Effect of Cerium Chloride on the Corrosion Resistance and Adhesion of Chromate Conversion Coatings

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The corrosion resistance of the CCC formed on AA6061 in a chromate conversion solution composed mainly of potassium dichromate, chromic anhydride and sodium fluoride is significantly improved by addition, compared with that of the CCC formed in chromate conversion solution without cerium chloride.

The corrosion resistance, adhesion and morphology of the chromate conversion coating formed on AA6061 in a chromate conversion solution containing mainly potassium dichromate, chromic anhydride and sodium fluoride, using cerium chloride 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 cerium chloride (from 20 to 40 mg/L), whereas the excessive cerium chloride (60 mg/L) deteriorates these properties of the chromate conversion coatings. 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 chromate conversion coatings.

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