Pulse-Reverse Electrodeposition of Thin Au Coatings on Ni-Coated Brass: Effects of Pulse Parameters on Microstructure and Corrosion Behavior

Pulse-reverse electrodeposition was investigated as a route to reduce Au consumption while maintaining coating continuity and corrosion performance in thin Ni/Au finishes. A pulse-plated Ni barrier layer with an average thickness of approximately 4.45 μm was first prepared on brass, followed by Au deposition from a potassium dicyanoaurate-based electrolyte containing a cobalt additive. Pulse frequency, duty cycle, forward current density, and reverse current density were evaluated with respect to Au thickness, surface morphology, corrosion potential, roughness, and electrochemical impedance. The processing window was selected hierarchically by requiring an Au thickness of 0.3–0.6 μm, a relatively noble corrosion potential, a compact surface with few visible defects, low roughness, and a consistent impedance response; charge-transfer resistance was not treated as the sole criterion. Within the present bath, substrate, electrode geometry, and power-supply configuration, 800 Hz, 22% duty cycle, 0.11 A·dm−2 forward current density, and −0.004 A·dm−2 reverse current density provided the most balanced overall response.