Abstract:The structural stability, electronic structures, elastic properties and thermodynamic properties of the main binary phases Mg₁₇Al₁₂, Al₂Ca, Mg₂Sn and Mg₂Ca in Mg-Al-Ca-Sn alloy were determined from the first-principles calculation. The calculated lattice parameters are in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Al₂Cahas the strongest alloying ability and structural stability. The densities of states (DOS), Mulliken electron occupation number, metallicity and charge density difference of these compounds are given. The elastic constants of Mg₁₇Al₁₂, Al₂Ca, Mg₂Sn and Mg₂Ca phases are calculated, and the bulk moduli, shear moduli, elastic moduli and Poisson ratio are derived. The calculations of thermodynamic properties show that the Gibbs free energies of Al₂Ca and Mg₂Sn are lower than that of Mg₁₇Al₁₂, which indicates that Al₂Ca and Mg₂Sn are more stable than Mg₁₇Al₁₂ phase. Hence, the heat resistance of Mg-Al-based alloys can be improved by adding Ca and Sn additions.

Key words: Mg-Al alloy; first-principles calculation; electronic structure; elastic properties; thermodynamic properties