Microstructure and Properties of Cerium-based Passivation Film Modified with Stearic Acid on Zn-5%Al Coating

Cerium-based passivation films were deposited on Zn-5%Al coating, followed by stearic acid modification of the films deposited for varying durations to form a superhydrophobic coating. The microstructure of the cerium-based coating was examined using scanning electron microscopy (SEM), and surface roughness was assessed via laser confocal microscopy (LCM). The chemical composition of the coating was analyzed by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Static contact angles were measured using a contact angle goniometer, and corrosion resistance was evaluated through electrochemical impedance spectroscopy (EIS) measurements performed on an electrochemical workstation. The results reveal that with the increasing of deposition time, the Ce content and film thickness on the Zn-5%Al coating increases continuously, accompanied by an increase in film thickness and a progressive enhancement of hydrophilicity. The stearic acid-modified film surface developed a micro-nanoscale rough structure, and the hydrophobicity increased progressively with prolonged passivation time. The modified film formed after 30 minutes of deposition achieved a water contact angle of 164°. The superhydrophobic surface is mainly composed of stearic acid, CeO2/Ce(OH)4, Ce2O3/Ce(OH)3, forming an air barrier that impedes liquid penetration into corrosive media. As the deposition time increases from 5 to 30 minutes, the corrosion resistance shows a progressive enhancement.