Cold Spraying Composite Coating On The Surface Of Magnesium Alloy And Properties Of Coating

In this paper,To study the effects of Zn and Ni elements on the properties of Cu-Al2O3coatings on magnesium alloys and the effects of Ni elements on the properties of Zn-Al2O3coatings on magnesium alloys.low pressure cold spraying technology was used to prepare Cu/Ni-Al2O3 coating,Cu-Al2O3 coating,Cu/Zn-Al2O3 coating,Zn/ni-Al2O3 coating,Zn-Al2O3 coating and other copper-based and zinc-based coatings on the surface of AZ31B magnesium alloy.In order to further penetrate into the study of the effect of Ni on the coating properties of Cu/Ni-Al2O3 coating,Cu/Ni composite coating was prepared by using mechanical mixed copper-nickel powders with a nickel mass fraction of 0%,20%,40%,60%and 80%,respectively,at this time in order to remove the effect of other factors on the coating properties,Cu/Ni composite coating does not contain any ceramic reinforcement phase,and in order to eliminate the negative impact of coating quality caused by the lack of enhanced phase,ultrasonic shot peening technology is used to treat the surface of Cu/Ni composite coating.The microstructure,phase structure and corrosion morphology of the coating were characterized and analyzed by electron scanning microscope（SEM）and its accompanying energy spectrum analyzer（EDS）,X-ray diffractometer（XRD）,laser confocal（3D）microscope,metallographic microscope and pose microscope.The microhardness of the coating was tested by microhardness meter,and the wear behavior and corrosion behavior of the coating were studied by means of friction and wear tester,electrochemical workstation and neutral salt mist test box.The main research conclusions of this paper are as follows:1.The optimum technological parameters for the preparation of the corresponding system coating were obtained by a large number of experiments.Low-pressure cold spraying equipment using compressed air with air pressure of 0.6⁰.8MPa,the working distance is set at 10mm,by adjusting the gas temperature,nozzle movement speed,powder supply rate,the coating thickness as the index,to obtain the best sedimentary process parameters.The deposition rate of different metal powders is quite different because of their properties,powder size and powder morphology,especially to prepare a variety of powder composite coatings,and the variation law of deposition rate should be mastered as far as possible.In this paper,the coating material uses dendrite copper powder,spherical zinc powder,surface rough spherical nickel powder and irregular alumina powder,alumina mainly plays the role of increasing the fluidity of coated powder materials and tamping coating.The following conclusions are obtained by using powder materials with different powder morphology:Spherical copper powder and dendrite copper powder have better fluidity,but the deposition rate of dendrite copper powder is higher under the same process parameters,but the porosity of the coating is also higher,while the spherical shape copper powder has low deposition rate,but its coating density is high,and the dendrite powder is more favorable to deposition.For the ball shape nickel powder,because the nickel itself has a certain magnetism,and the hardness is high,not easy to occur plastic deformation and other factors lead to nickel powder more difficult to deposit.2.The effects of Ni and Zn on the properties of Cu-Al₂O₃ coating on magnesium alloys and the effects of Ni elements on the properties of Zn-Al₂O₃ coatings on magnesium alloys were studied by preparing copper base and zinc base coatings.In the cold spraying copper base coating of magnesium alloy,Cu-Al₂O₃ coating,Cu/Ni-Al₂O₃ coating and Cu/Zn-Al₂O₃ coating can provide some corrosion resistance and wear protection for magnesium alloy matrix,Cu/Zn-Al₂O₃ coating can provide better grinding effect for magnesium alloy matrix,The Cu/Ni-Al₂O₃ coating obtained by doped Ni element has better microstructure,minimal coating porosity,and the corrosion resistance of Cu/Ni-Al₂O₃coating is the best compared with that of Cu-Al₂O₃ coating and Cu/Zn-Al₂O₃ coating,which can provide better corrosion protection for magnesium alloy matrix.In the cold spraying zinc base coating of magnesium alloy,the Zn/Ni-Al₂O₃ coating shows a better coating structure because of the presence of Ni elements,and in terms of mechanical properties,the Zn/Ni-Al₂O₃ coating obtained after doping with Ni element has higher wear resistance than the Zn-Al₂O₃ coating,Microhardness and good antiseptic properties.3.Further study of the effect of Ni content in Cu/Ni composite coating,because the lack of strengthening phase leads to its coating loose porous,through ultrasonic shot peening can improve the quality of the coating,reduce the porosity of the coating,and after peening after the treatment of cold spray pure copper coating than the coating without peening enhanced better corrosion protection effect,The self-corrosion potential of pure copper coating is improved by peening,and the self-corrosion current density is reduced,and the post-peening treatment has a positive effect on the improvement of the quality of cold spray coating.With the increase of nickel content,the porosity of Cu/Ni composite coating decreases gradually,the coating quality is obviously improved compared with that of pure copper coating,the microhardness of coating section increases with the increase of nickel content,and the nickel content of Cu/Ni composite coating is about 16.vol%,which has better anti-corrosion performance,However,the addition of nickel is not all favorable,the friction coefficient of Cu/Ni composite coating after doped nickel is larger than that of pure copper coating,combined with its grinding mark morphology analysis,it is found that the addition of nickel element also changes the wear mechanism of copper coating.