Nanostructured sol–gel coatings doped with cerium nitrate as pre-treatments for AA2024-T3: Corrosion protection performance

Abstract

Nanostructured hybrid sol–gel coatings doped with cerium ions were investigated in the present work as pre-treatments for the AA2024-T3 alloy. The sol–gel films have been synthesized from tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors. Additionally the hybrid sol was doped with zirconia nanoparticles prepared from hydrolyzed tetra- n-propoxyzirconium (TPOZ). Cerium nitrate, as corrosion inhibitor, was added into the hybrid matrix or into the oxide nanoparticles. The chemical composition and the structure of the hybrid sol–gel films were studied by XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy), respectively. The evolution of the corrosion protection properties of the sol–gel films was studied by EIS (electrochemical impedance spectroscopy), which can provide quantitative information on the role of the different pre-treatments. Different equivalent circuits, for different stages of the corrosion processes, were used in order to model the coating degradation. The models were supported by SEM (scanning electron microscopy) measurements. The results show that the sol–gel films containing zirconia nanoparticles present improved barrier properties. Doping the hybrid nanostructured sol–gel coatings with cerium nitrate leads to additional improvement of the corrosion protection. The zirconia particles present in the sol–gel matrix seem to act as nanoreservoirs providing a prolonged release of cerium ions. The nanostructured sol–gel films doped with cerium nitrate can be proposed as a potential candidate for substitution of the chromate pre-treatments for AA2024-T3.