Research On Corrosion Behavior And Residual Stress Of Arc-sprayed Coating

As a mature thermal spraying method,electric arc spraying technology is widely used because of its obvious protective effect and low cost.But in the process of spraying and serving,the residual stress has an great impact on the quality of arc spraying coatings.Especially in the process of environment medium corrosion,residual stress is one of the most important factors which lead to coating failure.Combined with the preparation,microstructure and the characterization of properties of coatings,and on the basis of salt spray corrosion effect on the properties of coatings,the ABAQUS software is used for studying the residual stress of the coating,and analyzed the influence on the residual stress of factors in the corrosion process,and providing a theoretical basis for reducing residual stress in coatings and improving service life of coatings.In the process of coating preparation,Q235 steel is chosen as matrix.Zn,Al and Zn-15 Al wires are chosen as the material of coatings.The orthogonal experimental method is used for determining the arc spraying process parameters,which choosing the bonding strength of coatings measured by drawing method as the evaluation criteria.After the preparation of coatings,the salt spray test is used for researching the corrosion resistance of coatings.By corrosion rate determination and macrostructure observation,the corrosion rate of Zn coating is lowest in the initial.But after 96 h,the corrosion rate of Zn-15 Al coating reduced to minimum.The microstructure observation by Electron Microprobe and analysis results by XRD show that the corrosion products distributed on the surface of Zn coating are net-like and contain lots of holes;the corrosion products on the surface of Zn-15 Al coating arrange closely;the surface of Al coating contains a large number of cracks.After 288h's corrosion,the arrangement of self-sealing effect of coatings is: Zn-15 Al coating>Zn coating>Al coating.In order to study the effect of salt spraying corrosion to the internal structure of coating,the sections of Zn and Zn-15 Al coatings with different corrosion time are analyzed usingElectron Microprob and EDS elements scanning.The structure of internal coatings are layered,with spherical porosity distributed randomly.With the increase of corrosion time,the color of porosity becomes deepen and a large number of Na element infiltrate into coatings.The corrosion products of Zn coating are zinc oxide,hydration hydroxide and chloride,while the corrosion products of Zn-15 Al coating are oxide and subcarbonate of Zn and Al.The presence of Al element in Zn-15 Al coating makes corrosion products more dense,and the effect of self-sealing becomes better.The porosity of coatings is measured by pixel method,and the result shows that with the increase of corrosion time,the porosity of Zn and Zn-15 Al coatings all increased.The porosity of Zn coating is higher,which means the corrosion products of Zn coating cover a wider range.SEM observation of porosity shows that spherical porosity developed into etch pit,and lots of cracks initiated around it.This is because stress concentration occurs easily near the porosity.Using finite element analysis software ABAQUS,the stress field of coatings with porosity in corrosion environment is simulated.Firstly,the initial residual stress in the coating forming process is simulated.The result shows that stress concentration occurs near the porosity,and tensile stress occurs in coating along the thickness direction.Along the coating/substrate interface,tensile stress exist in substrate and stress change sharply in this place.Then considering the corrosion environment,the working temperature,convective heat transfer coefficient,thermal expansion coefficient and thickness are selected.The increase of work temperature can reduce stress of coating.But when the temperature increase higher than100?,the stress in substrate will rise sharply.So the working temperature should be within100?.Increasing convective heat transfer coefficient will increase the temperature gradient,and increase stress in small area.If the difference of thermal expansion coefficient between coating and substrate increases,the stress in coating and substrate will increase.The increase of coating thickness will lead to the tensile stress scope increase both in the coating and along the interface.Considering the practical application of coating protection,the thickness should be controlled between 0.2mm to 0.4mm.