Achieving high-speed extrudability and superior strength-plasticity synergy in a low-alloyed Mg-Al-Mn-Ca alloy via trace Ce alloying and high-temperature pre-aging

: Grain coarsening and limited strengthening mechanisms under high-speed extrusion are key challenges restricting the application of low-alloyed magnesium alloys. This study developed a new low-alloyed Mg-1.2Al-0.5Mn-0.2Ca-0.5Ce (AMX1210-Ce, wt%) alloy by adding trace Ce to Mg-1.2Al-0.5Mn-0.2Ca alloy. A single-stage heat treatment (SSHT: 400 °C × 10 h) was applied to both alloys. After 30 m/min extrusion, all bars exhibited smooth and shiny surfaces, indicating excellent extrudability. Microstructural analysis revealed that the trace Ce addition refined the average grain size (AGS) of as-extruded AMX1210-SSHT from 24.6±12.8 μm to 8.4±3.2 μm, attributed to Ce-induced dendritic refinement and coarse Al-Ce and Al 8 Mn 4 Ce phases. Compared to AMX1210-SSHT, the tensile yield strength (TYS), ultimate tensile strength (UTS), and elongation (EL) of the AMX1210-Ce-SSHT increased by 32.0 MPa, 11.2 MPa, and 4.6%, respectively. To further enhance the mechanical properties, prior to extrusion, a dual-stage high-temperature pre-aging (HTPA: 500 °C × 4 h + 400 °C × 10 h) was applied to the AMX1210-Ce. HTPA further refined the AGS to 6.4±2.6 μm owing to strong pinning by high-density Al 8 Mn 4 Ce nanoparticles with a number density of 2.75 × 10 8 cm -2 . The AMX1210-Ce-HTPA alloy achieved TYS of 245.9 MPa, UTS of 289.1 MPa, and EL of 22.5%. The strengthening arises from synergistic effects of grain refinement, precipitation strengthening, and texture strengthening, while the enhanced plasticity is attributed to uniform fine-grain coordinated deformation, a low-intensity texture, and effective regulation of coarse phases.