Mechanism of grain boundary serration during hot deformation of AZ31 alloy: Role of grain boundary dislocations and grain boundary sliding

Despite the industrial significance of grain boundary serration for improving creep resistance and retarding crack propagation, the mechanism of grain boundary serration during hot deformation is still unclear. The results of several studies indicated that increased inhomogeneity of the stored energy under high-stress deformation suppressed grain boundary serration. Thus, traditional strain-induced boundary migration, in which the stored energy difference between adjacent grains acts as the driving force for grain boundary serration, must be modified for hot deformation. The experimental results of this study suggested that dissociated grain boundary dislocations from lattice dislocations, rather than the elastic energy of the lattice dislocations, cause the nucleation of serrated grain boundaries. Grain boundary sliding on the serrated grain boundary asymmetrically generated an elastic energy field and an accommodated serrated grain boundary. The presence of an elastic energy field was predicted by dislocation climbing and statically distributed dislocations near the elastic energy field. Since the asymmetrically deformed serrated grain boundary exhibited sub-migration behavior in the elastic energy field, it was concluded that the applied shear stress (applied by grain boundary sliding) on the serrated grain boundary dominated the growth of serrated grain boundaries until dynamic recrystallization occurred.