Experimental Study On Preparation Of Nano-Composite Coating By Pulsed Current-Jet Electrodeposition

As the third generation of rare earth permanent magnets,NdFeB is widely used in all walks of life with its excellent magnetic properties.However,the poor corrosion resistance of NdFeB materials restricts the development of its application field.The surface protection technology is usually used to deposit metal film on the surface of the magnet to improve its performance.The nanocomposite coating has better performance than ordinary coating in the aspects of hardness,corrosion resistance,wear resistance and so on.Pulsed current-jet electrodeposition?PCJE?is developed on the basis of jet electrodeposition,which has the advantages of simple process,high deposition efficiency and good quality of coating.In this paper,the experimental research on the preparation of nanocomposite coatings by PCJE was carried out on the improved experimental platform.Through the analysis of the properties of the coating obtained under different process parameters,the protective coating with better performance is sought.The main contents are as follows:?1?The method of PCJE is put forward and an experimental platform for electrodeposition is designed.Under the large current density,the coating prepared by conventional electrodeposition has the defect of pitting and charred,so the PCJE is proposed.Higher current density is used to improve the performance of all aspects of the coating.In order to meet the needs of experiment,we designed some key components such as fixture,nozzle system,pulse power supply and changed the control system to facilitate human-machine interaction.?2?Comparative experimental study of direct current-jet electrodeposition?DCJE?and PCJE.In order to study the influence of pulse current on the quality of the coating,DCJE and PCJE were used respectively to prepare Ni-Al₂O₃ nanocomposite coating.The surface morphology,grain size and microhardness of the coatings were characterized by SEM,XRD and microhardness tester.Compared with the coatings obtained by DCJE,the latter exhibited higher microhardness and better corrosion resistance,while the addition of proper amount of Al₂O₃ can optimize the coating performance.?3?Pure nickel coating and Ni-Al₂O₃ nanocomposite coating were prepared by PCJE.By changing the current density,the influence of current density on the surface morphology,adhesion strength and corrosion resistance of the coating was investigated,and the corresponding equipment was used for characterization analysis.The results shown that with the increase of current density,the grain size of pure nickel coating decreased gradually,while the grain size of the composite coating decreased first and then increased.Under the appropriate current density,the addition of nanoparticles enhanced the protective properties of the coating,so composite coating has stronger adhesion strength and corrosion resistance than pure nickel coating.?4?Anticorrosion mechanism of nanocomposite coating on sintered NdFeB surface is analyzed.NdFeB is easily eroded,it is mainly due to the direct contact with the corrosive medium.Coating on the surface of the magnet can effectively isolate the contact between the surface of NdFeB and the external environment,and the better the performance of the coating,the more significant the isolation effect.The introduction of the pulse power supply and the addition of the nanoparticles can improve the quality of the coating,so as to obtain a composite coating with better anticorrosion performance.