Investigation of shear bands induced nucleation and recrystallisation behaviour in a rare earth containing magnesium alloy

Abstract

Annealing is widely applied to the deformed magnesium alloys to tailor crystallographic texture and improve formability, significant efforts have been made to understand recrystallisation nucleation and grain growth. Nevertheless, it is still a highly debated field, attributes to the lack of large area in-situ microstructure datasets and effective data processing approach, especially the grains tracking strategy. In this work, the recrystallisation process of a Mg-2.4Zn-0.2Ce wt% alloy is systematically investigated with quasi-in-situ electron backscatter diffraction method to unravel the role of shear bands during recrystallisation annealing. A newly developed toolbox Track-Rex is adopted, allowing us to automatically track 40,900 grains within 10 min. The results show that shear bands were the preferential nucleation sites at early stage of annealing. However, with increased annealing time, the preferred nucleation sites shifted to the deformed grain boundaries, and the grains nucleated from shear bands were progressively consumed. Thus, the contribution of shear bands induced nucleation to the recrystallised texture is considerably reduced, from up to 51.2 % of area fraction in the early stage towards 20.89 % in the final annealing stage. In terms of texture evolution, all the recrystallised grains exhibit a scattered off-basal feature regardless to the nucleation sites. Additionally, the basal orientated grains were gradually consumed while off-basal grains had a higher possibility to retained. More specifically, within shear bands induced nucleation, recrystallised grains with low angle grain boundaries were easily consumed, while other grains exhibiting high angle grain boundaries were more likely to maintain along the recrystallisation procedure.