Coherent topologically close-packed (TCP) nanoplates play a crucial role in enhancing the strength and creep resistance of magnesium alloys. However, the thermodynamic formation mechanisms of several metastable TCP nanoplates remain unclear, and the traditional trial-and-error methods impede the rapid discovery of novel TCP precipitate-strengthened Mg alloys. In this study, using density functional theory calculations to construct convex hull diagrams and evaluate thermodynamic stability, our results clarify that the metastable ${\beta }_2^{\mathrm{\prime }}$ nanoplates in Mg-Zn alloys adopt the Mg(Mg, Zn)₂ composition with excess Mg in precipitates. This finding demonstrates the metastable nature of the ${\beta }_2^{\mathrm{\prime }}$ phase and resolves the long-standing puzzle of its structural similarity to the equilibrium MgZn₂ phase in the Mg-Zn binary phase diagram. Moreover, by integrating the thermodynamic and kinetic conditions for TCP precipitation, we developed a two-step high-throughput screening strategy to systematically identify Mg alloy systems capable of forming stable TCP nanoplates. Our screenings identify 43 previously unreported TCP nanoplates and indicate that the current development of TCP-strengthened Mg alloys should mainly focus on the Mg-RE(Ca)-Al systems. These findings reveal the atomic-scale compositional complexity in TCP nanoplates and establish a theoretical foundation for designing creep-resistant Mg alloys containing TCP nanoplates.

A gradient nanostructured WE43 Mg alloy with a top layer grain size of approximately 50 nm was fabricated using sliding friction technique (SFT). The formation mechanism of this gradient nanostructure (GS), the deformation mode and the strengthening effect were investigated in detail using TEM, EBSD and XRD. The results showed that microstructure evolution primarily underwent three stage to form the GS. In the early stage, deformation was dominated by a combination of multiple slip systems and twinning. In the intermediate stage, twins and coarse grains broke down into fine lath structures and smaller grains due to dislocation pile-ups and stacking faults (SFs). In the final stage, these fine grains were further refined into nanograins with the help of SFs. Compared with the original alloy, the introduced GS significantly enhanced the mechanical properties, and had a good work hardening capabilities. The strengthening mechanisms are primarily attributed to dislocation strengthening and grain boundary strengthening. This study offers valuable insights for the development of Mg alloy, aimed at enhancing performance and optimizing microstructure in engineering applications.

Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth (RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization (DRX) plays a crucial role in refining grain size of Mg wrought alloys. Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized, including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy, are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.