Increasing heat resistance of a Mg-Sm-Zn alloy via minor gadolinium addition

The addition of minor gadolinium (Gd) into Mg-4Sm-0.6Zn-0.4Zr alloy significantly enhances high-temperature strength and creep resistance, such as a decrease in the minimum creep rate by approximately five times and an increase in the yield strength by around 40 MPa at 200 °C. The presence of Gd results in the co-precipitation of both prismatic β-type and basal γ-type phases during creep, whereas only the basal γ-type phase is present in the Gd-free alloy. The prismatic β-type and basal γ-type phases are oriented perpendicular to each other in space, creating a closed configuration that effectively blocks dislocation motions compared to single basal γ-type precipitates. Therefore, the improved creep resistance in the Gd-enriched alloy is mainly attributed to the co-precipitation of prismatic β-type and γ-type precipitates during creep. Furthermore, rare earth (RE) atoms inherently provide stable solute hardening at high temperatures, which contributes to the increased high-temperature strength. The addition of Gd also enhances grain boundary stability by promoting the formation of more Mg3RE phases, thereby further enhancing the creep strength. These findings offer insights into the development of highly creep-resistant Mg alloys with low RE concentrations.