| The sintered Nd-Fe-B permanent magnet is called“The king of magnetic”,because its magnetic properties are much batter then other magnets,and it is widely used in various fields.It has been widely used in electrical machinery,mineral processing,new energy vehicles and other aspects.However,due to the lack of coercivity,corrosion resistance and temperature resistance of sintered Nd-Fe-B magnets,their applications in the above aspects are restricted respectively.Therefore,it is particularly important to improve these performances.It is found that the above properties of Nd-Fe-B magnets are largely determined by the state of the grain boundary of the magnet,so the modification of the grain boundary is particularly necessary.It is feasible to improve the properties of magnets by adding nanometer rare earth and its alloys to the grain boundary.In order to improve the coerced force,corrosion resistance,temperature resistance of sintered Nd-Fe-B magnets and save the rational application of precious rare earth metals,Ho-Al alloy,Ho and Al nanopowders were prepared by are method,they are added to the sintering(Pr Nd)31.5Fe66.7B0.98Cu0.05Co0.5Ga0.5magnetic powder respectively through the grain boundary.The modified sintered Nd-Fe-B magnetic blocks were prepared by powder mixing,orientation molding,sintering and tempering,the addition amount of various nano powder was 0wt%,0.1wt%,0.2wt%,0.3wt%and 0.4wt%,respectively.The magnetic properties,morphology,microstructure,temperature coefficient,hardness and corrosion resistance of sintered Nd-Fe-B magnets were studied by permanent magnet characteristic automatic measuring instrument,scanning electron microscope,X-ray diffraction apparatus and Vickers hardness tester.The results show thattransition metal,rare earth metal and alloy nano-sized powders prepared by DAPE.The magnetic properties of the magnet are improved with the increase of the addition amount of various metal and alloy nano-powders.When the addition amount of Ho-Al alloy nano-powder is 0.3wt%,the magnetic properties of the magnet are the best,and the coercivity is increased to 1150.0k A/m,which is about9.93%higher.The remanence magnetism almost does not decrease,and the remanence magnetism is 1.43T.The maximum magnetic energy product is increased to 389.2k J/m3,which is increased by 6k J/m3compared with that without addition,and increased by about1.57%.The density of the magnet increased to 7.55g/cm3,increased by 1.6%;In addition,the hardness of the magnet is 597.28HV,with an increase of about 8.1%.If the amount of Ho-Al alloy nano-powder is up to 0.4wt%,the self-corrosion current of sintered magnet in3.5%Na Cl solution changes to A minimum value of 0.066?A/cm2,which indicates that the corrosion resistance of magnet can be greatly optimized by adding Ho-Al alloy nano-powder at grain boundary.After 96h of corrosion at 60?,1atm and 100%relative humidity,the mass loss of sintered magnets with 0 and 0.4wt%Ho-Al alloy nano-powder is 37.9 mg/cm2and 2.0mg/cm2respectively,which shows a very significant difference between them.The magnetic properties and corrosion resistance of sintered Nd-Fe-B were significantly improved by grain boundary addition of Ho-Al nano-powder. |
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