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

• Heterogeneity level of bimodal structure can be accurately regulated. • Relationship between heterogeneity level and synergistic deformation is established. • Formed HDI stress alleviates moderate heterogeneity level, promoting the synergistic deformation. 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- Mg 17 Al 12 and Mg 3 Mn 2 Al 18 )-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.