Caused by a number of beneficial properties inherently from the zinc-nickel material, this electrodeposited alloy is used more and more for cathodically protecting layers on ferrous components like cast iron brake calipers. Direct plating from acidic solutions is the state-of-the-art solution for zinc-nickel surface finishing of these components. To contribute to the continuous improvement of the final component and reduce the finishing cost, areas for improvement have been scrutinized in a current finishing system. Areas for improvement have been identified in the uniformity of the nickel distribution within different current densities and in the handling and economy of the metallic zinc anodes used for zinc metal replenishment.
While today’s acidic zinc-nickel electrolytes suit and usually exceed the requirements for an alloy containing 10-15% nickel, nickel incorporation may drop just below 12% incorporation rate in areas which are plated at high current densities. Formation of white corrosion products is observed in those areas earlier than in areas bearing higher (>12%) nickel. Development on the zinc-nickel plating electrolyte’s additive system has resulted in a significantly more uniform plated deposit with improved resistance against white corrosion.
Previous disadvantages in the plating system including rising metal concentrations, anode passivation and insufficient zinc metal utilization will be overcome using the new membrane anode system. This separates the zinc metal anode from the plating bath. The electrolyte can then be operated at constant metal concentrations, constant anode voltages, with no need to remove anodes in idle periods, without any anode reactivation and significantly better anode metal utilization.
These developments provide important contributions for improved operating efficiencies through higher productivity and improved material economy. The significant effect of these developments on higher and more consistent quality of the plated layers finally also contributes to the overall reliability of cast iron brake systems.