Effect of cerium chloride on corrosion resistance and adhesion of chromate conversion coatings

The corrosion resistance, adhesion and morphology of the chromate conversion coating (CCCs) formed on AA6061 in a chromate conversion solution containing mainly potassium dichromate (K2Cr2O7), chromic anhydride (CrO3) and sodium fluoride (NaF), using cerium chloride (CeCl3) as additive, were investigated by using potentiodynamic polarization curves, EIS, adhesion test and SEM. The corrosion resistance and adhesion of the CCCs are improved greatly by adding a small amount of CeCl3 (from 20 to 40 mg/L), whereas the excessive CeCl3 (60 mg/L) deteriorates these properties of the CCCs. The results of polarization curves are in good agreement with those of EIS. SEM photographs show that the precipitation of cerium hydroxide significantly affects the morphologies of CCCs.