Environmentally friendly, rare earth-based inhibitors in conversion coatings and paint for the corrosion protection of aluminum alloys

Aluminum alloys such as 7075-T6 and 2024-T3 are commonly used in aircraft because of their strength to weight ratio. While the mechanical properties of these alloys are very good, they are particularly susceptible to corrosion. Coatings are commonly used to protect these aluminum alloys to corrosive attack. One type of coating, called a conversion coating, is a thin, inorganic film normally deposited directly on the bare metal surface. The other types of coatings, generically referred to as paints, include primers which are applied over a conversion coating. A primer consists of a binder, usually organic, and pigments, which are mostly inorganic particles dispersed in the binder. Part of the primer\u27s pigment content includes compounds that can provide corrosion protection. For the corrosion protection of aluminum, the most commonly used conversion coating and primer pigments contain Cr(VI) compounds. While highly effective, Cr(Vl) compounds are becoming undesirable due to their increasingly recognized toxicity and the greatly increased handling costs due to the health threat that they pose. For these reasons, much research has been conducted in recent years to find alternatives to chromates. The central purpose of the thesis work presented herein was to develop non-chromated conversion coatings and primers. To support this effort, the fundamental chemistry of cerium, a potential chromium replacement, was studied. Also undertaken was the development of a methodology for using the scanning vibrating electrode technique (SVET) to characterize pretreatments and coatings. As a consequence of this study, five patent applications were filed as well as numerous papers and reports --Abstract, page iv