Development and characterization of sol‐gel composite coatings on aluminum alloys for corrosion protection

For several years, Cr^IV compounds were used as effective and inexpensive corrosion inhibitors. Studies showed that these materials were toxic and carcinogenic. This has led to extensive research to develop alternative inhibitors. Organo‐silicate hybrid coatings appeared as an effective technique for forming protective layers on different metal alloys. A silane film was obtained by dip coating of the sample in sol solution prepared from the hydrolysis of 3‐glycidoxypropyltrimethoxysilane (GPTM), tetraethylorthosilicate (TEOS) with acid as catalyst and water as solvent instead of VOC (volatile organic compound). The sol solution was aged at ambient temperature to to enhance the effectiveness of the solution for the hydrolysis process. The sample was cured at 150 °C to ensure cross‐linking of the film. The experiments have shown that heat treatment leads to increased density and corrosion resistance of the films. Organic and inorganic inhibitors were added in different concentrations to improve the protection and self‐healing properties of the coating even after long‐time immersion in corrosive solution. The protection performance of the film was evaluated by electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl solution (pH value 7). The surface morphologies of the treated samples were investigated using SEM.