Achieving excellent mechanical properties in Mg-5Bi-3Al alloy via ultra-fine grain and high-density precipitates

The development of low-cost, high-performance Mg alloys is crucial to the industrial applications of large-scale production of Mg alloys. In this work, extruded Mg-5Bi-3Al alloy with excellent mechanical properties is successfully prepared by modifying the extrusion temperatures (240 °C and 300 °C). The extruded alloy obtained ultra-high strength (yield strength = 380 MPa, ultimate tensile strength = 418 MPa) and excellent plasticity (elongation = 10.2%) at the extrusion temperature of 240 °C, the main contributing factors are primarily attributed to the synergistic effect of ultrafine recrystallized grain size (∼0.5 µm) and high density of Mg₃Bi₂ precipitates. Stacking faults within the sub-micron Mg₃Bi₂ phase are observed in the E240 alloy, confirming the plastic deformation capability of Mg₃Bi₂ phase. The effects of extrusion temperature on the microstructure, mechanical properties, and work-hardening behavior of the extruded Mg-5Bi-3Al alloys at room temperature are systematically investigated. The results suggest that decreasing the extrusion temperature can refine recrystallized grain size and Mg₃Bi₂ phase size, and the quantity of Mg₃Bi₂ phase is increased, while increasing the extrusion temperature can improve the degree of recrystallization and weaken texture. The work hardening rate is increased with the increased extrusion temperature, mainly due to the coarsening of grains and precipitates, and the weakening of texture. This work provides an experimental basis for preparing high-performance wrought Mg-5Bi-3Al alloys.