Preparation Ce(III) conversion coatings on electrodeposited Zn-Ni alloy and comparison of their corrosion performance and morphology with Cr(VI) conversion coatings

摘要

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.