Effect of rare earth elements addition on microstructures and mechanical properties of A356 alloy

A356 is a heat treatable Al-Si-Mg hypoeutectic alloy with a normal composition of 7 wt-%Si and similar to 0.3 wt-%Mg which has widespread applications in the aerospace and automotive industries. The influence of the rare earth metals La and Ce on the microstructures and mechanical properties of A356 alloy has been investigated. The findings indicate that the modification efficiency of 1 wt-%La is similar to that achieved by commercial modification with 0.02 wt-%Sr, but the modification efficiency of Ce is lower than those of La and Sr. Two kinds of La or Ce rich intermetallics are found in this study: AlTiLa(Ce)Mg and AlSiLa(Ce) phases. Although the ductility of the rare earth modified alloys are both greatly enhanced, no positive effect on ultimate tensile stress that can be attributed to the formation of AlTiLa(Ce) Mg phase was observed.