Absorption of Water and Corrosion Performance of a Clear and Pigmented Epoxy Coating on Al-2024 Alloy

Abstract

The corrosion performance of Al-2024 substrates coated with an epoxy clear coating and a pigmented epoxy coating was investigated. The absorption of water in the pigmented coating was high compared to the clear coating. The clear coating provided a good barrier which is stable beyond 120 days of immersion in a 0.5 M NaCl solution. The shape of the Nyquist plot of the pigmented coating changed with immersion time and reveals the existence of physico-chemical processes in the coating and/or at the interface. Its impedance magnitude at low frequencies remained very high (~ 109 Ω.cm2) after 72 days of immersion in sodium chloride solution. Both coatings exhibited good dry adhesion on Al-2024. The wet adhesion of the clear coating was poor while the stress (~ 9 MPa) required in a pull off adhesion test of the wet pigmented coating remained high.