Effect of substrate cleaning solution pH on the corrosion performance of silane-coated cold-rolled steel

In this study cold-rolled steel (CRS) panels were cleaned in solutions of different pH values. The influence of the cleaning solution pH on the CRS surface chemistry was characterized and the corrosion performance of CRS panels was evaluated. Scanning electron microscopy (SEM) examination revealed differences in the surface morphologies of the samples and the X-ray photoelectron spectroscopy (XPS) results indicated that the CRS surface was very sensitive to the pH of the cleaning solution. Surface energy calculations revealed that minimum polar and basic components were achieved after cleaning the substrates near the isoelectric point (pH 9.5) of CRS which promoted strong silane adsorption onto the steel. FT-IR results indicated that there were variations in the length of the siloxane molecules formed after cleaning CRS in the different pH conditions. DC polarization and EIS results showed optimum anti-corrosion performance and strong bonding between the substrate and the primer coating for CRS cleaned at pH 9.5. The underlying mechanism for this is discussed.