Sealing of cerium oxide coating primers on anodized AA2024-T3 alloy by boiling in Lourier buffers

Abstract

Although their exceptional re-passivation ability, Al-alloys are susceptible to corrosion due to the amphoteric nature of the alumina passivation films. This issue is exacerbated by the disruption of these films by intermetallics on the surfaces of highly doped ones, like AA2024-T3 aircraft alloy. The combination of anodized aluminium oxide (AAO) and cerium conversion coatings (CeCC) shows promise as a coating primer. However, the defective structures of CeO2 and Al2O3 require additional sealing. This research proposes sealing the CeCC/AAO layer by boiling it for 10 minutes in two relatively neutral Lourier buffers, adjusted to pH 7.75, and in a mixture of them. The samples underwent a series of analyses to compare the impact of the sealing procedure on surface topology, properties (e.g., colour and wettability on two samples from each set), and corrosion protective ability. It was assessed after 24 hours of exposure to 3.5 % NaCl model corrosive medium on six samples from each set. The assessments included electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) techniques. The results indicate that the borate buffer improves the corrosion protection of the coating primers more effectively than the phosphate and mixed ones.