Study Of Corrosion Resistant Coating On Sink Roll In Molten Zinc-aluminum

The plating galvanized-aluminum has been widely used to improve the service life of steel products, but the servicing condition of equipment is very strict. The corrosion of molten zinc-aluminum can lead to failure for these metal equipments. Thus the sink roll need to be replaced and repaired, which not only reduces the production rate also increases the production costs. Resistant metal could be used to produce the sink roll for anti corrosion, but it always has high cost. It can improve the production efficiency and reduce the cost by depositing protecting coating on the substrate.In this paper, Al2O3-17%Ti O2, ZrO2-8%Y2O3, NiCr-Cr3C2 and Mo were chosen to study the corrosive resistance of Zn-55wt%Al corrosion solution. High velocity oxygen-fuel technology was used to spray NiCrAlY powder on the steel sample, then the plasma spraying technology was used to produce the protecting coatings. The corrosion process was observed by putting the specimen in the molten zinc-aluminum of 570℃. The microstructure, the infiltration of liquid metal, porosity and the new generated phase were carried out by scanning electron microscope, energy spectrometer, Image-J image processing software and X-ray diffractometer respectively combined with the failure mechanism studying.The result showed that, the coating and substrate has well adhesion except Al2O3-17%TiO2coating. The porosity of ZrO2-8%Y2O3 coating in the four coatings was the largest, which was15.2%, and the porosity of Al2O3-17%TiO2, NiCr-Cr3C2 and Mo coating was 5.3%, 9.8% and1.8%. In the condition of 570℃ molten Zn-55wt%Al, the longest time of anti corrosion was ZrO2-8%Y2O3 coating, which was 12 days. Finally crack appeared and the coating was failure.Mo coating’s anti corrosion time was the second longest, which was 10 days, MoO3 lead to coating failure. The time of anti corrosion for Al2O3-17%TiO2 coatings was 9 days, which was failure by cracks. Because of the reaction between Ni and Zn in molten metal, the time of failure time for NiCr-Cr3C2 coating was 6 days.From the corrosion tests, NiCr-Cr3C2 and Mo coatings were not suitable for protecting coatings. The time of anti corrosion was around 10 days for two kinds of coatings Al2O3-17%TiO2 and Zr O2-8%Y2O3, which could be used as sink roll corrosive resistant coatings.