On the rapid cooling cast solidification microstructures of Mg-Ca-Zn alloys

This work investigates the influence of Mg-Zn-Ca alloy compositions and rapid cooling conditions on microstructural evolution, with a focus on the formation and behaviour of intermetallic phases such as Mg₂Ca, MgZn, and Ca₂Mg₆Zn₃ during solidification. To achieve this, a combination of experimental characterisation and computational modelling was employed. The Scheil model, extended to ternary alloy systems, was used to simulate micro-segregation during solidification, while a multicomponent mean-field model was applied to predict solid-state phase transformations and the evolution of second-phase particles. CALPHAD-based thermodynamic calculations were integrated to refine the prediction of segregation pathways and phase distributions under non-equilibrium conditions. The model successfully differentiates solidification paths based on alloy composition, predicting that Mg-0.8Zn-0.2Ca (wt%) first forms Mg₂Ca phase segregation, whereas Mg-6.8Zn-0.2Ca (wt%) primarily segregates MgZn. Experimental validation using SEM-EDS characterisation confirms these predictions. Finally, intermetallic phase formation diagrams under different solidification conditions are presented, providing insights into the control of intermetallic phase formation in Mg-Zn-Ca alloys.

The online version contains supplementary material available at 10.1007/s10853-025-11431-2.