Effect of Hydrothermal Sealing on Wettability and Electrochemical Behavior of TMPSi Treated Anodized Aluminum

Sol-gel derived films can be deposited on metals to improve their corrosion resistance. Anodization pretreatment process is commonly used to enhance the corrosion protection of the aluminum alloys. In this work, the substrate was first anodized and sealed hydrothermally, then dipped into the trimethoxypropylsilane (TMPSi) sol as a precursor. The films made of TMPSi sol were examined for their corrosion inhibition properties and hydrophobicity. The surface characterization of the samples was evaluated with X-ray diffraction, field emission scanning electron microscope (FESEM), scanning electron microscopy, surface roughness measurement and static contact angle measurements. The effect of hydrothermal sealing before silane treatment on the hydrophobicity of surface was studied by static contact angle measurements. In order to evaluate the corrosion resistance of the samples, open circuit potential measurements and electrochemical impedance spectroscopy (EIS) were used. FESEM results showed that hydrothermal sealing increases the homogeneity of the surface morphology and thus corrosion resistance increases compared to the silane treated anodized surface. Surface roughness of that hydrothermal sealing sample before silane treatment increased surface roughness and hydrophobicity. Hydrothermal sealing before silane treatment tends to result in a more compact surface that prevents the contact of corrosive materials with porous structure. The electrochemical behavior of the samples was evaluated by EIS using 3.5% NaCl solution. According to the EIS results, samples, which were hydrothermally sealed in water and then coated by a TMPSi sol, showed highest corrosion resistance.