Characterization of galvanic couples under atmospheric electrolytes using electrochemical polarization and coupled array techniques

摘要

As much as 85% of stress corrosion cracks form at galvanic corrosions sites on military aircraft. Further, as the automotive industry moves towards light weight alloys, the risk of galvanic corrosion increases. It is essential, therefore, to replicate galvanic corrosion during laboratory testing. The difficulty of replicating corrosion failure modes in accelerated laboratory testing is a well-known challenge. Several recent studies have highlighted the importance of cyclic variations in the test environment in recreating corrosion damage. An understanding of the effects of these cyclic variations is critical to the development of improved accelerated tests. In this work, we seek to understand the relationships between cyclic atmospheric relative humidity on galvanic corrosion under thin film electrolytes. A relatively simple cell design used to perform electrochemical polarization tests under a thin electrolyte is demonstrated. Comparison of the polarization behavior of various metals under immersion and atmospheric exposures demonstrates an increase in galvanic corrosion rate under atmospheric conditions as a result of increased cathodic kinetics. In-situ measurements of the coupling and decoupling of galvanic couples as a function of RH are also shown using a multi-electrode array technique. Findings from these studies will be used to guide the development of accelerated atmospheric corrosion test parameters with the goal of inducing specific corrosion modes.