Real Time Monitoring of An Air Force Topcoat/Mg-Rich Primer System in B117 Exposure by Embedded Electrodes

The protection of metallic structures by organic coatings has traditionally been as a barrier, reducing the transport of water, ions, and oxygen from the environment to the substrate. Organic coatings are also used as repositories for corrosion inhibitors that passivate the substrate, and metallic particulates, that provide cathodic protection. Of the latter, Zn-rich primers are universally used for the protection of steel substrates with the zinc particles being sacrificially consumed while providing a mixed potential that mitigates the corrosion of the steel. Recently, Mg-rich primers have been developed for the protection of aluminum substrates, with a similar protection mechanism as that of Zn-rich primers. Real time monitoring of a Mg-rich primer on an AA 2024-T3 substrate, beneath a standard Air Force topcoat, was conducted where coatings were subjected to B117 exposure. Monitoring was accomplished using embedded electrodes placed between the primer and topcoat. Electrochemical impedance spectroscopy and electrochemical noise method experiments were conducted to access the performance of the primer in the aggressive salt spray environment. In-situ results were compared with results of ex-situ electrochemical experiments. Results associated with configurations that include and not include the substrate are presented to demonstrate the applicability of the embedded electrodes for real-time monitoring.