Nano-ceramic hexafluorozirconic acid based conversion thin film: Surface characterization and electrochemical study

An eco-friendly H2ZrF6-based conversion coating reinforced by nanoceramic metal oxide particles was used as a protective layer for cold-rolled steel (CRS) substrates. Initially, the pH and temperature of the solution were optimized and then the effects of immersion time as the most effective process parameter on anti-corrosion performance and morphological properties were studied. On this basis, comprehensive analyses such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrum (EDS) and atomic force microscopy (AFM) were used. Results showed the best anti-corrosion performance with the highest polarization resistance occurred when the pH and temperature of solution and immersion time were considered 4, 25 °C and 90 s, respectively. Uniform distribution of Zr along the surface of all treated samples was observed. FE-SEM images revealed that for the samples treated longer than 120 s, cracked morphology was evident.