The electrochemical behaviour of the bright chromium deposits plated with direct- and pulse-current in 1 M H2SO4

The electrochemical behaviour of bright Cr-deposits was studied in 1 M H2SO4 at 27 °C. The bright Cr-deposits were electroplated by using direct- or pulse-current (DC or PC) at 50 °C in a sulfate-catalyzed chromic acid bath with plating current densities of 30, 40, 50 and 60 A/dm2 respectively. The results show that the surface-crack density of bright Cr-deposits plated with either DC or PC decreased with increasing the plating current density, whereas the passive current densities in their anodic polarization curves increased when plating current densities increased. From the results of electrochemical tests, it was found that passive and active dissolution rates of the Cr-deposits were not affected by the amount of the surface cracks developed on the Cr-deposit. Corrosion resistance of the Cr-deposit plated with PC was better than that with DC. The critical current density in the anodic polarization curve of the former is approximately one order less than that of the latter. The Cr-deposit plated with PC can be passivated more easily than that with DC. The rate of active dissolution of Cr deposits is much higher than that of passive dissolution. The aforementioned results can be recognized with AC impedance test polarized in passive and open-circuit potentials.