Achieving high strength in Mg-Gd-Ag-Zr alloy through heterogeneous microstructure with multimodal grain structure and hierarchical precipitates

The development of high-strength Magnesium (Mg) alloys is a key research focus due to their relatively low strength compared to other structural metals. In this paper, a high-strength Mg-13.4Gd-2.2Ag-0.4Zr wt% alloy is achieved by carefully designing a multimodal grain structure combined with hierarchical precipitates, using a processing route of hot rolling followed by aging. The multimodal grain structure, characterized by three distinct grain size distribution peaks and a strong basal texture, arises from partial dynamic recrystallization during hot rolling. The hierarchical precipitates include microscale rod-like and particle-like beta precipitates at grain boundaries, twins, and deformation bands, as well as nanoscale beta precipitates (similar to 63 nm) dispersed within the grain interiors. The fully beta precipitates also demonstrate a modified precipitation pathway, differing from the beta' and gamma'' nanoprecipitates observed in conventional Mg-Gd-Ag alloys. This unique microstructure results in an ultimate tensile strength of 447 MPa, primarily attributable to the strong basal texture, hierarchical precipitates, hetero-deformation-induced (HDI) strengthening effect, and high-dislocation density.