Optimization of Friction Rolling Repair via Supercritical CO ₂ and Water Mist Hybrid Cooling: Microstructure and Mechanical Properties

Friction rolling solid‐state repair technology has emerged as a promising technique for the rapid repair and remanufacturing of large‐scale aerospace components. In this study, the cooling process in friction rolling repair was optimized and improved. Comparative experiments were conducted involving water mist cooling (WMC), supercritical CO 2 (SC‐CO 2 ) cooling, and supercritical CO 2 & water mist hybrid cooling (SC‐CO 2 & WMC) processes. Multilayer friction rolling solid‐state repair was performed on simulated stiffened panel defects using aerospace‐grade 2195 Al–Li alloy. Compared with the WMC process, the SC‐CO 2 & WMC process achieved a maximum peak temperature reduction of 17.8% and an average peak temperature reduction of 15.3%. In contrast, the SC‐CO 2 & WMC process presented the shortest thermal exposure time, averaging 30.5 s. Overall, the SC‐CO 2 & WMC process realized the combined effects of local rapid cooling and uniform temperature reduction. Correspondingly, the average grain sizes in the filling zones were 4.2, 2.4, and 3.9 μm. The SC‐CO 2 & WMC hybrid process achieves the highest hardness, with an average hardness of 150 HV in the filling zone. The filling zone exhibits an ultimate tensile strength (UTS) of 553 MPa, reaching 104.3% of the base metal, a yield strength of 320 MPa, and an elongation of 20.7%.