First principles investigation of binary intermetallics in Mg–Al–Ca–Sn alloy: Stability, electronic structures, elastic properties and thermodynamic properties

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 Al2Ca has 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.