Long-Term Marine Atmospheric Stress Corrosion Tests on High-Strength AlZnMgCu Alloys

To compare the stress corrosion resistance of the newer high-strength alloys, Aluminum Association (AA) 7049 and 7050, with the established AA 7075 alloy, smooth and precracked specimens from 32- and 76-mm-thick plates of each alloy were subjected to 105 months of exposure in a marine atmosphere. The smooth specimen results revealed that the performance of AA 7050-T7451 and 7049-T7351 approached that of 7075-T7351, even though their strength levels were equal to or greater than the specified minimum values for AA 7075-T651. The 76-mm plates of all of the alloys were more resistant than the corresponding thinner 32-mm plates. Threshold stress intensities (⁠K_Iscc⁠) for the 32-mm plates could not be estimated because of obvious self-loading effects in the precracked specimens. K_Iscc values for the 76-mm AA 7049 and 7050 plates were estimated to be less than 10 MPa m vs 25 to 30 MPa m for AA 7075-T7351. It remains unclear to what extent specimen self-loading affected this comparison.