Effect of Shot Peening and Plasma Electrolytic Oxidation on the Intergranular Corrosion Behavior of 7A85 Aluminum Alloy

The effects of shot peening (SP) and plasma electrolytic oxidation (PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85 (AA 7A85) were investigated by electrochemical polarization and electrochemical impedance tests. The intergranular corrosion mechanism of SP, PEO and PEO combined with sealing-treated AA 7A85 was studied by the metallographic analysis, residual stress testing, X-ray diffractometer analysis and scanning electron microscopy. The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion. SP would significantly improve its intergranular corrosion resistance. This is attributed to the combination action of residual compressive stress and grain refinement. PEO would reduce the largest corrosion depth by 41.6%. Moreover, PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating. However, PEO combined with the SiO₂ sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.