鎂合金具有低密度、高比強度與良好的制震性，因此近年來普遍應用於交通工業與3C產品上。鎂合金的HCP結構，使室溫變形的滑移系統不足導致成形性不佳，因此目前製作鎂合金元件成形技術上以壓鑄法（Die casting）與半固態製程為主流。壓鑄法操作溫度高（熔點以上），成形時常含有孔洞與較大的固化收縮率；利用半固態製程則可解決這些問題，且成品具有近淨形之優點。
　　半固態製程中的SIMA製程之最大優點，在於技術門檻與投資金額相對低廉。本研究透過熱擠時導入應變，改良傳統式SIMA製程之缺點，並探討不同熱擠之應變量於SIMA製程後微觀組織之變化，以釐清球狀晶演變機制；此外，本研究後段針對SIMA材進行半固態溫度壓縮實驗以探討其壓縮特性，且評估是否具有近淨形之特色與壓縮成形後之延性表現，以做為發展半固態製程之參考與依據。
　　實驗結果顯示，AZ61鎂合金經由熱擠型SIMA製程，可確實製造出具球狀晶組織之半固態胚料。選用擠型比大之擠型材，可縮短熱處理時間，獲得球狀晶胞徑也較小。本實驗AZ61鎂合金擠型材，由細微晶粒所組成，於熱擠型SIMA製程初期會發生Grain coalescence，部分細晶結合成粗大晶粒；隨著時間增加，材料內部部分融熔，液相生成並貫穿高能量晶界，使固相粒子被液相包覆而形成晶胞，且晶胞以Ostwald ripening逐漸粗大，且於持溫適當長時間下，最後成為球狀固相晶胞存在於液相基地的特徵組織。然而，當持溫時間過久，則無完整球狀晶胞。
　　根據半固態溫度壓縮性質探討結果，當壓縮溫度高於固相線溫度，材料變形阻抗急遽下降。具有球狀晶胞特徵組織之SIMA材，半固態溫度壓縮時，變形阻抗小於不具球狀晶胞之擠型材。藉由壓入螺帽成形試驗，SIMA材具有近淨形之優點；且藉由彎曲試驗評估成形之延性，經由退火處理可提升半固態壓縮後之SIMA材彎折時產生破壞之角度，因此SIMA材成形後之延展性可藉由後熱處理獲得改善。

Strain-induced melt activation (SIMA) is a process with development potential due to its simplicity and low cost. The semisolid billet of AZ61 Mg alloy was fabricated by the hot extruded SIMA process. The effects of extrusion ratio and heating condition on the microstructure feature, the semi-solid forming mechanism and compressive properties were discussed. The grain became more globular with appropriately increasing the reheating temperature and holding time. The dominant mechanism of grain coarsening at initial stage was grain coalescence, while Ostwald ripening at longer holding time. The deformation resistance of Mg alloys after SIMA process was lower than as-extruded at 500℃, 520℃, and 540℃. SIMA Mg alloys had the advantage of near net shape. To evaluate ductility of SIMA and as-extruded Mg alloys was by bending test. The ductility of SIMA Mg alloys was improved after heating treatment.

1. E. Aghion, B. Bronfin, D. Eliezer, "The role of the magnesium industry in protecting the environment", Journal of Materials Processing Technology, vol.117, pp.381-385, 2001.
2. J. F. Jiang, X. Lin, Y. Wang, J. J. Qu, S. J. Luo, "Microstructural evolution of AZ61 magnesium alloy predeformed by ECAE during semisolid isothermal treatment", Transactions of Nonferrous Metals Society of China, vol.22, pp.555-563, 2012.
3. S. Kleiner, O. Beffort, A. Wahlen, P. J. Uggowitzer, "Microstructure and mechanical properties of squeeze cast and semi-solid cast Mg-Al alloys", Journal of Light Metals, vol.2, pp.277-280, 2002.
4. H. Y. Wang, Y. H. Su, C. Y. A. Tsao, "Structural evolution of conventional cast dendritic and spray-cast non-dendritic structures during isothermal holding in the semi-solid state", Scripta Materialia, vol.37, pp.2003-2007, 1997.
5. M. M. Avedesian, H. Baker, "Magnesium and Magnesium Alloys", ASM, pp.16-18, 1999.
6. 蔡幸甫，「鎂合金產業技術及市場發展趨勢專題調查」，工研院IEK，2-5頁，民國90年10月。
7. M. M. Avedesian, H. Baker, "Magnesium and Magnesium Alloys", ASM, pp.37-43, 1999.
8. O. Lunder, T. K. Aune, K. Nisancioglu, "Effect of Mn additions on the corrosion behavior of mold-cast magnesium ASTM AZ91", Corrosion, vol.43, pp.291-295, 1987.
9. M. M. Avedesian, H. Baker, "Magnesium and Magnesium Alloys", ASM, pp.16-18, 1999.
10. ibid., pp.14-15.
11. J. W. Edington, K. N. Melton, C. P. Cutler, "Superplasticity", Progress in Materials Science, vol.21, pp.61-158, 1976.
12. T. Haga, P. Kapranos, "Thixoforming of laminate made from semisolid cast strips", Journal of Materials Processing Technology, vol.157, pp.508-512, 2004.
13. A. Paes, E. J. Zoqui, "Semi-solid behavior of new Al-Si-Mg alloys for thixoforming", Materials Science and Engineering A, vol.406, pp.63-73, 2005.
14. Z. Fan, "Semisolid metal processing", International Materials Reviews, vol.47, pp.49-85, 2002.
15. M. C. Flemings, R. G. Riek, K. P. Young, "Rheocasting", Materials Science and Engineering, vol.25, pp.103-117, 1976.
16. U. Tadashi, K. Kazuo, "United States Patent 2251343", Dec.6, 2005.
17. H. V. Atkinson, "Modelling the semisolid processing of metallic alloys", Progress in Materials Science, vol.50, pp.341-412, 2005.
18. K. P. Young, C. P. Kyonka, J. A. Courtois, United States Patent 4415374. Nov.15, 1983.
19. E. E. Glickman, M. Nathan, "On the kinetic mechanism of grain boundary wetting in metals", Journal of Applied Physics, vol.85, pp.3185-3191, 1999.
20. S. Kleiner, O. Beffort, P. J. Uggowitzer, "Microstructure evolution during reheating of an extruded Mg-Al-Zn alloy into the semisolid state", Scripta Materialia, vol.51, pp.405-410, 2004.
21. M. X. Xia, H. X. Zheng, S. Yuan, J. G. Li, "Recrystallization of preformed AZ91D magnesium alloys in the semisolid state", Materials & Design, vol.26, pp.343-349, 2005.
22. H. Y. Xu, Z. S. Ji, M. L. Hu, Z. Y. Wang, "Microstructure of AZ91D magnesium alloy semi-solid billets prepared by SIMA method from chips", Transactions of Nonferrous Metals Society of China, vol.20, pp.S749-S753, 2010.
23. J. F. Jiang, Y. Wang, J. J. Qu, Z. M. Du, Y. Sun, S. J. Luo, "Microstructure evolution of AM60 magnesium alloy semisolid slurry prepared by new SIMA", Journal of Alloys and Compounds, vol.497, pp.62-67, 2010.
24. E. Tzimas, A. Zavaliangos, "Evolution of near-equiaxed microstructure in the semisolid state", Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, vol.289, pp.228-240, 2000.
25. L. Zhang, Y. B. Liu, Z. Y. Cao, Y. F. Zhang, Q. Q. Zhang, "Effects of isothermal process parameters on the microstructure of semisolid AZ91D alloy produced by SIMA", Journal of Materials Processing Technology, vol.209, pp.792-797, 2009.
26. J. G. Wang, P. Lu, H. Y. Wang, J. F. Liu, Q. C. Jiang, "Semisolid microstructure evolution of the predeformed AZ91D alloy during heat treatment", Journal of Alloys and Compounds, vol.395, pp.108-112, 2005.
27. S. C. Hardy, P. W. Voorhees, "Ostwald ripening in a system with a high volume fraction of coarsening phase", Metallurgical Transactions A, vol.19, pp.2713-2721, 1988.
28. Y. Wang, G. Liu, Z. Fan, "Microstructural evolution of rheo-diecast AZ91D magnesium alloy during heat treatment", Acta Materialia, vol.54, pp.689-699, 2006.
29. 木內學，「半熔融‧半凝固加工21世紀展望」，塑性と加工，vol.35，369頁，1994。
30. H. Yan, B. F. Zhou, "Thixotropic deformation behavior of semi-solid AZ61 magnesium alloy during compression process", Materials Science and Engineering: B, vol.132, pp.179-182, 2006.
31. M. M. Avedesian, H. Baker, "Magnesium and Magnesium Alloys", ASM, pp.78-83, 1999.
32. J. G. Wang, P. Lu, H. Y. Wang, Q. C. Jiang, "Effect of predeformation on the semisolid microstructure of Mg-9Al-0.6Zn alloy", Materials Letters, vol.58, pp.3852-3856, 2004.
33. F. Pan, Z. Feng, X. Zhang, A. Tang, "The Types and Distribution Characterization of Al-Mn Phases in the AZ61 Magnesium Alloy", Procedia Engineering, vol.27, pp.833-839, 2012.
34. 侯彥羽，「改良式SIMA製程之累積應變量及鹽浴時間對6068鋁合金微觀組織及拉伸性質之影響」，國立成功大學材料科學及工程學系，碩士論文，2013年。
35. L. Wang, T. Chen, W. Jiang, Y. Feng, W. Dong, Z. Wang, Z. Liang, Y. Zhu, "Grain coarsening in semi-solid state and tensile mechanical properties of thixoformed AZ91D-RE", Journal of Rare Earths, vol.31, pp.319-326, 2013.
36. 木內學，「半熔融‧半凝固加工21世紀展望」，塑性と加工，vol.35，370-375頁，1994。
37. H. Yan, J. J. Wang, "Thixotropic compression deformation behavior of SiCp/AZ61 magnesium matrix composites", Transactions of Nonferrous Metals Society of China, vol.20, pp.811-814, 2010.