Abstract
Improved protective schemes are needed to provide corrosion resistant magnesium aircraft components. The U.S. Army has experienced significant corrosion problems with magnesium alloys, and these problems must be addressed before magnesium's inherent weight advantages can be fully utilized. Recently we had reported beneficial results achieved by interposing a baked epoxy resin sealer between the conversion coating and primer application. This paper assesses several advanced alternative treatments for protecting magnesium such as those employing an anodizing or chromate conversion pretreatment with an epoxy primer and a polyurethane topcoat. Test panels of magnesium alloys ZE41A-T5 and WE43-T6 were pretreated with either a chromate or non-chromate conversion coating. These were then coated with primer/topcoat combinations consisting of commercially available coatings, such as a high temperature polymer, a VOC compliant epoxy and polyurethane, and a non-chromate silicone oxide with an electrodeposited epoxy. Electrochemical impedance spectroscopy and salt fog tests were used to evaluate these specimens. Results indicate that there was good correlation between the salt fog and EIS, with several of the advanced protective schemes appearing to perform better than the currently used system.
