• Cryogenic treatment combined with cross-rolling significantly enhances the mechanical properties of AZ31 Mg alloy, with the 3-pass sample achieving the highest tensile strength (351 MPa) and hardness (76.1 HV) with excellent uniformity.
• The 2-pass sample exhibits superior ductility but suffers from poor hardness evenness, indicating a trade-off between strength and ductility depending on the number of rolling passes.
• The strengthening mechanism for the 3-pass sample is attributed to fine grains, bimodal structure, high dislocation density, and precipitation strengthening, providing a comprehensive understanding of the microstructural evolution.
• Increasing the number of passes to 4 or 5 leads to a decrease in overall performance due to repeated heat preservation, highlighting the importance of optimizing the number of passes in the process.