Anisotropic mechanical and corrosion properties of directionally solidified Mg-3Zn-0.2Ca alloy

A Mg-3 wt.%Zn-0.2 wt.%Ca alloy was fabricated by directional solidification, and its mechanical and corrosion properties were investigated from different crystallographic orientations. It was found that the directionally solidified (DSed) Mg-3Zn-0.2Ca alloy had a cellular structure with a preferred<11-20>growth orientation. The {0001} basal planes aligned approximately parallel to the growth direction of DSed alloy. The mechanical properties were measured with compression and nanoindentation tests by loading along with different directions, including the directions parallel (LD) and perpendicular (TD) to the growth direction of the DSed sample. The results indicated that the compression properties, strain hardening rate (θ), hardness (H), and elastic modulus (E) of the DSed Mg-3Zn-0.2Ca alloy were highly anisotropic. The anisotropies of the compression properties, θ, and H are caused by the activation of different deformation mechanisms. The anisotropic E comes from the difference of atomic bonding strengths at different crystallographic planes. The corrosion resistance of DSed Mg-3Zn-0.2Ca alloy exhibited anisotropy as well. The corrosion resistance of the specimen taken along LD is better than that of the specimen taken along TD. Besides, the LD and TD specimens experience much slighter corrosion than the as-cast specimen with randomly crystallographic orientation. The superior corrosion resistance of the LD specimen is beneficial from its surface distributed with more {0001} basal crystallographic planes.