今日的交通工業致力於產品輕量化和環保訴求，鎂合金具備低密度、高比強度、回收性佳等優點，因而逐漸受到重視；鎂因具備HCP結構，使得鎂合金的加工往往要在高於室溫的環境進行，為了節省成本及便利加工，降低鎂合金的加工溫度甚至室溫加工是必要的。摩擦攪拌製程(Friction Stir Process, FSP)可藉簡易製程達到晶粒細化的目的，進而改善材料的加工性，故本研究利用不同溫度拉伸試驗比較FSP前後的差異，並探討兩者的變形機制，了解FSP對鎂合金加工性的改善能力。
　　本研究採用AZ31鎂合金之完全退火材，先以不同轉速進行FSP，並將改質後試片以固定初始應變速率為8×10-4 sec-1的條件進行室溫拉伸試驗。接著選擇1500rpm下FSP後的試料進行相同初始應變速率的100℃~500℃之拉伸試驗，觀察其變形組織特徵，了解其變形組織及拉伸特性與溫度的關係，並與退火材進行相同實驗比對。
　　拉伸結果顯示，試料的降伏強度及抗拉強度隨溫度上升而減少，總延伸率隨溫度上升而增加，而均勻延伸率呈現先下降再持平而後上升的趨勢。
　　持溫試片及破斷次表面的觀察顯示，材料在200℃以下藉晶粒伸長造成應變；300℃時晶粒成長效應逐漸顯著，在拉伸過程中主要以動態再結晶和晶粒成長兩種現象交替發生；350℃以上晶粒成長快速，拉伸性質與FSP前相近，以FSP改質的目的失去效用。
　　低轉速FSP前後的拉伸試驗結果顯示，發現FSP後試料在150℃以下的降伏強度和抗拉強度較O材小，均勻延伸率則較大；根據破斷面遠端組織觀察結果，FSP後材料的晶粒變形較O材明顯，顯示FSP後材料在平行進給方向上有較佳的均勻變形。

　　Product lightening and environmental protecting are required in trans- port industry nowadays. Magnesium alloys are of great interest for use in lightweight structuredue to its low density, high specific strength, well re- cycled. Unfortunately, the disadvantage of Mg alloys is that they exhibit limit ductility due to their HCP structure. Therfore, significant develop- ment efforts are needed, which can improve their workability. Friction stir process (FSP) can get finer grains to improve the workability by dynamic recrystallization (DRX). On the basis of that, Mg alloy’s deformed pheno- menons and mechanical properties before and after FSP by tensile tests in several temperatures were discussed to comprehend FSP’s effect of work- ability improvement on Mg alloy.
　　A full-annealed magnesium alloy AZ31 was used to go through FSP in several rotation speed initially. The tensile tests of FSPed AZ31 were per- formed at constant initial strain rate of 8×10-4 sec-1 in room temperature. FSPed AZ31 with processed in 1500 rpm was chosen for the next step of the study.
　　The tensile test of FSPed AZ31 in 1500 rpm was performed from room temperature to 500℃ at the same initial strain rate. Then the temperature dependance of deformed microstructure and tensile properties was inve-
stigated in observations of deformed microstrusture. Furthermore, full-
annealed AZ31 was done the same experiments as comparisons.
　　The experimental results indicate that yield strength (Y.S.) and ultimate strength (U.T.S.) decreased with increasing temperature. Total elongation (T.E.) increased with increasing temperature. Uniform elongation (T.E.) decreased as the temperature increased from room temperature to 200℃, broadly maintained from 200℃ to 400℃, and increased as the tempera- ture was above 400℃.
　　According to the deformed and temperature-held microstructure, defor- mation was made of grain extension below 200℃. Grain growth started above 300℃, and it took place by turn with DRX during tensile process. Grain grew rapidly above 350℃. It would make the efficacy of FSP in vain.
　　Comparing with full-annealed AZ31, FSPed AZ31 in 1500 rpm has smaller Y.S., U.T.S., and bigger U.E. . It indicated that the latter got lower deformed impedance during cold work.

1. 陳錦修, ”鎂合金在汽車工業之應用”,工業材料雜誌186期,民國91年6月。
2. 張惠冠, ”我國自行車產業發展現況與趨勢分析”,工業材料雜誌188期,民國91年8月。
3. I.J. Polmear, ”Recent Developments in Light Alloys”, Materials Transactions
, JIM, Vol. 37, No.1, 1996, pp.12-31.
4. I.J. Polmear, “Magnesium Alloys and Applications”, Materials Science and
Technology, Vol. 10, No.1, 1994, pp. 1-15.
5. Z.Zhang, A. Couture and A.Lou, “An Investigation of the Properties of
Mg-Zn-Al Alloys”, Scripta Materialia, Vol. 39, No.1, 1998, pp.45-53.
6. M.M. Avedesian and H. Baker, “Magnesium and Magnesium Alloys”,
ASM Int., 1999, pp.13-21.
7. W.M. Thomas, E.D. Nicholas, J.C. Needham, M.G. Murch, P. TempleSmith
and C.J. Dawes, “Friction stir butt Welding”, International Patent Appli-
cation, No. PCT/GB92/02203 and GB Patent Application, No. 9125978.8,
1991.
8. Bangvheng Yang, Junhui Yan, Michael A. Sutton, Anthony P. Reynolds,
“Banded Microstructure in AA2024-T351 and AA2524-T351 Aluminum
Friction Stir Welds Part I. Metallurgical studies”, Materials Science and
Engineering A364, 2004, pp.55-65.
9. Michael A. Sutton, Bangvheng Yang, Anthony P. Reynolds, Junhui Yan,
“Banded Microstructure in AA2024-T351 and AA2524-T351 Aluminum Friction
Stir Welds Part II. Mechanical characterization”, Materials Science
and Engineering A, Vol.364, 2004, pp.66-74.
10. Yutaka S. Sato, Seung Hwan C. Park, Masato Michiuchi, Hiroyuki
Kokawa, “Constitutional liquation during Dissimilar Friction Stir Welding
of Al and Mg Alloys”, Scripta Materialia, Vol.50, 2004, pp.1233-1236.
11. W.M. Thomas and E.D. Nicholas, “Friction Stir Welding for the Trans-
portation Industries”, Materials & Design, Vol.18, No.4/6, 1997, pp.269
-273
12. R.S. Mishra, M.W. Mahoney, S.X. McFadden, N.A. Mara and A.K.
Mukherjee, “High Strain Rate Superplasticity in a Friction Stir Processed
7075 Al Alloy”, Scripta Materialia, Vol.42, 2000, pp.163-168
13. Z.Y. Ma, R.S. Mishra and M.W. Mahoney, “Superplastic Deformation
Behavior of Friction Stir Processed 7075 Al Alloy”, Acta Materialia, Vol.
50, 2002, pp.4419-4430
14. F.J. Humpheys and M. Hathrly, “Recrystallization and Related Annealing
Phenomena”, Pergamon, Oxford, UK, 1996
15. K.V. Jata and S.L. Semiatin, “Continuous Dynamic Recrystallization
during Friction Stir Welding of High Strength Aluminium Alloys”, Scripta
Materialia, Vol.43, 2000, pp.743-749
16. J.Q. Su, T.W. Nelson, R. Mishra, and M. Mahoney, “Microstrucural Inve-
stigation of Friction Stir Welded 7050-T651 Aluminium”, Acta Materialia,
Vol.51, 2003, pp.713-729
17. C.G. Rhodes, M.W. Mahoney, M.H. Bingel, and M. Calabrese, “Fine-grain
Evolution in Friction-Stir Processed 7050 Aluminium”, Scripta Materialia,
Vol.48, 2003, pp.1451-1455
18. Yutaka S. Sato, Mitsunori Urata, and Hiroyuki Kokawa, “Parameters
Controlling Microstructure and Hardness during Friction-Stir Welding of
Precipitation-Hardenable Aluminium Alloy 6063”, Metallurgical and
Materials Transactions A, Vol.33, 2002, pp.625-635
19. J.Q. Su, T.W. Nelson, and C.J. Sterling, “a New Route to Bulk Nano-
crystalline Materials”, Journal of Material Research, Vol.18, 2003,
pp.1757-1760
20. Yong-jai Kwon, Ichinori Shigematsu, and Naobumi Saito, “Mechanical
Properties of Fine-Grained Aluminium Alloy Produced by Friction Stir
Process”, Scripta Materialia, Vol.49, 2003, pp.785-789
21. Yong-jai Kwon, Ichinori Shigematsu, and Naobumi Saito, “Production of
Ultra-Fine Grained Aluminium Alloy using Friction Stir Process”,
Materials Transactions, JIM, Vol.44, No.7, 2003, pp.1343-1350
22. I. Charit and R.S. Mishra, “High Strain Rate Superplasticity in a
Commercial2024 Al Alloy Via Friction Stir Processing”, Materials and
Engineering A, Vol.359, 2003, pp.290-296
23. V.M. Segal, “Materials Processing by Simple Shear”, Material Science
and Engineering A, Vol.197, 1995, pp.157-164
24. C.I. Chang, C.J.Lee, and J.C. Huang, “Relationship between Grain Size
and Zener-Holloman Parameter during Friction Stir Processing in AZ31
Mg Alloys”, Scripta Materialia, Vol.51, 2004, pp.509-514