Grain refinement and stability in rare-earth magnesium alloys

Magnesium alloys are promising lightweight structural materials because of their low density and high specific strength, but their hexagonal close-packed structure leads to limited room-temperature ductility and pronounced anisotropy. This review summarizes the multi-stage roles of rare-earth elements in grain refinement and microstructural stability of magnesium alloys, and identifies 3–8 μm as a representative fine-grained range frequently associated with favorable strength–ductility coordination. Grain size governs the deformation-carrying mode and plastic accommodation by redistributing the contributions of twinning, slip, precipitation, and grain-boundary effects. Rare-earth elements act continuously during solidification, solid-state processing, and thermomechanical deformation through grain boundary segregation, precipitate pinning, and dynamic recrystallization control, while also contributing to texture weakening. The stability of this fine-grained platform is further constrained by temperature, component scale, and service time. Even under low rare-earth conditions, however, microstructural synergy remains achievable through process optimization, precipitate homogenization, and dynamic recrystallization regulation. Overall, this work clarifies the scientific basis of fine-grain strengthening in Mg–RE alloys from the perspectives of grain-scale control, mechanism redistribution, precipitation–texture–grain boundary coupling, and engineering boundary conditions, providing theoretical support and practical guidance for the design of high-performance, low-rare-earth lightweight magnesium alloys.