Thermodynamic modelling of the Zn-Zr system

The Zn-Zr system has been thermodynamically modelled by combining existing experimental data and first-principles calculations through the CALPHAD approach. In general, the agreement between the thermodynamic model and the experimental/first-principles results is satisfactory. The Zn2Zr3 and ZnZr2 intermetallic compounds do not belong to the accepted Zn-Zr phase diagram but their existence has been reported extensively in the literature, especially in experimental work on cast Mg-Zn-Zr alloys. The present work confirms their likely stability at high temperatures. A modified Zn-Zr phase diagram that includes these two compounds has been calculated. Additionally, three different models describing the excess Gibbs energy for the liquid and two for the solid solutions are used and their predictions are compared. The thermodynamic model with the best fit to the experimental data described the liquid phase as a solution of Zn, Zr and a ' Zn2Zr' associate. The resulting thermodynamic description for this binary is considered to be robust enough to be incorporated into the ternary description of the Mg-Zn-Zr system which will be used in the future for the analysis of the grain refinement of these alloys.