동적재료모델을 이용한 Zn-Al합금의 초소성 변형거동 해석 및 집합조직과 미세조직의 변화 고찰
Texture & Microstructure evolution and Superplastic Deformation Behavior of Zn-Al Alloys using Dynamic Material Model
- 발행기관 江陵大學校 大學院
- 지도교수 하태권
- 발행년도 2009
- 학위수여년월 2009. 2
- 학위명 석사
- 학과 및 전공 新素材工學科
- 원문페이지 92 p.
- 본문언어 한국어
초록/요약
Superplastic deformation behavior of a Zn-0.3wt.%Al was investigated. Ingot fabricated by vacuum induction melting (VIM) was hot-rolled at 200℃ into plates of 5 mm thickness after sectioning and solution heat treatment at 220℃ for 10 hrs. Grain size of hot-rolled plates was measured as about 20 mm. Hig·h strain rate compression tests (Gleeble) were also conducted on the hot-rolled plates at temperatures from 60 to 200℃ under the strain rate from 0.03 to 10/s to construct processing maps to evaluate microstructure evolution and instability regarding to superplastic deformation of the Zn-Al alloy. With the strain rate increased, serration behavior was observed to be prominent. Dynamic materials model(DMM) has been employed to explain the contribution from GBS of Zn alloy in this study. Equal channel angular pressing(ECAP) was carried out on the hot-rolled plates at temperatures from 60 to 200℃ for grain size refinement and enhancement of superplasticity of Zn-Al alloy. After repetitive ECAP in 4 passes at 60℃, grain size of about 6 mm was obtained, increasing up to 10 mm with the temperature of ECAP increased. Texture was also measured on the specimens produced by ECAP at various conditions to investigate the effect of ECAP on the texture evolution. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED. A series of load relaxation and tensile tests were conducted at various temperatures ranging from RT(24℃) to 200℃. Relatively large-grained (20mm) alloy showed lower elongation at 100℃ compared to those of ECAPed specimens. A high elongation of about 550% has been obtained for a specimen ECAPed at 60℃ by 4 passes at testing temperature of 100℃ under the strain rate of 2 × 10-4/s.
more목차
1. 서 론 = 1
2. 이론적 배경 = 3
2. 1. 초소성 현상 = 3
2. 1. 1. 초소성을 나타내는 미세조직 = 6
2. 1. 2. 결정립계 미끄러짐 = 8
2. 1. 3. 확산 수용에 의한 결정립계 미끄러짐 = 8
2. 1. 4. 전위운동 수용에 의한 결정립계 미끄러짐 = 11
2. 2. 동적재료모델(Dynamic materials modeling) = 14
2. 3. ECAP의 원리 = 18
2. 3. 1. ECAP die의 내부각(Φ)에 따른 효과 = 21
2. 4. 집합조직과 기계적 성질 = 23
2. 4. 1. 집합조직의 해석기술 = 23
2. 4. 2. 완전구속모델(Full constraint model) = 24
2. 4. 3. 이완구속모델(Relaxed constraint model) = 26
2. 4. 4. 변형률속도민감도모델(Strain rate sensitivity model) = 27
3. 실험방법 = 28
3. 1. ECAP 공정 = 28
3. 2. 집합조직의 측정 및 분석 = 30
3. 3. Gleeble 압축시험 = 31
3. 4. 응력이완시험 = 32
3. 5. 인장시험 = 34
4. 결과 및 고찰 = 35
4. 1. 응력이완시험 결과 = 35
4. 2. 인장시험 결과 = 36
4. 3. Gleeble 압축시험 결과 = 57
4. 4. 동적재료모델을 이용한 공정지도(Processing map) = 61
4. 5. 집합조직 및 미세구조의 변화 해석 = 70
5. 결 론 = 83
List of Tables = 85
List of Figures = 86
참고문헌 = 90
