| As the third generation of rare earth permanent magnet materials,Nd Fe B is widely used in various neighborhoods due to its excellent magnetic properties.With the country’s strong support for green and sustainable industries,a number of green industries such as new energy vehicles and wind power have developed rapidly,which has led to a rapid increase in the demand for high-performance sintered Nd-Fe-B magnets.However,the current sintered Nd-Fe-B magnets still have two serious problems in the extreme working environment:low coercivity and poor corrosion resistance,which will greatly reduce the application range of sintered Nd-Fe-B.To solve these two problems,the most direct method is to dope the magnet with heavy rare earth elements such as Dy and Tb.However,the addition of heavy rare earth elements will cause antiferromagnetic coupling with the Fe atoms in the magnet,which will greatly reduce the magnetic energy product of the magnet.On the other hand,although China is a large rare earth country in the world,the storage of heavy rare earth elements such as Dy and Tb in nature is very limited.Excessive exploitation and use will lead to a serious imbalance in the utilization of rare earth resources.In addition,heavy rare earth elements are very expensive due to scarcity of resources,and excessive use will greatly increase the production cost of magnets.Therefore,how to improve the coercivity and corrosion resistance of magnets without using or using as little as possible of heavy rare earths is an important issue that needs to be solved urgently today.In response to this problem,this article mainly starts with improving the magnetic properties and corrosion resistance of sintered Nd-Fe-B magnets,and uses grain boundary engineering technology to carry out research on the high performance of sintered Nd-Fe-B magnets:First,by designing the Dy-containing grain boundary phase Dy-Fe-Ga,the multi-main phase Nd-Dy-Fe-B basic magnet is restructured to realize the diffusion of Dy in the grain boundary layer of the main phase.The coercivity increased from 20.4 k Oe to24.5 k Oe,an increase of 20.1%.At the same time,the remanence and energy product of the magnet dropped from 13.2 k Gs,43.8 MGOe,to 12.8 k Gs,39.8 MGOe,and both remanence and magnetic properties are well maintained.Realize the efficient utilization of heavy rare earths;The second is to design a low melting point eutectic alloy Nd-Fe-Ga that does not contain heavy rare earth elements to reconstruct the grain boundary of high-performance sintered Nd-Fe-B commercial magnets.The Nd6Fe13Ga phase existing in the grain boundary is used to adjust the ferromagnetism of the grain boundary phase,thereby improving the demagnetization coupling ability of the grain boundary phase.Among them,when the addition amount of Nd-Fe-Ga is 3 wt.%,the improvement effect on the magnetic properties of the magnet is the best,and the Coercivity increased by2.91 k Oe,at the same time,the remanence of the magnet only dropped by 0.06 k Gs.At this amount of addition,the Nd6Fe13Ga phase presents an epitaxially distributed morphology along the main phase,which realizes the addition of no heavy rare earth to increase the coercivity of the magnet;The third is to design Cu powder with an average particle size of 1μm to modify the grain boundary of the sintered Nd-Fe-B scrap magnet.The addition of Cu in the grain boundary transforms the Nd-O phase with higher oxygen content in the grain boundary phase into the Nd-Cu-O phase with lower oxygen content.Compared with the original magnet,the magnet after the grain boundary modification of 0.3 wt.%Cu powder has a corrosion weight loss of only 0.03%of the original magnet after 168hours,which greatly slows down the corrosion rate of the magnet.At the same time,the coercivity of the magnet after the grain boundary modification only slightly decreases,which is 20.28 k Oe.After the grain boundary modification,the magnetic properties of the magnet can still meet the requirements of industrial motors for the coercivity of Nd-Fe-B magnets（20 k Oe）.Under the premise of keeping the magnetic properties basically unchanged,the corrosion resistance of the magnet is significantly improved. |
