First-principles calculations of the mechanical properties of Mg2Si intermetallic via ternary elements doping

Abstract

Site preference, structural stability and mechanical properties of Mg2Si doped by ternary elements were studied by first-principles calculation. Formation enthalpies show that light element impurity Al and rare earth elements Sc and Y tend to occupy the Mg site, while transition element Cu has a preference for the Si site. Shear modulus to bulk modulus ratio (G/B), Poisson’s ratio ν and Cauchy pressure show that the ductility of Mg2Si is improved for ternary element addition. The introduced parameter of ductility factor D indicates that the enhanced dislocation emission but suppressed micro-crack propagation is the key to enhancing ductility. Electronic structure indicates the brittleness is due to the strong covalent interaction between Mg-2p and Si-3p (Mg-3s and Si-3p/3s). While, with the incorporation of alloying elements, abundant electrons are injected into the matrix Mg2Si. Thereby, the covalent interaction is effectively suppressed and the ductility is improved.