Abstract:To improve the long-term corrosion resistance of 7075Al aluminum alloy, an alumina (Al2O3) coating was prepared first by cathodic liquid plasma electrolysis technology to achieve full coverage of the aluminum alloy substrate, and then a bis[3-(triethoxysilyl)propyl]tetrasulfide (BTESPT) silane coating and reduced graphene oxide (rGO) coating (BTESPT/rGO composite coating) was further prepared on the surface of the Al2O3 coating via dip coating and pulsed electrodeposition technology to fill the micro-cracks and micro-holes in the Al2O3 coating, further improving the long-term corrosion resistance of 7075Al alloy. The phase composition, surface morphology, electrochemical properties, impedance value and macroscopic surface morphology of the deposited coatings were analyzed. The results indicate that the impedance value of 7075Al coated with a single Al2O3 coating is still 4.6 Ω·cm2 after immersion in seawater for 25 d, which is significantly higher than 3.2 Ω·cm2 of 7075Al alloy. However, several etch pits are formed on the Al2O3 coating because the oxygen and chloride ions in seawater enter the interior of 7075Al alloy through the micro-cracks and micro-pores in the Al2O3 coating. In contrast, the uniform and dense Al2O3/BTESPT/rGO composite coating, prepared by the pulsed electrodeposition technique at 0.8 V deposition voltage, fills the micro-cracks and micro-pores generated in the process of Al2O3 coating deposition. The 7075Al alloy coated with the composite coating exhibit the most positive corrosion potential and the lowest corrosion current density, indicating the lowest corrosion tendency and corrosion rate. Throughout the period of immersion in seawater for 105 d, the impedance value of 7075Al coated with Al2O3/BTESPT/rGO composite coating varies within the range between 5.44 Ω·cm2 and 5.71 Ω·cm2. Furthermore, the Al2O3/BTESPT/rGO composite coating exhibits only slight color change on its surface, demonstrating excellent long-term corrosion resistance in seawater.