Achieving breakthrough high strength in AZ31 magnesium alloy bar via a novel single-pass extrusion process

AZ31 magnesium alloy generally suffers from insufficient room-temperature strength. Meanwhile, conventional processing routes offer limited strengthening efficiency, and severe plastic deformation (SPD) processes face difficulties in industrial upscaling. To address these bottlenecks, this work proposes a single-pass Spatial Symmetric Expansion Shear Extrusion (SSESE) process to achieve an efficient strength-ductility synergy in AZ31 alloy bars. The deformation behavior, microstructural evolution, and strengthening mechanisms were systematically investigated using finite element (FE) simulation, microscopic characterizations (OM, EBSD, TEM), and tensile testing. Results demonstrate that the SSESE process introduces high accumulated strain in a single pass. Microstructurally, the induced gradient strain field sequentially activates twin-induced, continuous, and discontinuous dynamic recrystallization (TDRX, CDRX, and DDRX), leading to significant grain refinement. Furthermore, the stepwise activation of basal and non-basal slips generates a [10–10]-[2–1–10]//ED bimodal prismatic texture. This strong deformation also induces high-density dislocations and the dynamic precipitation of nanoscale second-phase particles (Mg 17 Al 12 and Al 8 Mn 5 ). Consequently, the as-prepared AZ31 bar exhibits an ultimate tensile strength (UTS) of 364 MPa, a tensile yield strength (TYS) of 293 MPa, and an elongation to fracture (EF) of 10%. These values represent an 84.7% increase in UTS and a 42.9% improvement in ductility compared with the as-cast alloy. This simultaneous enhancement of strength and ductility is attributed to the synergistic effects of grain boundary, dislocation, dispersion, and heterogeneous texture strengthening. Ultimately, the SSESE process provides a highly effective and promising strategy for the industrial-scale fabrication of high-performance magnesium alloy bars.