Modeling of microstructure and microsegregation evolution in solidification of ternary alloys

Abstract The microstructure formed during solidification has a significant impact on the mechanical properties of materials. In this study, a two-dimensional (2D) cellular automaton (CA)-finite difference (FD)-CALPHAD model was developed to simulate the formation of microstructure and solute segregation in the solidification processes of ternary alloys. In the model, dendritic growth is simulated using the CA technique, while solute diffusion is solved by the FD method, and the CALPHAD method is employed to calculate thermodynamic phase equilibrium during solidification. The CA-FD-CALPHAD coupled model is capable of reproducing the evolution of continuous nucleation and growth of grains as well as the evolution of the microstructure and solute distribution during solidification of ternary alloys. In this study, Al–Zn–Mg ternary alloy is taken as an example to simulate the growth of equiaxed and columnar grains and the columnar-to-equiaxed transition (CET) under different solidification conditions. The simulation results are compared with experimental data from the literature, showing a good agreement. Besides, the study also investigates the evolution of temperature and multicomponent solute fields during solidification and the effects of alloy composition and cooling rate on the microstructure morphology. The results reveal that the initial alloy composition and cooling rate significantly affect dendritic morphology and solute segregation. Higher initial alloy concentrations promote the growth of side branches in equiaxed grains, leading to more pronounced solute segregation between dendrites. As the cooling rate increases, the average grain size of the equiaxed grains decreases accordingly. Additionally, a higher cooling rate accelerates the columnar-to-equiaxed transition, leading to a finer grain structure.