| Sintered Nd-Fe-B magnet is a polycrystalline and multi-phase permanent magnetic material, which is prepared from Nd, Fe and B as the main raw materials. Its magnetic properties are excellent, almost throughout all the national industrial application field. However, the poor stability of its magnetic properties hinders its expansion of application in the high-tech field. In order to improve the comprehensive performance of the magnets, people usually add heavy rare earth elements such as Dy. But the price of Dy floats between4to10million/ton, which greatly aggravates the economic burden of the enterprises. Therefore, researching for high-coercivity sintered Nd-Fe-B magnets with no or less Dy addition have been the development tendency within the industry. Our country is the main body of the production and consumption of sintered Nd-Fe-B magnets, but because of the majority of enterprises with obsolete equipments, backward techniques, the high-end products almost have less competitiveness in the market. The scholars and production enterprises are paying more and more attention to improve the preparation techniques and reducing the production cost, at the same time improving the magnetic properties.(Pr-Nd)32.5FebalNb0.65Cu0.20Al0.65B1.15+x wt%Dy2O3(x=0,0.4,0.8,1.2,1.6,2.0,2.4) sintered magnets were prepared on the industrial production line. Then the relationship between density, microstructure, orientation degree, magnetic properties and the mass fraction of Dy2O3were analyzed. The results show that when the mass fraction of Dy2O3is between0and2%, the density changes little. The addition of Dy2O3is more than2%, the density declines slightly. With the addition of0～0.8%Dy2O3, the average grain size decreases, and Nd-rich phase is more evenly distributed. When the mass fraction of Dy2O3is more than0.8%, there are appearing many abnormal growth grains in the microstructure, and the morphology of grain boundary deteriorates. As the content of Dy2O3increasing, the orientation degree rises linearly from1.71to2.24. And Hcj increases linearly from1220kA·m-1to1524kA·m-1as well. Br and (BH)max decrease linearly. Br decreases from1.296T to1.228T, and (BH)max decreases from325.3kJ·m-3to293.2kJ·m-3. While Hk/Hcj increases after the first drop with the increase of the content of Dy2O3. Dy enters into the grains, forming (Nd, Dy)2Fe14B phase which can improve magnetocrystalline anisotropy field. But Dy is antiferromagnetic coupling with Fe to reduce remanence and magnetic energy product.(Pr-Nd)32.7-xHoxFebalNb0.1Cu0.25Al0.85B1.08(wt%, x=0,1,3,5) sintered magnets were prepared on the industrial production line. Then the relationship between the amount of Ho and microstructure of the alloy ingots and the sintered magnets, magnet hardness, orientation degree, magnetic properties, temperature stability were analyzed. On the basis of adding a certain amount of Ho, the formation of a-Fe phase in the alloy ingots is inhibited, reunion phenomenon of Nd-rich phase is reduced, spacing of Nd2Fei4B columnar crystals is diminished, the microstructure of the magnets becomes more detailed and uniform. With the mass fraction of Ho increasing, magnet hardness rises linearly. The content of Ho increases every1%, the hardness increases by20-30HV. With the mass fraction of Ho increasing, orientation degree rises linearly. By adding5%Ho, orientation degree increases by about20%. And the intrinsic coercivity increases significantly, from1115.2kA·m-1to1268.8kA·m-1. While Hk/Hcj increases after the first drop substantially. Remanence and magnetic energy product decline slightly. Temperature stability improves obviously. The magnets adding1%mass fraction of Ho were kept at60℃,80℃ and100℃for1hour, irreversible flux loss reduced by2.16%,6.18%and10.96%respectively. Ho can refine the grains, optimize the distribution of grain boundary phase in the liquid phase sintering process state, promote the sintering densification process.By adding the liquid alloy to optimize the magnet composition, improving strip casting process, powder-preparing process, magnetically-aligning process, sintering process appropriately,45M and42H grades sintered Nd-Fe-B magnets without Dy addition and40SH sintered Nd-Fe-B magnets with adding1.4wt%Dy2O3have been successfully mass-produced on the industrial production line. The characteristics of the columnar crystals of alloy casting is obvious, powder particle size is small enough and its distribution is narrow, making orientation degree increase and the microstructure of the magnets become detailed and uniform. Typical magnetic properties for45M sintered Nd-Fe-B magnets are Br=1.367T(13.67kGs), Hcj=1151.33kA·m-1(14.46kOe),(BH)max=361.30kJ·m-3(45.39MGOe). Typical magnetic properties for42H sintered Nd-Fe-B magnets are Br=1.292T (12.92kGs), Hcj=1406.05kA·m-1(17.66kOe),(BH)max=325.64kJ·m-3(40.91MGOe). Typical magnetic properties for40SH sintered Nd-Fe-B magnets are Br=1.278T (12.78kGs), Hcj=1667.38kA·m-1(20.95kOe),(BH)max=318.17kJ·m-3(40.00MGOe)... |
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