Inherent effect of LPSO phase morphology on the dynamic recrystallization behaviors of extruded Mg-Gd-Y-Zn-Zr alloys

Complex phase constitutions are commonly observed in rare-earth magnesium alloys, and the morphology of long-period stacking-ordered (LPSO) phases significantly affects deformation and dynamic recrystallization (DRX) behavior. In this work, different LPSO-containing microstructures were tailored in a Mg-Gd-Y-Zn-Zr alloy by controlling the post-homogenization cooling route, including water cooling (WC), air cooling (AC), and furnace cooling (FC). The effects of LPSO phase morphology on DRX during hot extrusion were systematically investigated. DRX fractions of WC, AC, and FC samples were 6.5%, 23.1%, and 51.4%, respectively. In WC sample, dynamically precipitated lamellar LPSO phases suppressed DRX by impeding dislocation motion. In contrast, blocky LPSO phases in FC sample promoted dislocation accumulation, while pre-existing lamellar LPSO phases facilitated kink-band formation and continuous DRX. AC sample exhibited an intermediate DRX fraction due to the coexistence of different LPSO morphologies. Correspondingly, the WC sample achieved the highest ultimate tensile strength of 471 MPa, which was mainly attributed to the combined effects of strong basal texture, dislocation strengthening, solid-solution strengthening, and precipitation strengthening from dynamically precipitated lamellar LPSO phases. With decreasing cooling rate, grain boundary strengthening and kink-band-related strengthening became more pronounced in the AC and FC samples. The FC sample exhibited the highest elongation of 7.5%, owing to enhanced DRX, grain refinement, and texture weakening. These findings demonstrate that cooling-rate-controlled LPSO morphology is an effective strategy for regulating DRX behavior and tailoring the strength–ductility balance of Mg-Gd-Y-Zn-Zr alloys.