Grain refinement and improved mechanical properties of as-cast Mg-3Gd alloy by Zr addition

The influence of zirconium addition on the grain refinement and mechanical properties of an as-cast magnesium alloy was critically discussed. Results revealed that Zr significantly refined the grain size ( d ) from 358 μm in the base Mg-3Gd alloy to 23 μm with the addition of 0.8 wt% Zr, which was more pronounced compared to other RE-containing and RE-free alloys. This was attributed to the inoculation effect of α–Zr particles as heterogeneous nucleation sites and high growth restriction factor (GRF) of solute Zr. Shear punch testing (SPT) and hardness measurements revealed substantial improvements in shear yield stress (SYS), ultimate shear strength (USS), and Vickers hardness ( H V ) with increasing Zr content. Hall-Petch plots revealed that the grain size strengthening mechanism can adequately describe the change in the mechanical properties according to USS = 85 + 154/√d and H V = 27 + 69/√d. Correlation between the USS, H V , and ultimate tensile strength (UTS) was established, based on the von Mises criterion from the plasticity theory, providing a reliable method for predicting the mechanical behavior by SPT according to USS = 1.919 × H V and UTS = √3 × USS. Accordingly, the role of Zr as a grain refiner in Mg-3Gd alloys was unraveled, offering insights into the optimizing the mechanical properties of Mg-based alloys for structural applications.