Electrochemical Sacrificial Cathodic Prevention Provided by an Al-Co-Ce Metal Coating Coupled to AA2024-T3

Abstract

An Al-Co-Ce alloy system has been developed with two important protection abilities when deployed as a metal coating over AA2024-T3. These alloy coatings can both act as a sacrificial anode and supply soluble ions that could function as inhibitors. In this paper, the electrochemical (or electrolytic) throwing power of such an Al-Co-Ce metallic coating under atmospheric conditions is modeled. The criterion for protection is a galvanic couple potential distribution below the pitting potential of AA2024-T3. The effects of scratch size, pH, chloride concentration, metallic coating composition, and electrochemical kinetics of the materials involved were studied. Substantial sacrificial cathodic prevention of AA2024-T3 scratches could be achieved with Al-Co-Ce alloys with performance superior to conventional Alclad coatings in terms of both extent of polarization and maximum scratch size protected. The behavior of the metallic coating can be tailored and provides the best protection (i.e., largest cathodic polarization of the longest scratch lengths) when it contains a low Co content, is exposed to either high or low pH solutions of low chloride concentration, and the AA2024-T3 scratch exhibits slow cathodic kinetics. The Co content should be minimized, in order to maximize the electrochemical throwing power, but must be sufficient for retention of amorphicity.