Texture weakening and ductility improvement of Mg-1.1Mn-0.5Al alloy via medium temperature-high reduction rolling: twinning variants selection and dynamic recrystallization mechanism

Abstract

The weakening of basal texture is beneficial to improve the formability and mechanical properties of deformed magnesium alloys. In this paper, the microstructure and texture evolution of single pass rolled Mg-1.1Mn-0.5Al alloys with various reduction of 10%–60% at 200 °C were observed to reveal twin variants selection and mediated dynamic recrystallization (DRX) mechanism. The results showed that the type and volume fraction of activated twins were strongly related to rolling reduction. Primary {101¯2} tensile twins (TTWs), which were mainly activated in the 10% reduction rolled alloys, were not sufficient to induce recrystallization due to the absence of cumulative dislocation and lower plastic strain energy. In contrast, {101¯1}/ {101¯3} compression twins (CTWs) and {101¯1}−{101¯2}/ {101¯3}−{101¯2} double twins (DTWs) were preferred for recrystallization because of higher dislocation accumulation and stored strain energy. The occurrence of DRX was beneficial to absorb stored energy, relax stress concentration and weaken basal texture in adjacent domains. Due to the sufficient stress provided by massive basal slip dislocations, the type I and type II DTWs were more commonly observed than the type III and type IV variants, which involved much more dissociations of the mixed <c+a> dislocations in deformed magnesium alloys.