| In this thesis,phosphating treatment is applied to boiler steel 12Cr1MoVG matrix in order to obtain phosphating film in phosphating liquid with different free acidity.The filming OCP curve?potential-time curve?is used to test and analyze the forming process of phosphating film on 12Cr1MoVG.The surface morphology of phosphating film and the micromorphology of the film section are observed by scanning electron microscope.The thickness gauge is used to measure the thickness of the phosphating film,and the EDS spectrum is used to detect the main components and content of the phosphating film.The phase analysis of phosphating film is carried out by XRD method.The corrosion resistance of the film forming on the samples under different free acidity is measured by means of potentiodynamic polarization curve,artificial salt spray accelerated corrosion test and natural environment placing test.The results show that the microstructure of phosphate grains is granular stacking after the phosphating treatment in phosphating liquid with different free acidity for12Cr1MoVG matrix.With the increase of free acidity,the size of phosphate grain decreases and the distribution of grain is uneven.With the increase of the free acidity of the phosphating liquid,the density,fineness and thickness of the phosphating film on the boiler steel 12Cr1MoVG decrease obviously,which show a certain regularity.After the phosphating treatment,the phosphating film on the surface of the sample mainly contains elements such as Zn,Ca,Fe,P and O.With the increase of the free acidity of phosphating liquid,the content of each element in phosphating film presents different trends respectively.The free acidity of phosphating liquid has no obvious effect on the content distribution of each element in the phosphating film.The phosphating film after the phosphating treatment in phosphating liquid with different free acidity is mainly composed of compounds Zn2Ca?PO4?2 and Zn2Fe?PO4?2.The corrosion current density of the matrix material is large,the corrosion potential increases slightly and the corrosion current density greatly decreases after the phosphating treatment,which indicate that the corrosion rate of the coating sample is lower than that of the matrix.After the phosphating treatment,the corrosion resistance of the matrix material is improved due to the protective effect of the film.Under the low free acidity of phosphating liquid,the corrosion potential of film forming on the sample is slightly higher and the corrosion current density is slightly lower.At this time,the corrosion rate of film forming on the specimen is lower and the corrosion resistance is better.The corrosion resistance of phosphating film on 12Cr1MoVG is the best when the free acidity is lower.The rust is observed after 1248 hours in salt spray corrosion test,and the corrosion resistance decrease with the increase of free acidity.Under the different free acidity of phosphating liquid,the 12Cr1MoVG tube after phosphating treatment shows no obvious corrosion behavior in the natural environment,and the difference of corrosion resistance in atmospheric environment is not obvious which shows the excellent atmospheric corrosion resistance.The result of atmospheric corrosion test also indicates that the free acidity of phosphating liquid has little effect on the corrosion resistance of phosphating film.With the increase of the free acidity of the phosphating liquid,the adhesion of the phosphating film on the boiler steel12Cr1MoVG decrease obviously,which show a certain regularity. |
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