Achieving ultra-high extrusion speed and strength-ductility synergy in a BAZ531 magnesium alloy via differential-thermal extrusion

High-speed extrudability is critical for the efficient production of metallic extruded products. This study employs a differential-thermal (DT) extrusion method to achieve an ultra-high extrusion speed of 83 m/min for the newly developed Mg-5Bi-3Al-1Zn (BAZ531, wt%) alloy while maintaining good surface quality. Finite element simulations confirmed that the DT extrusion heat remained below the alloy's initial melting point, preventing surface cracks. The DT process refined the average grain size to 15.2 mu m, 0.6 times that of the equal-thermal (ET) extruded alloy, by delaying dynamic recrystallization due to a lower temperature increase. The BAZ531-DT alloy exhibited excellent mechanical properties, with a tensile yield strength of 283 MPa, ultimate tensile strength of 331 MPa, and elongation-to-failure of 19 %. Grain refinement and strong texture enhanced strength, while refined grains improved ductility by effectively suppressing twinning. This work demonstrates significant potential for advancing high-speed extrusion of Mg-Bi-based alloys with superior mechanical performance.