Characterization and corrosion protection of nano-titanium dioxide doped BTSE-GPTMS sol–gel coating on cast Al–Si alloy

A hybrid organic–inorganic sol–gel coating was prepared on the surface of cast aluminum–silicon (Al–Si) alloy via dip coating method to improve the anticorrosion ability. In the present work, bis(triethoxysilyl) ethane (BTSE) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were employed as the precursors to prepare hybrid sol–gel (BG) coating. Nano titanium dioxide (nano-TiO 2 ) was introduced to improve the corrosion resistance of the coating. The microstructures of the BG/nano-TiO 2 (BG-T) coating was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and Fourier-transform infrared (FT-IR) spectroscopy. The results showed that there was a chemical reaction between nano-TiO 2 and BG coating and a complete defect-free coating formed on the surface of Al–Si alloy. Moreover, there were a few only minor cracks appeared on the surface of BG-T coating after 15 days immersion in 3.5 wt.% NaCl solution. The corrosion resistant performances of the coatings were evaluated by the electrochemical tests. The results showed that the nano-TiO 2 particles elevated the corrosion potential and depressed the corrosion current, thereby improved the corrosion resistance. The long-term immersion tests of BG and BG-T coating further showed that the BG-T coating possesses an excellent long-term stability for corrosion protection.