<p>This study utilized ultrasonic-assisted semi-solid stirring casting technique to prepare 7075Al/SiC_np composites and investigated the effect of pre-extrusion on the microstructure and mechanical properties of the composites after T6 treatment. The microstructure of aged aluminum matrix composites was composed of GP zones, the η' (MgZn₂) phase, the η (MgZn₂) phase, and the θ (Al₂Cu) phase. The MgZn₂ phase, which emerged through the evolution of GP zones and nucleation within the matrix during the aging process, was the principal strengthening phase. The results indicated that the low-temperature pre-extrusion could accumulate substantial strain energy during aging, which promoted the precipitation of uniformly dispersed fine MgZn₂ particles. Moreover, under low-temperature extrusion, nanoparticles were more uniformly distributed, which accelerated the formation of GP zones and enhanced the precipitation of the strengthening phase. The tensile strength of the composite increased by 278 MPa, while the elongation improved by 7.7%, in comparison with the as-cast material. The significant enhancement of the composites' mechanical properties can be primarily attributed to grain boundary strengthening from fine grains, dislocation strengthening caused by low-temperature pre-extrusion, and the synergistic effects of aging precipitates and Orowan strengthening by nano-SiC particles. In addition, the work hardening is mainly affected by dislocations. With the decrease in pre-extrusion temperature, a large number of dislocations were generated in the composites, which was due to the more Orowan strengthening mechanism caused by low-temperature pre-extrusion.</p>