High Temperature Deformation Behavior and Processing Maps of AZ31 Alloy Deformed in Tension versus Compression

The effect of the applied state-of-stress on the processing maps depicting the mechanisms for hot working of hot extruded Mg-3Al-1Zn alloy has been evaluated. Flow stresses at various temperatures in the range 300 – 500 °C and strain rates in the range 0.0003 – 1 s^-1 have been measured by deforming in compression and in tension. Processing maps have been developed from the respective flow stress data at a strain of 0.1. The maps are essentially similar irrespective of the mode of deformation – compression or tension, and exhibited two domains in the temperature and strain rate ranges: (1) 375 – 500 °C and 0.0003 – 0.01 s^-1, and (2) 450 – 500 °C and 0.1 – 1 s^-1. On the basis of slower strain rates, high tensile ductility, and the apparent activation energy (152 kJ/mole closer to that for self-diffusion), Domain #1 is interpreted in terms of the occurrence of climb controlled dynamic recrystallization. In Domain #2, which occurs at higher strain rates and has an apparent activation energy near to 165 kJ/mole, dynamic recrystallization occurs that involves second order pyramidal slip {11-22} <11-2-3> and recovery by cross-slip of screw dislocations. The state-of-stress imposed on the specimen (compression or tension) does not have any significant effect on the processing maps or the kinetics of hot deformation.