Microstructure and mechanical property of large-diameter and low-alloyed Mg-Mn-Ca-Ce-Al alloy

Large-diameter, low-alloyed Mg-1.0Mn-0.4Ca-0.2Ce-0.1Al (wt%, MXEA) alloy bars were produced by a low-temperature secondary extrusion (SE) process. The MXEA alloy underwent primary extrusion (PE) followed by homogenization treatment. Specifically, the samples subjected to SE exhibited enhanced mechanical properties, namely a yield strength (YS) of 357 MPa, ultimate tensile strength (UTS) of 366 MPa, and elongation (EL) of 6.8%. However, the PE-MXEA alloy resulted in inferior mechanical properties with UTS of 305 MPa, YS of 308 MPa, and EL of 13.1%, respectively. Microstructure characterization shows that the coarse dynamically recrystallized (DRXed) grains are formed in PE samples, while the SE at 260 ℃ could effectively refine the grain structure, with an average size of ~750 nm. Moreover, the heterogeneous microstructure with strong texture is formed in SE MXEA samples, where non-DRXed regions contained high-density residual dislocations. Furthermore, the extrusion process promoted precipitation of nano-sized Mg 2 Ca, Al-Mn, and Mg 12 Ce phases. The synergistic effects of grain refinement strengthening, texture strengthening, dislocation strengthening, and precipitation strengthening collectively enhanced the overall mechanical property. By optimizing low-temperature extrusion parameters, this study provides guidance for designing the large-sized magnesium products. • A high-strength, large-diameter (45 mm) Mg alloy bar was produced via a novel low-temperature secondary extrusion. • A heterogeneous microstructure with a bimodal grain structure and strong fiber texture was successfully constructed. • The synergy of multiple strengthening mechanisms was quantitatively identified and calculated. • The alloy achieves an excellent strength-ductility synergy (YS of 357 MPa, UTS of 366 MPa, and EL of 6.8%).