Cast-iron is a well suited material for manufacturing automotive brake components due to excellent mechanical and thermic properties. The application of a well chosen cathodically protecting coating adds durable appearance and preservation of the functional properties of the components.
The selection of the right coating is driven by multiple factors of which economic considerations will always rank within the highest priorities next to protection performance and the appearance of the coating. Aiming for the highest possible performance in cathodic corrosion protection coatings leads directly to zinc-nickel coatings.
Zinc-nickel coatings are already state-of-the-art in the finishing of mild steel and carburized steel materials in the automotive industry, mostly being plated from alkaline plating solutions.
The application of alkaline solutions to cast iron material is not feasible under industrial conditions at an acceptable reject rate due the electrochemical properties of the cast iron in these electrolytes.
Therefore, as a workaround a two layer system with a first zinc layer from acidic electrolytes to cover the cast iron followed by zinc-nickel from an alkaline electrolyte was the often chosen alternative for this application. Those two layer systems are more expensive and bear multiple risks which hamper the reproducibility of the achieved corrosion protection performance.
Alternatively, ammonium containing acidic electrolytes are applied directly to the cast iron material. Those electrolytes could not always be applied due to environmental and technical considerations.
The newest generation of Atotech's acidic zinc-nickel electrolytes provides consistent deposition of zinc-nickel with homogenous nickel incorporation directly to the cast iron material while being free of ammonium and boric acid. With perfectly matched trivalent chromates and reactive inorganic sealers, a state-of-the-art high end system for cathodic corrosion protection and appearance is applied.