Breaking strength-ductility trade-off in magnesium alloy by semi-solid extrusion process: Multi-slip activation in “Bimodal Grain”

• The first combination of semi-solid rheo-forming and extrusion processes for the fabrication of high-strength and high-plasticity magnesium alloys. • A bimodal microstructure characterized by high-density geometrically necessary dislocations (GNDs) and enhanced pyramidal slip activation achieved via temperature gradient. • Investigating the influence of distinctive crystallographic texture on the activation of multiple slip systems. • Explored the mechanism of multi-slip motion. Through the innovative integration of semi-solid rheo-casting with extrusion shear process, the short-process fabrication of low-alloyed wrought Mg-2Zn-1Mn alloy is achieved in this study. Uniaxial tensile testing of low-temperature extrusion shear specimens (200 ℃) demonstrates the exceptional strength-ductility synergy, yield strength of 277 MPa, yield strength ratio of 0.95, and elongation of 24 %. Microstructural observations reveal the mechanisms underlying its high strength-plasticity synergy at room temperature. This study investigates the effects of different temperature gradients on the microstructure by analyzing experiments conducted at three temperatures: 300 ℃, 250 ℃, and 200 ℃. Ultimately, the formation mechanism of the bimodal microstructure obtained at 200 ℃ is elucidated. The distinctive crystallographic texture oriented at 34° relative to the loading axis direction effectively mitigates stress concentration by inducing the synergistic activation of multiple slip systems. Furthermore, the transition trends of different slip systems and texture evolution during tensile deformation are validated through Visco-Plastic Self-Consistent (VPSC) simulations and corroborated by microstructural analysis. With geometrically necessary dislocation (GND) density (4.28 × 10¹⁵ m⁻²) and pyramidal slip activation (∼45 %). This study has successfully broken through the bottleneck of strength-ductility trade-off in magnesium alloys, providing theoretical support for the development of high-reliability magnesium alloys.