Substrates like brass, copper, steel, and zinc are generally plated with copper, and nickel Nickel under-layer provides a diffusion barrier. Depending on the application, coatings of Pd, Pd-Ni, Pd-Co, Au-Co, Sn, and Sn-Pb are applied on the surfaces as a final finish. This investigation assessed the corrosion behavior of some of these finishes in neutral sodium chloride and other selected electrolytes. With the aid of Linear Polarization and Tafel plots, corrosion rates in these mediums were estimated. Potentiodynamic polarization curves predict corrosion behavior under extreme oxidizing conditions. Corrosion characteristics and corrosion products were identified by Scanning Electron Microscopy (SEM), and by X-ray Diffraction methods. The corrosion products formed were compared with those formed under exposure to salt spray and mixed flowing gas. Probable mechanisms were postulated based on corrosion products. Electrochemical techniques are shown to provide a quick predictor of the behavior of electrofinishes in a corrosive environment and may be employed in assessing the quality of a given coating without undergoing long and laborious environmental testing.
展开▼
