Effect of hole cold expansion on fatigue performance of corroded 7B04-T6 aluminium alloy

Corroded specimens of fastener hole composed of 7B04-T6 Al-alloy sheet were subjected to hole cold expansion and fatigue test. The fatigue performance of the specimens was analysed. It was found that accelerated corrosion up to 14 h exposure in corrosion solution created aggregated pits which resulted in almost 80% loss of fatigue life of the hole specimen. Cold expansion resulted in improvement in surface integrity and substantial alleviation of the aggregated pits of the corroded hole as well as introduction of beneficial residual compressive stress. Fractography observation of fracture surface shows that the as corroded hole exhibited multi-site fatigue while the corroded holes after cold expansion showed single-site fatigue. The averaged fatigue life of the DCE 3.2% specimens was 2 times of the as corroded ones, and that of the DCE 5.7% specimens was 3 times of the as corroded ones, which demonstrated the capability of the hole cold expansion process in fatigue enhancement of corrosion damaged holes in 7804-T6 Al-alloy.