Relationship between electrochemical processes and environment-assisted crack growth under static and dynamic atmospheric conditions

Abstract

AbstractEnvironment-assisted cracking (EAC) of aluminum alloys in corrosive atmospheres is a significant maintenance and safety issue. EAC is influenced by the interaction of stress, environment, and microstructure. Atmospheric conditions and corrosion kinetics are dynamic due to diurnal cycles and changing operating conditions. Temperature, relative humidity, and surface contaminants interact to control thin-film electrolyte properties. Within a crack, the separation of the anode and cathode may occur due to concentration gradients between the crack tip, mouth, and external surface. Conventional immersion testing is not well suited to study factors and interactions leading to atmospheric EAC because the bulk electrolyte conditions for immersion testing are different from the thin-film properties. Additionally, standard three-electrode immersion measurements are not well suited to directly investigate the variation and distribution of cathodic and anodic currents on a sample surface and within an EAC crack. In this work, atmospheric electrochemical tests have been conducted using a segmented, multielectrode sensor with an artificial crevice to quantify local, dynamic anodic and cathodic current distributions. These tests are compared to EAC growth rate measurements. Maximum EAC growth rates are observed when high cathodic current is measured at the tip of artificial crevices, suggesting a hydrogen embrittlement mechanism.