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Military aircraft employ coating systems formulated to provide good long-term exterior durability performance, including resistance to corrosion and topcoat degradation. Other desirable properties include chemical resistance, flexibility, adhesion and cleanability. These coating systems are traditionally formulated with volatile organic solvents and use primers and pretreatments which contain hexavalent chromium compounds.
With the increasing regulatory pressures around the world over the last three decades, there have been greater efforts by raw material suppliers and paint formulators to move to coating systems which are less toxic and more environmentally benign. These coating systems include pretreatments and primers which are free of hexavalent chromium and polyurethane topcoats which are water-based. For aircraft applications, the primary challenge is to achieve in-service performance that is at least equal to the traditional systems.
In this presentation, we compare the anticorrosive performance of two commercially-available chromate-free priming systems, available from two different paint companies, with a fully chromated system currently employed on Australian defence aircraft. We then examine the results of corrosion testing with each of these priming systems when the solvent-based topcoat is substituted by a new experimental water-based polyurethane topcoat formulated at our Defence Science and Technology laboratories.