Methods for Regulating Depth of Corrosion Fissures in Simulated Fastener Holes of 7050-T7451 Aluminum Alloy

This study presents a new test method for inducing controlled corrosion damage within simulated fastener holes of aluminum alloys, aimed at pretreating fatigue test specimens. The method involves insulating the outer surfaces while exposing the fastener hole surface to electrolytes containing 0.66 M NaCl + 0.1 M AlCl3 with varying concentrations of K2S2O8. The evolution of corrosion damage within the fastener hole was examined as a function of exposure duration, electrolyte composition, and volume, as well as the effect of galvanic coupling with an SS316 cathode. Results indicate that fissure depth increases with an increase in K2S2O8 concentration, but does not progress further after 24 h to 48 h of exposure in the chemical, or freely-corroding, exposure test. In contrast, galvanic coupling with an SS316 plate significantly accelerates corrosion, leading to much deeper fissures in a shorter time. The importance of electrolyte replenishment has been explored using electrochemical measurements, revealing the impact of evolving electrolyte chemistry. Beyond its application in specimen pretreatment to study environmentally assisted cracking, this method provides a simple yet effective approach for studying localized corrosion and potentially evaluating mitigation strategies for fastener holes in aerospace structures.