Insights into the corrosion mitigation efficacy of modified SiO2/GO-based epoxy composite coatings for aluminum alloy AA6061 in marine applications

The corrosion protection of aluminum alloys is severely compromised by marine environments, demanding the formulation of efficient protective coatings. Epoxy resin, diglycidyl ether of bisphenol A (DGEBA), and curing agent diethylenetriamine (DETA) were used with the mixing ratio of 100:12 to synthesize functionalized SiO₂/GO-based composite coatings and investigate the corrosion protection efficacy for aluminum alloy AA6061 in marine environments. To boost the coatings' barrier and anticorrosive attributes, functionalized silica (FSiO₂, with 0, 3, 6, 9, 12, and 15 wt%) and graphene oxide (GO) were jointly incorporated into the DGEBA/DETA epoxy-hardener system for producing composite coatings. The functionalization of silica particles using 3-aminopropyl-triethoxysilane and synthesis of GO was successfully carried out, according to the Fourier transform infrared spectroscopy evidence. The structural properties were investigated by X-ray diffraction. The hydrophobicity tests were conducted for the measurement of the contact angles. The highest static contact angle (126° ± 2) and the lowest contact angle (74° ± 1.5) were recorded for the sample EHS₉GO₂ and AA6061, respectively, which showed that EHS₉GO₂ coating had the most hydrophobic behavior. An adhesion test (method B, tape test) was performed on prepared coatings to check the quality of adhesion with the substrate aluminum alloy AA6061. The neat epoxy coating (EHS₀GO₀) displayed a fair adhesion rating of 3B, while EHS₉GO₂ coating exhibited excellent adhesion (5B) with substrate AA6061. Furthermore, electrochemical impedance spectroscopy and potentiodynamic polarization tests were employed for assessing the electrochemical behavior and anticorrosion performance of the prepared coatings. It was observed from the Bode plot, that the impedance magnitude/modulus for EHS₉GO₂ at lower frequencies was the highest as compared to other samples during immersion in the artificial seawater. The bare aluminum alloy substrate AA6061 had the highest corrosion rate of value 0.10483 ± 0.00198 mm/year, due to the direct contact with the electrolyte. Moreover, the highest value of E_corr (356 ± 0.42 mV) and lowest values of I_corr (0.18 ± 0.03µA), β_a (48.7 ± 2 mV/decade), and β_c (28.8 ± 1 mV/decade) were witnessed for EHS₉GO₂ coating, showing significant anticorrosion efficiency against the corrosive electrolyte.