Molten Zinc Corrosion Mechanism of HVOF Sprayed WC-Co Coatings

摘要

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 immersion in the 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 the nanostructured coating is less corrosion resistant than the conventional one in molten zinc. The molten zinc intrudes through cracks to attack the substrate which causes major destruction of the coating.