Cerium–permanganate conversion coatings for a Zn–Co alloy

The present work aims at investigation of the corrosion resistance of cerium–permanganate conversion coatings (CPCC) electrolessly deposited on a Zn–Co (0.6%) alloy. For comparison, Zn–Co (0.6%) alloy with a commercial chromate treatment was also examined. CPCCs on a Zn–Co (0.6%) alloy have been studied by potentiodynamic polarization and the immersion test. The experimental results of potentiodynamic polarization and the immersion test showed that the corrosion resistance of CPCC on a Zn–Co (0.6%) alloy is close to the corrosion resistance of chromate conversion coating on Zn–Co (0.6%). The microstructure of conversion coatings was analysed by scanning electron microscopy (SEM) and the composition of conversion coatings was analysed by X-ray photoelectron spectroscopy (XPS). It has been found that the cerium–permanganate conversion coating is homogeneous as compared with the chromate coating. XPS has determined that the CPCC contains the following compounds: CeO2(IV), Ce2O3(III) and Mn oxides and hydroxides.