Hot deformation behavior and processing map of coarse-grained Mg-Gd-Y-Nd-Zr alloy

Compression tests of Mg-Gd-Y-Nd-Zr alloy have been performed in the compression temperature range from 623 K to 803 K and the strain rate range from 0.005 s−1 to 5 s−1. The high temperature deformation behavior was characterized based on an analysis of the stress-strain behavior, kinetics and processing map. The constitutive equation of the Mg-Gd-Y-Nd-Zr alloy is established, which describes the flow stress as a function of the strain rate and deformation temperature. The average apparent activation energy for hot deformation is calculated to be 250.0 kJ/mol. Based on the dynamic material model and the Prasad's instability criterion, the processing maps for the alloy are constructed at strains of 0.1 and 0.7. The processing map developed at strain of 0.7 exhibits two domains with higher value of power dissipation: one occurring in the temperature range of 720-760 K and in the strain rate range of 0.005-0.01 s−1, which is associated with dynamic recrystallization and dynamic precipitation; the other occurring in the temperature range of 760-803 K and strain rate range of 0.01-0.5 s−1. According to the processing map and microstructure observation, the optimum hot working condition for Mg-Gd-Y-Nd-Zr alloy is determined to be 773 K and 0.05 s−1.