Corrosion behavior of a sol-gel ZrO2 pore-sealing film prepared on a micro-arc oxidized aluminum alloy

An ultraviolet photosensitive ZrO2 precursor solution was prepared using acetylacetone as the chelating agent and n-butanol zirconium (Zr(OC4H9)4) as the raw material. Sol-gel-derived ZrO2 pore-sealing films were fabricated on a micro-arc oxidized aluminum alloy (MAO-Al). The coated ZrO2 sol-gel films were treated by either UV irradiation or a heat treatment process. The corrosion properties of the ZrO2/MAO-Al materials in a 3.5 wt % NaCl solution were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray diffraction (XRD) measurements showed that the ZrO2 layer was amorphous. Scanning electron microscopy (SEM) results revealed that cracks could easily form in the ZrO2 films that were heat treated at 100 °C and 300 °C, thus degrading the corrosion resistance of the samples. However, UV irradiation can help to prevent cracking. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that UV light decomposes the organic species in a ZrO2 sol-gel film at low temperatures, facilitating the formation of a Zr-O-Zr network in the film. The anticorrosion ability of a sample with a ZrO2 film irradiated by UV light at 100 °C is enhanced compared with those of samples coated by a ZrO2 layer and heat treated at 100 °C or 300 °C.