Electrochemically detecting defects in an Air Force topcoat/Mg-rich primer system with embedded electrodes

Cathodic protection of aluminum aircraft structures by Mg-rich primers has been demonstrated. The primers are a feasible alternate for the environmentally unfriendly chromate primers that currently mitigate corrosion on aircraft by passivating the AA 2023-T3 structure. The mechanism of protection is similar to that of Zn-rich primers for steel substrates, where a mixed potential drives the consumption of the metal-particulate while promoting cathodic reactions on the less active substrate. The traditional method for accessing the cathodic protection provided by primers is by monitoring the open circuit potential, but this requires a standard reference electrode with the coating being under immersion. Apart from being inappropriate for field application, this method only addresses the local conditions of the coating that is under immersion. Electrochemical impedance spectroscopy and electrochemical noise method experiments were conducted to access the performance of a Mg-rich primer beneath a standard Air Force topcoat under exposure to B117 conditions. Embedded electrodes located between the primer and topcoat were used to acquire electrochemical data. Analysis of results is presented that demonstrate the feasibility of electrochemically detecting the presence of defects scribed into the coating remote from the electrodes.