A novel chromium-free surface pretreatment for aluminum is described herein. The new approach is to prepare aluminum surfaces prior to the application of a polymer topcoat by converting the surface with an inorganic/organic pretreament. These conversion films are about 10-20 nm in thickness and composed of an inorganic inner layer and an outer organic layer. The organic portion of the film is highly functionalized which aids in improving adhesion of organic topcoats. In performance testing, it is equivalent to a commercial chromate conversion coating in extended saltspray and marine coastal exposures. This non-chrome pretreatment is environmentally friendly, contains no toxic metals and the organic portion of the film is biodegradable. Processing is typical of chromating or phosphating operations.
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