Investigating the Impact of Accelerated Testing Variables on the Exfoliation Corrosion of AA2060

Abstract

Aluminum-lithium alloys are attractive for aerospace applications because of their improved strength-to-weight and stiffness-to-weight ratios, fracture toughness, and corrosion resistance compared to legacy alloys such as AA2024 and AA7075. Many standardized accelerated tests are used to evaluate the corrosion resistance of high-strength aluminum alloys, but these tests can produce drastically different results for the same alloy. The purpose of this study is to provide a quantitative, technical understanding of the roles of key testing variables in two accelerated tests for exfoliation corrosion, EXCO and ANCIT. Accelerated testing was performed on under-aged and near peak-aged tempers of aluminum-lithium alloy AA2060, and a five-factor design of experiments was used to determine the impact of key testing variables on the corrosion potential and polarization resistance of AA2060. It was found that ANCIT testing produced exfoliation in the susceptible temper (T36) in a much shorter time than EXCO testing did. ANCIT was also more aggressive toward the -T86 temper compared to EXCO. The design of experiments showed that the addition of an oxidizing agent (NO3−) to the testing solution had a statistically significant impact on both corrosion potential and polarization resistance. The solution pH, as well as the interaction between solution pH and added oxidizing agent, had statistically significant effects on polarization resistance.