7XXX series aluminum alloys are often used in aircraft applications due to their high strength-to-weight ratio. However, due to their susceptibility to cracking after fusion welding, structural components are joined using fasteners. These fasteners are of a dissimilar metal that is more noble than the aluminum alloy, which along with the coating damage from operation, introduces the risk of galvanic corrosion. Corrosion and cracking in areas of known stress concentrators, such as fasteners found during naval aircraft teardowns, suggest the need to explore the effect of stress on corrosion in environments relevant to atmospheric corrosion of airframe materials. AA7075-T6 panels with a countersunk SS316 fastener were exposed to static mechanical loads and both static and cyclic environmental conditions. Panels were treated with a non-chrome conversion coating (MIL-DTL-81706 Type 2), primer (MIL-PRF-23377 Class N Type 1), and topcoat (MIL-PRF-85285 Class H Type IV) and tested at 3 static load conditions (0σy, 0.4σy, and 0.9σy). Static environmental tests were conducted at 3 relative humidity (RH) values (60, 75, and 95%) for 2 weeks. In addition, a cyclic accelerated corrosion exposure with holds at 3 RH values (90, 60, and 40%) was carried out until sample fracture. Metallographic imaging of the through-hole cross-section and analysis with an in-house Python code allowed characterization of the corrosion morphology in the fastener through-hole. This analysis was complemented with SEM imaging to investigate the effects of environmental and mechanical loading on features susceptible to crack initiation. Increased corrosion pitting events and average pit height were observed under constant RH in stressed conditions. This work will provide insight into the effects of static stresses and environmental loading on galvanic corrosion kinetics and morphology, which will assist in the design of future aircraft structures to mitigate galvanic corrosion risks and improve maintenance predictions.
