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

## TL;DR

This study explores how Mg–Ca–Zn alloy compositions and rapid cooling affect microstructure, focusing on intermetallic phase formation during solidification.

## Contribution

A novel combination of experimental and computational methods is used to predict and validate intermetallic phase segregation in Mg–Zn–Ca alloys.

## Key findings

- The Scheil model and CALPHAD calculations accurately predict micro-segregation in Mg–Zn–Ca alloys.
- SEM–EDS confirms that Mg–0.8Zn–0.2Ca forms Mg2Ca phase segregation, while Mg–6.8Zn–0.2Ca forms MgZn.
- Intermetallic phase formation diagrams are developed to guide control of phase evolution under different solidification conditions.

## Abstract

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.