Study on multi-field composite strengthening, surface integrity, and microstructural evolution mechanism of 7075-T6 aluminum alloy

Multi-energy field composite reinforcement technology has become a critical technique for improving the service life of key components in aviation engines. This paper aims to investigate the strengthening mechanism of highspeed cutting and solid particle-entrained waterjet peening (HSC-WJP) composite reinforcement on 7075-T6 aluminum alloy. Samples subjected to single solid particle-entrained waterjet peening (WJP) reinforcement were selected as the control group. The surface quality and microstructure evolution of 7075-T6 aluminum alloy after composite reinforcement were examined using SEM, EDS, XRD, TEM, and HRTEM techniques. The research results indicate that, under the same jet parameters, HSC-WJP composite reinforcement is superior to single WJP reinforcement in terms of surface roughness, except when the jet pressure is below 25 MPa and the track spacing is 0.53. The surfaces of the 7075-T6 aluminum alloy workpieces after reinforcement are mainly characterized by the presence of pits and micro-pores. Surface roughness shows a positive correlation with jet pressure and nozzle traverse speed. After HSC-WJP composite reinforcement, the surface roughness decreases by 0.132 mu m compared to single WJP reinforcement, and the size of surface pits is reduced by 4-20 mu m. Surface roughness decreases first, then increases, and then decreases again with increasing target distance, while it increases first and then decreases with increasing path spacing. A significant precipitation-free zone (PFZ) is present in the 7075-T6 aluminum alloy after reinforcement, and its width is positively correlated with the nozzle traverse speed. When the nozzle traverse speed is 120 mm/min, the average size of the PFZ at grain boundaries after single WJP reinforcement is 12-20 nm, while it decreases by approximately 3 nm after HSC-WJP composite reinforcement. The main precipitate phase in the reinforced aluminum matrix is eta ' phase, and under the same jet parameters, the HSC-WJP grain size is smaller, approximately 25-34 nm, and exhibits significant dislocation walls and dislocation tangles, with a higher dislocation density compared to single WJP reinforcement.