Evaluation of Aluminum after One-Year Deep Sea Exposure

Abstract

Evaluation of 17 typical aluminum alloys exposed for over 13 months at a depth of 2370 ft in the Pacific Ocean confirm earlier 6-month tests. The aluminum-magnesium alloy systems continue to show excellent sea water resistance, and the claddings on X7002 and 7079 highstrength alloys completely protect the core metal. Pit depth and weight loss data from replicate panels exposed 1 year near the surface at Harbor Island, N.C., indicate that the corrosion resistance at test depth generally is roughly comparable to that for surface exposures. Exceptions appear to be alloy 3003 and the high-purity aluminum, which had considerably deeper pitting and higher corrosion rates at the deep-sea location. Results point to the desirability of keeping the copper content below 0.06% for aluminum alloys in deep-sea applications. As anticipated, high-strength aluminum alloys with substantial zinc or copper content must be protected, and a higher potential cladding or external anodes proved effective. This test showed that the cladding alloy may be used up at a faster rate in the deep sea than near the surface.