In this study, the ternary Mg-Al-Ca phase diagram was constructed by combining the three constituent binary systems of Mg-Al, Al-Ca and Mg-Ca. The Mg-Al system is taken from COST 507 database. The thermodynamic descriptions of the Mg-Ca and Al-Ca systems are obtained by modelling the Gibbs energy of all phases as a function of composition and temperature. The model parameters were
optimized by minimizing Gibbs energy considering phase equilibria and thermodynamic data available in the literature. A self-consistent thermodynamic database was constructed with the optimized parameters of the three subsystems. The binary phase diagrams, their thermodynamic properties, the ternary phase diagram and the critical points were calculated from this database and compared with experimental results from the literature.