The strength and deformation mechanisms in magnesium can be significantly affected by anisotropy, high strain rates, and pressure. In this study, pressure shear plate impact (PSPI) experiments are conducted to measure the strength of extruded polycrystalline magnesium at pressures varying from 5 to 10 GPa at a nominal strain rate of 10⁵ s⁻¹. The experimental technique enables to first shock load the material sample to the desired normal stress in one direction, and then shear the material in a perpendicular direction. A recently developed hybrid analysis method for PSPI experiments is used to extract the stress–strain curves of magnesium from the particle velocity records measured at the rear surface of the target. The PSPI experimental results reveal a slower twinning saturation at high pressures. To better understand the material behavior under the combined stress states in the PSPI experiments, the results were compared with that of a specimen deformed by a two-step process of quasi-static compression followed by dynamic shear loading at relatively low pressure. The two-stage loading at low pressure, and the calculation of temperature rise in the PSPI experiment revealed that the combined effect of the reorientation and the temperature rise lower the flow strength of magnesium at high pressures under multiaxial loading
