Characterization of hot deformation behavior of as-extruded AZ31 alloy through kinetic analysis and processing maps

The hot deformation behavior of as-extruded AZ31 magnesium alloy was studied by uniaxial compression experiments at temperature range of 250 degrees C-500 degrees C under the strain rate of 0.005s(-1)-5s(-1). The thermal effect on flow stress change in the softening stage increases with the decrease of temperature and increase of strain rate. With kinetic analysis of alloy, the activation energy was calculated as 191 kJ mol(-1). Through dynamic material model, the processing maps were constructed with true stress-strain data. The energy dissipation efficiency increases as the strain increases. The alloy exhibits a wide stable processing domain: 280 degrees C-450 degrees Cand 0.005s(-1)-0.05s(-1), along with the dissipation peak efficiency of 30.5%. With the processing map and subsequent microstructure observations, the optimum process parameter ranges of hot working were determined as: 300 degrees C 400 degrees Cand 0.005s(-1) -0.05s(-1). Furthermore, higher energy dissipation efficiency was observed in the low temperature unstable region (250 degrees C-275 degrees C, 0.005s(-1) -0.02s(-1)). The transition between the instability region and stable domain was associated to a sharp dynamic recrystallization (DRX) volume fraction increase. A substantial DRX with grain refinement also existed in the high temperature-strain rate region, although it was marked as an instability region in the processing map.