摘要
A356(Al-7Si-0.35Mg)合金屬於亞共晶型Al-Si合金，其微結構為初晶鋁、共晶矽及富鐵相。未改良之共晶矽會以粗針狀型態出現，而此種型態將對合金之機械性質造成相當不良之影響；現今常以Na、Sr及Pb作為改良劑改良共晶矽型態。本研究目的在於探討添加不同含量稀土元素La、Ce對A356合金之微結構及其機械性質之影響。
實驗設計添加各種不同含量(0.2、0.4、0.6、0.8及1.0wt.%)La、Ce之A356合金，以金相觀察(OM)、破斷面觀察、電子微探儀(EPMA)、影像分析及熱分析法觀察合金微結構並評估其共晶矽改良與否及其改良之程度；並以硬度試驗、拉伸試驗及品質指標來評估A356合金之機械性質。
實驗結果顯示，稀土元素La的添加量達至0.6wt.%以上時，其共晶矽開始有較明顯的改良效果，延伸率及品質指標也開始有較明顯提升的現象；當La添加至1.0wt.%時，其共晶矽已完全改良至球狀纖維化共晶矽，延伸率及品質指標也有相當大幅度的提升，其改良效果類似於工業上常用之改良劑Sr。當稀土元素Ce的添加量達至0.6wt.%時，其共晶矽開始產生改良效果，延伸率及品質指標也開始有較明顯提升的現象；當添加1.0wt.% Ce時，其共晶矽呈現出層狀結構，類似於以Sb改良後之微結構，其延伸率及品質指標相較於未經改良之A356合金亦有大幅度的改善。

Abstract
Modification of the Al-Si eutectic from a flake-like to a fine fibrous silicon structure can be achieved in two ways ; by addition of certain elements(chemical modification) or with a rapid cooling rate(quench modification). Several elements are known to cause chemical modification. The most common elements used in industry today are Sr and Na, which change the silicon morphology from coarse and plate-like to fine and fibrous, and Sb which causes a refinement in the plate-like silicon structure. The aim of the present paper was to investigate the individual effects of rare earth element La and Ce on the eutectic microstructure and mechanical properties in A356 (Al-7Si-0.35Mg) alloys.
In this study, eutectic microstructures and mechanical properties in samples modified by minor rare earth La and Ce in an A356 alloy have been determined by optical microscopy(OM), scanning electron microscopy(SEM),thermal analysis, image analysis, hardness test and tensile test.
The fine fibrous eutectic structure that was obtained with La additions is typical of that obtained with conventional modifiers such as Sr and Na. Modification on the eutectic microstructure and mechanical properties improves with increasing additions of La until a fully modified eutectic structure is obtained at 1.0 wt.% La.
Large additions of Ce did not modify the eutectic silicon and only resulted in a small refinement of the plate-like morphology. The behavior of the majority of rare earth element Ce is therefore more similar to that of Sb than Sr or Na.

陸、 參考文獻：
1、 高木仁三郎著、陳雲譯, ”元素小百科”,幼獅文化事業公司,初版, (1991), p.23
2、 J.E.Gruzleski and B.M.Closset , The Treatment of Liquid Aluminum - Silicon Alloys, AFS, (1990), pp.25-228
3、 J.E.Hatch,”Aluminum：Properties and Physical Metallurgy” , London,
Butterwordths and Co., Ltd., (1976),pp.346-347
4、 S. Shivkumar, C. Keller and D. Apelian,”The Influence of Molten Metal
Processing on Mechanical Properties of Cast Al-Si-Mg Alloys” AFS
Transactions , (1990), pp. 905-911
5、 材料手冊Π、非鐵金屬材料,中國材料科學學會，(1983), p.20
6、 S. Z. Lu and A. Hellawell , “The Mechanism of Silicon Modification in
Aluminum-Silicon Alloys : Impurity Induced Twinning ”, Metall. Tarns. A. , vol.18A, (1987), pp.1721-1733
7、 K. Nogita , J. Drennan and A. K. Dahle , “Evaluation of Silicon Twinning
in Hypo-Eutectic Al-Si Alloys”,Mater. Trans. , vol.44, (2003),pp.625-628
8、 P. N. Crepeau, “Effect of Iron in Al-Si Casting Alloys：A Critical
Review”, AFS Transcations, vol.103, (1995), pp.361-365
9、 林裕煥 , “微量Sr與Be對Al-11%Si合金機械性質之影響” , 國立中央大學
機械工程研究所碩士論文 (1996)
10、 A. M. Samuel, F. H. Samuel , “Observations on the/formation of β-Al5FeSi Phase in 319 Type Al-Si alloys”, Journal of Materials Science, vol.31,(1999), pp.231-238
11、 L. Wang, “Iron-Bearing Compounds in Al-Si Diecasting Alloys：Morphology
and Conditions Under Which They Form”, AFS Transcations, vol.107,
(1999), pp.231-238
12、 F. H. Aamuel, P. Quellet, “Effect of Mg and Sr Additions on the Formation of Intermetallics in Al-6Wt Pct Si-3.5 Wt Pct Cu-(0.45)to(0.8)Wt Pct Fe 319- Type Alloy”, Metallurgical and Materials Transactions A, Vol.29A,
(1998), pp.2871-2884
13、 Paih-Shiarng Wang, Sheng-Long Lee, Jing-Chie Lin, “Effects of solution
temperature on mechanical properties of 319.0 aluminum casting alloys
containing trace beryllium”, Journal of Materials Research, vol.15,
(2000), pp.2027-2035
14、 F. H. Samuel, A. M. Samuel, “Decomposition of Fe-Intermetallics in
Sr-Modified Cast 6xxx Type Aluminum Alloys for Automotive Skin”,
Metallurgical and Materials Transcations A, Vol.32A, (2001), pp.2061-2075
15、 廖義吉, “微量Be與非平衡熱處理對319鑄鋁合金性質之影響”, 國立中央
大學機械工程研究所碩士論文 (1996)
16、 F. H. Aamuel, A. M. Aamuel, “Modification of Iron Intermetallics by
Magnesium and Strontium in Al-Si Alloys”, Int. J. Cast Metals Res., vol.10, (1997), pp.147-157
17、 G. K. Sigworth, S. Shivkumar and D. Apelian, “The Influence of Molten Metal Processing on Mechanical Properties of Cast Al-Si-Mg Alloys”, AFS Transcations, vol.97, (1989), pp.811-824
18、 E. N. Pan, M. W. Hsieh, S. S. Jang and C. R. Loper, Jr., “Study of the
Influence of Processing Parameters on the Microstructure and Properties
of A356 Aluminum Alloys”, AFS Transactions, vol.97, (1989), pp.397-414
19、 S. Shivkumar, S. Ricci, Jr. B. Steenhoff, D. Apelian and G. Sigworth, “An Experimental study to Optimize the Heat Treatment Of A356 Alloy”, AFS
Transactions, vol.97, (1989), pp.791-810
20、 蘇鏘, ”稀土元素：您身邊的大家族”, 初版,北京：清華大學、暨南大學, (2001)
pp.21-26
21、 徐光實, “神奇之土”, 初版, 湖南科學技術出版社, (1995), pp.23-25
22、 B.Closset, R.A.L.Drew and J.E.Gruzleski, “Eutectic Silicon Shape Control
by In Situ Measurement of Resistivity ” ,AFS Transactions, vol.94,
(1986), pp.9-16
23、 P.N Crepeau, “Effect of Iron in Al-Si Casting Alloys: A Critical Review”, AFS Transaction, vol.103, (1995), pp.361-365
24、 Stuart D. McDonald, Kazuhiro Nogita and Arne K. Dahle, “Eutectic
nucleation in Al-Si alloys”, Acta Materialia, vol.52, (2004), pp.4273-
4280
25、 Jun Wang, Shuxian He, Baode Sun, Ke Li, Da Shu and Yaohe Zhou, “Effect of melt thermal treatment on hypoeutectic Al-Si alloys”, Materials
Science and Engineering A, vol.338, (2002), pp.101-107
26、 Kazuhiro Nogita, Stuart D. McDonald and Arne K. Dahle, “Eutectic
Modification of Al-Si alloys with Rare Earth Metals”, Materials
Transactions, vol.45, (2004), pp.323-326
27、 K. Nogita, A. Knuutinen, S.D. McDonald and A.K. Dahle, “Mechanisms of
eutectic solidification in Al-Si alloys modified with Ba,Ca,Y and Yb”,
Journal of Light Metals, vol.1, (2001), pp.219-228
28、 D.H. Xiao, J.N. Wang, D.Y. Ding, H.L. Yang, “Effect of earth Ce addition on the microstructure and mechanical properties of an Al-Cu-Mg-Ag alloy, Journal of Alloys and Compounds, vol.352, (2003), pp.84-88
29、 Leonhard Heusler, Wolfgang Schneider, “Influence of alloys elements on the thermal analysis results of Al-Si cast alloys”, Journal of Light
Metals, vol.2, (2002), pp.17-26
30、 ASTM B557 M-81,Annual Book of ASTM Standards, Vol.03.01,(1990)
31、 A.Knuutinen, K. Nogita, S.D. McDonald, A.K. Dahle, ”Porosity formation
in aluminium alloy A356 modified with Ba,Ca,Y,Yb”, Journal of Light
Metals, vol.1, (2001), pp.241-249
32、 A.Knuutinen, K. Nogita, S.D. McDonald, A.K. Dahle, ”Modification of Al-Si alloys with Ba,Ca,Y,Yb”, Journal of Light Metals, vol.1, (2001), pp.229-240
33、 K. Nogita, A.K. Dahle,”Eutectic solidification in hypoeutectic Al-Si
alloys:electron backscatter diffraction analysis”, Materials
Characterization, vol.46, (2001), pp.305-310
34、 A.K. Dahle, K. Nogita, S.D. McDonald, C. Dinnis ,L. Lu, ”Eutectic
modification and microstructure development in Al-Si Alloys”, Materials
Science and Engineering A , vol.413-414, (2005), pp.243-248
35、 A.K. Dahle, K. Nogita, J.W. Zindel, S.D. McDonald, L.M. Hogan, ”Eutectic nucleation and growth in hypoeutectic Al-Si alloys at different strontium levels”, Metallurgical and Materials Transactions A., vol.32A,
(2001), pp.949-959
36、 Y.C. Lee, A.K. Dahle, D.H. StJohn, J.E.C. Hutt, “The effect of grain
refinement and silicon content on grain formation in hypoeutectic Al-Si
alloys”, Materials Science and Engineering A , vol.259, (1999), pp.43-52
37、 Kazuhiro Nogita, John Drennan and Arne Kristian Dahle, “Evaluation of silicon twinning in hypo-eutectic Al-Si alloys”, Materials Transcations
vol.44, (2003), pp.625-628
38、 Geng Huiyuan, Li Yanxiang, Chen Xiang, Wang Xue,”Effect of boron on
eutectic solidification in hypoeutectic Al-Si alloys”, Scripta
Materialia, vol.53, (2005), pp.69-73