Influence of deposition conditions on the protective behavior of tetraethyl orthosilicate sol–gel films on AA5754 aluminum alloy

The aim of this work is to compare the effect of two deposition methods, dip-coating and electrophoretic deposition, on the characteristics of tetraethyl orthosilicate (TEOS) sol–gel films on AA5754 aluminum alloy, especially in what concerns to their resistance against corrosion. The influence of pH bath on the hydrolysis of the system was analyzed. Moreover, the effect of some experimental parameters, such as deposition time and deposition voltage, was also evaluated. The results showed that pre-hydrolysis rate of the orthosilicate bath depends on the solution pH, and that at pH 2 complete hydrolysis of the solution was obtained after only 20 min. Moreover, it was observed that electrodeposited TEOS films provided better corrosion resistance than films obtained by dip-coating. The improved corrosion resistance was ascribed to a higher uniformity and density of the polysiloxane films and to an in situ modification of the aluminum–polysiloxane interface by the cathodic voltage.

► We compare polysiloxane films obtained by dip-coating and electrophoretic deposition.
► Thickness and composition of dip-coated films do not change by modifying deposition time.
► Uniform and dense films are obtained under electrophoretic deposition at low deposition voltages and times.
► SiO2 aggregates and defects form on electrophoretic deposited films when deposition voltage and time increase.
► Electrodeposited films show higher corrosion resistance than those obtained by dip-coating.