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 image phase, end-members of the image 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 image 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 image 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.