Effect of Phosphate Conversion Coating Containing Cobalt Ion on the Corrosion Resistance of 6061 Aluminum Alloy

摘要

Corrosion properties and phase analysis of zinc phosphate conversion coating (ZPCC) formed on the T6-6061 aluminum alloys, after immersion in phosphating bath containing various amounts of Co+2 (0, 5, 9, 13 g/L), was investigated by the mean of scanning electron microscope (SEM), electrochemical spectroscopy impedance (EIS) and potentiodynamic polarization technics (Toefl plots). Results showed that with increase in cobalt ion concentration to 9 g/L, crystals size reduced and pores on the surface decreased to lowest amount. So that impedance module of sample which is containing 9 g/L of cobalt ion, is almost 4 and 2 times greater than the pure sample and that which is containing 5 g/L of cobalt ions, respectively. Moreover, results of potentiodynamic polarization showed that incrimination of cobalt ion dosage lead to both decrease corrosion current density and shifts potential to positive amounts.