New Test Methods to Evaluate Corrosion Protection Performance of Non-Chromated Exterior Aircraft Coating Systems

Paints and coatings play an important role in protecting aircraft structure from corrosion. New coating materials are subjected to lengthy testing protocols to assure that they provide the required performance for the intended duration and service environment. Industry-standard methods such as ASTM B117 neutral salt spray and ISO 4623 filiform corrosion have been widely used over many decades for qualifying coating systems for aerospace applications; however, it is well known that results of accelerated laboratory tests do not always accurately predict performance in service environments with respect to both the ranking of materials and the type and severity of corrosion. This lack of robust correlation between laboratory testing and service performance presents a risk for selecting the best material systems for a given application and poses a particular challenge in the ongoing efforts to eliminate toxic hexavalent chromium corrosion inhibitors from aerospace coatings, where the goal is to replace conventional chromated surface treatments and primers with non-hazardous alternatives that have equivalent or better performance over the full service life.

Several new test methods and approaches have been developed to evaluate corrosion protection of non-chromated exterior coating systems on aluminum surfaces, with a focus on improving correlation with in-service performance. Results will be presented for cyclic corrosion, outdoor exposure, and disbonded paint protection testing, with factors studied including coating type and method of surface preparation. The new methods and approaches complement the standard corrosion tests and provide, as a whole, better capability for choosing durable non-chromated exterior coating systems that will provide the required level of corrosion protection for aircraft in all service environments.