Thermodynamic and kinetic modelling on the microstructure and mechanical behaviour of Mg-Zn-Ca(-Ag) alloys based on CALPHAD approach

Advances in lightweight structural materials have intensified interest in magnesium alloys, particularly those strengthened by Zn, Ca, and Ag additions. This research presents a comprehensive study of the thermodynamic and kinetic behaviour of Mg-Zn-Ca and Mg-Zn-Ca-Ag alloys using an integrated CALPHAD-based modelling and experimental approach. The solidification process is analysed using an extended Scheil model, capturing non-equilibrium phase evolution and solute segregation during casting. A mean-field model is developed to simulate the nucleation, growth, and coarsening of strengthening phases during heat treatment, enabling the prediction of precipitate evolution over time. Together, these models provide a framework for simulating phase transformations across the entire processing route from casting to homogenisation and ageing treatment.
The modelling results are supported and validated by advanced characterisation and mechanical experiments. Zn is shown to play a central role in age-hardening by promoting the formation of fine strengthening precipitates. Ca is beneficial in refining grain structure and modifying texture and tends to form Laves phases during solidification. These coarse particles are thermodynamically stable and dissolve slowly during homogenisation, limiting solute uniformity. Ag additions can promote mechanical performance by accelerating the nucleation of fine precipitates, improving strengthening responses. By linking CALPHAD predictions with observed microstructure and mechanical behaviour, this work establishes a predictive design strategy for magnesium alloys.
These findings are directly applicable to the development of lightweight structural materials, aligning with Industry 4.0 schemes that include data-driven materials design and digital manufacturing. By integrating Scheil-based solidification modelling and mean-field simulations within a CALPHAD framework, this research shows how computational tools can aid digital alloy development. These simulations frameworks enable virtual prototyping, optimise thermal processing routes, and reduce experimental workload, which accelerating the transition from concept to application in smart manufacturing environments.