Cerium treatments for temporary protection of electroplated steel

The present work aims at evaluating the corrosion performance of a cerium immersion treatment on zinc electroplated. For comparison, zinc coatings pretreated with a commercial chromate treatment were also examined. The corrosion behaviour of pretreated zinc surfaces under immersion in sodium chloride was investigated by potentiodynamic polarization to evaluate the effect of cerium on the oxygen reduction reaction. The influence of immersion time, temperature of cerium solutions, stirring influence, cerium concentrations, cerium salt, pH of the solution and oxidation state of cerium are also investigated. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were used to characterize the sample surfaces after treatments. In order to compare the corrosion performance of cerium pretreated samples, an accelerated test in a humid chamber was carried out. The results indicate that the cerium film formed on the zinc surfaces markedly suppressed the cathodic process. The accelerated corrosion test shows that white rust formation is delayed although the protection given by this treatment is less efficient than with commercial chromate treatments.