In this work, phytic acid (PA) and 3-mercaptopropyltrimethoxysilane (MPTS) underwent a condensation process to produce a phytic acid–silane (abbreviated PAS) passivation solution. Additionally, it was applied to the surface of cold-rolled steel to create a composite phytic acid–silane film. The functional groups of the passivation solution were analyzed by Fourier transform infrared spectroscopy (FT-IR). The composite film was evaluated using an electrochemical workstation, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and pull-off test. These techniques allowed for the characterization of the film’s micromorphology, oxidation, chemical composition and adhesion strength. The results show that the PAS composite film provides higher protection efficiency compared to cold-rolled steel substrates, low phosphorus passivation films, single phytate passivation films and commercial phosphate films. This composite film also has a higher adhesion strength, which is beneficial for subsequent coating, and a possible corrosion resistance mechanism was proposed as well. The PAS layer successfully prevents the penetration of corrosive media into the cold-rolled steel surface utilizing P–O–Fe bonds, thus improving the corrosion barrier effect of the substrate.
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