Microstructure And Magnetic Properties Of Sintered NdFeB Permanent Magnets

NdFeB is widely used in both civil and military fields because of its excellent magnetic properties.The melting and sintering processes are the key steps to determine the properties of NdFeB in preparing process.In addition,the element doping is one of the effective ways to control the structure and properties of NdFeB.For NdFeB factories,how to obtain all kinds of high-performance magnets through existing production lines,and how to realize cost-effective are the technical problems that need to be solved urgently.In this paper,N50,35 H and 35 SH NdFeB products produced by Shanxi Huiqiang Magnets Co.,Ltd are taken as the tracking subjects.The microstructure and properties of N50,35 H and 35 SH are analyzed systematically for melting strip casting and sintering process.The effects of Co doping and double alloy process on the magnetic properties of sintered NdFeB magnets were also studied.The main contents and results are as follows:1.The structure and morphology of N50,35 H,and 35 SH strip casting were studied.It is found that with the increase of DyFe content,the rare earth-rich phases distribute uniformly and the exchange coupling between grains weakens,which is beneficial to the preparation of sintered NdFeB magnets with high coercivity.In additio n,the thickness of the strip casting can be controlled by the rotating speed,the larger the rotational speed,the thinner the strip casting.The thinner one can restrain the growth of ?-Fe phase,inducing a high orientation.2.The effects of doping DyFe alloy and Co on the microstructure and magnetic properties of sintered NdFeB magnets were studied.When the content of DyFe is 2.4wt.%,the coercivity of the magnet increases from 12.31 kOe to 20.88 kOe,and the remanence decreases from 14.33 kG to 12.11 kG.The coercivity of sintered NdFeB increases significantly with a small amount loss of remanence.The microstructure and coercivity of N grade products can be optimized by changing the addition of Co.When the content of Co is 1wt.%,the coercive force increased from 11.01 kOe to 12.33 kOe.3.(Ce,PrNd)FeB and NdFeB dual main phase magnets with less rare earth content and excellent magnetic properties were prepared by double alloy technology.When 25% of Nd in the magnets was replaced by Ce,the coercivity and remanence of the magnets could reach 12.2 kOe and 12.76 kG,respectively,meeting the demand of N35 produce market.The cost is reduced to 77.45% of that of the same grade NdFeB products.In summary,we obtained the different grades NdFeB magnets by traditional process and double alloy method,and the microstructure and morphology were analyzed for the key process.The results provide an important guidance for the process improvement and performance enhancement of high performance NdFeB magnets,and determine the process route for mass production of low-cost dual-main-phase magnets.