<p>This study employs refill friction stir spot welding (RFSSW) technology to achieve solid-state metallurgical repair of cavity defects in AA7075-T6 aluminum alloy, with a focus on investigating the correlation between process parameters and microstructural characteristics. Through parameter optimization (rotational speed of 2000 rpm, plunge speed of 0.5 mm/s, and plunge depth of 3.3 mm), high-quality joints free from cracks or porosity were obtained in single-pass repairs without preheating. Microstructural characterization revealed the formation of equiaxed recrystallized grains (8–12 μm) in the repaired zone, with interfacial reaction layers containing Al₂CuMg (S-phase) and MgZn₂ (η-phase) precipitates. The weld nugget zone achieved a microhardness of 143.1 HV (95.4% of the base material), and tensile tests demonstrated a maximum strength of 448.53 MPa (85.4% of the base material’s strength), representing a 15–20% improvement over conventional fusion welding repairs. Through dynamic recrystallization analysis and precipitate evolution studies, the regulatory mechanism of thermo-mechanical coupling on joint performance was elucidated: while dynamic recrystallization refined grain structure, thermal cycling promoted the dissolution of η-phase and subsequent reprecipitation of S-phase, thereby optimizing interfacial bonding strength. These findings confirm the significant advantages of RFSSW technology for precision repair of high-strength aluminum alloys.</p>