Effect of electroplating current density on surface quality and corrosion properties of Cr(III)-Ni coating

Chromium (VI) and its alloys used to be widely utilized in industries, because of their great corrosion and wear properties. However, due to their intense toxicities, their uses are currently obsolete in many countries. Nevertheless, it has been shown recently that the best substitute for Cr (IV) is Cr (III), which is not toxic and has similar properties, particularly when it is used as the main constituent or as an alloying element in coatings. In this paper corrosion properties of Cr-Ni coatings applied on St37 steel substrate, obtained from Cr (III) and Ni (II) contained bath, has been investigated. The electroplated coatings have been optimized using their physical appearance such as their surface morphology and uniformity in their thicknesses, etc. They were then subjected to potentiodynamic polarization and EIS (Electrochemical Impedance Spectroscopy) tests in 3.5% NaCl water solutions in order to evaluate their corrosion behavior. Chemical analyses of the coatings have been carried out using EDS (Energy Dispersive Spectroscopy) methods. SEM (Scanning Electron Microscopy) revealed that the predominant surface morphology had a cracked nodular structure while the nodules and cracks grow as electroplating current densities increased.