鐵為鋁合金中常見之雜質元素，於鑄造冷卻過程中，與鋁形成針狀β-Al5FeSi富鐵相，造成合金之延性損害。A357合金(Al-7Si- 0.6Mg-0.05Be)含有微量鈹，能使針狀富鐵相，轉變為對延性較無害之節球形富鐵相，但因鈹有毒性屬於致癌物質，工業使用上仍受限制。 藉由微結構觀察與機械性質試驗，添加鈧於Al-7Si-0.6Mg合金中，結果顯示鈧能使針狀β-Al5FeSi富鐵相，轉變為細小圓球狀的Sc-Fe富鐵相(Al12Si6Fe2(Mg,Sc)5)。此Sc-Fe富鐵相相較於β-Al5FeSi富鐵相，有較低之硬度與彈性模數，較不易形成裂縫起始點，且其圓球形態能降低對鋁湯流動阻礙，於合金由融溶態凝固時，能有效減少樹枝晶間縮孔的產生。當添加0.04與0.12 wt.% Sc於Al-7Si-0.6Mg合金中，鈧能使合金之延性分別提升115與110%，品質指標分別增加17與19%，破裂韌性之NYR亦分別提升9與12%。因此Al-7Si-0.6Mg合金能藉由鈧來改善其機械性質。Iron is the most deleterious impurity in aluminum alloys. Iron tend to combine with aluminum to form acicular β-Al5FeSi phases which induce ductility damage during solidification of molten metal. It can be found shape of acicular iron-bearing transform into nodular iron-bearing in A357 alloys(Al-7Si-0.6Mg-0.05Be). Because beryllium belong to carcinogenic substance, which used limited in industry. According to microstructure observation and mechanical test, found that the shape of acicular β-Al5FeSi phase transform into tiny globular Sc-Fe phase(Al12Si6Fe2(Mg,Sc)5) after scandium addition in Al-7Si-0.6Mg alloys. Hardness and elastic modulus of Sc-Fe phase is lower than β-Al5FeSi phase, make it difficult to become crack initiation in the Al matrix. Moreover, globular shape of iron-bearing phase can improve fluidity, cause the intradendritic shrinkage could be reduced during solidification. When Al-7Si-0.6Mg alloys contain 0.04 and 0.12 wt.% Sc, elongation increased 115 and 110%, quality index promote 17 and 19%, NYR of fracture toughness increased 9 and 12%, respectively. As a result, mechanical properties of Al-7Si-0.6Mg alloys can be advanced by adding scandium.
