Study On The Electrodeposition Of Copper On NdFeB Magnet From CuCl-EMIC Ionic Liquid

NdFeB materials are the 3rd generation rare earth permanent magnet materials which developed at the end of the 20th century.It has the advantages of light weight,small size,excellent magnetic properties and abundant raw materials.It is widely used in automobile industry,electrical engineering,microwave technology and other fields.However,NdFeB materials contain the active rare earth element Nd,which is multiphase structure and has large potential difference between phases.Therefore,it is very easy to be corroded in practical use,which results in the attenuation of magnetic properties and device failure.In order to improve the corrosion resistance of NdFeB materials,surface anti-corrosion technology is usually used to prepare protective coatings on NdFeB surface.In this paper,CuCl-EMIC ionic liquid was used to electroplate copper layer on NdFeB matrix after anodic activation pretreatment.The effects of copper wire refining on the properties of CuCl-EMIC ionic liquids,NdFeB pretreatment process and electrochemical parameters on electrodeposition of copper were studied.Cyclic voltammetry curves of CuCl-EMIC ionic liquids and potentiodynamic polarization curves of copper-plated samples were measured by electrochemical workstations.The morphology,composition and phase structure of NdFeB matrix and copper coatings were investigated by scanning electron microscopy,energy dispersive spectrometry and X-ray powder diffraction.The roughness and the binding force of NdFeB surface and copper coatings were measured by roughness tester and drawing tester.The effect of copper wire refining on the properties of CuCl-EMIC ionic liquid was studied.The results showed that the newly prepared dark green CuCl-EMIC ionic liquids contain impurities such as Cu(II)which could be removed by copper wire immersion,resulting in clear and transparent light green CuCl-EMIC ionic liquids.CuCl-EMIC ionic liquid melt at room temperature in the molar ratio range of 2/3 to 3/2,and when the molar ratio is 1,the system has the maximum reduction peak current density.The pretreatment process of NdFeB was studied.The results showed that NdFeB was easily oxidized again after pickling,and copper coatings could not cover the whole surface of the substrate,the binding force was only 3.5 MPa.The oxide film on the surface could be effectively removed by anodic activation.After NdFeB was activated by 25 mA/cm2 for 2 minutes,the surface became flat,the hole was reduced,the surface copper coating was uniform and compact,and the binding force was over 9.2 MPa.The effect of electrochemical parameters on electrodeposition of copper on NdFeB surface was studied.The results showed that when the cell voltage is less than 0.6 V,red-brown coatings with metallic luster can be obtained.The porosity of copper coatings on NdFeB surface decreases with the increase of coating thickness.When the thickness is 6 ?m,the corrosion potential of copper plated samples is similar to that of pure copper,and the porosity is 5.23×10%.The copper coatings grow preferentially along(220)crystal plane,and the higher the current density,the more obvious the preferential growth trend.