Corrosion resistance and microstructural characterization of Ti-Zr-V/waterborne resin composite conversion coating on 1060 aluminum alloy

Abstract

A Ti-Zr-V/waterborne resin composite conversion coating (TZVRC) was prepared on an aluminum substrate using a simple and environmentally friendly coated-bake, non-washing one-step film-forming method. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, neutral salt spray (NSS) testing, and scanning electron microscopy (SEM) results indicated that TZVRC exhibited the best corrosion resistance and topcoat adhesion when the concentration of sodium orthovanadate in the composite conversion solution was 1 g/L. It also exhibited a relatively uniform and dense microstructure. The corrosion resistance of the coating is comparable to traditional chromate conversion coatings. The corrosion current density (icorr) is 0.1426 μA/cm², the corrosion rate is 0.0015 mm/year, the coating resistance (Rc) reaches 384 kΩ·cm², and the coating thickness is approximately 0.4 µm. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that the upper part of the coating primarily consisted of cured waterborne resin, while the bottom part was mainly composed of insoluble inorganic substances. Additionally, there were concentration gradient variations in the distribution of inorganic components within the lower part of the coating. Near the interface between the aluminum substrate and the bottom of the coating, the main components were Al, AlPO4, Al2O3, and AlF3, while the upper layer of the inorganic substances primarily consisted of TiO2, ZrO2, complexes of V ions, AlPO4, Al2O3, and AlF3. This composite conversion coating not only possesses excellent corrosion resistance but also eliminates the post-film washing step, streamlining the process. Additionally, the composite conversion system, which combines waterborne resin with inorganic components, offers a potential solution for the integration of chemical conversion coatings and primers on aluminum surfaces.