High temperature plastic deformation of a heat-treated AZ31 magnesium alloy

High-temperature plastic deformation and dynamic recrystallization were investigated in an extruded and heat-treated AZ31alloy in the temperature range between 200 and 400°C. High-temperature straining resulted in partial dynamic recrystallization above 250°C; at 400°C recrystallization was complete and a moderate grain growth was observed. The peak flow stress dependence on temperature and strain rate was described by means of the conventional sinh equation; calculation of the activation energy for high temperature in the whole range of temperature deformation gave Q=155 kJ/mol, i.e. a value that is reasonably close to, but greater than, the activation energy for self-diffusion in Mg. When the data obtained at the lowest temperature were excluded from the calculation, the activation energy increased to 180 kJ/mol. This difference in the activation energy value can be explained by the occurrence of dynamic recrystallization in the high-temperature regime; this observation was substantially confirmed by the plots of strain-hardening rate as a function of stress that were used to identify the onset of dynamic recrystallization