Enhancing intergranular corrosion resistance of 7055 Al alloy by ultrasonic shot peening

High strength 7000 series Al alloys are quite sensitive to intergranular corrosion (IGC) and generally a trade-off between IGC resistance and hardness exists in such Al alloys. Here, by using ultrasonic shot peening (USSP) we fabricate a gradient AA7055 whose IGC is significantly enhanced in both 57 g/L NaCl + 10 mL/L H2O2 solution and 3.5 wt% NaCl solution, whereas the surface hardness increases by 10 %. TEM microstructure characterization and nanoscale investigation of corrosion indicate that the improvement in IGC resistance can be attributed to the disappearance of grain boundary precipitates and precipitate free zones. Surface hardening mechanism is also revealed.