Evaluation of corrosion resistance of organic coatings on aluminium alloy AA2024 for aerospace applications

The study pertains to the evaluation of corrosion resistance offered by organic coatings applied on AA2024 alloy. High copper content present in this alloy reduces corrosion resistance. In the present study two layers of organic coatings have been given on normal anodized surface. Zinc rich self etching primer, epoxy based alkyd primer and strontium chromate based primer are used as under coats. Epoxy based alkyd finish coat, and polyurethane based finish coat have been used as topcoats. Electrochemical impedance spectroscopy has been used to evaluate the corrosion resistance of the coated surfaces. The combination of strontium chromate based primer and epoxy based alkyd topcoat is found to be having the lowest rate of corrosion and zinc rich self etch primer with polyurethane based topcoat is having the highest rate. The lower rate of corrosion of the coated surface with strontium chromate based primer may be attributed to the formation of zinc phosphosilicate conversion layer.