Investigation of Dense Al2O3 Coating Performance in Molten Zinc

Surface treatment for sink rolls in continuous galvanizing line is an important issue due to the unfavorable environment of the molten zinc. This study investigated the corrosion-behavior of high-velocity-oxy-liquid-fuel (HVOLF) sprayed WC-12Co, Cr₃C₂NiCr and Hybrid-LVOF sprayed Al₂O₃-TiO₂, Al₂O₃ coatings in molten zinc-bath. All coated samples were tested in a zinc-bath for 30 days and cross-sectioned to examine the microstructure and corrosion attack. The results showed that the molten zinc react with coating material causing major destruction of HVOLF sprayed WC-12Co and Cr₃C₂NiCr coatings. Whereas, Hybrid-LVOF sprayed dense Al₂O₃-TiO₂ and Al₂O₃ coatings performed very well for longer exposure times of 30 days in a molten zinc-bath. The structural integrity and no penetration of Zn into the coating were observed without any thickness reduction in both coatings. However, Zn accumulation was observed on the Al₂O₃-TiO₂ coating surface and Zn react with TiO₂ and form Zn₂TiO₄. Whereas, no Zn reaction were take place with Al2O3 coating. A very small amount of γ-Al₂O₃ is present which upon exposure converts to stable α-Al₂O₃. MECPL Jodhpur has developed a special process to solve this problem and it could be greatly improved the service life of a sink roll.