Thermodynamic modeling of the Mg-Zn-Nd system and its application to solidification

Abstract

The excellent thermal conductivity and mechanical properties of Mg-Zn-Nd alloys are closely linked to the formation of intermetallic compounds and the solubility in the αMg matrix after their formation. However, recent experimental findings on new ternary compounds highlight gaps in the understanding of the phase equilibrium relationships, which complicates design of advanced Mg-Zn-Nd alloys. To address this, all the experimental phase equilibrium data available in the literature were critically evaluated. Thermodynamic modeling of the Mg-Zn-Nd system was performed based on the selected reliable experimental data and updated binary thermodynamic descriptions. The seven ternary compounds (τ1 to τ6 and (Mg,Zn)₁₂Nd) in the Mg-Zn-Nd system were modeled using compound energy formalism (CEF), particularly considering the consistency between their homogeneity range and crystallographic sublattices. The thermodynamic model parameters optimized in this study satisfactorily reproduced the isothermal sections, isoplethal sections, and liquidus projections. Combined with the Scheil–Gulliver model, the solidification behavior of Mg-Zn-Nd alloys was predicted. The predicted results were consistent with the experimental data, further demonstrating the reliability and practical applicability of the thermodynamic description developed in this study.