Subsurface Evolution and Residual Stress Behavior of 7075 Aluminum Alloy Under Multi-Field Water Jet Impact

This study investigates the compound surface modification of 7075 aluminum alloy through the High-Speed Cutting-Solid Projectile Embedded Water Jet (HSC-SPEWJ) method. The research employed SEM, XRD, TEM, and HRTEM techniques to assess how process parameters such as jet pressure, nozzle distance, and nozzle traverse speed influence surface properties, including surface quality, roughness, microhardness, residual stress, and microstructural evolution in the alloy. The results indicate that the surface of the alloy treated with the SPEWJ process primarily exhibits features such as “craters,” microcracks, and micropores, with the lowest surface roughness recorded at 0.6214 μm. The modification leads to the formation of a plastic deformation layer with depths varying between 28 and 78 μm, with the maximum depth of 78 μm achieved at a jet pressure of 15 MPa. This treatment results in an 8.8% increase in the maximum microhardness when compared to the untreated sample. The greatest work-hardened layer observed extended to a depth of 100 μm. Furthermore, the surface residual compressive stress reached −210.37 MPa, with the stress field extending to 356 μm below the surface. The HSC-SPEWJ treatment also facilitated the formation of high-density dislocations and grain refinement in the alloy, while the size of the Precipitate-Free Zone (PFZ) was reduced by 5 to 10 nm relative to the untreated sample.