Temperature-dependent mechanical properties of as-cast Mg-Gd-Zr alloys evaluated by shear punch testing

Abstract

The temperature-dependent shear mechanical properties of Mg-3Gd-xZr (x = 0, 0.2, 0.5, and 0.8 wt%) alloys were investigated using the shear punch testing (SPT) across a temperature range of 25–400 °C. The Zr addition led to a remarkable grain refinement, where the average grain sizes of 348 ± 43, 101 ± 39, 42 ± 8, and 23 ± 4 μm were obtained for x values of 0, 0.2, 0.5, and 0.8, respectively. This refinement improved the ultimate shear strength (USS), which peaked at 115 MPa for testing at 25 °C for the 0.8 wt% Zr alloy, compared to the value of 92 MPa for the Zr-free sample. As the temperature increased above 300 °C, a transition from the cold deformation regime to the hot working one occurred, leading to a sharp decline in USS and a reduced sensitivity of flow stress to the grain size, which manifested itself into the rapid fall of the Hall-Petch slope. For the hot working range, the dislocation glide and climb in the climb-controlled regime was characterized as the underlying deformation mechanism with the activation energy ranging from 135 to 168 kJ/mol. These findings elucidate the interplay between grain refinement, temperature, and deformation mechanisms, providing a foundation for the application of Mg alloys in high-performance situations.