Microstructure, corrosion behaviour and thermal stability of AA 7150 after ultrasonic shot peening

Microstructure, corrosion behaviour and thermal stability of ultrasonic shot peened AA7150 were studied in this work. After ultrasonic shot peening, exfoliation susceptibility decreases, intergranular corrosion is inhibited for both normal and transverse planes, pitting potential shifts to the positive direction. The enhanced localized corrosion resistance is attributed to the formation of equiaxed nano-grains on surface layer. Pre-existing ageing-induced eta' and eta precipitates dissolved immediately after shot peening, however, after 18 months' natural ageing, nanograined precipitates with more coarsened size than pre-existing ones, re-precipitate on the peened surface layer and leads to surface softening.