High temperature compressive deformation behavior of an extruded Mg-8Gd-3Y-0.5Zr (wt.%) alloy

The deformation behavior of an extruded Mg-8Gd-3Y-0.5Zr alloy has been characterized by compression tests in the temperature range of 400-490 °C and strain rate range of 10−4 s−1 to 10−2 s−1 with the objective to evaluate the superplastic deformation conditions as well as the rate-controlling mechanisms. The strain rate sensitivity index m decreases with increasing temperature in the strain rate range of 10−4 s−1 to 5 × 10−4 s−1, which was attributed to grain growth. Optimum superplasticity characterized by grain boundary sliding accommodated by dislocation creep was obtained at 400 °C and at 10−4 s−1. Dynamic precipitation leading to precipitates distributed mainly in the grain boundaries was responsible for the stable microstructure and the increase of the stress during deformation under this condition. Moreover, at strain rate higher than 5 × 10−4 s−1, it remained relatively constant of about m ≈ 0.3 and the activation energy Q was found to be equal to 131 kJ/mol which was close to the activation energy for lattice diffusion of Mg.