Preparation and evaluation of corrosion behavior of GPTMS–TEOS hybrid coatings containing Zr and Ce on aluminum alloy 6061-T6

Abstract

Environmentally friendly organic–inorganic hybrid coatings with different amount of Ce and Zr content were prepared by a sol–gel method and deposited on aluminum alloy 6061-T6. Attenuated total reflectance-Fourier transform infrared spectroscopy and scanning electron microscopy were used to structural study of the hybrid coatings. Adhesion strength of sol–gel coatings to the substrate was also evaluated using pull-off test. Corrosion behavior of the samples was evaluated by cyclic potentiodynamic and linear polarization tests. The obtained results display that adhesion strength of the coatings was enhanced with an increase in zirconium and cerium content. Corrosion analysis showed a decrease in corrosion current density of coated samples two to four orders of magnitude compared to the bare alloy 6061. Decreasing in corrosion current density and increasing in polarization resistance were observed by an increase in Zr and cerium content. The sol–gel-coated layer doped with 20 g/l cerium nitrate offered excellent protection against corrosion. Unlike the bare alloy 6061, the crack-free samples showed no sensitivity to pitting corrosion. The present investigation has been based on preparation of hybrid sol–gel coatings with different amount of zirconium and cerium content using dip coating method. Effect of cerium and zirconium content on thickness, adhesion strength and pitting corrosion behavior of the coatings were investigated. Significant decrease in corrosion current density was observed compared to uncoated substrate. Increase in polarization resistance was observed by an increase in zirconium and cerium content.