Magnesium (Mg) alloys are the lightest metallic structural materials, holding significant potential for automotive, aerospace, electronic, and biomedical applications. However, their broader adoption is impeded by inherent drawbacks, including low strength, limited ductility, and poor corrosion resistance. High-pressure torsion (HPT) has proven effective in generating ultrafine-grained (UFG) Mg alloys, resulting in substantial property enhancements. This review critically assesses the microstructure evolution of HPT-processed Mg alloys covering not only grain refinement but also solute segregation, texture evolution, dissolution and precipitation of second phases, allotropic transformation, crystal-to-amorphous transition and nanocrystallization. In particular, it elucidates the impact of these microstructures’ evolutions on mechanical properties, including yield strength, hardness and superplasticity. Additionally, the review discusses the improvements in the addresses the functional augmentation of HPT-processed Mg alloys, specifically corrosion behavior, hydrogen storage capabilities, and biomedical performance.

In the present work, the biomedical as-cast pure Mg, Mg–1Ca and Mg–2Sr alloys were processed with equal channel angular pressing (ECAP) technique to develop ultrafine microstructure within the materials, and their microstructures, mechanical properties, degradation behavior, cytocompatibility in vitro and biocompatibility in vivo were studied comprehensively. Finer-gained microstructures and improved mechanical properties of these three materials after ECAP were confirmed compared to their as-cast counterparts. Moreover, after ECAP the degradation rate of pure Mg was increased while that of Mg–1Ca or Mg–2Sr alloys decreased compared to the as-cast counterparts. Additionally, good in vitro cytocompatibility and in vivo biocompatibility of these three materials were revealed by cell cultural tests using osteoblastic MC3T3-E1 and human mesenchymal stem cells (hMSC) and in vivo animal tests at the lateral epicondyle of SD-rats’ femur. This study offers an alternative powerful avenue to achieve good comprehensive properties of magnesium-based biodegradable metals. It might also help to extend the applied range of magnesium-based biodegradable metals in orthopedic field.