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Perhaps you can have a Plating shop treat the aluminum part(s) with an Aluminum Conversion Coating solution followed by priming and painting with coatings specified for marine applications. Why the consideration of a Conversion Coating? Chemical conversion coating of aluminum prior to painting has been a standard practice in the Marine and Architectural industries for decades. Hexavalent chromium films provide corrosion protection by forming an impervious layer that acts as a barrier, short-circuiting the flow of electrons from cathodic to anodic sites therefore providing electrochemical protection. [Some platers offer a chrome free substitute due environmental issues.] Anything short of a chemical conversion coating will have impaired performance. If the above is impractical, use a vinyl wash primer prior to applying the zinc chromate primer. Aluminum requires de-oxidation prior to application of paint. It’s reactive characteristics if unchecked will result in adhesion failure and blistering. Liquid aluminum brightener solutions sold in automotive paint stores containing ammonium bi-fluoride will remove oxides of aluminum and slightly etch the surface. FOLLOW ALL SAFETY PRECAUTIONS WHEN WORKING WITH ANY CHEMICAL PRODUCT Pre-clean with a non-silicated alkaline cleaner designed for aluminum parts, rinse with warm water, then treat with the de-oxidizing solution per the manufacture’s recommendations. Prime immediately after drying with a two component Zinc Chromate Vinyl Wash primer to obtain a film thickness of 0.2 mils dry. The catalyst portion of the wash primer contains phosphoric acid thereby enhancing corrosion resistance and adhesion of the aluminum components. Consult your paint supplier for a compatible epoxy primer and topcoat to follow application of the wash primer. Good Luck!
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