Unraveling dendritic segregation in multi-component Mg alloys via a CALPHAD-integrated multiphase-field framework

Dendritic segregation, ubiquitous microstructural inhomogeneity during solidification, severely deteriorates mechanical performance and processing stability. Despite advances in phase-field simulation, existing models often rely on oversimplifications (e.g., constant thermophysical parameters, dilute solution approximation, or binary-alloy bias), leading to inaccurate prediction of segregation behavior in industrial multi-component Mg alloys. To address this gap, a coupled computational framework is proposed via integrating the multiphase-field method, CALPHAD-based thermodynamic calculations, and a Taylor expansion-driven extrapolation algorithm for thermodynamic driving force. This framework enables high-fidelity simulation by capturing temperature-dependent thermophysical parameters and inter-solute interactions, while reducing computational complexity compared to conventional multi-component phase-field models. The model is systematically validated by evaluating non-constant vs constant thermophysical parameters, anisotropy coefficients, thermodynamic driving force, and solid fractions. Results show that the segregation intensity is dominated by partition coefficient (k) and diffusion coefficient (D), with smaller k and D causing severer segregation, and the multi-dendrite competition increases segregation ratios due to more solute accumulation. The segregation ratios increase with the undercooling and also the cooling rate. Despite different solute diffusivities, the segregation ratios of both Al and Zn decrease with increasing Al and Zn contents. The solute segregation of investigated elements ranks Zn > Gd > Y > Al. This work reveals the dynamic formation mechanism, morphology-segregation coupling, and multi-dendrite interaction inaccessible to simplified models (e.g., Scheil-type calculations), advancing fundamental understanding of dendritic segregation and providing an efficient tool for optimizing Mg alloy design.