Abstract: In this study, a high-ductility AZ91 magnesium alloy was fabricated by the novel continuous rheo-squeeze casting-extrusion (CRSCE) process. The semi-solid slurry was prepared by ultrasonic vibration (UV) treat-ment, then solidified under pressure, and finally hot extruded. UV treatment can reduce the Al element content in primary grains and increase it in secondary grains. The refined Mg₁₇ Al₁₂ phase was scattered along secondary grain boundaries and then stretched into narrow, fibrous bands during the hot extrusion. The fibrous bands with proper separation distances can accelerate the dynamic recrystallization (DRX) process and suppress the growth of DRXed grains. Microcracks were initiated inside the brittle Mg₁₇ Al₁₂ phase and tended to propagate along the continuously distributed Mg₁₇ Al₁₂ phase during the tensile test. Thus, the tiny Mg₁₇ Al₁₂ phase in the billet and narrow, fibrous bands in as-extruded rods can prevent cracks from spreading and enhance ductility. Therefore, excellent comprehensive mechanical properties were obtained, with an ultimate tensile strength of 326.3 MPa and an elongation of 16.46 %. The CRSCE method offers a novel way to fabricate high-ductility and high-alloyed magnesium alloys without ho-mogenization. Microstructure regulation mechanisms of CRSCE, microstructural hereditary laws, and the effect of the Mg₁₇ Al₁₂ phase on mechanical properties were further discussed.

Key words: AZ91 magnesium alloy, Mg₁₇ Al₁₂ phase, Rheo-squeeze casting, Ultrasonic vibration, Continuous casting-extrusion, Ductility