Outdoor Exposure Results for Pretreated and Topcoated Aluminum Armor Alloys 2519, 5083, and 7039

Report No. ARL-TR-3283
Authors: John V. Kelley and Brian E. Placzankis
Date/Pages: September 2004; 36 pages
Abstract: Over the last few decades, it has been determined that chemical treatments containing hexavalent chromium (Cr+6) are risks to both human health and the environment. One of the mainstays in corrosion prevention of aluminum alloys has been the use of chromate conversion coatings to promote adhesion and inhibit corrosion. Because of the push to reduce the use of Cr+6, many nonchromate treatments have been evaluated over the years. This report compares the relative performance of six nonchromate pretreatments with grit-blasted and chromated control samples in outdoor exposure at Cape Canaveral, FL. Recently obtained outdoor exposure data have been analyzed to determine the effectiveness of the pretreatments, indicating a different failure mode than typically seen in accelerated corrosion chambers. Corrosion attack at the edges is prevalent in outdoor exposure, while attack at scribe is uncommon. The substrate of most concern, aluminum 2519, seemed to be less of a factor than originally anticipated when no pretreatment was used. All samples have been monitored throughout the test using electrochemical impedance spectroscopy. Adhesion tests were performed upon completion of outdoor exposure. The data is compared with earlier accelerated corrosion data performed on matching samples.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2004