from the figure the shear strength value decreases from 10 to 30
minutes of holding time, but increase at 45 minutes because there is no crack which.
The absence of crack at 45 minutes holding time enhances the shear strength of the
dissimilar material welding. It is because the formation of the layer is near similar
with eutectoid composition of the solidified liquid area. As time proceeds from 10
minute to 30 minutes it correlated with the growth and the formation of intermetallic
layer indicating in this case this condition may be subject to the layers that are
responsible for the poor mechanical properties of furnace parts after long heating
cycle. 30 minutes of holding time has the lowest value based on the testing result. It is
because there is bigger crack as compared to the other holding times which can be
seen from the pictures of SEM in figure 4.3. The lowest shear strength value at 30
minutes holding time is possibly associated to the formation of crack which is
responsible for vulnerability of shear stress. This result is supported by finding of
Tong and Qin (2014).
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CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS
A. Conclusion
1. The occurrence of diffusion process was observed at 950°C between aluminum
and carbon steel generating intermetallic layers inside the interfacial zone.
2. With the rising of holding time, the intermetallic layer thickness was increased.
Fracture or incomplete bonding was demonstrated in the specimens during 30
minutes holding time. However, it was not appeared in the specimens in terms of
45 minutes holding time. From the aspect of diffusion penetration it can be said
that at the same holding time Fe rich-element promoter interfused less that Cu
rich-element promoter. The findings from macrostructure, microstructure and
SEM test showed that Al- Fe joint occupied the best result with element promoter
content of 60/40 % at 45 minutes holding time. No interlayer space found at this
specimen. Moreover, on the basis of result derived from mapping it can be
mentioned that in terms of poor interface bonding, Cu molecules were placed just
around the interface area, while, in case of strong interface bonding, Cu molecules
are scattered throughout the specimen.
3. The maximum shear strength value of specimen with filler composition Fe 80%
Cu 20% using 45 minutes holding time was 8.2 MPa. The lowest shear strength
values were specimen with filler composition Fe 60% Cu 40%, Fe 80% Cu 20%
and without filler at 30 minutes holding time. The biggest hardness value was
681.1 HV on without filler at 10 and 45 holding time minutes.
B. Suggestion
1. The suggestion for the future researchers who will be conducting this research
area is to use less ratio filler composition of Cu, as using more Cu for filler
composition it generates the porosity of the all adherent materials.
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CURRICULUM VITAE
Name ALI JEBRIL SAAD JEBRIL
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