Characteristics and corrosion behavior of La₂O₃/silane/Al₂O₃ films on Al-Zn-Mg-Cu/TiB₂ composite materials

Introducing TiB₂ particles into Al-Zn-Mg-Cu alloy makes it a high-strength material suitable for lightweight applications, but it also significantly increases its corrosion sensitivity. Here, anodic Al₂O₃ oxide films with La₂O₃/silane sealing were used, and the effects of solution concentration and applied potential on the microstructures of these films were systematically investigated. The mechanism whereby TiB₂ affected the formation of the Al₂O₃ oxide film was also revealed. The results indicated that a uniform anode oxide film, almost free from pores, was formed at a solution concentration of 180–200 g L⁻¹ and a potential of 15 V. After La₂O₃/silane sealing, the composite anode oxide film exhibited excellent resistance to electrochemical corrosion. The self-corrosion current density of the La₂O₃/silane/Al₂O₃ film was 0.011 μA cm⁻², and only around 2% of that of an anode oxide film with traditional hydrothermal sealing. The radius of the impedance arc was maximized, effectively hindering charge transfer and significantly reducing the oxidation of metal ions. This was mainly attributed to the combined effect of physical and chemical barrier protection by the La₂O₃/silane/Al₂O₃ film, as well as the synergistic action of active inhibition and self-repair.