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

H Zarei and R Hosseini Rad

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.