Influence of Surface Nanocrystallization and Partial Amorphization Induced by Ultrasonic Shot Peening on Surface Properties of 7075 Aluminum Alloy

This paper investigates the influence of ultrasonic shot peening (USP) on the surface microstructure, hardness, roughness, and corrosion resistance of 7075 aluminum alloy. After the USP treatment, both surface nanocrystallization and partial surface amorphization of 7075 aluminum alloy were observed by XRD, SEM, and TEM methods. The results showed that the average surface grain size was refined to about 30 nm, while maximal surface amorphization percentage reached 43.68%. Both surface hardness and roughness increased with the peening duration, and their interplay was discussed. The maximal surface hardness achieved in this work was 249.60 HV, which is 46% higher compared to the original specimen. Besides, corrosion resistance initially increased with the peening duration and then decreased when the peening duration exceeded 200 s. The influence of both surface microstructure and roughness on the corrosion resistance was also analyzed.