Multifunctional UV Curable Corrosion-Inhibiting Coating Systems

Corrosion resistant ultraviolet (UV) curable coatings containing non-chromate inhibitors and no volatile organic compounds were developed and evaluated for DoD applications. Replacement of corrosion coatings on high strength aluminum alloys used for military aerospace applications was the main focus for the technology developed. The technical effort involved formulation and evaluation of inhibitors in acrylate based polymer systems with different pigments, monomers, oligomers, and additives. Coatings were applied to Al 2024-T3 and Al 7075-T6 substrates with different pretreatments, including chromate conversion coatings, trivalent chrome passivation (TCP), and cerium based conversion coatings, as well as substrates that did not have a pretreatment layer. This approach would replace the current three layer, environmentally unfriendly coating system with a benign, two layer multifunctional UV (MUV) coating system. Application of MUV coatings with Hybricor 204 corrosion inhibitor repeatedly demonstrated the ability to protect scribed, chromate conversion coated Al substrates during ASTM B117 salt spray testing. In some instances MUV coatings on TCP and cerium based conversion coatings were able to pass salt spray testing. It was determined that MUV coatings on 300 nm thick cerium based conversion coatings electrolytically deposited using non-chloride cerium salt solutions were able to match the performance of MUV coatings on chromate conversion coatings during salt spray testing. MUV coating properties such as flexibility and fluid resistance demonstrated the potential to meet aerospace requirements in a number of formulations.