Fatigue response of pre-corroded chromic-acid-anodized AA7050-T7451 and phase-field analysis of stress-dependent localized dissolution

Understanding the effects of environmental exposure and cyclic loading on localized damage is important for assessing the fatigue performance of anodized aluminium. This study investigates the fatigue response of chromic-acid-anodized AA7050-T7451 and the stress-dependent evolution of localized corrosion. Cyclic-immersion and intermittent-salt-fog exposures were followed by mass-loss measurements, microscopic observations and axial fatigue testing in laboratory air at R = 0.06. Small average mass losses coexisted with localized surface changes and appreciable fatigue-life scatter. At 180 MPa, the cyclic-immersion groups exhibited sample mean fatigue lives 57.1–73.6% below the uncorroded reference, with a non-monotonic dependence on exposure duration. Increasing the maximum nominal stress from 180 to 200 MPa reduced the mean fatigue life by 22.0–45.9% at the same cyclic-immersion durations. A two-dimensional displacement–phase-field–concentration model examined localized dissolution under cyclic loading for initial cavity depths of 0.01 and 0.02 mm. Higher cyclic stress promoted local plastic deformation and increased interface mobility, accelerating inward dissolution. At 900 s, increasing the maximum nominal stress from 160 to 240 MPa increased total defect depth by 45.2–51.2%, whereas lateral width changed by no more than 2.2%. At 240 MPa and 900 s, the larger initial cavity developed 45.8% greater additional penetration, demonstrating the influence of initial geometry on subsequent damage evolution. These findings provide a mechanistic explanation for stress-enhanced localized corrosion and highlight the importance of considering exposure history, loading conditions and initial defect geometry jointly in the fatigue assessment of anodized aluminium.