Mechanistic Studies of Intergranular Stress Corrosion Cracking in Al-Mg Alloys under Atmospheric Exposure Conditions

The effect of atmospheric environments on the intergranular stress corrosion cracking (IG-SCC) behavior of AA5083-H131 and AA5456-H116 was investigated using fracture mechanics-based testing, high-fidelity monitoring of crack growth kinetics, and electrochemical potential measurements. The IG-SCC susceptibility was found to decrease in atmospheric environments as compared to full immersion at −0.8 V_SCE. Critically, the decrease in IG-SCC susceptibility was most prevalent for higher levels of sensitization and the more susceptible AA5083-H131 alloy. These results are analyzed in the context of a coupled anodic dissolution and H-embrittlement mechanism, wherein the reduction in IG-SCC susceptibility in the atmospheric environments results from cathodic limitation of the governing IG-SCC mechanism, leading to 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 observed for environments without a set potential, and correlates well with known potential-dependent IG-SCC observations.