The Corrosion Resistance of Nickel-Chromium and Copper- Nickel-Chromium Coatings on Mild Steel Substrates

Summary

Atmospheric corrosion tests have been carried out in Birmingham over a period of up to four years on mild steel panels electroplated with various nickel-chromium and copper-nickel-chromium coating systems. The performance of the following systems was investigated: (1) single layer bright nickel with microcracked and microporous chromium topcoats both with and without copper undercoats; (2) double layer nickel with microcracked and microporous chromium topcoats both with and without copper undercoats; (3) double layer nickel with conventional chromium both with and without copper undercoats. Panels with various thicknesses of single layer bright nickel and double layer nickel were included in the trials and two thicknesses of copper undercoat were investigated. The results show that the substitution of a copper undercoat for part of the nickel coating thickness does not have a beneficial effect upon the corrosion resistance of the coating system and may, particularly under thinner nickel coatings, have a detrimental effect. Improved corrosion resistance can be achieved by using a thick copper undercoat in addition to a nickel coating of conventional thickness (30 μm). In general, however, the results indicate that much better corrosion resistance can be achieved by using a conventional thickness of double layer nickel coating than by using a combination of copper plus bright nickel.