: The concept of superprimers, i.e., primers for metals with the conversion coating built in, has proven to be feasible. Such primers can be applied on any bare metal, provided it is reasonably clean. These primers are based on water-dispersed organic resins and organofunctional silanes, which assure good adhesion both to the substrate and the overcoat. In this paper we will discuss an epoxy-novolac based system for AA20242-T3, but we will also present an overview of other coatings. The corrosion protection performance of these coatings has been evaluated using electrochemical methods and performance tests. All of the developed coatings survive 2000 hrs in ASTM B117 salt spray test. The systems have also been extensively characterized. The characterization methods have provided information on the formation of the coatings and the mechanism by which the coatings protect the metal substrates.

The concept of superprimers, i.e., primers for metals with the conversion coating built in, has proven to be feasible. Such primers do not require a chromate (or other) conversion treatment of the metal and can be applied on any bare metal. The VOC content in the primer is kept low by using water-dispersed organic resins. Because of the high concentration of organofunctional silanes contained in the superprimer, its adhesion, both to the substrate and to overcoats, is excellent. The corrosion resistance of the primer can further be improved by adding corrosion-inhibiting pigments such as micronized zinc phosphate into the formulation. The corrosion protection performance of these coatings has been evaluated using performance tests and electrochemical methods. The primers have also been characterized with a variety of surface analytical methods. It will be shown that 2000h of salt spray resistance has been obtained with the primers both on AA2024-T3 and HDG steel. This study will mainly present an overview of the chromate-free primers studied in our laboratory and will attempt to explain the mechanism by which one of the coatings, the epoxy–acrylate-based primer deposited onto aluminum, protects the metal from corrosion.