Molten Zinc Corrosion Mechanism of HVOF Sprayed WC-Co Coatings

Surface treatment for sink rolls is an important issue due to the hostile environment in the zinc pot. Thermal sprayed WC-Co coating is one of the solutions to prolong the life of the rolls and to improve the quality of the galvanized steel sheets. In this study, a high velocity oxy-fuel (HVOF) spray gun was used to prepare nano-structured and conventional WC-Co coatings. After immersed in zinc pot for six weeks, some coatings were seriously damaged. Cross-sectional microstructure and elemental analysis were performed to determine the corrosion morphology and mechanism. The results showed that the binder Co could be dissolve due to the inter-diffusion of Co and molten zinc. Localized crack growth could be enhanced by the intrusion of molten zinc and accelerates the degradation of the coatings.