Effect of ethylene glycol dimethacrylate on VOC reduction, rheological, mechanical and anticorrosion properties of a hybrid sol-gel coating on AA2024-T3 and sulfuric acid anodized AA2024-T3

An inorganic–organic coating based on methacrylic-functionalized silica and zirconia was synthesized by sol-gel technology as replacer of Cr(VI)-based treatments used to protect both unconverted and electrically converted AA2024-T3 for aeronautic application. The effect of a bi-methacrylate organic precursor in the formulation was studied with the aim to reduce the sol viscosity and coating thickness while crosslink was increased and volatile organic compounds (VOC) were diminished in the formulation. The viscoelastic behavior was studied by rheometry, and the properties of the coating material were related to its corrosion protection capability, studied by electrochemical impedance spectroscopy and neutral salt spray tests. The mechanical properties of the resulting coatings were studied by dynamic microindentation and rotary wear tests. The formulations containing the organic precursor provided coatings with higher degree of crosslinking and lower VOC. The derived coatings were thinner and provided outstanding corrosion protection with low thickness on unconverted AA2024-T3 and as sealant of hard sulfuric acid anodized AA2024-T3. The hardness was improved in comparison to coatings without the organic precursor although abrasion resistance was better for coatings with higher inorganic character.