표제지
Abstract
초록
목차
1장 서론 18
1.1. 연구배경 18
1.2. 문헌조사 19
1.3. 연구목적 22
References 24
2장 이축교번단조금형 설계 및 유한요소해석 26
2.1. 연구목적 26
2.2. 이축교번단조금형 설계 27
2.3. 유한요소해석 조건 32
2.3.1. 유한요소모델링 32
2.3.2. 재료물성 33
2.4. 유한요소해석 결과 37
2.4.1. 단조 pass에 따른 변형 해석 결과 37
2.4.2. 가공경화지수에 따른 변형해석 결과 44
2.4.3. 단조 pass별 평균 변형률 추정 51
2.5. 결론 56
References 58
3장 냉간 이축교번단조 변형이 Al-Mg계 합금의 미세조직 및 기계적 특성에 미치는 영향 59
3.1. 연구목적 59
3.2. ECO-Almag alloy 소개 60
3.3. 실험절차 61
3.3.1. 기본소재 미세조직분석 61
3.3.2. 이축교번단조 62
3.3.3. 단조소재의 기계적 특성 및 미세조직 분석 64
3.4. 실험결과 64
3.4.1. 기본소재 미세조직 64
3.4.2. 냉간 이축교번단조 결과 79
3.4.3. 기계적 특성 81
3.4.4. 냉간단조 미세조직 86
3.5. 결과고찰 96
3.6. 결론 104
Reference 106
4장 온간 이축교번단조 변형이 Al-Mg계 합금의 미세조직 및 기계적 특성에 미치는 영향 109
4.1. 연구목적 109
4.2. 실험방법 109
4.3. 실험결과 112
4.3.1. 기계적 특성 112
4.3.2. 온간단조 미세조직 123
4.4. 결과고찰 128
4.5. 결론 139
References 140
5장 이축교번단조에 의한 SPD가 Mg-Al-Zn계 합금의 미세조직 및 기계적 특성에 미치는 영향 141
5.1. 연구목적 141
5.2. AZ31 합금 142
5.3. 실험방법 144
5.4. 실험결과 145
5.5. 결과고찰 158
5.6. 결론 164
References 166
6장 총괄결론 168
Table 3.1. Analyzed compositions of areas shown in Fig. 3, 4, and 9 by STEM-EDS. 69
Table 3.2. Tensile properties of biaxial alternate forged Almag workpieces. 84
Table 3.3. The estimated effective strain depending on the number of forging passes calculated from the Fig. 2.18. 101
Table 4.1. Tensile properties of Almag workpieces forged at 373 K. 114
Table 4.2. Tensile properties of Almag workpieces forged at 473 K. 115
Table 4.3. The estimated effective strain depending on the number of forging passes calculated from the Fig. 2.18. 132
Table 5.1. Tensile properties of biaxial alternate forged AZ31B workpieces. 152
Table 5.2. The estimated effective strain depending on the number of forging passes calculated from the Fig. 2.18. 161
Fig. 2.1. Schematic 3D views of (a) the octagonal rod-shaped dies and workpiece for biaxial alternate forging, (b) the die cavity shape and cross-section design, and... 29
Fig. 2.2. Schematic views of biaxial alternate forging process using octagonal rod-shaped dies. 30
Fig. 2.3. Dimensions of tensile specimen (ASTM: B557M-10) depending on nominal diameter (a) 4mm and (b) 6mm of reduced section. 31
Fig. 2.4. Finite element modeling for simulation of biaxial alternate forging. 35
Fig. 2.5. True stress-strain curves fitted to power law depending on n value. 36
Fig. 2.6. Shape of the deformed workpiece with increasing number of forging passes. 40
Fig. 2.7. Changes in damage values depending with increasing number of forming passes, as calculated through normalized Cockcroft-Latham damage criterion. 41
Fig. 2.8. (a) Effective strain distribution and (b, c) effective strain profiles throughout the workpiece, depending on the number of forging passes. 42
Fig. 2.9. Effective strain profiles along the (a) horizontal, (b) diagonal, and (c) vertical directions, depending on the distance from the center of the cross section.... 43
Fig. 2.10. Comparison of deformed shapes depending on strain hardening exponent after the four forging passes. 46
Fig. 2.11. The protruding length at the end of the workpiece. 47
Fig. 2.12. Changes in damage value of (a) side end and (b) the core depending with increase number of forging passes and n values, as calculated through... 48
Fig. 2.13. Effective strain profiles along the (a) horizontal, (b) diagonal, and (c) vertical directions, depending on the n values. (d) difference in effective strains... 49
Fig. 2.14. (a) Effective strain distributions and (b) metal flow lines in the cross-section of workpieces after the four forging passes depending on the n values. 50
Fig. 2.15. Maximum effective strain profiles depending on the number of forging passes and the n values. 52
Fig. 2.16. Mean effective strain profiles of measuring areas for tensile tests using (a) D4 specimen and (b) D6 specimen depending on the number of forging... 53
Fig. 2.17. Mean effective strain map of measuring areas for tensile tests using (a) D4 specimen and (b) D6 specimen. 54
Fig. 2.18. Estimation of effective strain values of measuring areas for tensile tests using (a) D4 specimen and (b) D6 specimen. 55
Fig. 3.1. (a) Biaxial alternate forging die and (b) experimental set-up. 63
Fig. 3.2. (a) Scheil cooling of ECO-Almag6 alloy and (b) enlargement. 70
Fig. 3.3. (a) Bright-field TEM image of analyzed area, (b) enlargement of the analyzed area, (c) high-resolution image marked with solid line in Fig. 3.3(b), and... 71
Fig. 3.4. (a) Bright-field TEM image of analyzed area, (b) enlargement of analyzed area, (c) high-resolution image marked with solid line in Fig. 3.4(b), and... 72
Fig. 3.5. (a) STEM-EDS mapping results of analyzed area shown in Fig. 3.3(b). 73
Fig. 3.6. (a) STEM-EDS mapping results of analyzed area shown in Fig. 3.4(a). 74
Fig. 3.7. Phase diagram plotted for Si versus Ca mass fractions at 490 ℃ calculated by FactSage 7.3. The contents of Mg and Fe are fixed at those... 75
Fig. 3.8. Phase diagram of Al-Al₄Ca-Mg₂Si three-phase system isothermal at 490 ℃ calculated by FactSage 7.3. 76
Fig. 3.9. (a) Bright-field TEM image of analyzed area, (b) enlargement of the analyzed area, (c) high-resolution image marked with solid line in Fig. 3.9(b),... 77
Fig. 3.10. Phase diagram plotted for temperature versus Ti mass fractions calculated by FactSage 7.3. The contents of Mg and Fe are fixed at those... 78
Fig. 3.11. (a) Images of workpieces depending on forging passes, (b) side end shapes of biaxial alternate forged Almag6-extruded workpieces and (c)... 80
Fig. 3.12. Tensile specimen shapes extracted from biaxial alternate forged workpieces. 83
Fig. 3.13. Change in tensile properties of Almag workpieces, (a) forged from the billet and (b) forged from the extruded rod, as a function of the number of... 85
Fig. 3.14. OM microstructures of forged Almag billets with pass numbers of cold forging. 89
Fig. 3.15. EBSD results of Almag8 billets after cold forging. (a) 1 pass, (b) 2 pass, (c) 3 pass and (d) 4 pass. 90
Fig. 3.16. OM microstructures of extrusions with pass numbers of cold forging. 91
Fig. 3.17. (a) Bright-field TEM image of analyzed area, (b) enlargement of the analyzed area, (c) high-resolution image marked with solid line in Fig. 13(b),... 92
Fig. 3.18. (a) Bright-field TEM image of analyzed area, (b) enlargement of the analyzed area, (c) high-resolution image marked with solid line in Fig. 14(b),... 93
Fig. 3.19. (a) Bright-field TEM images of twins in the extruded workpiece after three forging passes and (b) enlargement. 94
Fig. 3.20. Bright-field TEM images of fine grains and dislocations in the extruded workpiece after five forging passes. 95
Fig. 3.21. Strain distribution in the cross-sections of workpieces in (b) experimental samples and in (c) finite element simulation results 99
Fig. 3.22. (a) True stress-strain curve of extruded Almag6 rod obtained from compression test at room temperature (b) Curve fitting result using power-law equation. 100
Fig. 3.23. Change in tensile properties of Almag workpieces, (a) forged from the billet and (b) forged from the extruded rod, as a function of effective strain. 102
Fig. 3.24. Comparison of the mechanical properties of Almag alloys and commercial 5xxx aluminum alloys. 103
Fig. 4.1. (a) Experimental set-up for warm biaxial alternate forging and (b) die heating system using cartridge heaters. 111
Fig. 4.2. Change in tensile properties of Almag workpieces forged from the billet at (a) 373K and (b) 473K as a function of the number of forging passes. 116
Fig. 4.3. Change in tensile properties of Almag6 workpieces and Alma8 workpieces forged from the billet as a function of the number of forging... 117
Fig. 4.4. Change in tensile properties of Almag workpieces forged from the extruded rod at (a) 373K and (b) 473K as a function of the number of forging passes. 118
Fig. 4.5. Change in tensile properties of Almag6 workpieces and Alma8 workpieces forged from the extruded rod as a function of the number of... 119
Fig. 4.6. Mechanical properties comparisons of Almag workpieces between forged from the billet and the extruded rod. 120
Fig. 4.7. Tensile property maps of Almag workpieces forged from the billet depending on the number of forging passes and forging temperatures 121
Fig. 4.8. Tensile property maps of Almag workpieces forged from the extruded rod depending on the number of forging passes and forging temperatures. 122
Fig. 4.9. OM microstructures of billets with pass numbers of forging at 373 K. 124
Fig. 4.10. OM microstructures of extrusions with pass numbers of forging at 373 K. 125
Fig. 4.11. OM microstructures of billets with pass numbers of forging at 473 K. 126
Fig. 4.12. OM microstructures of extrusions with pass numbers of forging at 473 K. 127
Fig. 4.13. (a) True stress-strain curve of extruded Almag6 rod obtained from compression test at 373 K and (b) curve fitting result using power-law equation. 130
Fig. 4.14. (a) True stress-strain curve of extruded Almag6 rod obtained from compression test at 473 K and (b) curve fitting result using power-law equation. 131
Fig. 4.15. Tensile property maps of Almag workpieces forged from the extruded rod depending on effective strain and forging temperatures. 133
Fig. 4.16. A simple and quantitative representation of the paradox of ductility and strength where the normalized stress is plotted against the normalized elongation. 134
Fig. 4.17. Quantitative representation of a strength-ductility relationship from the data demonstrated in Fig. 3.13(a) and Fig. 4.2. 135
Fig. 4.18. Quantitative representation of a strength-ductility relationship from the data demonstrated in Fig. 4.3. 136
Fig. 4.19. Quantitative representation of a strength-ductility relationship from the data demonstrated in Fig. 3.13(b) and Fig. 4.4. 137
Fig. 4.20. Quantitative representation of a strength-ductility relationship from the data demonstrated in Fig. 4.5. 138
Fig. 5.1. Phase diagram plotted for temperature versus Al mass fraction in Mg-Al-Zn-Mn system calculated by FactSage 7.3. The contents of Zn and Mn... 143
Fig. 5.2. Appearance of workpieces depending on the number of forging passes after forging at 300 ℃. 149
Fig. 5.3. OM microstructures of AZ31 workpiece cross-sections after forging at 300 ℃. 150
Fig. 5.4. OM microstructures of AZ31 workpiece cross-sections depending on observed areas and forging passes after forging at 300 ℃. 151
Fig. 5.5. Tensile properties of extruded AZ31B workpieces depending on forging passes after forging at 300 ℃. 153
Fig. 5.6. EBSD results of as-extruded AZ31B workpiece. (a) IQ map, (b) IPF map, (c) GB map, (d) Pole figure. 154
Fig. 5.7. EBSD results of 1 pass forged AZ31B workpiece. (a) IQ map, (b) IPF map, (c) GB map, (d) Pole figure. 155
Fig. 5.8. EBSD results of 3 pass forged AZ31B workpiece. (a) IQ map, (b) IPF map, (c) GB map, (d) Pole figure. 156
Fig. 5.9. Grain size distributions of scanned area of (a) as-extruded, (b) 1 pass and (c) 3 pass forged AZ31B workpieces and comparison of the average grain size depending on the number of forging passes. 157
Fig. 5.10. (a) True stress-strain curve of extruded AZ31B rod obtained from compression test at 300℃. 160
Fig. 5.11. Tensile properties of extruded AZ31B workpieces as a function of effective strain after forging at 300 ℃. 162
Fig. 5.12. Quantitative representation of a strength-ductility relationship from tensile test results of Table 5.1. : for comparison purposes, references on AZ31... 163
Fig. 6.1. Quantitative representation of a strength-ductility relationship from tensile test results of Table 3.2 and Table 5.1. 172