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

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.