A general thermodynamic model for the long-period stacking ordered phases in magnesium alloys

A thermodynamic model Mgx(Xs, Mg)6(Xl, Mg)8 (Xs and Xl are elements smaller and larger than Mg) for long-period stacking ordered phases (LPSOs) was proposed based on two key factors: the Xs6Xl8-type L12 clusters and the variation of chemical compositions. In general, all available LPSOs can be described with this model. As a representative system, Mg-Y-Zn with three LPSOs was investigated using the CALPHAD (calculation of phase diagram) approach aided with first-principles calculations. Two new three-phase equilibria were predicted and were validated by key experiments. The model-based descriptions will be the basis for the research and development of magnesium alloys.