A sol-bath-gel approach to prepare hybrid coating for corrosion protection of aluminum alloy

We developed a sol-bath-gel method to prepare a hybrid coating for corrosion protection of aluminum alloy. The sol-bath-gel treatment included dipping the aluminum alloy into silane sol at 50 °C for 30 min, slowly withdrawing it, and then drying at room temperature. This procedure overcame the drawbacks of conventional sol-gel methods while retaining the advantages of sol-gel and chemical bath approaches. The morphology and compositions of the as-prepared hybrid coating were characterized by digital microscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and energy dispersive spectroscopy (EDS) mapping. The corrosion resistance and durable protection ability of the as-prepared hybrid coating were investigated and compared with the traditional chromate coating by the potentiodynamic polarization technique, and electrochemical impedance spectroscopy (EIS). The results showed that the aluminum alloy surface is coated with a continuous, homogeneous, and compact aluminum (hydr)oxide-silane hybrid film, which is composed of ca. 200 nm particle array that was tightly and regularly packed. The corrosion resistance of the as-prepared hybrid coating was 32,395 Ω cm2, which is higher than that for the chromate conversion coating (12,094 Ω cm2). The as-prepared coating suppresses the anodic dissolution of the aluminum alloy substrate, resulting in a large decrease in corrosion current and long-term protection.