Corrosion stability of cerium-doped cataphoretic epoxy coatings on AA6060 alloy

Abstract

In this study, corrosion protection efficiency of undoped epoxy and epoxy coating doped with cerium on aluminum alloy AA6060 is evaluated over prolonged exposure to 3wt% NaCl solution by electrochemical impedance spectroscopy (EIS). Different amounts of Ce(NO3)(3) are added into the epoxy suspension used for the cataphoretic deposition. Suspension stability is characterized by zeta potential and particle size values. Water content and thermal stability of the coatings were determined by thermogravimetric analysis. Insufficient corrosion stability, very close to that of undoped epoxy, is revealed for the coating with 1mM Ce. Higher cerium doping contributes to a significant increase in corrosion stability (2-3 orders of magnitude greater charge-transfer resistance). Epoxy coating doped with 5mM Ce displays a pronounced self-healing ability and the best corrosion protection and adhesion, owing to evenly distributed cerium precipitates on the aluminum surface. In the case of 10mM Ce-doped coating, the formation of Ce clusters and higher porosity causes a certain lowering of the protective ability. EIS measurements on epoxy coating with artificial defect confirm these findings.