Effect of hydrolysis time on the corrosion resistance of sol-gel coated AA2024-T3 anodized in TSA

Abstract

In this study, the corrosion resistance of AA2024-T3 specimens anodized in TSA and subsequently post-treated in a Ce-H2O2 solution and sealed by a hybrid sol–gel coating (3-glycidoxypropyltrimethoxysilane and tetraethoxysilane), with hydrolysis solution aging times of up to 6 months, was investigated by means of electrochemical impedance spectroscopy (EIS). The results demonstrated that, whichever the aging time, the Ce post-treatment enhances the performance of the sol-gel coating; moreover, for both surface conditions, the corrosion protection was maximized for a hydrolysis time of 14 days, even though the corrosion performance of samples protected with the solution aged for 6 months was similar to that aged for 1 day. Correlation of these results with FTIR and viscosity measurements of the aged hydrolysis solution suggest that the protective performance of the coating is heavily influenced by in-solution condensation reactions; excessive condensation leads to the formation of oligomers, resulting in increasingly flawed coatings with specific delamination points as revealed by SEM imaging. The relatively long shelf life of the hydrolysis solution is a good prospect for the industrial use of the proposed treatment.