Abstract
Zn–Ni alloy coatings were electroplated on steel after an appropriate pretreatment from tartrate cyanide free alkaline bath. Zn–Ni coatings were obtained with a derivative of imidazol as a brightener agent to form fine grain particles. The Zn–Ni alloy coatings were analysed for phase structure by X-ray diffraction. A cerium based chemical conversion process was developed as an alternative to the chromate process. The cerium conversion coatings improved the corrosion performance. The corrosion behaviour of bare and treated Zn–Ni alloy coatings on steel was evaluated during exposure to 0·5 N NaCl using Tafel polarisation and electrochemical impedance spectroscopy measurements. The morphology and corrosion performance of conversion coatings generated on Zn–Ni alloy coatings in Cr(VI) and Ce(III) treatments were studied and compared. This process may be useful as primer for paints and polymer coatings on steel.
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