Corrosion Resistance of Passivation Films Prepared on Electroplated Nickel Coating from Chromium-Free Water-Borne Passivation Solutions

Chromium-free water-borne passivation solutions containing silane coupling agent (KH-550) or organic-inorganic corrosion inhibitors were used to passivate electroplated Ni coating so as to improve its corrosion resistance. The hydrolysis process and stability of the two kinds of passivation solutions were investigated by means of infrared spectrometry. The morphologies of the two kinds of passivation films were observed with a scanning electron microscope, and their corrosion resistances were evaluated based on measurement of Tafel curves and electrochemical impedance spectra. Results show that the passivation solution containing KH-550 is unstable, since the silane coupling agent is liable to hydrolyze forming silanol which can be crosslinked to form polymerized passivation film. Treatment with the two kinds of passivation solutions contribute to significantly improve the corrosion resistance of electroplated Ni coating, but the uniformity of the two kinds of passivation films needs to be improved.