國立高雄科技大學
機械工程系博士班
博士論文

應用 TIG 與摩擦攪拌焊接法探討鋁合金與不銹鋼及鋁合
金與雙相鋼間銲接接頭之銲接特性
Study on the Welding Features of the Weld Joint between
Aluminum Alloy to Stainless Steel and Aluminum Alloy to Dual
Phase Steel by Using TIG and Friction Stir Welding

研究生：阮文一
指導教授 ：黃世疇 教授

中華民國 107 年 12 月

I


應用 TIG 與摩擦攪拌焊接法探討鋁合金與不銹鋼及鋁合
金與雙相鋼間焊接接頭之焊接特性
Study on the Welding Features of the Weld Joint between
Aluminum Alloy to Stainless Steel and Aluminum Alloy to Dual
Phase Steel by Using TIG and Friction Stir Welding
學生: 阮文一

Van Nhat Nguyen

指導教授 ：黃世疇 教授

Shyh-Chour Huang

國立高雄科技大學
機械工程系博士班
博士論文

Department of Mechanical Engineering
National Kaohsiung University of Science and Technology
In Partial Fulfillment of the Requirements for the Degree of Doctor of
Philosophy in Mechanical Engineering

December 2018
Kaohsiung, Taiwan, Republic of China
中華民國 107 年 12 月
II


III


應用 TIG 與摩擦攪拌焊接法探討鋁合金與不銹鋼及鋁合
金與雙相鋼間焊接接頭之焊接特性
研究生：阮文一

指導教授：黃世疇 教授
國立高雄科技大學
機械工程系博士班

摘要

由於重量輕，耐腐蝕性和高抗氧化等優點，鋁合金與不銹鋼，鋁合金和雙相鋼
之間的焊接在工業上有廣泛的應用。然而，要將金屬焊接在一起，仍然存在許多挑

戰。 例如，鋼的熔點遠大於鋁的熔點，機械性能和化學成分的差異。 特別是在不銹
鋼與焊縫之間的界面處，容易形成金屬間化合物（IMC）層的脆性和裂縫。 這些問
題將對接頭的強度和焊接質量產生負面影響。 為了防止 IMC 層的形成和焊接接頭質
量缺陷的產生，必須發展合宜的焊接方法與焊接參數。
在本研究中，摩擦攪拌焊接（FSW）和鎢極惰性氣體（TIG）焊接分別用於焊接鋁
AA6351 / DP800 鋼和鋁 A6061-T6 / SUS304L 鋼。
鋁合金和不銹鋼，鋁合金和雙相鋼之間的銲件有許多優點，如重量輕，耐腐蝕
性和耐氧化性高，因而得到了更廣泛的工業應用. 然而，要將金屬焊接在一起，仍
然存在許多挑戰. 例如，鋼的熔點遠大於鋁的熔點，機械性能和化學成分的差異. 特
別是在不銹鋼與焊縫之間的界面處，容易形成金屬間化合物（IMC）層的脆性和裂縫.
這些問題將對接頭的強度和焊接質量產生負面影響. 因此有必要有一個適當的焊接

IV


方法和設定的焊接參數來防止 IMC 層的形成和發展並形成缺陷，從而提高焊接接頭
的質量. 在這項研究中，摩擦攪拌焊（FSW）和鎢惰性氣體（TIG）焊接分別用於焊
接鋁 AA6351 / DP800 鋼和鋁 A6061-T6 / SUS304L 鋼.
通過攪拌摩擦焊方法成功地進行了 AA6351 與 DP800 鋼之間的搭接。利用掃描電
子顯微鏡（SEM）和 X 射線衍射（XRD）技術研究焊縫的顯微組織特徵。調查結果表
明，在鋼和鋁合金之間的界面出現的金屬間化合物層的厚度小於 7 微米，並進行相
存在於 IMC 層包括 Al3Fe 系，Fe3Al 金屬，和 Al2Fe 相. 還檢查了熱循環以顯示溫度
分佈與金屬間化合物層的形成之間的關係
分析了採用 TI G 焊和 ER4047 填充金屬對鋁與鋼對接的特點. 並使用光學顯微
鏡（OM），掃描電子顯微鏡（SEM），能量色散 X 射線衍射（EDS）來顯示微觀結構.
試驗結果表明，焊縫外觀良好，無缺陷，且熱影響區非常小. 此外，在鋼與焊縫之
間的界面處還發現了金屬間化合物層和裂縫，其厚度為 2μm。在包含 Fe4Al13，Fe2Al5
和 FeAl3 相的金屬間層中形成新相。通過維氏硬度試驗和拉伸試驗方法研究了焊接接
頭的機械性能。結果，不銹鋼，焊縫和金屬間層中的硬度的平均值分別為 218HV，
79HV 和 411HV。最大抗拉強度達到 226.5 Mpa，斷裂位置發生在焊接釬焊表面。


關鍵字：鎢極惰性氣體工藝，攪拌摩擦焊工藝，填充金屬，DP800 鋼金屬間化合物層，
微觀結構，機械性能，熱循環。

V


Study on the Welding Features of the Weld Joint
between Aluminum Alloy to Stainless Steel and
Aluminum Alloy to Dual Phase Steel by Using TIG and
Friction Stir Welding
Student: Van Nhat Nguyen

Advisor: Shyh-Chour Huang

Department of Mechanical Engineering
National Kaohsiung University of Science and Technology

Abstract
Due to the advantages such as light weight, corrosion resistance and high
oxidation resistance, the connection between aluminum alloys and stainless steel,
aluminum alloys and dual phase steel has used more widely in industrial applications.
However, to weld the metal together, there are still many challenges. Such as, the
melting point of steel is much larger than that of aluminum, the difference in
mechanical properties and chemical composition. Especially at the interface between
the stainless steel and weld seam easily form an intermetallic compound (IMC) layer
brittle and cracks. These problems will have a negative impact on the strength of the
joint and the quality of the weld. To prevent the formation and development of the
IMC layer and the formation of defects improving the quality of the welding joint, it
is necessary to have a proper welding method and set of welding parameters. In this

study, Friction Stir Welding (FSW) and Tungsten Inert Gas (TIG) welding were used

VI


to weld Aluminum AA6351/DP800 steel and aluminum A6061-T6/SUS304L steel,
respectively.
Lap joint between AA6351 to DP800 steel was carried out successfully by a
friction stir welding method. The scanning electron microscopy (SEM) and X-ray
diffraction (XRD) technique was utilized to investigate the microstructural characteristics of
the weld. The survey results showed that at the interface between steel and aluminum alloy
have appeared intermetallic compound layer with a thickness less than of 7μm, and the phases
exist in IMC layer includes Al3Fe, Fe3Al, and Al2Fe phases. Thermal cycles were also
examined to show the relationship between the distributions of temperature with the
formation of the intermetallic layer.
The characteristics of Butt joint between aluminum and steel by using TIG welding with
ER4047 filler metal were analyzed. The optical microscopy (OM), scanning electron
microscopy (SEM), energy dispersive X-Ray diffraction (EDS) have been done to
demonstrate the microstructure of the weld. Test results illustrated that the appearance of the
weld good, no defects, and the heat-affected zone is very small. Further, an intermetallic
compound layer and cracks was also found at the interface between the steel and the welding
seam, its thickness of 2 µm. The new phases formed in an intermetallic layer comprising
Fe4Al13, Fe2Al5, and FeAl3 phases. The mechanical properties of the welded joint have been
explored by means of a Vickers hardness test and tensile test method. As a result, the average
value of hardness in the stainless steel, in the welding seam, and in the intermetallic layer is
218 HV, 79 HV, and 411 HV, respectively. Maximum tensile strength reached 226.5 Mpa
and the fracture location occurred at the welding-brazing surface.

Keywords: Tungsten Inert Gas (TIG) process, Friction Stir Welding (FSW) process, Filler
metal, DP800 steel Intermetallic compound layer (IMC), Microstructure,

Mechanical properties, Thermal Cycles

VII


Acknowledgments
During my studies and research at the National Kaohsiung University of Science
and Technology, I received great support from my teachers, my family, my friends,
and my coworkers. Through this opportunity, I want to present my deep sincere thanks
to them.
First, I would like to express honest thanks and respect from my heart to my
academic supervisor, Professor Shyh-Chour Huang, who pointed me to the direction
of research, gave me motivation and support me throughout this study work. Without
his dedicated help, my research will not be as successful today.
Second, I am also extremely thanks to Mr. Quoc Manh Nguyen, Mr. Tien Dat Vu,
for their support to do experimental and data collection.
Third, I would like to thank the leadership of the mechanical engineering
department of the Hung Yen University of Technology and Education for their help
to my focuses to research.
In addition, I would like to choose this opportunity to indicate my sincere thanks
to the members of the Computer Aided Engineering Application and Design LAB has
helped me very enthusiastic during my time at National Kaohsiung University of
Science and Technology.
Finally, I would also like to send my sincere thanks to I would like to send my
sincere thanks to my younger brother Van Hai Nguyen and my younger sister Thi Lan
Anh Nguyen. They have replaced me with care, raised my mother, and help me to
solve all the work in the family. A very special thanks and respect for my wife, who
has been with me overcome many difficulties, she has replaced me with care and
education for my children.


VIII


Contents
摘要 ...................................................................................................................... IV
Acknowledgments ............................................................................................ VIII
Contents ............................................................................................................ VIII
List of Tables ....................................................................................................... XI
List of Figures ................................................................................................... XII
Chapter 1 Introduction ........................................................................................ 1
1.1. Overview ......................................................................................................... 1
1.2. Scope and Objectives of the Dissertation ........................................................ 3
1.3. Dissertation Outline ......................................................................................... 4
Chapter 2 Literature Reviews ............................................................................. 5
2.1. Overview of Previous Research ...................................................................... 5
2.2. Overview of Some Welding Methods ............................................................. 8
2.2.1. Tungsten Inert Gas Welding ..................................................................... 8
a. Current Models Used in TIG Welding ....................................................... 9
b. The Shielding Gases and Gas Mixtures Used in TIG Welding ................ 11
c. Electrodes.................................................................................................. 13
2.2.2. Gas Metal Arc Welding .......................................................................... 13
2.2.3. Friction Stir Welding .............................................................................. 15
a. Microstructural Characteristics ................................................................. 16
b. Tools of Friction Stir Welding Process .................................................... 17
2.2.4. Laser Welding ........................................................................................ 19
2.2.5. Ultrasonic Welding ................................................................................. 22
VIII


2.2.6. Resistance Welding ................................................................................ 24

2.2.7. Explosive Welding ................................................................................. 26
2.3. Welding Defects ............................................................................................ 27
2.3.1. Cracks ..................................................................................................... 28
2.3.2. Porosity ................................................................................................... 29
2.3.3. Undercutting ........................................................................................... 30
2.3.4. Lack of Fusion ........................................................................................ 32
2.4. Heat Transfer during Welding ....................................................................... 32
2.5. Measurement Methods .................................................................................. 33
2.5.1. Optical Microscope ................................................................................ 33
2.5.2. Scanning Electron Microscopy............................................................... 34
2.5.3. X-Ray Diffraction ................................................................................... 35
2.5.4. Vickers Hardness Test ............................................................................ 36
2.5.5. Tensile Testing ....................................................................................... 37
2.6. Summary........................................................................................................ 38
Chapter 3 Experimental Procedure .................................................................. 39
3.1. The Influence of Welding Parameters on the Quality of TIG Weld ............. 39
3.1.1. Welding Current ..................................................................................... 39
3.1.2. Welding Voltage ..................................................................................... 39
3.1.3. Filler Metals ............................................................................................ 40
3.1.4. Shielding Gas .......................................................................................... 40
3.2. The Influence of Welding Parameters on the Quality of Friction Stir Weld 41
3.2.1. Rotational Speed and Travel Speed ........................................................ 41

IX


3.2.2. Welding Tool .......................................................................................... 42
3.3. Experimental Preparation .............................................................................. 42
3.3.1. Tungsten Inert Gas Welding Process ..................................................... 43
3.3.2. Friction Stir Welding Process ................................................................. 48

3.3.3. Preparation for Microstructure Measurement ........................................ 51
3.3.4. Preparation for the Tensile Test ............................................................. 52
3.4. Summary........................................................................................................ 53
Chapter 4 Tungsten Inert Gas Welding Results and Discussion ................... 54
4.1. The Appearance of Welding Joint ................................................................. 54
4.2. The Microstructure of Welding Joint ............................................................ 55
4.3. Tensile Strength Test ..................................................................................... 62
4.4. Hardness Test ................................................................................................ 65
4.5. Summary........................................................................................................ 67
Chapter 5 Friction Stir Welding Results and Discussion ..................................... 68
5.1. The microstructure of Lap Joints ................................................................... 68
5.2. Shear Tensile Test ......................................................................................... 73
5.3. Comparison between Tungsten Inert Gas Welding Method and Friction Stir
Welding Method ................................................................................................... 74
5.4. Summary........................................................................................................ 75
Chapter 6 Conclusions and Future Works ...................................................... 76
6.1. Conclusions ................................................................................................... 76
6.2. Suggestion for Future Works......................................................................... 77
References............................................................................................................ 79

X


List of Tables
Table 3. 1. Chemical compositions and mechanical properties of the A6061-T6
alloy [75]............................................................................................................... 44
Table 3. 2. Chemical compositions and mechanical properties of SUS304L [76]
Table 4. 1. The chemical composition of the alloying elements appears at the EDS
test positions……………………………………………………………………..57
Table 4. 2. Tensile strength test results of the welding joint between aluminum

alloy A6061-T6 and stainless steel SUS304L ...................................................... 63

XI


List of Figures
Figure 2. 1. Tungsten inert gas welding process .................................................... 8
Figure 2. 2. Schematic diagram of the direct current TIG welding; .................... 10
Figure 2. 3. TIG welding cycle with pulse current [35] ....................................... 11
Figure 2. 4. The relationship between the depth penetration and the shielding gas
Figure 2. 5. Gas metal arc welding process .......................................................... 14
Figure 2. 6. Schematic of the friction stir welding process .................................. 16
Figure 2. 7. Schematic of transverse cross-section zone of the FSW weld [36] .. 16
Figure 2. 8. Welding tools used in the FSW process ........................................... 19
Figure 2. 9. Diagram of the laser beam welding method ..................................... 20
Figure 2. 10. Schematic of the ultrasonic welding principle ................................ 22
Figure 2. 11. Resistance welding process (a) Spot welding; (b) Seam Welding . 26
Figure 2. 12. Explosive welding method .............................................................. 26
Figure 2. 13. Types of welding defects ................................................................ 28
Figure 2. 14. Location of the cracks ..................................................................... 29
Figure 2. 15. Model of Porosity............................................................................ 29
Figure 2. 16. Undercut defect ............................................................................... 31
Figure 2. 17. Illustrates the location of lack of fusion .......................................... 32
Figure 2. 18. Optical microscope equipment ....................................................... 34
Figure 2. 19. Scanning electron microscopy equipment ...................................... 35
Figure 2. 20. X-ray diffraction equipment............................................................ 36
Figure 2. 21. Micro-hardness tester machine ....................................................... 37
XII



Figure 2. 22. Tensile test process ......................................................................... 37
Figure 3. 1. (a) X6332B milling machine; (b) Base material plates .................... 46
Figure 3. 2. (a) Type of welding joint (Unit: mm); .............................................. 47
Figure 3. 3. Friction Stir Welding Setup (Unit: mm) ........................................... 50
Figure 3. 4. Diagram of the preparation process for microstructural examination
samples; (a) Cutting samples; (b) Casting samples; (c) Grinding and polishing
samples ................................................................................................................. 52
Figure 3. 5. The shape and dimension of the tensile specimen (Unit: mm) ......... 53
Figure 4. 1. (a) Image for weld bead appearance; (b) The sample cross-section 55
Figure 4. 2. SEM images of the weld joint between Al/Steel; ............................ 57
Figure 4. 3. (a-c) SEM images of spectrum1, spectrum2, and spectrum3; (d-f) the
appearance of the alloying elements in spectrum1, spectrum2, and spectrum3 .. 59
Figure 4. 4. (a) Location of linear scanning; (b) The result of the linear scanning
test ......................................................................................................................... 59
Figure 4. 5. (a) Mapping image; (b-f) the distribution of Fe, Cr, Mn, Si, C, Al, Ni
elements ................................................................................................................ 60
Figure 4. 6 XRD results of the weld specimen ..................................................... 61
Figure 4. 7. The Fe-Al binary phase diagram [42] ............................................... 61
Figure 4. 8. The tensile test results ....................................................................... 62
Figure 4. 9. (a) Image of the fracture position of the tensile test; (b) Surface of fault
in stainless steel side; (c) Surface of fault in the aluminum side ......................... 64
Figure 4. 10. Defects on the fracture surface of the tensile test ........................... 64

XIII


Figure 4. 11. EDS analysis results on the fracture surface of tensile specimens; (a,
b) Electron microscopy image; (c) Corresponding amounts at spectrum1; (d)
Corresponding amounts at spectrum2 .................................................................. 65
Figure 4. 12. The location of hardness testing process ........................................ 66

Figure 4. 13. Microhardness profile ..................................................................... 67
Figure 5. 1. Thermal cycle for (a) 800 rpm 25 mm/min and (b)………………..69
Figure 5. 2. The appearance of intermetallic layer phases on the interface of the
welded specimens are generated by different welding parameters ...................... 71
Figure 5. 3. The intermetallic layer thickness changes in different welding joints.71
Figure 5. 4. The X-ray test results of the welds created with different welding
parameters; (a) 800 rpm 25 mm/min; (b) 800 rpm 50 mm/min; 800pm and 75
mm/min; (d) 400 rpm 25 mm/min; (e) 400 rpm 50 mm/min and (f) 400 rpm/75
mm/min ................................................................................................................. 72
Figure 5. 5. The shear tensile test results of lap joints ......................................... 73
Figure 5. 6. The fracture surface of the shear test specimen (a) DP800 steel side
and (b) AA6351 alloy side ................................................................................... 74

XIV


Chapter 1 Introduction
1.1. Overview
Welding is a technological process used to connect two or more parts together
by using a temperature source to heat the connection point to a molten state or
plasticizer and then the molten metal self-crystallization or using a pressure to form
welds. The filler metals have been added and combined with basic metals to form
a pool of molten metal, which then crystallizes into a welded joint. Weld joints
usually have a tensile strength equal to or higher than the base metal. The welding
state can be liquid, flexible, and even cool. In the welding process if the metal
reaches a liquid state, in most cases the self-formed weld without pressure.
Sometimes in some welding processes, it is not necessary to use extra pressure to
form the weld because the metal at the welded position only needs to reach the
plastic state. Welding process usually has some advantages and limitations as
follows:

The welding joints are characterized by continuity and are not removable.
With the ability to work the joints made by welding method allows saving
more than 15-20% compared to the bolt joints and compared with the casting
method, the welding method saves more than 50% of the volume of metal.
Welding allows fabrication of complex structures, super, overweight from the
same materials or materials with very different properties. Suitable for different
conditions and environments. Welding creates strong bonding and high tightness
to meet the working requirements of important structures such as hull, tanks,
boilers, pressure equipment.
The welding process is simple, easy to implement, and high productivity
compared to other technologies, easy to carry out mechanics, automation in the
production process. The residual stresses and deformations are usually generated

1


in the weld structure so that it affects the shape, size, and workability of the
structure.
Friction stir welding process has been invented in recent years. The appearance
of this process has solved many difficulties in the welding process of aluminum
and aluminum alloy that conventional welding methods cannot pass through. The
welding bond of this process is formed in a solid state with high quality without
the use of complementary metal. This method has quickly become the first choice
in manufacturing structures in industries such as trains, airplanes, boats, shipping.
This welding process uses a cylindrical tool, which is forced onto the parts or work
piece with a fixed-shoulder placement. The tool will rotate and move along the
joint to be fixed so that the heat-by-friction between the tool and the work piece
will soften and yield without transformation during the phase (i.e., from solid to
molten). The heat flow that is moving from the leading edge of the tool onto the
following edge has the distinct possibility of bringing about material deformation.

This method can be used for welding of the same material or welding of dissimilar
materials [1-4].
Another name for tungsten inert gas welding is gas tungsten arc welding and
it uses argon, helium or Ar + He gas as a shield gas to protect the molten metal and
filler rod throughout the welding process. This method uses a non-melting tungsten
electrode and transfers electrons from the power source to the surface of the workpiece. Electric arc generated between the welding surface and the electrode
generates heat to melt the filler metal and metal to form the weld. Due to the simple
implementation process, the weld was easily formed so this method was used to
weld for almost of metals [5-8]. It plays an important role in the production of
structures by the welding method.
This dissertation presents studies on the characteristic of welding joints
between A6061-T6 / SUS304L and AA6351 / DP800 produced by TIG welding
and friction stir welding method, respectively.

2


1.2. Scope and Objectives of the Dissertation
The bonding between dissimilar materials not only provides the good
properties of the materials but also reduces the volume of the structure, reduces the
cost of the products, and increases the life of the structure. Therefore, the welded
joint between aluminum alloy and steel has been gradually increasing in recent
years [9, 10]. However, due to the great difference in physical properties,
mechanical properties, and the formation of an intermetallic layer at the interface
between the steel surface and the welding seam [11-17]. To solve these problems,
there are different welding methods have been studied and used [18-23]. Among,
the friction stir welding method and TIG welding method have been used as
potential methods for welding between aluminum alloy to dual phase steel, and
aluminum alloy to stainless steel.
The purpose and objects of this dissertation are:

Investigates on lap joint between AA6351 alloy and DP800 steel by using
friction stir welding process. Microstructure and mechanical properties of butt
joint between the A6061 alloys to SUS304L stainless steel by TIG welding with
filler wire ER4047 were examined.
Determine the relationship between the thermal cycler with the formation and
development of inter-metallic layer. Developed a numerical model to simulate
temperature field, residual stress, and distortion of the dissimilar welded joint.
Investigated the influence of the combination of welding parameters on the
change of thickness of the intermetallic layer. Examination of microhardness and
tensile strength of welding joints. Examined the microstructure and the formation
of defects inside welds. The formation of a new phase in the inter-metallic layer.

3


1.3. Dissertation Outline
The contents of the chapters of the dissertation show the related theories and
the conclusions of the experimental analysis of the welding joint of dissimilar
materials by using the TIG welding method and the friction stir welding method.
There are six chapters in this dissertation and the contents presented in the chapters
are summarized as follows:
Chapter 1 indicates the introduction, scope and objectives, and dissertation
outline of this study.
Chapter 2 presents an overview of previous research on welding of different
materials. It provides an overview of issues related to welding processes such as
an overview of some welding methods, welding defects, heat transfer during
welding. In addition, the characteristics of the welding materials used in welding
processes are also discussed in this chapter. It also briefly describes the
measurement methods used to test the properties of the weld after welding.
Chap 3 describes the influence of welding parameters on the quality of the TIG

welding joint and the friction stir welding joint. The preparation of experimental
welding process and preparation the test samples after welding are also presented
in this chapter.
Chapter 4 presents the results obtained during the survey on the microstructure
and mechanical properties of the butt joint between A6061-T6 alloy and SUS304L
steel by TIG welding method.
Chapter 5 shows that the results and discussions in welding joints between
AA6351 alloys and DP800 steel by the friction stir welding process. This chapter
also donates a comparison of the properties of welding bond between different
materials produced by TIG welding method and FSW method.
Chapter 6 presents the main conclusions and recommendations for further
research direction.

4


Chapter 2 Literature Reviews
2.1. Overview of Previous Research
Welded joints between aluminum alloy and stainless steel have been used
extensively in industrial applications. There are many reports were presented on
the characteristics of welding joints between them such as microstructures,
mechanical properties, residual stress, deformation, and the factors affecting on
the formation and development of the IMC layer.
The reports that can be pointed out as follows: Liu et al. [24] concluded that
the butt joint between aluminum alloy Al6061 and TRIP 780/800 steel with a
thickness of 1.4 mm was successfully welded by a friction stir welding method. In
this report, the tensile strength and composition of the interlayer have been
investigated. The results showed that the tensile strength was 85% compared to the
basic tensile strength of aluminum and the thickness of the interlayer formed at the
Al-Fe interface was less than 1µm. Lan et al. [25] also utilized friction stir welding

process to weld Al6061 alloy and TRIP 7800 Steel under butt configuration. They
investigated the macrostructure and microstructure of the welded joint obtained
with different welding conditions. An intermetallic compound layer was formed at
the Al-Fe interface with a thickness of less than 1µm. The fault locations of all
specimens occur in the aluminum heat affected zone.
The various welding mode parameters of the friction welding method have
been used by Taban et al. [26] to create a welding joint between A6061-T6
aluminum alloy and AISI 108 steel. The microstructure and mechanical properties
of the joints have been analyzed scanning electron microscopy (SEM), energy
dispersive spectroscopy (EDS), X-ray elemental mapping, focused ion beam (FIB)
with ultra-high-resolution SEM and transmission electron microscopy (TEM) in
TEM and STEM modes, tensile test, and micro-hardness testing. The analysis
results pointed out that the tensile strength of weld joint was 250 MPa and the FeAl

5


and Fe2Al5 phases were found in an intermetallic layer 250 nm thick. Movahedi et
al. [27] studied the effects of annealing temperature and duration on the tensile
strength of the welding joint between Al-5083 alloy sheet and St-12 steel sheet.
This report has exhibited that the joint strength increases when the annealing
temperature of the bonded joints at 300 degree C and 350 degree C increases. The
strength of the welded joint is significantly reduced when the annealing
temperature of 400 degree C and the annealing duration of 60 minutes.
Chang et al. [28] considered on the microstructure and mechanical properties
of 6082 aluminum alloy and SYG960E ultrahigh strength steel welded joints
formed by MIG welding with filler metals such as (ER5087) Al-Mg and (ER2319)
Al-Cu. They divided the cross-section of the weld joint into three regions, the weld
zone (WZ), the bond zone (BZ), and interface zone (IZ). The needle-like Fe4Al13
and lath-shaped Fe2Al5 layers were found in the interface zone. They also show

that the formation and development of the intermetallic layer at the interface zone
have been suppressed by Cu element and the tensile strength of the bonded welds
made by the Al-Cu filler wire higher than the tensile strength of solder joint created
by Al-Mg filler wire. The microstructure and mechanical properties of the
aluminum-steel weld are investigated by Cui et al. [29]. The tensile strength of the
weld joint made by the Zn-Al filler rod obtains of 133.6 MPa was illustrated in this
report. In addition, they also found that the Fe2Al5 phase was present in both joints
create by Zn-Al and Al-Si-Cu filler wire.
Shah et al. [30] utilized TIG welding method and two different types of filler
metal ER4043 and ER4047 to weld aluminum AA6061-O and galvanized iron in
a lap configuration. A comparison of the microstructure and mechanical properties
of the solder specimens obtained with the two-filler metals was carried out. As
results have indicated that the thickness of the interlayer formed in the weld joint
with the ER4047 filler metal (20 - 40 μm) thicker than that of the IMC layer made
in the weld joint with the ER4043 (4 - 7μm). The tensile strength of the specimen
made by ER4043 filler wire higher than the specimen made by ER4047 filler wire.
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Song et al. [31] analyzed the spreading behavior and microstructure characteristics
of the welded joint of the 5A06 aluminum alloy to SUS321 stainless steel by using
TIG welding. The spreading behavior of the filler wire divided into two parts, one
covering the upper surface of the joint, the other flowing down to the underside of
the bond. At the aluminum side formed fusion welding joint due to the very low
melting point of aluminum, at the stainless steel side forming the braze weld due
to the melting point of the steel is high. Interlayer formed in the cross-section of
the weld specimen is uneven. From the weld to the stainless steel, the interlayer is
divided into three sections. The average tensile strength of the butt joint obtained
120.0Mpa. In the report [32] Lin et al. studied dissimilar tungsten inert gas welding
between 5A06 aluminum alloy and SUS321 austenite stainless steel sheets with a

thickness of 3mm. At the interface of the welded joint and the stainless steel, a thin
interlayer has been found with a thickness of 3-5 μm. The mechanical properties
result measurement of the weld joint indicate that the average microhardness
values of the IMC layer, welded seam, and stainless steel are 644.7 HV, 104.5 HV
200 HV respectively. A tensile strength of the welding joint reaches 172.5 Mpa
and developmental cracks start from the bottom of the bonding to the welding
seam.
The laser welding-brazing process with ER4043 filler wire has been used by
Sun et al. [33] for bonding AA6061 aluminum alloy and Q235 low-carbon steel of
2.5mm thickness. The microstructure and mechanical properties of the weld joints
with different bevel angles of the steel sheet surface have been analyzed in this
work. The results of the report indicate the following: an intermetallic layer and a
zinc-containing zone were found at the brazing interface. Thickness and shape of
the intermetallic layer are not uniform and vary along the weld surface. The
fracture position during the tensile test takes place in the brazing area, and the
tensile strength values of the welded joints with bevel angles steel sheet of 450,
300 is obtained at 110 Mpa, 150 Mpa, respectively.

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2.2. Overview of Some Welding Methods
A Russian scientist discovered the electric arc phenomenon in 1802 and
pointed out that it could be used to melt the metal. Until today, it has many different
welding methods are found and applied to weld for a variety of different materials.
They include the following methods: Resistance Welding, Metal Inert Gas
Welding, Tungsten Inert Gas Welding, Submerged Arc Welding, Plasma Welding,
Laser Welding, Ultrasonic Welding, and Explosive Welding.

2.2.1. Tungsten Inert Gas Welding

Tungsten inert gas (TIG) welding is a method of molten soldering using an
electric arc, which is formed between the non-melting electrode and the welding
zone. The welding pool and arc are protected by an inert gas such as Argon (Ar),
Helium (He), or Ar + He gas to prevent harmful effects of oxygen and nitrogen in
the air. Welding arc region has very high temperatures can reach up to 61000C.
The TIG welding process is described in Figure 2.1.

Figure 2. 1. Tungsten inert gas welding process

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TIG welding methods have some characteristics as follows:
TIG welding produces high-quality welds for most metals and alloys.
No splashes during welding.
Can be weld anywhere in space.
The high concentration of welding process allows the welding speed to be
increased, reducing the distortion caused by welding.
It is difficult to protect the welding pool in a windy environment and easily
automate the welding process.
TIG welding is used in many different manufacturing sectors; it can weld
carbon steel, stainless steel, brazing, and aluminum welding. In addition, TIG
welding can also be welded to the plate, bar, tube, welded pressure vessels.

a. Current Models Used in TIG Welding
Direct current (DC): During the TIG welding by direct current (DC), the
welding electrode is connected directly to the former of the power supply, the
anode of the welding power connected to the welding material. Welding arc is
formed between the welding electrodes and welding materials in the environment
argon, helium, or a mixture of argon + helium was ionized. The temperature at the

center of the electrode and at the arc near the welding electrode is very high up to
several thousand degrees centigrade, which quickly melts the base metal and filler
metal to form a welded pool. The schematic diagram of the DC/TIG welding
process is demonstrated in Figure 2.2.

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Figure 2. 2. Schematic diagram of the direct current TIG welding;
(a) DCEN; (b) DCEP
The choice of electrode type and size depends on the relationship between the
operating mode and the current. With advantages such as high durability, high
current resistance, good anti-contamination, electronic emission, and easy to
induce arc. So that the Wolfram with 1.2% thorium electrode has been selected to
use in the direct current TIG welding process. In addition, tungsten electrodes with
lanthanum oxide or cerium oxide are also used because lanthanum oxide and
cerium oxide make the arc formation easier, the arc's stability is higher and low
electrode corrosion. The diameter of the electrodes used in the direct current
electrode negative (DCEN) welding process must be greater than the direct current
electrode positive (DCEP) welding process. During the welding process, the
temperature of the arc is very large and it can melt the electrode.
Alternating current (AC): The TIG welding process by using alternating
current is suitable for use in the welding of aluminum, magnesium and their alloys
because at the molten solder the aluminum oxide layer forms very quickly. In the
welding process, a positive half cycle was used to bombard the oxide film on the
base metal surface and cleans its surface. The negative half cycle has the effect of
heating the base metal.
Pulsed direct current (PDC): This method uses direct current with pulsed cycle
interruption and the weld is formed from the individual point of overlap. This


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