Reducing the tension-compression yield asymmetry in an extruded ZK60 alloy by ultrafine grains

Abstract

Ultrafine-grained ZK60 alloys were successfully fabricated by powder metallurgy followed by hot extrusion at different temperatures. The effects of the texture changes of ultrafine-grained ZK60 magnesium alloy on the asymmetry of tension-compression yield under different extrusion temperatures, and the relation between texture evolution and mechanical properties of the alloys during axial tension-compression deformation were studied. The results show that, in the ultrafine-grained ZK60 alloy, the initial texture of the alloy is a weak (0002) basal fiber texture. As the extrusion temperature increases from 523 to 623 K, the fibrous texture of the base material is weakened, and the tension-compression yield asymmetry is depressed from 1.1 to 1.0. During axial tensile deformation, twinning is not activated. With increasing tensile strain, no significant rotation of crystal grains occurs, and the stress remains stable until tensile fracture occurs. In the early stage of axial compression yield, no significant rotation of crystal grains occurs. As the compressive strain increases until the end of the compressive strain, the (0002) basal plane of the crystal grains rotates in a direction approximately perpendicular to the compression axis. At this point, the grain orientation factor is low, and the slip system is still in a hard orientation and is inhibited by the ultrafine grains. Twinning is difficult to start, so that the strain hardening rate rises rapidly until compression fracture occurs. Therefore, the weak extruding fiber texture of the basal plane and the ultrafine-grained structure both determine the deformation mechanism of ZK60 alloys at room temperature during axial tension and compression deformation, thereby significantly depressing the axial tension-compression asymmetry of ZK60 alloys.