Evaluation of Anticorrosion Properties of Epoxy-Silane Hybrid Nanocomposite Coating on AA6082 Aluminum Alloy

Abstract

The protection properties of (3-aminopropyl)trimethoxysilane (APTMS) incorporated epoxy coating on aluminum alloy were studied by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis in seawater. The epoxy-APTMS coated Al alloy displayed higher charge transfer resistance (Rct) as well as film resistance (Rf) at 1 day immersion. However, both Rct anf Rf values decreased slowly compared to pure epoxy coated alloy which showed significant decrease in Rct and Rf values with increase in immersion time in chloride media. The released Al3+ ions were detected using SECM by applying the tip potential of –0.85 V. It was evident from the SECM measurement that the dissolution of Al3+ ions was impeded at the scratch of epoxy-APTMS coated Al alloy due to the presence of electron donating amino group in APTMS which inhibited Al alloy degradation. The enrichment of Mg, Mn, Si and Al at the scratch of epoxy-APTMS coated Al alloy was confirmed by Field emission-scanning electron microscopy/energy dispersive X-Ray spectroscopy (FE-SEM/EDX) analysis. Focused ion beam-transmission electron microscopy (FIB-TEM) analysis proved the presence of thin films of nano level oxide layers containing Mg, Mn, Si and Al in the coatings, which decreased the corrosion rate of Al alloy. The enhanced adherence of epoxy-APTMS coating to Al alloy was due to the strong chemical bonding between epoxy-APTMS and Al alloy. Therefore, the pronounced protection performance against corrosion and good adhesion strength was due to the incorporation of APTMS with epoxy coatings.