Abstract
There are a number of instances in which wrought Mg alloys show marked work hardening followed by work softening during compressive deformation in a warm temperature range. Work softening is unfavorable for the warm forging of wrought billets, because it induces plastic instability. In this study, the effect of initial texture on work hardening and work softening has been examined using a hot-extruded AZ61 alloy bar. The hot-extruded bar had a strong fiber texture of {0001} parallel to the extrusion axis. By upsetting it with a low strain rate on the 10-4 s-1 order at 400°C, the fiber texture was almost completely randomized. In the warm compression of the randomly textured AZ61 alloy, the flow stress became steady without work softening after showing a low degree of work hardening. It has been confirmed that high degrees of work hardening and work softening in the warm compression of hot-extruded specimens are caused by stress concentration on grain boundaries and stress relaxation by dynamic recrystallization, respectively. In steady-state deformation, the microstructures and textures of both specimens showed almost no differences, resulting in nearly the same flow stresses.
