Contribution of first-principles energetics to Al-Mg thermodynamic modeling

Despite numerous investigations, all previous efforts on thermodynamic modeling of Al-Mg have suffered from inaccurate energetics of solid phases. In the present work, the first-principles calculations were performed using VASP based on the pseudo-potentials and a plane wave basis set. The enthalpies of formation of the ε-Al30Mg23 phase, end-members of the γ-Al12Mg17 phase, and three laves phases at the Al2Mg composition were calculated at 0 K. Special quasi-random structures (SQS's) were used to mimic random fcc and hcp solution phases, and their enthalpies of mixing were predicted by first-principles calculations. The Al occupancy in the γ-Al12Mg17 phase is also studied by first-principles calculations, and the sublattice model (Mg)5(Al,Mg)12(Al,Mg)12 was verified as the proper model to describe the γ-Al12Mg17 phase. The complete thermodynamic description of the Al-Mg binary system was evaluated by this combined CALPHAD/first-principles calculations approach and was shown to be in a good agreement with experimental data with better defined energetics of solid phases than the previous modeling.