Synergistic deformation of bimodal-structured AZ80 Mg alloy for excellent strength-ductility synergy via regulating the heterogeneity level

The trade-off between strength and ductility has long been a challenge for Mg alloy. To address this issue, bimodal-structured AZ80 Mg alloys with varying heterogeneity levels were fabricated via low-temperature extrusion in this work. The results reveal the microstructure comprising second-phase particle (SP_p, β-Mg₁₇Al₁₂ and Mg₃Mn₂Al₁₈)-reinforced fine grains (FGs) FGs and SP_p-free coarse grains (CGs), with the heterogeneity level decreasing as extrusion temperature increases. As the heterogeneity level decreases, the synergistic deformation capacity initially improves, reaching a maximum at the moderate heterogeneity level of 0.31 GPa and 0.238, and then declines. This exceptional capacity is attributed to the hetero-deformation induced (HDI) stress, which effectively alleviates the strain gradients by activating 〈c + a〉 dislocations and non-basal 〈a〉 dislocations during deformation. An optimal combination of 287 MPa in yield strength, 393 MPa in ultimate tensile strength, and 14.96% in elongation is achieved in the alloy with a moderate heterogeneity level. The excellent strength-ductility synergy originates from the enhanced capacity of dislocations accumulation driven by remarkable capacity of synergistic deformation and the synergistic strengthening mechanisms. This work provides a new insight into the design of bimodal structure to produce high-performance Mg alloys.