Recrystallization and microstructural evolution during hot extrusion of Mg₉₇Y₂Zn₁ alloy

Abstract

This study revealed that the extrusion temperature has a great influence on microstructure and mechanical properties of the Mg₉₇Y₂Zn₁ alloy. The average grain sizes increased from 3 μm to 8 μm with increasing extrusion temperatures from 623K to 773 K. Both dynamic recrystallization (DRX) and static recrystallization (SRX), which occur during and after deformation, respectively, were observed. The alloy, which extruded at a relatively high temperature, exhibited lower strength because the strain strengthening was balanced by the softening that originated from DRX. Three types of morphologies, namely, big recrystallized grains, fine recrystallized grains, and non-recrystallized grains, were observed in the extruded microstructures obtained at 623 K. The dislocation density was quite high in the fully recrystallized grain. The extruded microstructures obtained at 773 K were composed of large grains with more uniform size. Their degree of recrystallization was higher and the dislocation density also declined. All dislocation in the grain were distinguished as 〈c+a〉 dislocations. Submicron scale precipitates were distributed along the newly formed recrystallized grain boundaries and had a remarkable pinning effect on the recrystallized grain growth after extrusion at 773 K. The precipitates can be divided into two main types: mixed type and single type.