Effects of scandium addition on iron-bearing phases and tensile properties of Al–7Si–0.6Mg alloys

Iron is the most deleterious impurity in aluminum alloys and can easily combine with aluminum to form an acicular β-Al5FeSi phase that reduces ductility during the solidification of the molten metal. Adding scandium (Sc) to Al–7Si–0.6Mg alloys can transform the acicular β-Al5FeSi phase into a comparatively harmless nodular Sc–Fe phase (Al12Si6Fe2(Mg,Sc)5). This Sc–Fe phase has a lower hardness and elastic modulus than the β-Al5FeSi phase; it is thus less likely to initiate cracks in the Al matrix. Moreover, the nodular Sc–Fe phase can improve the fluidity of Al during solidification, reducing interdendritic shrinkage. Tensile testing measurements showed that the elongation of Al–7Si–0.6Mg alloys with 0.04 and 0.12 wt% Sc can be respectively increased by 115% and 110% compared to Al–7Si–0.6Mg without Sc. The corresponding quality indices are increased by 17% and 19%, respectively, suggesting that the tensile properties of Al–7Si–0.6Mg alloys can be enhanced by adding scandium.