Microstructure evolution and constitutive relation establishment of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy under high strain rate after severe multi-directional deformation

Abstract

At room temperature, dynamic mechanical response of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy under high strain rate after severe multi-directional deformation were measured by a Split-Hopkinson pressure bar equipped with a set of limited strain rings under the strain rates of 0.001, 1800, and 2300 s−1 along the extrusion direction (ED). An electron back-scattering diffraction and a transmission electron microscopy were used to characterize the microstructure evolution of the alloy. When compressed along ED direction at the strain rate of 2300 s-1, prismatic and pyramidal < a > slip mechanisms first occurred in the ultra-fine grain band, and then tensile twins, basal slip, prismatic slip, pyramidal slip, dynamic recovery, and recrystallization occurred in the equiaxed fine-grained region. At the same strain rate (7% strain), various deformation mechanisms in the ultra-fine grain region and equiaxed fine-grained region, as well as the dynamic recovery and recrystallization mechanisms in the equiaxed fine-grained region were strengthened with the increase of strain rate. Based on the phenomenological Johnson–Cook relationship and the microstructure evolution analysis during deformation, a new constitutive relation was constructed by inserting a softening term with strain into the formula to calculate the stress–strain curve, which was in good agreement with the experimental data.