First-principles study of elastic and electronic properties of MgZn2 and ScZn2 phases in Mg-Sc-Zn alloy

Research highlights: MgZn2 and ScZn2 are the important strengthening phases, and have recently led to a renewed interest in the research and development of Mg-based alloys, so theoretical investigations on the elastic properties of MgZn2 and ScZn2 are necessary and urgent. The present paper investigated the elastic and electronic properties of MgZn2 and ScZn2 phases in Mg-Sc-Zn alloy by means of first-principles calculation. The elastic constants and other mechanical parameters such as bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of polycrystalline aggregates were studied, and the ductility and plasticity were further discussed. Furthermore, the electronic structure was investigated for understanding the underlying mechanism of the structural stability and elastic properties. These results would be valuable for the further optimization and design of Mg-rare earth alloys with excellent mechanical properties. - Abstract: The structural, electronic and elastic properties of typical hexagonal-close-packed MgZn2 and ScZn2 phases in Mg-Sc-Zn alloy were investigated by means of first-principles calculations within the framework of density functional theory (DFT). The calculated lattice constants were in good agreement with the experimental values. The obtained cohesive energy and formation enthalpy of both phases are negative, showing their structural stability from energetic point of view. The five independent elastic constants were calculated, and then the bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of polycrystalline aggregates were derived. The ductility and plasticity of the MgZn2 and ScZn2 phases were further discussed. The elastic anisotropy of the two phases was also analyzed. Finally, the electronic density of states (DOS) and charge density distribution were also calculated to reveal the underlying mechanism of structural stability and mechanical properties.