Influence of sol-gel process parameters on the protection properties of sol–gel coatings applied on AA2024

• Influence of sol-gel ageing on the corrosion performance of sol-gel coatings has been studied.
• Sol-gel ageing at room temperature creates microdefects in the coating matrix thus decreasing protective effectiveness.
• Cerium nitrate chemically interacts with sol-gel during long term ageing at room temperature.
• Ageing at low temperature improves sol-gel shelf-life and retains protection effectiveness of the sol-gel coatings.

The present work explores effects of shelf-life, temperature and the presence of cerium nitrate additive on the protective performance of sol–gel coatings applied on AA2024. These are important parameters when industrial applicability of coating formulations is considered. The studied sol–gel system is based on a combination of metalorganic precursor titanium(IV) propoxide and hybrid epoxy silane 3-glycidoxypropyltrimethoxysilane. The synthesized sol–gel formulations without or with addition of 0.007 M Ce(NO3)3 were aged during different times at temperatures 25 °C or − 6 °C. FTIR results show that the intensities of the bands associated to SiOSi increase with respect to SiOH groups during the aging process as a result of extended condensation. However, such transformations occur less rapidly at low temperature. The electrochemical impedance spectroscopy measurements clearly show that sol–gel coatings corresponding to the sol–gel aged at low temperature exhibit similar corrosion protective capabilities compared to the coating obtained without sol–gel aging. It is also observed that the protection performance of the sol–gel coatings with cerium nitrate obtained after two weeks of sol–gel aging is lower compared to the coatings without cerium additive. This effect is attributed to the enhanced reactivity of the sol–gel due to cerium(III) presence.