微量鈧與鋯對A357鋁矽鎂合金微結構與機械性質之影響

Effect of minor Zr and Sc on the microstructures and mechanical properties of A357 Al-Si-Mg alloys

許勤偉(Chin-Wei Hsu)

指導教授 ： 李勝隆

國立中央大學/工學院/機械工程學系/碩士(2015年)

摘要

本研究藉由微結構觀察與機械性質測試，來評估微量鋯與鈧對Al-7Si-06Mg合金時效處理(T6)與250℃下熱暴露之機械性質影響，結果顯示經T6熱處理(160℃*6hrs)之合金可析出Mg2Si強化相，從而提升導電度與合金強度。添加微量鈧元素可將針狀富鐵相（β-Al5FeSi相）轉變成文字型Sc-Fe相(Al12Si6Fe2(Mg,Sc)5)，且Sc可以減少合金之縮孔，有效提升合金之延性。而添加微量鋯可以使合金具有晶粒細化效果，於T6態下，具有最高的強度，然而微結構中的針狀富鐵相與棒狀(Al,Si)3(Ti,Zr)介金屬相與縮孔減損合金之延性。
微量鋯或鈧之Al-7Si-06Mg合金於高溫 (250℃)下析出Al3Zr、Al3Sc和 Al3(Sc,Zr)等散佈相，有效抑制合金強度的下降，其熱穩定性明顯優於含微量鈹之A357合金，且以含Sc之合金效果最為顯著，且可以利用微量Zr取代部分昂貴的Sc，藉以提升合金之熱穩定性是可行的。

關鍵字

A357合金 ； Al3(Sc,Zr) ； 機械性質 ； 熱穩定

並列摘要

The principal aim of this research is to evaluate the effect of minor additions of zirconium and scandium on the microstructure and mechanical properties of Al-7Si-0.6Mg alloys during aging treatment (T6) and heat exposure (250℃). The results indicated that the Al-7Si-0.6Mg alloys can increase the conductivity and intensity of alloys by precipitating Mg2Si during T6 heat treatment. Addition of scandium in Al-7Si-0.6Mg alloys could make the shape of acicular β-Al5FeSi phase transform into tiny globular or Chinese script Sc-Fe phase (Al12Si6Fe2(Mg,Sc)5) and decrease the shrinkage of alloys to improve the ductility of material. Addition of zirconium in Al-7Si-0.6Mg alloys have the highest strengthening during T6 heat treatment because of the effect of grain refining. However Addition of zirconium will form rod-like (Al,Si)3(Ti,Zr) phases and niddle-like β-Al5FeSi phases to induce ductility damage on the microstructure.
Al-7Si-0.6Mg alloys of minor additions of zirconium and scandium precipitate dispersion phase of Al3Zr, Al3Sc and Al3(Sc,Zr) during the heat exposure(250℃*100hrs). It could efficiently inhibit the alloy strength decrease and it’s thermal stability is greater than A357 alloys. Particularly, the alloys of scandium addition have the best effect. Moreover it is possible to substitute zirconium for parts of scandium additions to promote the thermal stability.

參考文獻

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