The Evolution of As-cast Microstructure of Ternary Mg-Al-Zn Alloys: An Experimental and Modeling Study

A numerical formulation of solidification model which can predict the microsegregation and microstructural features for multicomponent alloys is presented. The model incorporates the kinetic features during solidification such as solute back diffusion, dendrite tip undercooling, and secondary arm coarsening. The model is dynamically linked to thermodynamic library for accurate input of thermodynamic data. The modeling results are tested against the directional solidification experiments for Mg-Al-Zn alloys. The experiments were conducted in the cooling rate range of 0.13 to 2.33 K/s and microstructural features such as secondary arm spacing, primary dendrite arm spacing, second phase fraction, and microsegregation were compared with the modeling results. Based on the model and the experimental data, a solidification map was built in order to provide guidelines for as-cast microstructural features of Mg-Al-Zn alloys in a wide range of solidification conditions.