On the threshold stress for superplasticity in Mg–Al–Zn alloys

Abstract

High threshold stresses for superplasticity are often reported in both Mg–Al–Zn alloys and reinforced magnesium alloys . However, the threshold stresses in Mg–Al–Zn and reinforced alloys differ in their temperature and grain size dependence. It is shown in this work that the origin of the apparent threshold stresses in the Mg–Al–Zn alloys arise from an inadequate assumption of an n = 2 power law in the transition zone between grain boundary sliding and slip creep or to a grain growth effect on the flow stress at low strain rates .