The Study Of Preparation And Corrosion Resistance In Molten Al-Si Alloys On MoB-CoCr Composite Coatings

MoB-CoCr coating has excellent properties such as corrosion resistance and wear resistance,and has high application potential in the field of hot dip plating.In this paper,the MoB-CoCr coating was prepared on 316L stainless steel substrate by using high velocity oxy-fuel spray technology.The influence of spraying parameters,bonding layer and Y₂O₃ on the coating performance was studied,and the coating before and after corrosion was analyzed.The changes in structure and phase explain the failure mechanism of the coating during the corrosion process and effectively improve the corrosion resistance of the coating.The main findings are as follows:(1)MoB-CoCr coating was prepared by high velocity oxy-fuel spray(HVOF)technique,and the influence of spraying parameters on the coating performance was studied.The results show that increasing the length of the barrel and shortening the spraying distance can reduce the porosity of the coating and improve the fracture toughness of the coating;after the coating is corroded in the molten aluminum-silicon solution,a layer of corrosion with AlCo as the main phase is formed on the surface.Due to the large difference in coefficient of thermal expansion between the MoB-CoCr coating and the 316L stainless steel substrate,cracks will occur during the corrosion process,and crack propagation will cause the coating failure.(2)The corrosion resistance of the coating to molten Al-Si was studied systematically.The results show that the crack density of the coating decreases in the process of corrosion.After 3 days of corrosion,the crack density of the coating is only1/4 of that of the MoB-CoCr coating.After the coating had been corroded in molten Al-Si for 3 days,a layer of corrosion with AlCo and Mo(Si,Al)₂ as the main phases was formed on the surface.With the extension of the corrosion time,the thickness of the corrosion layer does not change significantly,but the coating has a certain brittleness and leads to the growth of microcracks under the action of thermal stress,resulting in the increase of crack density.(3)The corrosion resistance of the coating after doping with Y₂O₃ was studied,and the corrosion mechanism of the coating in molten Al-Si was analyzed.The results show that the fracture toughness of the coating is improved after doping with Y₂O₃,so the coating shows good crack propagation resistance under thermal stress;after the coating is corroded in molten Al-Si for 6 days,a layer of AlCo and Mo(Si,Al)₂ is the corrosion layer of the main phase.After 9 days of corrosion,the coating did not peel off,showing excellent corrosion resistance to molten aluminum and silicon.As the content of Y₂O₃ increases,the corrosion resistance of the coating increases first and then decreases.Among them,when the Y₂O₃ content is 1%and 2%,the coating has the most excellent corrosion resistance,and the crack density after corrosion is only 1/3 of the undoped,thus showing the lowest crack density.