The interaction between pitting corrosion, grain boundaries, and constituent particles during corrosion fatigue of 7075-T6 aluminum alloy

Concomitant corrosion fatigue research was performed on 7075-T6 aluminum alloy to gain an increased understanding of how microstructure influences pit growth, pit-to-crack transition, and critical crack propagation to fracture. Two thicknesses of rolled sheet and an extrusion of 7075-T6 aluminum alloy were etched and subjected to concomitant corrosion fatigue in a 3.5% sodium chloride solution. Testing was interrupted at various intervals to obtain information on pit generation, growth, and potential cracking. Results indicated that microstructure has a significant influence on pit-to-crack transition and fatigue crack propagation. Constituent particles competed with corrosion pits as critical crack nucleation sites, with some affecting the critical crack by either nucleation of additional cracking or linkage with the main crack. Post-fracture analysis confirmed the presence of noncritical cracks within the corroded region, related to pitting and constituent particles.