Effect of Organic Adsorbants on the Aqueous Stress Corrosion Cracking of AA 7075-T651 Aluminum Alloy

The effect of eight different organic adsorbants on the stress corrosion cracking (SCC) behavior of the Aluminum Association (AA) 7075-T651 alloy in 3.5 wt% NaCl was studied by fracture mechanics testing techniques, using self-loaded double cantilever beam (DCB) specimens. A normalization procedure, whereby the stress intensity (K_I) was ratioed with respect to the experimental fracture toughness (K_IC) for each specimen, improved the sensitivity of the test method for detecting relative differences in crack propagation rates. The studies revealed that none of the adsorbants, which included alkyl sulfonates, alkyl amines, and aromatic-based heterocycles, retarded SCC. In fact, the majority accelerated SCC in the K_I-dependent regions of crack propagation behavior. Some supplementary corrosion weight loss studies revealed that no correlation existed between the effect of adsorbants on general corrosion inhibition and their effect on SCC. The results were discussed in terms of transport phenomena inside cracks and the effect of adsorbed species on the kinetics of several mechanistic SCC models.