Abstract: The Bi-Mg binary system had been assessed by adopting the ionic melt and the modified quasi-chemical models to describe the liquid phase with short range ordering behavior. In general considerations of the development of the thermodynamic database of the multi-component Mg-based alloys and the consistency of the thermodynamic models of the related phases, the Gibbs energy descriptions of all the phases in the Bi-Mg binary system were reasonably re-modeled and critically re-assessed in the present work. Especially for the liquid phase, the associate model was used with the constituent species Bi, Mg and Bi₂Mg₃. The Mg-rich terminal phase hcp_A3 was modeled as a substitutional solution following Redlich-Kister equation and the Bi-rich terminal phase Rhombohedral_A7 was treated as a pure Bi substance since the extremely small solubility of Mg in Bi. The low and high temperature non-stoichiometric compounds α-Bi₂Mg₃ and α-Bi₂Mg₃ were described by the sublattice models (Bi,Va)₂Mg₃ and (Bi)₁(Bi,Va)₃Mg₆ respectively based on their structure features. A set of self-consistent thermodynamic parameters of the Bi-Mg system was obtained and the experimental thermodynamic and phase equilibrium data were well reproduced by the optimized thermodynamic data.

Key words: Bi-Mg binary system, Thermodynamic assessment, Gibbs energy expression, Associate model