Volume 6, Issue 4 (July 1978)
Marine Atmosphere Stress Corrosion Tests on Precracked Specimens from High-Strength Aluminum Alloys: Effect of Corrosion-Product Wedging
Stress corrosion tests on precracked double-cantilever beam specimens from 2000- and 7000-series aluminum alloys have been in progress for up to seven years at a marine-atmosphere exposure site near Daytona Beach, Fla. One of the most significant results of these tests concerns the effects of specimen self-loading (because of exfoliation and corrosion-product wedging) on the relative crack growth resistance of different alloys. Self-loading is apparently affected by copper content but is not limited to copper-bearing alloys. Copper-free alloy 7039-T64, for example, showed self-loading effects after 3 to 4 years' exposure. Naturally aged 2XXX alloys and peak-aged, copper-containing 7XXX alloys were most sensitive to self-loading, usually showing the effects within six months. However, cracks in 7075-T73, a stress corrosion resistant alloy, also continued to propagate at rates that were not insignificant after several years' exposure, whereas alloy 2024-T851 appeared more resistant to corrosion-product wedging than 7075-T73.