Corrosion Resistance of Coatings for High-Strength Fastening Parts

Three kinds of corrosion resistant coatings, zinc pack coating, zinc pack coating with silicate sealing and zinc pack coating with both Dacromet and aluminiferous sealing, were prepared on the substrate of steel for high-strength fasteners. The differences of morphology and element content before and after neutral salt spray test were investigated to analyze the corrosion characteristics of coatings by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Electrochemical characteristics were also investigated by electrochemical impedance spectroscopy and electrochemical polarization. The results show that the zinc pack coating with silicate sealing and the zinc pack coating with both Dacromet and aluminiferous sealing had much better corrosion resistance than zinc pack coating, and the corrosion resistance of the zinc pack coating with both Dacromet and aluminiferous sealing was the best in three kinds of coatings. During corrosion process, the main corrosion mode of the zinc pack coating was stress corrosion of the zinc coating layer, and the main corrosion modes of the zinc pack coating with silicate sealing were both general corrosion and pitting corrosion of the sealing layer. For the zinc pack coating with both Dacromet and aluminiferous sealing, peeling effect between sealing layer and Dacromet layer was observed.