Coupled effects of extrusion temperature and extrusion ratio on texture evolution and mechanical anisotropy of a Mg–4.5Zn Alloy

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This study investigates the coupled effects of extrusion temperature (300−400 °C) and extrusion ratio (6:1, 12:1, and 18:1) on the texture, mechanical behavior, and fracture behavior of a Mg−4.5Zn alloy. The alloy underwent solution treatment followed by extrusion. Microstructural analysis reveals that extrusion induces significant grain refinement through dynamic recrystallization (DRX), resulting in a heterogeneous structure characterized by necklace-type recrystallized regions. Lower extrusion temperatures and higher extrusion ratios promote finer DRXed grains due to increased stored energy and restricted grain growth. Texture analysis demonstrates a typical basal fiber texture, with its evolution depending on both extrusion temperature and ratio as a result of deformation-induced reorientation, DRX, grain rotation, and temperature-dependent slip activity. Mechanical testing demonstrates substantial improvements in both strength and ductility after extrusion, attributed to Hall−Petch strengthening and texture modification. The extruded alloy exhibits reduced tension–compression asymmetry compared with the as-cast condition, indicating mitigated plastic anisotropy. The optimal combination is achieved at 300 °C with an extrusion ratio of 18:1, yielding a tensile yield strength of 265 MPa, an ultimate tensile strength of 289 MPa, and an elongation of 16.5%. Furthermore, the ultimate compressive strength, compressive elongation, and microhardness reach 467.49 MPa, 27.86%, and 90.52 HV, respectively. Fractographic analysis confirms a transition from brittle cleavage fracture in the as-cast condition to ductile fracture after extrusion, which is associated with grain refinement. These findings elucidate the critical process–structure–property relationships in binary Mg−Zn alloys and provide guidance for optimizing extrusion parameters to enhance mechanical performance.