Unusual twin induced recrystallization and corresponding texture optimization in a cold rolled Mg-Gd-Zr alloy during annealing

Abstract

Twins play an important role in the texture transition during annealing. In a cold rolled high rare earth content magnesium (Mg) alloys with {10–12} extension twins, {11–21} extension twins, {10–11} compression twins and {10–11}-{10–12} double twins and frequent twin-twin interactions, quasi-in-situ electron backscatter diffraction method was used to observe the twin induced static recrystallization (SRX) and related effect on texture during annealing. The results show that basal component was consumed owing to the SRX occurred in basal oriented {10–12} twins and SRXed grains with several specific orientations show preferential grain growth. SRX widely operated in the {10–12} extension and {11–21} extension twins, but absent in most {10–11} compression and {10–11}-{10–12} double twins, which is different to traditional twin induced SRX. Most compression/double twins detwinned while only partial tension twins detwinned. Operation of {11–21} twins and resultant twin-twin interaction facilitate the formation of serrated twin boundaries, which can serve as nucleation sites. Activation of <c + a> dislocation and related dislocation interaction in high dislocation density areas promote the formation of new grain boundaries and related SRX. Profuse <c + a> dislocations in basal oriented twins release the strain accumulation in compression/double twins and thus result in the absence of SRX. The twin size difference, storage energy and dislocation-twin interaction commonly functioned to the detwinning during annealing. The near-coincide site lattice boundaries that show high mobility were considered to be the important contributor to the preferential grain growth of SRXed grains.