Passivation of galvanized surfaces to improve their corrosion resistance

Abstract

A systematic study gh,as been performed to study the effect of concentration of Cr6+, temperature of the bath and the temperature of galvanized products at the time of passivation, tolerance of the bath contamination and synergistic effects of some anions and cations with Cr6+ and Cr3+, on the corrosion resistance performance of passivated galvanized surface. It is observed that the coating resistance increases with the concentration of the chromic acid (CA) The maximum salt spray resistance (about 100 hours) is observed at >=2% of CA. However, at this concentration, an objectionable yellow colouration appears at surface. A rise in temperature of the bath results in an improvement of the resistance to white rusting. However, above 80 degrees C, the performance is deteriorated. The temperature of galvanized surface has a deteriorating effect on the performance of the coating. Effect of some possible contaminants such as Na+, Ni2+, Cu2+, SO42+, etc. have also been investigated. Electrochemical studies, surface reflectance, surface studies (SEM), EDAX etc have been performed to study its impact on the corrosion resistance of the coating.