Research Of Composition And Morphology And Corrosion Behavior Of Thermal Spraying Zinc Aluminum Coatings

Metal materials are widely used in various fields of national economy,but they always face the problem of corrosion damage in the practical application environment.In the past few decades,researchers at home and abroad have been devoted to studying the phenomenon and mechanism of metal corrosion,exploring the factors affecting the service life of metal materials and how to improve their corrosion resistance,hoping to reduce the various problems caused by metal corrosion.As a coating with excellent corrosion resistance,zinc-aluminum coatings are widely used in the corrosion protection of metal materials,but the current research on the corrosion resistance of zinc-aluminum coatings is mainly focused on the zinc-aluminum coatings with low aluminum content.while the research on the corrosion resistance of zinc-aluminum composite coatings with a wider range of aluminum content is relatively less,and the related research is mainly to conduct long-term exposure tests to analyze the changes in coating morphology and weight.However,the research on the changes of corrosion products during the corrosion process and the electrochemical corrosion behavior is still lacking.In this paper,pure zinc,pure aluminum,and three zinc-aluminum coatings with different aluminum contents are prepared by flame spraying technology.By means of metallographic microscope,super depth of field microscope,SEM,EDS,XRD,neutral salt spray test,immersion test and electrochemical test,the changes of corrosion morphology,corrosion products and corrosion electrochemical properties of different coatings with time are analyzed.The composition,morphology and corrosion behavior of zinc-aluminum coatings with different aluminum contents are studied.The main research results are as follows:(1)The surface roughness of the Zn-Al coatings is relatively large,and there are pores and pits.The distribution of Zn and Al in the coatings is not uniform,and there is a phenomenon of component segregation.In the preparation process of Zn-Al coatings,due to the different deposition efficiency of Zn and Al,the mass fraction of Zn in the coatings is lower than the value in the original powder,and the mass loss is as high as 42%?47%.(2)After the neutral salt spray test for 1080h,the pure Zn,pure Al,Zn-Al25,Zn-Al50 and Zn-Al75 coatings did not show red rust,indicating that the five coatings can still provide protection for the substrate after the salt spray test for 1080h.The corrosion products on the surface of the Zn-Al coating are broken,and there are local pitting pits.The quality change of the coating in the neutral salt spray test shows that the corrosion rate of the five coatings is large in the early stage of corrosion.As the corrosion process progresses,the corrosion rate of the coating slows down.Zn-Al25 coating has the lowest corrosion rate.(3)The immersion test results showed that after 60 days of experiment,the surface of Zn coating is almost covered by white corrosion products Zn5(OH)6(CO3)2 and Zn5(OH)8Cl2·H2O,and the surface of Al coating is distributed the corrosion product Al(OH)3.Corrosion products on the surface of the Zn-Al25 coating show dots of different sizes,circular pitting occurred in some areas on the surface of the Zn-Al75 coating,and corrosion products peel off on the surface of the Zn-Al75 coating.The corrosion products on the surface of the three Zn-Al coatings are about the same,the main components are Zn6Al2(OH)16CO3·4H2O and Zn0.70Al0.30(OH)2(CO3)0.15·xH2O,The corrosion products of Zn-A125 composite coating also contain Zn5(OH)6(CO3)2 and Zn5(OH)8Cl2·H2O.(4)The electrochemical test results show that the self-corrosion potential of the five kinds of coatings is always lower than that of the substrate during the entire corrosion cycle,which can provide effective cathodic protection for the substrate.Diffusion and mass transfer exist in the process of corrosion.The corrosion rate of pure Zd coating is as high as 10-4A·cm-2,and three kinds of Zn-Al coatings show lower corrosion rate.The comparison shows that the Zn-Al25 coating has the lowest corrosion rate and the best corrosion resistance.