Effects of addition of polyvinyl pyrrolidone (PVP) as a corrosion inhibitor to Zr/V-based conversion coating on aluminum alloy

Polyvinyl pyrrolidone was selected as a green additive for zirconium-based conversion treatment on aluminum alloy substrate. Scanning electron microscope, energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used to investigate the effect of polyvinyl pyrrolidone on the morphology and composition of the conversion coating. Neutral salt spray, electrochemical impedance spectroscopy, and Tafel polarization tests were used to characterize the corrosion resistance of the conversion coating. The results show that the conversion coating was mainly composed of metal oxide (ZrO2, VO2, V2O5, etc.), metal fluoride (ZrF4, Na3AlF6) and polyvinyl pyrrolidone. The density of Na3AlF6 crystal is increased by adding polyvinyl pyrrolidone into the conversion bath. This is due to the adsorption of polyvinyl pyrrolidone molecules on the surface of the substrate, which trap metal ions and thus facilitate the coating formation reaction. The corrosion resistance of the substrate treated by conversion coating containing polyvinyl pyrrolidone was significantly improved. When the amount of polyvinyl pyrrolidone introduced into the conversion bath is 1.5 g/L, the conversion coating can provide excellent corrosion resistance to the substrate. In addition, the non-polar groups in the polyvinyl pyrrolidone molecule can effectively improve the adhesion between the conversion coating and the electrophoretic coating.

Automated summary

Polyvinyl pyrrolidone was used as a green additive in zirconium-based conversion treatment on aluminum alloy substrate. The addition of polyvinyl pyrrolidone improved the corrosion resistance of the conversion coating by increasing the density of Na3AlF6 crystal and enhancing the adhesion between the conversion coating and the electrophoretic coating. The conversion coating was mainly composed of metal oxide, metal fluoride, and polyvinyl pyrrolidone as confirmed by various analytical techniques.