Effect Of Powder Particle Size And Coating Thickness On The Corrosion Resistance Of WC-10Co-4Cr Coating Prepared By HVAF

Aluminum because of its excellent mechanical properties,lightweight material of choice for products,but poor surface properties,particularly wear resistance and corrosion resistance poor shortcomings severely limits its application.Aluminum is one of the hot surface modification technology applied research in recent years,aluminum alloy material.The method of surface modification techniques,many aluminum alloys,the coating properties prepared advantages and disadvantages,the thermal spray because of quickly and efficiently deposited on the base wear,corrosion and other functional coating,it is increasingly receiving attention.In this paper,the high velocity air fuel technology(HVAF)was used to prepare 3 kinds of WC-10Co4Cr corrosion-resistant coatings with different powder particle sizes and 3 spray passes(coating thickness)on the surface of 7A04 ultra-high-strength aluminum alloy.Usded scanning electron microscope(SEM),XRD(X-ray diffractometer),Leica TMHVS-1000Z microhardness tester,MFT-4000 multifunctional surface performance tester,the microstructure and physical properties of the coating had been tested and analyzed.The electrochemical corrosion behavior of the base material and coating was tested by Chi660e electrochemical workstation.Study corrosion coatings in marine environments used Test Method immersed in artificial seawater.Through the completion of the above experiment,the influence of powder particle size and spraying pass(coating thickness)on the coating quality was analyzed and compared,and the study focuses on the influence of powder particle size and spraying passes(coating thickness)on the corrosion resistance of the coating and its mechanism.After analyzing and discussing the experimental results,the following conclusions are drawn:(1)The WC-10Co-4Cr coating prepared by the high velocity air fuel technology(HVAF)had a compact appearance and good performance.(2)There were WC,Co and W₂C phases in the WC-10Co4Cr coatings of different powder particle sizes and different spraying passes(coating thickness).W₂C was formed by the oxidative decarburization of WC during the spraying process.The smaller the particle size of WC in the powder,the greater the specific surface area,and the greater the degree of decomposition during the spraying process.The more spraying passes,the longer it takes to prepare the coating,the longer the high-temperature flame flow acts on the coating,and the higher the coating temperature,the more severe the oxidative decarburization of the WC phase.(3)The porosity,microhardness and bonding force of WC-10Co4Cr coatings with different powder particle sizes and different spraying passes(coating thickness)were characterized.The analysis showed that the porosity of all prepared coatings was less than1.5%,and the coatings were relatively dense.Among them,the porosity of the coatings with a powder particle size of 5-15?m is the lowest at 1.09%.The Vickers microhardness of all the prepared coatings was about 1000HV_0.3,which was much higher than the hardness of the7A04 aluminum alloy substrate,which can play a good protective effect on the substrate.Among them,the hardness of the coating with a powder particle size of 45?55?m was the highest among the coatings with different powder particle diameters of 995 HV_0.3,and the hardness of the 12-pass coating was the highest among the coatings with different spraying passes.Three WC-10Co-4Cr coatings with different particle sizes prepared by HVAF had very high bonding strength.The influence of powder particle size on the bonding force of the coating was in the form of a normal distribution.Among them,the critical load force of the coating with a powder particle size of 25?35?m was 174.7N.(4)The electrochemical corrosion performance of the coating with the powder particle size of 5-15?m and the 8-pass coating in 3.5%Na Cl solution was better.Immersion corrosion mechanism WC-10Co-4Cr coating was:since the Cr₂O₃ ceramic passivation film formed during the corrosion process cannot completely cover the corrosion surface,C_OO and WO₃formed by the corrosion of bare Co binder phase,but they were unstable and will dissolve and fall off during the corrosion process,and the exposed coating surface Corrosion pits will appear during the corrosion process,and will gradually grow as the corrosion progresses due to the existence of the potential difference.