Developing a Benzimidazole-Silica-Based Hybrid Sol–Gel Coating with Significant Corrosion Protection on Aluminum Alloys 2024-T3

Abstract

The inherent reactivity of Al–Cu–Mg alloys is such that their use for building structural, maritime, and airplane components with great strength/weight ratios would not be possible without good anti-corrosion systems. These systems could be considered as imitations of the protection mechanism found in the conventional hexavalent chromium-based system, but with additional limited environmental impact, and in particular without toxic or carcinogenic effects. These coatings also are intended to be eco-friendly, using less of the valuable raw materials and energy than more traditional methods. Silica-based hybrid protective coatings have been shown to exhibit excellent chemical stability combined with the ability to reduce the corrosion of metal substrates. However, research shows that sol–gel has some limitations in terms of the period of the anti-corrosive properties. Therefore, this work reports the performance of a silica-based hybrid sol–gel coating encapsulated with benzimidazole (BZI) that can be applied to light alloys to form an inherently inhibited and crack-free coating. This coating was applied on AA 2024-T3 and cured at 80 °C. The high corrosion resistance performance results from the combination of good adhesion, the hydrophobic property of the silica-based hybrid coating, and the presence of the encapsulated (BZI) film-forming volatile corrosion inhibitor, which is released at pores within the coating system, resulting in film-forming, reducing the reaction at cathodic sites. The evaluation of this mechanism is based on using electrochemical testing techniques. The anti-corrosion properties of the coatings were studied when immersed in 3.5% NaCl by using electrochemical impedance spectroscopy (EIS) and potential-dynamic polarization scanning (PDPS). The chemical confirmation was performed by infrared spectroscopy (ATR-FTIR), supported by analyzing the morphology of the surface before and after the immersion testing by using scanning electron microscopy (SEM). The benzimidazole-silica-based hybrid coating exhibited excellent anti-corrosion properties, providing an adherent protective film on the aluminum alloy 2024-T3 samples compared to sol–gel-only and bare metals, as a cost-effective and eco-friendly system.