A comparative study on grain boundary segregation and solute clustering in Mg-Al-Zn and Mg-Zn-Ca alloys

Magnesium, the lightest structural metal, has limited industrial application due to its poor formability at room temperature. However, the mechanism for the effect of alloying elements on formability has not yet been clarified. To deduce this effect, we study recrystallization, a phenomenon that occurs in the last stage in the manufacturing process, of Mg-Al-Zn and Mg-Zn-Ca solid solutions, which show recrystallization behaviors similar and different to that of pure Mg, respectively. By developing a new atomistic simulation method of migrating grain boundaries in hcp structure materials, we investigate the representative recrystallization phenomena occurring in solid solutions: grain boundary segregation, solute clustering, and grain boundary migration. It is found that the grain boundary segregation occurring in both ternary Mg alloys is not synergistically stronger than those in their constituent binary Mg alloys, but is sufficient to retard the onset of the grain boundary migration. However, solute clusters are actively formed only in the Mg-Zn-Ca alloys and strongly drag grain boundaries during the migration, which strengthens the dragging effect of the Mg-Zn-Ca alloys compared to that of the Mg-Al-Zn alloys. The strong dragging effect originated from solute clusters could be another cause of the change in the recrystallization behavior of Mg alloys.