EFFECT OF HOLDING TIME ON THE PHYSICAL AND … · meneliti pengaruh holding time terhadap...

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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

perpustakaan.uns.ac.id digilib.uns.ac.id

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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




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

Place/Date of birth 10. 07. 1985. TAMIMI

Gender Male

Marrital Status Married

Religion Muslim

Citizensip Libyan

Address BLOCK 300, Number Home 204 Tamimi Libya

E-mail [email protected]

[email protected]

BBM, PIN: 7D5DD3BE

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