Preparation and corrosion resistance of chromium-free Zn-Al coatings with two different silane coupling agents

Abstract In this paper, the chromium-free Zn-Al coatings prepared with different mixing ratios of 3-glycidoxypropyltrimethoxy (GPTMS) and methyltrimethoxysilane (MTMS) were presented. The morphology, composition and formation mechanism of the coatings were observed and studied by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis. Polarization tests and immersion tests were used to study the corrosion resistance of the coatings. The results showed that the coatings had similar morphology to Dacromet coatings. The silane molecules were hydrolyzed and condensed to form three-dimensional cross-linking networks. The coatings with GPTMS had nobler corrosion potential and lower corrosion current density. The immersion time of the coating in the 5 wt% NaCl solution could reach 58 days when the mixing ratio of GPTMS/MTMS was equal to 1.