Effect Of Alloying Element M(M = Ni,Cr,y)on Corrosion Resistance Of Co-Si Intermetallic Compound In Liquid Zinc

The hot-dip galvanizing is one of the most economical and effective processes to delay the corrosion of metal materials,and it plays an important role in promoting the development of national economy.However,the equipment on the hot-dip galvanizing production line has been corroded by molten zinc for a long time,resulting in equipment failure,which is also a major problem so far.Therefore,the development of an overall molten corrosion-resistant material with excellent corrosion resistance and mechanical properties has become a hot spot in this field.In this paper,the Co-Si intermetallic compound is used as the matrix,and the appropriate proportions of Ni,Cr,and Y elements are added.After the static corrosion test of Co-Si alloy in the zinc solution at 460^oC,the microstructure of the as-cast alloy matrix and the corrosion interface is observed using a scanning electron microscope?SEM?.The phase composition was analyzed by X-ray diffraction?XRD?,the chemical composition of each phase was analyzed by energy dispersive spectrometer?EDS?,the corrosion resistance was studied using the depth method,and the toughness and brittleness of the material was evaluated using the micro hardness method.The results show:CoSi and CoSi₂ do not interact with the zinc solution,and exhibit good corrosion resistance in both 460°C and 550°C zinc liquid.Co₂Si easily reacts with liquid zinc,the corrosion rate is high,and the corrosion mechanism is uniform corrosion.It reacts with zinc liquid at high temperature to form a periodic layered plate structure,which is composed of CoSi and Co Zn₁₃ phases.Although CoSi₂ does not react with zinc liquid and has excellent corrosion resistance to zinc liquid,its intrinsic brittleness hinders its wide application.Ni element and Y element improve the plastic toughness of the alloy matrix,purify the grain boundaries and improve the bonding force between the grain boundaries,so that they will generate fewer cracks after long-term corrosion,thereby slowing the corrosion rate of Ni-Y-CoSi₂ alloy in the zinc liquid.The corrosion resistance of alloy in zinc liquid has been improved to a certain extent.When the content of Ni and Y element is 12.83wt.%and is 1.06wt.%of alloy,a cluster of CoSi phase precipitates on the CoSi₂ matrix,and the hardness value is 1187HV.Compared with CoSi₂,the hardness of alloy containing CoSi and CoSi₂ phases is increased by about 460HV.The alloy exhibits better corrosion resistance during the long-term corrosion in zinc liquid at 460^oC,the corrosion rate is 0.33?m/h,and the corrosion resistance to zinc liquid is46 times that of 1Cr18Ni9Ti and 12 times that of 316L stainless steel.The intermetallic compound Co₂Si has good plasticity and toughness,but it is easy to react with zinc liquid and has poor corrosion resistance.By using Co₂Si with good plastic toughness as the matrix,the content of fixed Y element is 0.50wt.%,and the addition of Cr element with different content improves its corrosion resistance.The results show that the alloy has the best corrosion resistance in liquid Zn,the Cr element content is 10.18wt.%.The corrosion rate is 6.13?m/h at 460^oC,which is significantly lower than that of Co₂Si with corrosion rate of 10.32?m/h;after adding Cr element,the reaction layer is thinner,the loss of alloy matrix is reduced,the corrosion rate is reduced,and the corrosion resistance of the substrate is enhanced.The main mechanism of the effect of Cr element is that during the corrosion process,Cr element preferentially diffuses from the matrix to the corrosion interface and segregates on the side of CoSi phase,which hinders the diffusion of zinc element.