A new surface modification process of steel by pulse electrolysis with asymmetric alternating potential

A new surface modification process by pulse electrolysis with asymmetric alternating potential is introduced. In the process proposed, metal substrates dissolved when anodic potential was applied, and the metal ion dissolved from substrates codeposited with other metal ions existing in solution when cathodic potential was applied. By repeating this process, an alloy surface can be obtained from a solution containing a single metal salt, which can make it easier to dispose of the waste solution. As a plating bath, an aqueous solution containing 0.2 kmol m−3 Cr2(SO4)3–1.0 kmol m−3 KCl–1.0 kmol m−3 NH4Cl–0.1 kmol m−3 NH4Br–0.65 kmol m−3 H3BO3–1.0 kmol m−3 HCOOK was used. A steel rod was used as the working electrode. Smooth and lustrous deposits were obtained at anodic potentials lower than 0.2 V vs. standard hydrogen electrode (SHE) and at a cathodic potential of −1.1 V vs. SHE. In particular, smooth deposits without microcracks, which are scarcely observed on chromium plating surfaces, were obtained at a anodic potential of 0.1 V vs. SHE. The elemental analysis of the cross section indicated that a Cr–Fe alloy layer formed on the surface and the chromium content gradually decreased in the direction of the substrate.