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
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
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
