Influence of ultrasonic surface rolling treatment and shot peening on surface microstructure and corrosion behavior of CuNiSi alloy

Due to excellent strength and conductivity, CuNiSi alloy is widely used in high-speed railway contact network and other fields. However, owing to the complex application environment, CuNiSi alloy often experiences corrosion failure. Based on this, the surface of CuNiSi alloy was treated by ultrasonic surface rolling treatment (USRT) and shot peening (SP) process, and the nanocrystalline layer was successfully prepared on the alloy surface. Meanwhile, the microstructure, hardness and residual stress of surface layer was characterized. The results show that USRT and SP process does not change the phase composition of alloy surface, but introduce a large number of deformation twins and dislocations on the surface, resulting in significant grain refinement. USRT and SP samples exhibit enhanced surface hardness and residual compressive stress compared to the untreated sample. The electrochemical test results reveal that USRT and SP samples exhibit significantly enhanced corrosion resistance in 3.5 wt% NaCl solution, which can be attributed to the stable oxidation film introduced by the high density of grain boundaries and residual compressive stress.