Effect Of Compound Addition Of Oxides On The Magnetic Properties Of Sintered Nd-Fe-B

Sintered Nd-Fe-B magnets have excellent properties and are widely used in many fields.However,the defects of coercivity and corrosion resistance of sintered Nd-Fe-B magnets limit their further application.Therefore,finding a more effective way to improve the shortcomings of sintered Nd-Fe-B magnets has always been the focus of researchers.The grain boundaries of magnets have a very important influence on the magnetic properties and corrosion resistance of magnets.Therefore,it is necessary to improve the properties and corrosion resistance of magnets by adding elements or compounds at grain boundaries.In order to improve the magnetic properties and corrosion resistance of sintered Nd-Fe-B magnets,（PrNd）_15.5B₆Cu_0.1Fe_balMg（wt%,x=0.1-0.3）permanent magnet were prepared by adding MgO/Mg nanopowders at grain boundary and sintering with binary alloy method.The magnetic properties,morphology,microstructures,hardness and corrosion resistance of sintered Nd-Fe-B magnets with 0 wt%,0.1wt%,0.2wt%and 0.3wt%MgO/Mg（mass ratio is 1:2）nanopowders were studied in detail by FE-2100H permanent magnetism automatic measuring instrument,scanning electron microscopy,X-ray diffractometer,Vickers hardness tester and CHI660E electrochemical workstation.The results show that the magnetic properties of the magnets increase first and then decrease with the increase of MgO/Mg（mass ratio 1:2）nanopowders content.When the content of MgO/Mg nanocomposite powder is 0.1wt%,the comprehensive magnetic properties of the magnets are the best.At this time,the coercivity of the magnets is 1183 kA·m^-1,the remanence is1.22T and the maximum magnetic energy product is 288 kJ·m^-3,the magnetic properties of the magnet are slightly improved by 0.2%,0.6%and 1.7%compared with those of the magnet without addition;The maximum density of the magnet is 7.49g·cm^-3;The orientation of the magnet is the best,and the peak-to-intensity ratio of I_（006）/I_（105）diffraction reaches 1.466;The hardness of the magnet is increases obviously,which is 8%higher than that of the magnet without adding,reaching 590.09HV.The Tafel curve shows that with the increase of MgO/Mg nanopowders,the corrosion potential increases from-1.093V to-0.929V,the corrosion potential increases by 15%,the corrosion current density decreases from 223.87μA·cm^-22 to 42.66μA·cm^-22 by 81%compared with 0wt%magnet,and the corrosion resistance increases obviously.The electrochemical impedance spectroscopy shows that the radius of the high frequency capacitive arc of the magnet with appropriate amount of MgO/Mg nanopowders is larger than that of the high frequency capacitive arc of 0wt%magnet,increasing the charge transfer resistance.When the magnet is corroded for 96 h,the mass loss of sintered magnet with adding 0.3wt%MgO/Mg nanopowders is only 2.3 mg·cm^-2,without adding is 35.2 mg·cm^-2.Therefore,adding MgO/Mg nanopowders at grain boundary can improve the corrosion resistance of sintered Nd-Fe-B magnets.