Electrochemical Noise Monitoring of the Cathodic Protection of Mg-Rich Primers Available to Purchase

Mg-rich primers provide cathodic protection of aluminum substrates similar to that provided by Zn-rich primers for steel substrates. This protection is due to the mixed potential that develops between the more active Mg particles in the binder and the aluminum substrate. Monitoring the open-circuit potential provides a measure of the cathodic protection of the primer with values changing from a mixed potential value of –1.2 V vs. saturated calomel electrode (SCE) to values consistent with the bare aluminum substrate. The application of the electrochemical noise method is presented for monitoring the performance of a Mg-rich primer beneath a topcoat. Embedded electrodes located between the topcoat and primer were used to perform measurements in a reverse configuration for electrodes on separate panels and electrodes on the same panel under immersion. The open-circuit potential was measured to track the cathodic protection behavior of the Mg-rich primer. Analysis of the measured current and potential noises and the calculated noise resistance, localized index, and associated parameters is presented. The influence of a scribe introduced to the panels on the noise measurement is demonstrated. The analysis was used to address the feasibility of noise measurement for in situ monitoring of the cathodic protection provided by the Mg-rich primer.