High temperature deformation behavior of extruded AZ31B magnesium alloy

Uniaxial isothermal compression tests were conducted on cylindrical specimens extracted from an extruded AZ31B rod along both the extrusion and radial directions over the temperature range of 300 °C-500 °C, at strain rates of 10−3 s−1-1.0 s−1. The anisotropy of flow observed at high strain rates in specimens oriented along the extrusion direction can likely be attributed to the dominance of tensile twinning at temperatures below 400 °C, and pyramidal slip for temperatures above 400 °C. The degree of anisotropy increased with deformation strain rate, with specimens deformed at the lowest strain rate of 10−3 s−1 exhibiting little to no anisotropy. Samples oriented along the radial direction exhibited strong anisotropy of flow at low deformation temperatures, and the extent of anisotropy decreased with increasing deformation temperature. It was determined that the occurrence of basal slip at select locations away from the compression axis likely resulted in preferential elongation of the sample along the circumferential direction of the extruded rod. Moreover, cracking was observed at 300 °C and macroscopic shear bands were observed at deformation temperatures below 450 °C, which suggested that low temperature deformation was less favorable. It was observed that finer dynamically recrystallized (DRX) grains could be obtained by processing at lower temperatures and/or higher strain rates. However, greater microstructural homogeneity was achieved through processing at high temperatures and low strain rates. Furthermore, it was evident that the area fraction of DRX grains increased with strain. Grain growth after deformation occurs rapidly within the first 60 s, and little to no grain growth was observed beyond that.