Electropolymerised polyaniline films as effective replacement of carcinogenic chromate treatments for corrosion protection of aluminium alloys

Owing to the carcinogenic nature of chromate coatings, alternate coatings with intrinsically conducting polymers such as polyaniline (PANI) and polypyrrole (Ppy) have been developed. Hence a study has been made on the effect of electropolymerised PANI films on corrosion protection performance of epoxy coating on AA 2024 and AA 7075 aluminium alloys. Polyaniline was electropolymerised on both the alloys by galvanostatic method. A post treatment of cecrium was given to seal the pinholes of PANI film. Epoxy coating was applied over these films and their corrosion protection performance was found out by EIS studies in 3% NaCl and salt spray test. EIS studies have shown that the coating resistance (Rc) of PANI with the epoxy coated aluminium alloys has remained above 106 Ω cm2 whereas the alloys coated with epoxy alone have shown the Rc values less than 104 Ω cm2. Besides, the salt spray tests showed a better corrosion protection of PANI with epoxy coated aluminium alloys.