Microstructure and mechanical properties of hypoeutectic Al-Si alloy with Sc and Zr additions

The Al-Si alloy group is one of the most commonly used for casting due to its superior
fluidity. However, these alloys do not exhibit very good mechanical properties because of the
large α-Al grains and the coarse, plate-like structure of the eutectic Si. The addition of minor
alloying elements is necessary to improve the mechanical properties. This study investigates
the effects of scandium (Sc) and zirconium (Zr) additions as minor alloying elements on the
microstructure and mechanical properties of Al-7Si-0.3Mg alloy. The macrostructure and
microstructure were examined by optical microscopy and scanning electron microscopy. The
mechanical properties were investigated by analyzing hardness and tensile properties. The
results demonstrated that the addition of Sc and Zr reduces the primary α-Al grains in
Al-7Si-0.3Mg alloy. Moreover, Sc impacts the eutectic Si structure, transforming the coarse
plate-like into a finer fibrous structure. As a result, it substantially improved the hardness and
tensile properties. More importantly, the addition of Sc and Zr reduces the sensitivity to
microstructure changes due to variations in cooling rates during solidification.