Investigation of IG-SCC Growth Kinetics in Al-Mg Alloys in Thin Film Environments

The effect of thin film environments on the intergranular stress corrosion cracking (IG-SCC) behavior of AA5083-H131 was investigated using fracture mechanics-based testing, high-fidelity monitoring of crack growth, and electrochemical potential measurements. A protocol for conducting thin film IG-SCC fracture mechanics experiments with anodized aluminum oxide membranes is developed and the ability to maintain films of specific thicknesses without impeding oxygen diffusion during testing is validated via electrochemical impedance spectroscopy testing and computational modeling. The IG-SCC susceptibility was found to increase once a critical thin film thickness of 82 μm was achieved; above this thickness a duality in IG-SCC susceptibility behavior was observed. These results are analyzed in the context of a coupled anodic dissolution and hydrogen (H) embrittlement mechanism, where susceptibility is found to scale with the cathodic limitation of the governing IG-SCC mechanism. Specifically, thinner film thicknesses led to limitations on the amount of cathodic current availability, which caused a decrease in the dissolution at the crack tip, a less aggressive crack chemistry development, and thus lower levels of H production. A close correlation between the open-circuit potential of the bulk surface and the crack growth kinetics was also observed, consistent with trends reported in previous IG-SCC studies on this alloy.