Experimental investigation on damage evolution and failure mechanism of pre-corroded AA7075-T6 under multiaxial fatigue loading

Abstract

To investigate the tension–torsion fatigue failure of pre-corroded AA7075-T6, fatigue damage accumulation, macro-crack formation and propagation are quantitatively characterized through 3D-DIC based strain maps and damage severity curves, micro-cracking characteristics are further examined by SEM, TEM, and EBSD observation. Experimental results show that corrosion pit induces fatigue macro-cracks formation, and the identified nucleation time, amount, and location are diverse for different loading conditions. Four dominated fatigue micro-crack initiation forms and corresponding mechanisms were analyzed, namely, pit bottom, sidewall dis-continuous surface, corrosion micro-feature (micro-pits/jut-ins), and pit subsurface, which depends on multi-factors involving corrosion macro-morphology, corrosion micro-morphology, loading condition and underlying microstructure.