Preparation of Gradient Nanostructured Cu–Al Alloy Matrix and Evolution Microstructure and Properties

Cu–Al alloy with a gradient nanostructured surface layer is prepared by ultrasonic shot peening (USP). The effect of different shot peening times on the microstructure and properties of the modified layer is systematically investigated. The results show that the surface phase structure is not changed by USP technology, but a gradient nanocrystalline layer is formed on the surface, and the surface grains are obviously refined. The nanocrystalline mechanism is characterized by dislocation movement and mechanical twinning. USP can greatly improve the mechanical properties, tribological properties, and corrosion properties of the alloy. When the shot peening time is 15 min, the modification effect is the best. The hardness is as high as 254.1 HV_0.2, which is 2.4 times that of the matrix, and the average coefficient of friction is only 0.231. The volume wear amount and volume wear rate are 4.434 × 10⁷ μm³ and 0.1848 μm² N⁻¹, respectively. The strengthening mechanism of nanosized samples is grain refinement and work hardening, and the wear mechanism is abrasive wear and slight oxidation wear. The improvement of the corrosion performance of nanosized samples is mainly due to the formation of the dense passivation film on the surface.