Novel anti-corrosion silicon dioxide coating prepared by sol–gel method for AZ91D magnesium alloy

Silicon dioxide sols which can be directly applied on the surface of AZ91D magnesium alloy to improve its corrosion resistance were prepared by two-step process. In this study, tetraethyl orthosilicate (TEOS) and triethoxyvinylsilane (VTEO) were employed as the precursors to prepare SiO2 (TV) sol, as a comparison, the other SiO2 (T) sol prepared by only tetraethyl orthosilicate (TEOS) as precursor was also investigated. Fourier transform infrared (FT-IR) spectrum was performed to analyze the structure differences between the SiO2 (TV) sol and SiO2 (T) sol. The surface morphology of the silicon dioxide coatings was characterized by scanning electron microscope (SEM). The results show that more uniform and denser coatings can be obtained from SiO2 (TV) sol. The corrosion resistance of the AZ91D magnesium alloy coated by silicon dioxide coatings was examined by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl aqueous solution. The results indicate that the corrosion resistance of the AZ91D substrate is greatly improved by the SiO2 (TV) sol coatings.