摘要

噴覆成型製程(Spray Forming Process)是近年來逐漸在創造先進材料以及金屬基複合材料上嶄露頭角的一種先進製程技術。其所製造出來的材料同時具有粉末冶金以及鑄造兩種製程的優點，卻沒有這兩種製程的缺點。由於噴覆成型材料具備的微細等軸晶組織在半固態時會有變凝行為，所以可以選擇另一先進的加工製程-半固態成型製程(semisolid forming)作為成型技術。金屬於半固態時，其表現出來的特性接近固體，可以任意的移動運送而不損及其原來的形狀，但強度和固態金屬相比則仍相差甚遠。金屬於半固態時的低強度、易成型的特性所開發出來的便是半固態成型製程。本實驗主要目的在於利用噴覆成型製程製作出SFP_Al-50wt.%Si材料，並嘗試找出此材料在半固態狀態時的變形行為特性。
將原始鑄錠以噴覆成型製程製作後，在材料微結構上產生：1.矽晶細化。2.矽晶形狀改變。3.矽晶分佈均勻。4.層狀共晶結構組織消失等變化。由於矽晶的細化以及形狀較接近球形，材料在半固態狀態下的固相及液相間的相對運動會變得比較流暢
固相分率(f.s)對於半固態變形而言是個影響很大的因素，縱使在數值上只有很小的差異，可是在變形性能的表現上卻可能會截然不同。
由影像分析結果我們可以發現幾個區域由試片中央往外側分佈：1.矽晶顆粒集中區。2.固態相矽晶顆粒及液態相平均散佈區域。3.液態偏析區。
由實驗結果分析，半固態變形過程中會有以下幾個主要的機構：1.固態矽晶顆粒的擠壓及破裂。2.固態相（矽晶顆粒）間的接觸滑動。3.液相與固相的同時移動（兩相間的比例為一動態平衡關係）。4.液態相與固態相（矽晶顆粒）間的相對運動。半固態成型時的成形速率及成型溫度會有一個最佳值，高或低於此最佳條件，其成型性便會劣化。
於本研究中，最佳的半固態變形條件為750℃持溫壓縮，壓縮速率60mm/min。

ABSTRACT

Spray forming process is recently concerned to make advanced materials and MMCs. The material that’s made by this process have the advantages that formerly in PM process and Cast.process at the same time, and no disadvantages which are happened in PM and Cast. For the equi-axed microstructure that was observed in some of Spray forming materials, these Spray forming materials will show the thixotropic behavior. For this reason, we can sequentially choose semi-solid forming process as the next forming process. The material that under semisolid state will still maintain the shape and some strength as solid was, but it’s much more easily to deform.
The purposes of this research are producing the Spray forming Al-50wt.%Si alloy and figure out the characteristic of deformation of this material under semisolid state.
The microstructure differences between row material (Cast ones) and Spray forming one are: 1. Silicon particles are much finer in spray one. 2. The shape of silicon particles are different. 3. Silicon particles distribute well-proportioned in Spray forming material. 4. The eutectic layer structure disappeared in Spray forming material.
Solid fraction is an important and effective factor in semisolid deformation, though the difference between solid fraction values may be small, but the deformation behavior will be very different.
Observing the results of image analysis, we can find some variant areas from the center of specimen to outer. These areas are: 1. High Silicon fraction area 2. Silicon fraction equals to original value area. 3. Liquid phase segregated area.
The mechanisms of Al-50wt.%Si semisolid deformation are: 1. The squeezing and crack of silicon particles. 2. Sliding of silicon particles. 3. Silicon particles and liquid phase travel at the sane time. 4. Liquid phase travel alone. The deformation rate and deformation temperature have an optimized value, at this condition, the material will show the best formability.
In this research, the best semisolid deformation condition is: hold at 750℃ and compress specimens at initial compress speed=60mm/min.

1. C. P. Chen and C.-Y. A. Tsao, ”SEMI-SOLID DEFORMATION OF NON-DENDRITIC STRUCTURES─Ⅰ.PHENNOMENOLOGICAL BEHAVIOR”, Acta mater, 1997, Vol. 45, No. 5, pp. 1955-1968
2. Spencer, D. B., Mehrabian R. and Flemings, M. C.,”Metal Trans.”, A. , 1972, 3A, pp.1925-1932
3. Christian Pluchon, Willem Loué, Pierre-Yves Menet, Michel Garat, ”DEVELOPMENT OF SEMI-SOLID METAL FORMING FEEDSTOCK AND FINISHED PARTS”,
4. R. Raj, ”A MECHANISTIC BASIS FOR HIGH STRAIN RATE SUPERPLASTICITY OF ALUMINUM BASED METAL MATRIX COMPOSITES”, MATERIAL SCIENCE & ENGINEERING A, A212, 1996, pp.14-21
5. Andreas Alexandrou, Francois Bardinet, Willem Loué, “MATHEMATICAL AND COMPUTATIONAL MODELING OF DIE FILLING IN SEMISOLID METAL PROCESSING”, Journal of Materials Processing Technology 96, 1999,pp.59-72
6. S. C. Bergsma, M. C. Tolle, M. E. Kassner, X. Li, E. Evangelista, “SEMI-SOLID THERMAL TRANSFORMATIONS OF Al-Si ALLOYS AND THE RESULTING MECHANICAL PROPERTIES”, Material Science and Engineering A237, 1997, pp. 24-34
7. Gilmer R. Burgos, Andreas N. Alexandrou, Vladimir Entov, ”THIXOTROPIC RHEOLOGY OF SEMISOLID METAL SUSPENSIONS”, Journal of Materials Processing Technology 110,2001, pp. 164-176
8. Woei-Shyan Lee, Wu-Chung Sue, Chi-Feng Lin, Chin-Jyi Wu, ”THE STRAIN RATE AND TEMPERATURE DEPENDENCE OF THE DYNAMIC IMPACT PROPERTIES OF 7075 ALUMINUM ALLOY”, Journal of Materials Processing Technology 100,2000, pp. 116-122
9. P. J. WARD, H. V. ATKINSON, P. R. G. ANDERSON, L. G. ELIAS, B. GARCIA, L. KAHLEN, J-M RODRIGUEZ-IBABE, “SEMI-SOLID PROCESSING OF NOVEL MMCs BASED ON HYPEREUTECTIC ALUMINUM-SILICON ALLOYS”, Acta mater, vol. 44, No.5, pp. 1717-1727
10. M. Gupta, E.J. Lavernia, ”EFFECT OF PROCESSING ON MICROSTRUCTURERAL VARIATION AND HEAT-TREATMENT RESPONSE OF A HYPEREUTECTIC Al-Si ALLOY”, Journal of Materials Processing Technology 54, 1995, pp. 261-270
11. L. Djapic Oosterkamp, A. Ivankovic, G. Venizelos, “HIGH STRAIN RATE PROPERTIES OF SELECTED ALUMINUM ALLOYS”, MATERIAL SCIENCE & ENGINEERING A,A278, 2000, pp. 225-235
12. D. E. Albert and G. T. Gray Ⅲ, “MECHANICAL AND MICROSTRUCTUREAL RESPONSE OF Ti-24Al AS A FUNCTION OF TEMPERATURE AND STRAIN RATE”, Acta mater, Vol. 45,1997,pp. 343-356
13. S. Fujino, N. Kuroishi, M. Yoshino, T. Mukai, Y. Okanda, K. Higashi, “HIGH-STRAIN-RATE SUPERPLASTIC BEHAVIOR IN A SUPER-RAPIDLY-SOLIDIFIED Al-Si SYSTEM ALLOY”, Scripta Materialia, Vol. 37,No. 5, pp. 673-678
14. E. Tzimas, A. Zavaliangos, “MECHANCAL BEHAVIOR OF ALLOYS WITH EQUIAXED MICROSTRUCTURE IN THE SEMISOLID STATE AT HIGH SOLID CONTENT”, Acta mater, Vol. 47,1999,pp. 517-528
15. H. P. Stüwe, P. Les, “STRAIN RATE SENSITIVITY OF FLOW STRESS AT LARGE STRAINS”, Acta mater, Vol. 46,1998,pp. 6375-6380
16. Toshiji Mukai, Koichi Ishikawa, Kenji Higashi, “INFLUENCE OF STRAIN RATE ON THE MECHANICAL PROPERTIES IN FINE-GRAINED ALUMINUM ALLOYS”, MATERIAL SCIENCE & ENGINEERING A,A204, 1995, pp. 12-18
17. Bear J., ”Dynamics of fluids in porous media”, American Elserver, New York, 1972
18. D.R. Poirier, G.H. Geiger, “Transport Phenomena in materials processing”, TMS,1994
19. C.R. Boer, N. Rebelo, H. Rydstad, G. Schroder, ”Process Modeling of metal forming and thermo-mechanical treatment”, Springer-Verlag Berlin Heidelberg NewYork Tokyo, 1985
20. E. Tzimas, A. Zavaliangos, A. Lawley and C. Pumberger, ”Physical mechanisms of the flow resistance of semisolid materials at a high volume fraction of solid”, Proceedings of the 4th international conference on semi-solid processing of alloys and composites, Sheffield, June 1996.
21. Kapranos P., Kirkwood D.H. and Sellars C.M., Proceedings EUROMAT 1989 conf. 1989,P.165
22. Rudnicki J. W. and Rice J. R., J. Mech. Phys. Solids, 1975,vol. 23,P.271
23. 陳志彬,”半固態合金變形行為研究”, 國立成功大學材料科學及工程研究所碩士論文,1995
24. J. Valer, F. Saint-Antonin, ”Influence of Processing on Microstructure and semi-solid Behavior of Al-Ge alloys”, Proceedings of the 5th international conference on semi-solid processing of alloys and composites, June 1998.