Enhancing corrosion resistance of anodized aluminum alloy 6061 via multicomponent silica sol-gel sealing

Abstract

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To mitigate ionic transport through connected pores in anodic aluminum oxide (AAO), a multicomponent silica sol-gel sealing process was applied to AA6061. By varying concentrations of nano-silicon dioxide (SiO2)—specifically, 0, 2, 4, and 8 g·L-1—the relationships among coating microstructure, electrochemical response, and corrosion resistance were systematically evaluated. The results indicate that the response to a SiO2 concentration of 2 g·L-1 is the most favorable among the tested concentrations. The number of open pores decreased, pore apertures narrowed, and cross-sectional densification was enhanced by this concentration. The total resistance, contributed by both porous and barrier layers, was 191 kΩ·cm2. The corrosion current density decreased to 0.61 μA·cm-2. The sealed coating showed a lower corrosion rate in phosphoric acid immersion and maintained surface integrity after 720 h of neutral salt spray exposure. These findings indicate that silica is incorporated within the pores, effectively filling and extending diffusion pathways. As a result, the pores become less accessible, and the connectivity of the pore network is reduced. The results indicate an effective range of SiO2 concentration for anodized AA6061, where improved corrosion resistance and enhanced protective characteristics of the anodic oxide layer contribute to greater material durability in corrosive environments.