Constitutive analysis and processing map of an extruded Mg-3Gd-1Zn alloy under hot shear deformation

Hot shear deformation behavior of the as-extruded Mg-3Gd-1Zn (GZ31) alloy was investigated by constructing processing-maps and developing constitutive equations. Hot shear punch tests (SPT) were conducted on the specimens taken perpendicular to the extrusion direction, and processing maps were developed from shear punch data within the temperature range of 573-773 K and shear strain rate range of 3.3×10−3-1.3×10−1 s−1. Based on the processing maps, the optimum processing condition was identified as 713-773 K and 0.009-0.020 s−1 in the safe region with a maximum efficiency parameter, while the flow instability region was found to occur in the temperature range 580-650 K and shear strain rate range of 0.07-0.13 s−1. The characteristic microstructures of the safe and unsafe domains were dynamically recrystallized and partially recrystallized grains, respectively. Constitutive equations were formulated using the sine hyperbolic function. Dislocation creep was found to be the dominant deformation mechanism based on the activation energy of 197 kJ mol−1 and the power-law stress exponents of 4.5-5.5, obtained from the sine hyperbolic function.