A Mechanism of Improved Paint Adhesion by Ni Surface Conditioning Prior to Dry-in-place Chromate Treatment

In this study, we investigated a mechanism for improving paint adhesion by using Ni surface conditioning prior to dry-in-place chromate treatment, which is usually applied to hot dip Zn-coated steel sheets as a paint base. The results showed that the scattered deposits of Ni on the Zn surface formed micro cells with the Zn as the anode and the Ni as the cathode. Through these micro cells, insoluble chromate film (Cr(III)) deposited on the Ni through an electrochemical reaction of reducing the Cr(VI) in the dry-in place chromate solution. This mechanism of generating chromate film should contribute greatly to improved paint adhesion.