Recrystallization and texture evolution of Mg–3%Al–1%Zn–(0.4–0.8)%Sr alloys during extrusion

Abstract

Microstructure and texture evolution during the extrusion of AZ31 magnesium alloy containing 0.4 and 0.8wt%Sr has been investigated. Following extrusion at 250°C, the microstructure consists of fine recrystallized and large elongated grains along with Al4Sr stringer precipitates. Extrusion at 350°C results in larger and more uniform grain size. Grain refinement and nucleation of new grains were associated with sub-grain formation in the elongated grains, grain boundary bulging, and nucleation at the particle interfaces. Texture measurements in the extrusion deformation zone show an increase in the basal ring fiber-texture from the undeformed zone toward the die opening. Compared to AZ31 without Sr, the texture intensity increases with increasing Sr at 250°C, whereas the strength of extrusion fiber texture decreases at 350°C. The Al solubility in the α-Mg matrix decreases with increasing the Sr and the Al solute atmosphere around the dislocations weakens. Due to the reduction of the solute drag effect, dislocation movement is facilitated and dynamic recrystallization becomes more intensive resulting in strengthening the texture during extrusion at 250°C. The decrease in texture intensity at 350°C extrusion is attributed to the activation of particle-stimulated nucleation (PSN) that leads to the nucleation of new grains with high orientation mismatch to the parent grains.