Superplastic magnesium alloys: A critical review of processing, deformation mechanisms, and particulate reinforcement strategies

Magnesium alloys exhibit poor room-temperature formability due to their hexagonal close-packed (HCP) structure, which limits their widespread application. Superplastic forming offers an effective solution, enabling elongations typically from ∼400% to over 1000%, and exceeding 3000% under optimized severe plastic deformation (SPD) conditions. This review provides a critical and systematic assessment of the microstructural design principles governing superplasticity, emphasizing the roles of fine equiaxed grains (<10 μm), thermal stability, and texture weakening, as well as the processing routes required to achieve them. Grain boundary sliding (GBS) is confirmed as the dominant deformation mechanism, while its stability relies on accommodation mechanisms including dislocation creep, diffusion creep, and dynamic recrystallization. The capabilities and limitations of advanced processing techniques, such as equal channel angular pressing (ECAP), high-pressure torsion (HPT), and friction stir processing (FSP), are comparatively evaluated in terms of grain refinement efficiency and industrial applicability. Particular attention is given to particulate reinforcement strategies, where fine and well-dispersed particles enhance superplasticity through grain refinement and boundary stabilization, whereas coarse or agglomerated particles promote cavitation and premature failure. Future developments are expected to benefit from machine learning-assisted optimization of composition, processing, and microstructure–property relationships, enabling accelerated design and improved predictability of high-performance superplastic magnesium alloys.