Fatigue damage evolution and failure of pre‐corroded aluminum alloy 7075‐T651 under air and corrosion environments

Abstract This paper presents characterization for fatigue failure analysis of precorroded AA7075‐T651 under air and exfoliation corrosion (EXCO) environments, with respect to damage accumulation, macrocrack and microcrack behavior via 3D digital image correlation (DIC), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). It is shown that that corrosion pits induce fatigue cracking with different nucleation times, and locations. It is furthermore shown that while the corrosive environment accelerates crack formation, it significantly hinders fatigue crack propagation at low stress amplitudes due to crack closure and tip passivation. Five dominant fatigue microcrack initiation types (pit bottom, corrosion tunnel, corrosion micropit, corrosion jut‐in, and chapped feature) and relevant mechanisms were identified, related to corrosion pit macro–micro morphology, material microdefect, local material grain structure, and loading condition.