Improved performance of Ti-based conversion coating in the presence of Ce/Co ions: Surface characterization, electrochemical and adhesion study

Abstract

Abstract Novel chromium-free conversion coatings based on titanium-cerium (Ti/Ce-CC) and titanium-cobalt (Ti/Co-CC) were prepared to enhance the anti-corrosion resistance and adhesion property of the organic coating applied on Al-2024 substrate. The surface characteristics of the modified titanium conversion coating (Ti-CC) were evaluated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Tungsten microelectrode and contact angle measuring device. The electrochemical behavior of conversion coatings was evaluated by electrochemical impedance spectroscopy (EIS) measurement. Anti-corrosion and adhesion properties of polyurethane coating were evaluated by EIS, salt spray test and pull-off measurement. FE-SEM and AFM results show that by the addition of cerium and cobalt ions, the morphology of Ti-CC was completely changed. Oxide and hydroxide form of the different valence of cerium and cobalt ions were existed on the surface based on XPS spectra. The maximum surface energy is obtained for Ti/Ce-CC. Electrochemical data revealed that the Ti/Ce-CC enhance the anti-corrosion resistance to a significant degree (271.11 × 103 Ω.cm2) compare to the bare sample (3.70 × 103 Ω.cm2). The polyurethane coating applied on Ti/Ce-CC showed minimum delamination, highest anti-corrosion resistance and better adhesion strength in comparison with the Ti/Co-CC, Ti-CC and bare coated samples.