Robust corrosion resistance and self-healing characteristics of a novel Ce / Mn conversion coatings on EV31 magnesium alloys

Abstract

Magnesium alloys have been widely employed in the aerospace and aviation applications due to the unique properties. Nevertheless, Mg alloys were sensitive to corrosion attacks. The use of hexavalent chromium has been strictly banned because of severe toxicity and harm, even though it provided useful protective coating. Many efforts have been made to find the alternative process to hexavalent chromium conversion process.In this study, the Ce / Mn conversion coating was developed on EV31 Mg alloy. A thin, homogeneous, and compact conversion coating layers was formed. The electrochemical impedance spectroscopy (EIS), potentiodynamic polarization tests and salt spray test (SST) were used to evaluate the corrosion resistance of the coatings accompanying with a cross-cut scratches. The total impedance of the Ce / Mn conversion coating rose to 2.3 × 103 Ω‧cm2 compared with 3.4 × 102 of the bare EV31. Furthermore, the Ce / Mn conversion coating passed the 168 h of SST with less than 3% corrosion area, and meanwhile the self-healing worked effectively. Both barrier protection and characteristic self-healing effect enhanced corrosion resistance on EV31. Furthermore, a corrosion mechanism for the coating in practice was proposed to discussion.