Effect of Lamellar Montmorillonite on Corrosion Protection of Sol-Gel Coating

In order to improve the brittleness and poor film-forming property of the inorganic coating, a montmorillonite sol-gel coating was prepared on the surface of AA2024 aluminum alloy by sol-gel method with tetraethyl orthosilicate as raw material and lamellar montmorillonite as filler. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the micro-morphology and polymerization principle of the coating. The electrochemical behavior of the coating in 3.5% NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy test, and compared with pure silica sol coating and substrate. The results showed that the lowest thickness of montmorillonite nanosheets was about 10 nm and the diameter was about 500 nm. Montmorillonite was evenly distributed in the coating. In the process of sol polymerization, montmorillonite guided the ordered polymerization of sol particles in the sol, which improved the density of the coating and reduced the defects of the coating during curing. The corrosion current density of montmorillonite sol-gel coating was 1.04×10^-8 A·cm^-2, about one order of magnitude lower than that of pure silica sol coating which was 1.22×10^-7 A·cm^-2. The resistance of montmorillonite sol-gel coating was higher than that of pure silica sol coating, and the R_ct of montmorillonite sol-gel coating was always much higher than that of pure silica sol coating, which indicated that montmorillonite sol-gel coating had longer protective effect.