The Performance of Alcan 65S-T6 Aluminum Alloy Embedded in Certain Woods Under Marine Conditions

Abstract

Laboratory and marine exposure tests were carried out to assess the performance of Alcan 65S-T6 (6061-T6) aluminum alloy embedded in certain woods under marine exposure conditions. The tests also involved the assessment of several protective paint systems designed to protect the wood in the simulated hull sections used in the tests.The relative corrosivity to aluminum of the woods tested under ship hull conditions is: rock elm (least), mahogany and British Columbia fir (most). Only very slight corrosion occurs when the aluminum is coated with zinc chromate priming paint even in the most corrosive woods after extended immersion periods in sea water. Alcan 65S-T6 (6061-T6) has a corrosion resistance greatly superior to that of Alcan 24S-T3 & 4 (2024-T3 & 4) under the same marine exposure conditions. Anodizing increases the corrosion resistance of both alloys, particularly if this treatment is followed by a coat of zinc chromate primer. The use of wooden dowels to protect aluminum embedded in these woods is also beneficial. Among the variations in paint systems which were tested, the most complete paint system, comprised of sealer + barrier layer + copper antifouling paint provided maximum protection from corrosion. Where pitting occurred on 65S-T6 (6061-T6) embedded in sea water wetted wood, it has been shown that the rate of penetration falls off sharply with time. 6.4.2