Evaluation of Zn-rich Primers by Cyclic Salt Spray and Immersion Tests

Corrosion protection of steel used in USMC components is currently achieved by abrasive blasting and the application of CARC primer and topcoat, creating a physical barrier between the metal substrate and the environment. This methodology does not appear to provide sufficient corrosion protection, especially if the coating is partially disrupted exposing the base metal. As a result, special interest exists to assess the corrosion protection of steel components by Zn-rich primers under long-term harsh operating conditions. Corrosion performance of commercially available Zn-rich primers with and without CARC primer and topcoat was evaluated by cyclic salt spray and immersion tests. The cyclic salt spray exposure test consisted of humidity exposure, salt spray with a solution containing sodium chloride, calcium chloride, and sodium bicarbonate, and a high temperature drying cycle. After exposure, the coated panels were examined using the ASTM D1654 and ASTM D714. Electrochemical tests were conducted to monitor corrosion rates and to identify the degree of Zn-rich corrosion protection. Preliminary test results revealed a clear distinction in the corrosion performance of the Zn-rich primers tested in both exposure conditions.