Title Page
ABSTRACT
Contents
CHAPTER Ⅰ. INTRODUCTION 18
1.1. RESEARCH MOTIVATION 18
1.2. NECESSITY OF THIS RESEARCH 20
1.3. BRIEF INTRODUCTION OF THE WORKS 23
REFERENCES 25
CHAPTER Ⅱ. FRICTION STIR LINEAR WELDING OF ALUMINUM-CLAD THIN SHEETS 28
2.1. INTRODUCTION 28
2.2. EXPERIMENTAL SET-UP 29
2.3. RESULTS AND DISCUSSION 33
2.3.1. Process response and optical microscopy 33
2.3.2. Clad-core intermixing study by EPMA 33
2.3.3. Precipitation behavior within the SZ by SEM 34
2.3.4. Microstructural characterization by EBSD 37
2.3.5. Mechanical properties analysis of the FSW joint 47
2.4. CONCLUSIONS 51
REFERENCES 52
CHAPTER Ⅲ. GAS POCKET-ASSISTED UNDERWATER FRICTION STIR SPOT WELDING 57
3.1. INTRODUCTION 57
3.2. MATERIALS AND EXPERIMENTAL METHODS 59
3.2.1. Materials 59
3.2.2. Experimental methods 59
3.3. RESULTS AND DISCUSSION 65
3.3.1. Process responses and optical microscopy 65
3.3.2. SEM analysis on the top and cross-sections of the weld 69
3.3.3. Microstructural analysis by EBSD 73
3.3.4. Mechanical properties analysis 78
3.3.5. Corrosion properties analysis 82
3.4. CONCLUSIONS 87
REFERENCES 88
CHAPTER Ⅳ. FABRICATION OF ALUMINUM MATRIX COMPOSITE BY FRICTION STIR PROCESSING 95
4.1. INTRODUCTION 95
4.2. MATERIALS AND EXPERIMENTAL PROCEDURES 97
4.2.1. Materials 97
4.2.2. Experimental procedures 97
4.3. RESULTS AND DISCUSSION 102
4.3.1. Process response and optical microscopy 102
4.3.2. Raman spectroscopy analysis 102
4.3.3. SIMS analysis on GO survivability in Al matrix 105
4.3.4. Morphological characterization of GO using TEM 109
4.3.5. EBSD analysis of the produced AMC 113
4.3.6. Mechanical properties of the fabricated AMC 119
4.4. CONCLUSIONS 123
REFERENCES 124
CHAPTER Ⅴ. SUMMARY AND FUTURE WORKS 128
5.1. RESEARCH SUMMARY 128
5.2. FUTURE WORK 132
Table 2.1. Chemical compositions of the BM 31
Table 2.2. Possible elemental compositions (at.%) of various precipitates 39
Table 2.3. Mechanical properties of the BM and FSW joint 50
Table 3.1. Chemical compositions of AA5083-H112 59
Table 3.2. Optimized weld parameters 61
Table 3.3. Measured dimension of the welding region (spots) 66
Table 3.4. Possible compositions of precipitates 69
Table 3.5. Corrosion parameters obtained from the polarization curves 83
Table 4.1. Chemical compositions of AA1050-H14 97
Table 4.2. FSP parameters 98
Table 4.3. Measured data obtained from the tensile curves 121
Figure 1.1. Clad material application in battery electric vehicles (BEV) and the various clad materials available for automotive sectors. 21
Figure 1.2. Underwater welding challenges at a glance in present days. 22
Figure 2.1. (a) Schematic representation of linear (butt) FSW of Al-clad-Al thin sheets, (b) process parameter optimization of FSW of Al-clad thin sheets. 32
Figure 2.2. Force-torque responses during the FSW of Al-clad thin sheets. 35
Figure 2.3. (a) Macrograph of the Al-clad Al FSW cross-section. The black rectangles indicate various regions in the BM, TMAZ, and SZ for EBSD, and a white dashed rectangle (A) represents the area... 35
Figure 2.4. (a) EPMA Si-mapping of the region (A). Magnified images of the sites marked: (b) BM (BT/BB); (c) TMAZ and AS interface; (d-j) various regions of the SZ (R1-R7), respectively.[이미지참조] 36
Figure 2.5. SEM images of the formation of precipitates in the various regions of the SZ of the Al- clad-Al FSW joint cross-section: (a) the AS (P₁), (b) middle of the SZ (top, P₂), (c) the bottom of... 39
Figure 2.6. (a, b) Fe-SEM images of BM (BT/BB) and RS of SZ (P₄) and their corresponding EDS elemental mapping of Al, Si, Mn, and Fe.[이미지참조] 40
Figure 2.7. Microstructural analysis of Al-clad thin sheet (a-a₁) BSE image of BM and corresponding EDS line scanning spectrums along the yellow dashed line; EBSD generated (b) IPF map, (c)... 41
Figure 2.8. Microstructural analysis of the TMAZ (AS side) (T) of Al-clad-Al FSW joint using EBSD generated (a) IPF map, (b) GBCD map, (c) KAM map, and (d) GOS map. 44
Figure 2.9. BSE images of (a-c) AS (S₁), middle of the SZ (S₂), and RS (S₃) regions of the SZ; (c₁) corresponding (S₃) element line scanning spectra along the yellow dashed line; EBSD-generated... 45
Figure 2.10. EBSD-generated (a-c) KAM maps, (d-f) GOS maps for the SZ of the Al-clad-Al FSW joint sequentially with AS (S₁), middle of the SZ (S₂), and RS (S₃). 46
Figure 2.11. {111} Pole figures acquired from (a) AA4343 (BT), (b) AA3003 (BB), (c) TMAZ (T), and (d-f) in the SZ - AS (S₁), middle (S₂), and RS (S₃), respectively for Al-clad-Al FSW joint.[이미지참조] 47
Figure 2.12. (a) FSW joint cross-section indicating indentation marks under the transparent layer of the microhardness distribution; (b-c) 2D microhardness mapping of the weld cross-section BM to... 48
Figure 2.13. (a) Engineering stress vs. engineering strain curves of the BM and the FSW specimen (all-weld) in black (sample fabrication inset); (b) transverse tensile specimen schematic and broken... 49
Figure 2.14. (a, b) SEM macro-fractography of the broken tensile specimens in the BM and the FSW weld sequentially; (c, d) enlarged views of the regions marked with black rectangles in (a, b). 50
Figure 3.1. Schematic view of (a) the tank, (b, c) sample attachment inside the tank for GAFSSW and its actual view with adapter, (d, e) gas tubes attachment with adapter and actual view with its... 63
Figure 3.2. (a) The complete setup with the tank for GAFSSW, (b) water vortex began initiating gas flow, (c) gas pocket formed and enclosed with the adapter, (d) rotating tool plunged next to... 64
Figure 3.3. The process parameter optimization ways for GSAFSSW. 65
Figure 3.4. (a) Force, (b) torque, (c) temperature profiles for FSSW, UFSSW, and GAFSSW. 67
Figure 3.5. Top and bottom surface pictographs of (a, a₁) FSSW, (b, b₁) UFSSW, (c, c₁) GAFSSW. 68
Figure 3.6. (a-c) Optical micrographs of the FSSW, UFSSW, and GAFSSW cross-sections. 68
Figure 3.7. SEM image of the top surface of (a) UFSSW, (b) GAFSSW, (c, d) corresponding EDS spectra with elemental compositions. 70
Figure 3.8. SEM images of the formation of the precipitate in (a) BM, S₁, and S₂ regions in the SZ of (b, c) FSSW, (d, e) UFSSW, and (f, g) GAFSSW. 71
Figure 3.9. BSE image of GAFSSW (S₂) and their corresponding EDS chemical mapping of Mg, Fe, Si, Al, and Mn, respectively. 72
Figure 3.10. Microstructure analysis by EBSD generated IPF maps of (a) BM, (b-d) S₁, and (b₁- d₁) S₂ regions: (b-b₁) FSSW, (c-c₁) UFSSW, and (d-d₁) GAFSSW. 75
Figure 3.11. Grain boundary characteristics study by EBSD generated GBCD (a-g) and GOS (a₁-g₁) maps: (a-a₁) BM; (b-b₁), (d-d₁), (f-f₁) for the locations of S₁; (c-c₁), (e-e₁), (g-g₁) for the... 76
Figure 3.12. EBSD generated KAM maps of (a) BM, (b-b₁) S₁ and S₂ regions of FSSW, (c-c₁) for UFSSW, and (d-d₁) for GAFSSW. 77
Figure 3.13. (a) Schematic micrograph of the weld cross-section indicating the location for microhardness measurements, 2D surface microhardness map for (b) FSSW, (c) UFSSW, and (d)... 80
Figure 3.14. (a) Schematic micrograph of the weld cross-section indicating the locations for indentation tests, L-H curves, and stress-strain curves for (b, c) S₁ and (d, e) S₂ locations obtained... 81
Figure 3.15. (a) OCP curves concerning time and (b) electrochemical potentiodynamic polarization curves of the tested samples, (c) avg. Ecorr vs. CR plot, data obtained from potentiodynamic...[이미지참조] 85
Figure 3.16. Schematic representation of GAFSSW operation in the sea (a) Step - 1: FSW-BOT set up, (b) Step - 2: welding with the gas pocket on the desired location of the workpiece. 86
Figure 4.1. (a) Schematic of AMC fabrication using FSP, (b) SEM image of GO particles, (c) a detailed picture of the fabricated AMC. 101
Figure 4.2. (a) Axial force distribution, (b) temperature curves obtained during FSP-only and FSP with GO conditions. 103
Figure 4.3. OM macrographs of the cross-sections of (a) FSP-only and (b) FSP with GO conditions. 104
Figure 4.4. Raman spectrums of (a) GO, (b) AS, and (c) RS of FSP with GO and FSP-only SZ. 105
Figure 4.5. (a) Schematic of SIMS location, (b) Al and C depth profiles. 106
Figure 4.6. Microprobe Cs⁺ scanning beam induced total ion imaging of C in (a, b) FSP-only and (c, d) FSP with GO SZ. (e) SEM image on the SIMS site, (f) magnified SEM images from the... 107
Figure 4.7. (a) Tilted view of GO at SIMS site under FIB-SEM, (b) Sample extraction (black arrow) using both sides of FIB, (c) SEM image of the extracted sample, (d) magnified image of the marked... 108
Figure 4.8. (a) TEM micrograph of the entire specimen focused for analysis, (b, c) magnified TEM images of Zone 1 and Zone 2, high-resolution TEM (HR-TEM) images of (d) GO reinforcement,... 110
Figure 4.9. HAADF STEM image on the specimen and corresponding EDS elemental area mapping of Al, C, N, O, S, Pt, and W, respectively. 111
Figure 4.10. (a) line scanning spectra show the elemental profile of the present trace elements with Al and C, (b) Magnified view of the line scanning spectra C has a slightly higher concentration... 112
Figure 4.11. Microstructural analysis of AA1050 (BM) (a) IPF map, (b) KAM map, (c) GBCD map, and (d) GOS map, respectively. 116
Figure 4.12. EBSD analysis on the SZ AS (S₁); IPF, KAM, GBCD, GOS maps for (a-d) FSP-only and (e-h) FSP with GO conditions. 117
Figure 4.13. EBSD analysis on the RS (S₂) of the SZ; IPF, KAM, GBCD, GOS maps for (a-d) FSP-only and (e-h) FSP with GO conditions. 118
Figure 4.14. Microtexture analysis by {111} pole figures (a) BM; AS (S₁) and RS (S₂) of the SZs of (b, d) only FSP and (c, e) FSP with GO conditions. 119
Figure 4.15. Microhardness mapping of (a) FSP-only and (b) FSP with GO conditions. 121
Figure 4.16. (a) Tensile tests curves of BM (in black color), FSP-only (in red color), and FSP with GO (in blue color) specimen merged, (b-d) Fractography of the fractured tensile specimen for BM,... 122
Figure 5.1. Photographic representation of the summary of Chapter 2. 129
Figure 5.2. Photographic representation of the summary of Chapter 3. 130
Figure 5.3. Photographic representation of the summary of Chapter 4. 131