Comparison on corrosion behaviour of arc sprayed and zinc-rich coatings

The microstructures of the arc sprayed (AS) and zinc-rich (ZR) coatings were observed by scanning electron microscopy (SEM). Furthermore, the different anti-corrosion properties were investigated through electrochemical experiments including potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The SEM observations revealed that the AS coating was more porous and coarser, while the ZR coating surface was composed of uniform spherical particles. The corrosion potential of AS coating was shifted to a more negative value than that of the ZR coating. From EIS results, it was proposed that the ZR coating exhibited much larger impedance values than the AS coating. General models are applied to simulate EIS data of the AS coating, while two transmission line models (modified de Levie's type) are used to account for ZR corrosion behaviour. The ZR coating performed better as a protective passive film during the long-term immersion test while the cracks that occurred in the cross section of ZR coating indicated that the adhesive strength of the AS coating was superior to that of the ZR coating.