Preparation and performance characterization of Mo/Ti/V composite coating on 7075 aluminum alloy
Molybdenum/titanium/vanadium composite conversion coatings were prepared on the sur-face of 7075 aluminum alloy using molybdate and titanate as the main salts, sodium metavanadate as the film-forming promoter and sodium phytate as the organic additive. The microscopic morphology, el-emental composition and chemical composition of the film layer were analysed with the aid of scanning electron microscope (SEM), energy spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS), and the corrosion resistance of the substrate and the film layer were investigated using an elec-trochemical workstation. The experimental results showed that the optimum formulation of conversion solution was 2 g·L-1 sodium phytate solution, 1.5 g·L-1 sodium metavanadate solution, 1.5 g·L-1 hexaflu-oro titanate solution and 25 g·L-1 ammonium molybdate solution, and the optimum film formation con-ditions were 15 minutes and 35 ℃. The main components of the coating were Al2O3, MoO2, MoO3, V2O5 and TiO2. Mo/Ti/V conversion coating positively shifted the corrosion potential of the 7075 alumi-num alloy by 260.401 mV and reduced the self-corrosion current density by 9.912 μA·cm-2, which effec-tively improved the corrosion resistance of the substrate.
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