In this study, AZ91D (Mg-9Al-Zn) alloys reinforced with 2 vol% TC4 (Ti–6Al–4V) particles fabricated by semi-solid stir casting were extruded at different ratios, resulting in observed grain refinement effects. The research findings demonstrate that both TC4 and β-Mg₁₇Al₁₂ phases contribute to promoting dynamic recrystallization (DRX) nucleation. With increasing extrusion ratio, the β-phase (Mg₁₇Al₁₂) gradually fractures into smaller particles, leading to progressive grain refinement. Furthermore, the transition from 〈01–10〉 fiber texture to non-basal texture in the α-Mg matrix after hot extrusion is attributed to improved DRX behavior and activation of non-basal slip. As the extrusion ratio increases, the tensile strength and elongation (EL) of TC4_p/AZ91D composite improve significantly, reaching optimum comprehensive mechanical properties at an extrusion of 40:1 with a yield strength (YS) of 257 MPa, an ultimate tensile strength (UTS) of 357 MPa, and an EL of 9.7%. This remarkable strengthening effect is primarily attributed to β-phase reinforcement, grain refinement strengthening, and strain hardening.