WO2017024927A1 - 稀土永磁体及稀土永磁体的制备方法 - Google Patents

稀土永磁体及稀土永磁体的制备方法 Download PDF

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WO2017024927A1
WO2017024927A1 PCT/CN2016/090622 CN2016090622W WO2017024927A1 WO 2017024927 A1 WO2017024927 A1 WO 2017024927A1 CN 2016090622 W CN2016090622 W CN 2016090622W WO 2017024927 A1 WO2017024927 A1 WO 2017024927A1
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rare earth
magnet
heavy rare
permanent magnet
heat treatment
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PCT/CN2016/090622
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English (en)
French (fr)
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陈治安
钮萼
朱伟
陈风华
何叶青
饶晓雷
胡伯平
王浩颉
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北京中科三环高技术股份有限公司
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Priority to DE112016003688.4T priority Critical patent/DE112016003688B4/de
Priority to US15/519,410 priority patent/US10014099B2/en
Priority to JP2017510893A priority patent/JP6772125B2/ja
Publication of WO2017024927A1 publication Critical patent/WO2017024927A1/zh
Priority to US15/592,964 priority patent/US10062489B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/007—Heat treatment of ferrous alloys containing Co
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/30—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes using a layer of powder or paste on the surface
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/60—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C24/00—Coating starting from inorganic powder
    • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/80—Apparatus for specific applications
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/80—Apparatus for specific applications
    • H05B6/806—Apparatus for specific applications for laboratory use

Definitions

  • the invention belongs to the technical field of preparation of rare earth permanent magnets, in particular to a method for preparing a rare earth permanent magnet for improving the intrinsic coercive force of a magnet without substantially losing residual magnetism, and a rare earth permanent magnet prepared by the method. .
  • the Dy 2 Fe 14 B or Tb 2 Fe 14 B crystal has a higher magnetocrystalline anisotropy field than the Nd 2 Fe 14 B crystal, that is, has a larger theoretical intrinsic coercive force.
  • the magnetic anisotropy field ratio Nd of the solid solution phase (Nd, Dy) 2 Fe 14 B or (Nd, Tb) 2 Fe 14 B formed after Dy and Tb partially replace Nd in the main phase Nd 2 Fe 14 B 2 Fe 14 B is large, so that the coercive force of the sintered magnet can be remarkably improved.
  • the method of adding Dy and Tb is usually as follows: direct addition of Dy, Tb in the alloy melting process; or double alloying method of Dy/Tb alloy and NdFeB alloy.
  • the drawback of these two methods is that the saturation magnetization of the magnet is significantly reduced, especially the direct smelting method, resulting in a decrease in the remanence and maximum magnetic energy product of the magnet.
  • the magnetic moments of Nd and Fe are arranged in parallel, the magnetic moments of the two are superimposed in the same direction; Dy/Tb and Fe are antiferromagnetic coupling, and the magnetic moment and Fe magnetic moment of Dy/Tb Reverse stacking results in a weakening of the total magnetic moment.
  • the deposits containing Dy and Tb are scarce and mainly distributed in a few areas.
  • the price of Dy and Tb metals is much higher than that of Nd metal, which leads to a significant increase in the production cost of magnets.
  • the grain boundary thermal diffusion process has been used to effectively increase the intrinsic coercive force of sintered NdFeB magnets, and to rarely reduce the remanence and magnetic energy product of the magnet.
  • the process first coats a layer of a substance containing a heavy rare earth element, such as a metal powder or a compound of Dy or Tb, by coating, deposition, plating, sputtering, adhesion, etc., and heat-reducing the heavy rare earth element along the rich
  • the liquid grain boundary phase of Nd diffuses into the interior of the magnet.
  • the diffusion rate of Dy/Tb in the grain boundary is much faster than the diffusion of Dy/Tb into the grain of the main phase in the grain boundary.
  • the coercive force of the NdFeB sintered magnet is determined by the anisotropy of the main phase particles
  • the NdFeB sintered magnet coated with the high concentration heavy rare earth element shell has high coercive force outside the main phase crystal grains.
  • the higher concentration region is limited to the surface layer of each main phase grain, and the volume ratio of the volume to the main phase grain is very low, so the remanence (Br) and maximum magnetic energy product of the magnet do not substantially change.
  • CN1898757A disclosed in the patent application of Shin-Etsu Chemical Co., Ltd., discloses a plating technique of a surface of a magnet.
  • the sintered blank is processed into a thin magnet, and the magnet is dip coated with a slurry formed by dispersing a rare earth micron-sized fine powder in water or an organic solvent, and then under a vacuum or an inert gas atmosphere at a temperature not higher than the sintering temperature.
  • the magnet is heat treated.
  • the above method can improve H cj to a certain extent, and both require a grain boundary thermal diffusion process at about 900 ° C for several hours to move the heavy rare earth element on the surface of the magnet to the inside of the magnet, and in the main phase of the magnet A high content of shell layer is formed on the surface of the crystal grain, and finally the purpose of improving the coercive force of the magnet is achieved.
  • the heating mechanism is mainly radiation and conduction, and the heating efficiency is low.
  • the region where the thermal diffusion of the heavy rare earth metal element grain boundary is concentrated only in a certain range of the surface layer of the magnet, the partial heating of the core of the magnet not participating in the diffusion process means waste of energy, thereby increasing the production cost.
  • the process can be simplified, the heat treatment time can be shortened, the energy consumption can be reduced, and the production cost of the magnet can be reduced.
  • a first object of the present invention is to provide a rare earth permanent magnet.
  • a second object of the present invention is to provide a method of preparing a rare earth permanent magnet.
  • the present invention provides a rare earth permanent magnet which has a volumetric diffusion phenomenon of heavy rare earth elements from a surface of the magnet along the direction of the magnetic field orientation to a depth of 5 ⁇ m to 100 ⁇ m inside the magnet to form a volume diffusion layer region;
  • the region is divided into magnet units having a volume of 10*100*5 um, and the concentration difference of the heavy rare earth elements of the magnet units at each position in the volume diffusion layer is 0.5 at% or less.
  • at% is an atomic content of several hundred.
  • the heavy rare earth elements are Tb and Dy.
  • the rare earth permanent magnet of the present invention preferably, there is a grain boundary diffusion region between the volume diffusion region of the magnet and the internal magnet, and the difference between the heavy rare earth content in the internal magnet and the heavy rare earth content in the non-diffusion magnet is not more than 0.1at%; at least 70% of the grains in the grain boundary diffusion region have a shell-core structure, wherein the content of the heavy rare earth element in the core is lower than the content of the heavy rare earth element in the shell, at least The difference is 1 at%, preferably 1 to 4 at%.
  • the magnets are, in order from the outside to the inside, a volume diffusion zone, a grain boundary diffusion zone, and an internal magnet.
  • the present invention provides a method for preparing a rare earth permanent magnet as described above, comprising the steps of:
  • Step 1 preparing a blank magnet
  • Step 2 preparing a heavy rare earth source slurry: any one or more of a powder of a heavy rare earth element metal, an alloy containing a heavy rare earth element, a solid solution containing a heavy rare earth element, and a compound containing a heavy rare earth element, and an organic solvent Mixing uniformly to form a heavy rare earth source slurry;
  • Step 3 applying a heavy rare earth source slurry to at least one surface of the blank magnet to form a coating layer
  • Step 4 Microwave heat treatment: microwave heat treatment is performed on the coated blank magnet under vacuum conditions; the heat treatment temperature is 650 ° C to 1000 ° C, and the heat preservation time is 1 minute to 60 minutes.
  • the method for preparing a rare earth permanent magnet according to the present invention further comprises, after step 4, step 5, performing conventional heat treatment on the blank magnet obtained after the microwave heat treatment in step 4, and the temperature of the conventional heat treatment is 400 ° C to 600 ° C, and the heat is maintained.
  • the time is 60 minutes to 300 minutes.
  • the blank magnet has a thickness of not more than 10 mm in a direction of a minimum thickness.
  • the heavy rare earth element includes, but is not limited to, Dy, Tb, and Ho; the metal powder of the heavy rare earth element contains at least one heavy rare earth element, and the powder average particle The degree is from 1 ⁇ m to 100 ⁇ m.
  • the compound containing a heavy rare earth element includes: a hydride of a rare earth metal, a fluoride of a rare earth metal, an oxide of a rare earth metal, and a nitrate salt of a rare earth metal. At least one.
  • the method for preparing a rare earth permanent magnet according to the present invention further, the alloy containing a heavy rare earth element is represented by R a -M b or expressed as R x T y M z ;
  • R is selected from at least one of the heavy rare earth elements
  • M is selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In At least one of Sn, Sb, Hf, Ta, W, Pb, and Bi, and T is at least one selected from the group consisting of Fe and Co;
  • x, y and z are the atomic percentages of the corresponding elements, and: 15 ⁇ b ⁇ 99, the remainder is a; 5 ⁇ x ⁇ 85, 15 ⁇ z ⁇ 95, the remainder is y, and y is greater than 0 .
  • the organic solvent is at least one of an alcohol, an ester, and an alkane.
  • the coating layer has a thickness of less than or equal to 0.5 mm.
  • the method for preparing a rare earth permanent magnet according to the present invention further comprising, prior to step 3, the step of surface treating the green magnet to remove the oxide layer on the surface.
  • the method for preparing a rare earth permanent magnet according to the present invention further comprising, after the step 3, the step of subjecting the coated green magnet to a dry volatilization treatment to remove the organic solvent in the coating layer.
  • the drying temperature is from 20 ° C to 200 ° C, and the drying time is at least 1 minute.
  • the method for preparing a rare earth permanent magnet according to the present invention further, after the completion of step 5, cooling the blank magnet to 100 ° C or less by rapid cooling or cooling with a furnace, and then surface treating the blank magnet to remove the blank A coating on the surface of the magnet.
  • the invention improves the intrinsic coercive force Hcj of the sintered NdFeB magnet without affecting the product remanence Br and the maximum magnetic energy product (BH)max, and can effectively improve the heating efficiency, shorten the heat treatment time and reduce the energy. Consumption, reducing the production cost of the magnet.
  • the invention combines the microwave heat treatment with the grain boundary thermal diffusion to improve the magnetic crystal anisotropy field of the main phase crystal grain surface layer by improving the boundary characteristics of the grain boundary and the interaction with the main phase crystal grains, thereby improving the sintering.
  • the intrinsic coercive force Hcj of the NdFeB magnet has little effect on the remanence Br and the maximum magnetic energy product (BH)max.
  • the conventional process uses conventional heat source heating for grain boundary thermal diffusion.
  • the main mechanism of heating is radiation and conduction, and the heating is carried out from the outside to the inside, and the heating time is long.
  • the heating method is adopted.
  • Cold source heating mainly uses microwave and sample to generate absorbing effect, and by adjusting the microwave emission frequency, the skin depth can be matched with the diffusion depth.
  • Electromagnetic It can be converted into heat energy and achieve the purpose of heating. It belongs to the field of body heating. This method has the characteristics of fast heating speed and uniform heating.
  • Figure 1 is an electromagnetic wave spectrum
  • Example 2 is a demagnetization curve of a magnet in Example 1 and Comparative Examples 1-1, 1-2, and 1-3;
  • Example 3 is a demagnetization curve of a magnet in Example 2 and Comparative Examples 2-1, 2-2, and 2-3;
  • Figure 4a is a backscattered photograph at the edge of the polished section of the magnet of Example 1;
  • Figure 4b is a backscattered photograph of the edge of the polished section of Comparative Example 1-1 magnet;
  • Figure 5a is a backscattered photograph at the edge of the polished section of the magnet of Example 2;
  • Figure b is a backscattered photograph of the edge of the polished section of Comparative Example 2-1;
  • Figure 6a is an energy spectrum analysis of the edge of the polished section of the magnet of Example 1;
  • Figure 6b is a regional characteristic electron micrograph at the edge of the polished section of the magnet of Example 1.
  • Figure 7 is an energy spectrum analysis of the edge of the polished section of Comparative Example 1-1 magnet.
  • the invention combines the microwave heat treatment process with the grain boundary thermal diffusion technology to improve the magnetocrystalline anisotropy field of the main phase grain surface layer by improving the grain boundary characteristics and the interaction with the main phase crystal grains, thereby The intrinsic coercive force of the sintered NdFeB magnet is improved without reducing the remanence and magnetic energy product.
  • the microwave is an electromagnetic wave between radio waves and infrared rays, with a wavelength of 1 mm to 1 m and a frequency of 300 MHz to 300 GHz (since the frequency of the microwave is high, also called ultra-high frequency electromagnetic waves), as shown in FIG.
  • microwaves Compared with electromagnetic waves in other bands, microwaves have the characteristics of short wavelength, high frequency, strong penetrating power and obvious quantum characteristics. Its wavelength range is the same order of magnitude or smaller than the size of a general object on the earth. Like other visible light (except for lasers), microwaves are polarized and coherent waves. According to the physical laws of light, its interaction with matter can be transmitted, absorbed or reflected according to its physical properties, that is, it is selective. At the same time, microwaves have transit time effects, radiation effects, and skin effects.
  • the microwave Since the microwave has a skin effect on the metal, the depth of the absorption is not deep, and for the thermal diffusion of the grain boundary, the diffusion also occurs at a certain depth on the surface of the sample (macro magnet and single crystal), and therefore, the microwave can be changed.
  • the emission frequency matches the absorbing depth to the depth of the grain boundary thermal diffusion.
  • the microwave-heated magnet sample can quickly achieve the overall temperature rise, which achieves heating, and largely avoids the inside of the magnet where the grain boundary heat diffusion does not occur (The heating loss of macro magnets and individual crystal grains saves energy and reduces costs.
  • microwave heating has been widely used. These attempts and applications mainly utilize the activation mechanism and volume effect of microwave heat treatment and the high absorbing efficiency of some materials.
  • the near-solid density metal bulk material due to the skin absorbing effect, a large amount of microwave is reflected, the depth of action is insufficient, and there is a significant temperature gradient inside the block. Therefore, the conventional technical thinking is that microwave heating cannot Directly used in the uniform heat treatment process in the traditional sense.
  • a blank magnet is prepared; the so-called conventional process is usually: batch-alloy smelting-strip preparation-pulverization-forming-forming-sintering to prepare a blank magnet.
  • the blank magnet has a thickness of no more than 10 mm in the direction of the minimum thickness.
  • a heavy rare earth source slurry a powder of a heavy rare earth element metal, an alloy containing a heavy rare earth element, a solid solution containing a heavy rare earth element, a compound containing a heavy rare earth element, or a nitrate salt of a rare earth metal or More than one type, mixed with an organic solvent to form a heavy rare earth source slurry;
  • the heavy rare earth elements include, but are not limited to, Dy, Tb, and Ho; the metal powder of the heavy rare earth element contains at least one heavy rare earth element, and the average particle size of the powder is from 1 ⁇ m to 100 ⁇ m.
  • the compound containing a heavy rare earth element includes at least one of a hydride of a rare earth metal, a fluoride of a rare earth metal, and an oxide of a rare earth metal.
  • An alloy containing a heavy rare earth element is represented by R a -M b or as R x T y M z ;
  • R is selected from at least one of the heavy rare earth elements
  • M is selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In At least one of Sn, Sb, Hf, Ta, W, Pb, and Bi, and T is at least one selected from the group consisting of Fe and Co;
  • x, y and z are the atomic percentages of the corresponding elements, and: 15 ⁇ b ⁇ 99, the remainder is a; 5 ⁇ x ⁇ 85, 15 ⁇ z ⁇ 95, the remainder is y, and y is greater than 0 .
  • the organic solvent is at least one of an alcohol, an ester, and an alkane.
  • an alcohol for example, ethanol, propanol, ethyl acetate, n-hexane.
  • the coating layer has a thickness of less than or equal to 0.5 mm.
  • the drying temperature is from 20 ° C to 200 ° C and the drying time is at least 1 minute.
  • microwave heat treatment microwave heat treatment of the coated blank magnet under vacuum; heat treatment temperature is 650 ° C ⁇ 1000 ° C, holding time is 1 minute ⁇ 60 minutes; after microwave heat treatment, take rapid cooling or cooling with the furnace Way to cool the blank magnet to below 100 ° C;
  • the microwave frequency is 2450 ⁇ 50 MHz, and the power is between 0 and 10 kW.
  • the skin depth is matched to the diffusion depth by adjusting the microwave emission frequency.
  • the temperature of the conventional heat treatment is 400 ° C ⁇ 600 ° C, and the holding time is 60 minutes - 300 minutes.
  • the billet magnet is cooled to below 100 ° C by rapid cooling or by furnace cooling.
  • the sintered NdFeB billet magnet is prepared by a conventional process but does not include a tempering treatment step.
  • the magnet composition (wt.%) is (PrNd) 30.5 Al 0.25 Co 1.0 Cu 0.1 Ga 0.1 Fe bal B 0.97 , and the magnet size is ⁇ 7 mm ⁇ 3.3 mm.
  • the orientation direction is parallel to the axial direction.
  • the surface of the magnet was uniformly coated with a slurry by a smear coating, and the upper and lower end faces of the magnet were coated to a thickness of 0.2 mm.
  • the sample was placed in a vacuum environment for normal temperature dealcoholization for 30 minutes;
  • the magnet coated with the slurry is then subjected to a two-stage heat treatment.
  • the first stage is to put the surface coated with the slurry into a microwave microwave oven for microwave heating treatment, the microwave frequency is 2450MHz, the heating temperature is set to 920 ° C, the heat is kept for 3 minutes, and the microwave emission is stopped after the heat preservation is completed;
  • the sample was cooled by air cooling, and after the sample temperature was below 100 ° C, the sample was taken out.
  • the second-stage heat treatment is performed, and the first-stage heat-treated sample is placed in a conventional vacuum heat source heating furnace for vacuum heat treatment at 480 ° C for 150 minutes, and then the sample is cooled to 100 ° C by furnace or air-cooling to take out the magnet;
  • the residual heavy rare earth source layer on the surface of the magnet is removed by machining to perform magnet performance detection.
  • Comparative Example 1-1 The only difference between Comparative Example 1-1 and Example 1 was that the first stage heat treatment was carried out by conventional heat source heating for 120 minutes.
  • Comparative Example 1-2 The difference between Comparative Example 1-2 and Comparative Example 1-1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • Comparative Example 1-3 The difference between Comparative Example 1-3 and Example 1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • H k is the value of the applied magnetic field when the magnet's magnetic induction is equal to 90% remanence.
  • the magnet composition (wt.%) is (PrNd) 30.5 Al 0.25 Co 1.0 Cu 0.1 Ga 0.1 Fe bal B 0.97 , and the magnet size is ⁇ 7 mm ⁇ 3.3 mm.
  • the orientation direction is parallel to the axial direction.
  • the surface of the magnet was uniformly coated with a slurry by a smear coating, and the coating thickness of both end faces of the sample was 0.15 mm.
  • the sample was placed in an open environment for normal temperature dealcoholization for 120 minutes;
  • the magnet coated with the slurry is subjected to two-stage heat treatment;
  • the first stage is to put the surface coated with the slurry into a microwave microwave oven for microwave heating treatment, the emission power is 2450MHz, the heating temperature is set to 900 ° C, and the heat is kept for 3 minutes. After the heat preservation is completed, the microwave emission is stopped, and the furnace is cooled to the furnace. After the sample temperature is below 100 ° C, the sample is taken out.
  • the residual heavy rare earth source layer on the surface of the magnet is removed by machining to perform magnet performance detection.
  • Comparative Example 2-1 The only difference between Comparative Example 2-1 and Example 2 was that the first stage heat treatment was carried out by conventional heat source heating for 150 minutes.
  • Comparative Example 2-2 The difference between Comparative Example 2-2 and Comparative Example 2-1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • Comparative Example 2-3 The difference between Comparative Example 2-3 and Embodiment 2 is that there is no surface coating process before the magnet is subjected to heat treatment.
  • H k is the value of the applied magnetic field when the magnet's magnetic induction is equal to 90% remanence.
  • the sintered NdFeB billet magnet was prepared by a conventional process (but not including the tempering step), and the magnet composition (wt.%) was (PrNd) 30.5 Al 0.25 Co 1.0 Cu 0.1 Ga 0.1 Fe bal B 0.97 , and the magnet size was ⁇ 7 mm ⁇ 3.3. Mm, the orientation direction is parallel to the axial direction.
  • the surface of the magnet is uniformly coated with a slurry by a smear coating method, and the coating thickness of the upper and lower end faces of the magnet is preferably 0.2 mm; the sample is placed in a vacuum environment and subjected to normal temperature dealcoholization for 30 minutes;
  • the magnet coated with the slurry is placed in a vacuum microwave oven for microwave heating treatment, the microwave frequency is 2450 MHz, the heating temperature is set to 900 ° C, the heat is kept for 3 min, and the microwave emission is stopped after the completion of the heat preservation.
  • the sample was cooled by air cooling, and after the sample temperature was below 100 ° C, the sample was taken out.
  • the second-stage heat treatment is performed, and the first-stage heat-treated sample is placed in a conventional vacuum heat source heating furnace for vacuum heat treatment at 480 ° C for 150 minutes, and then the sample is cooled to 100 ° C by furnace or air-cooling, and the magnet is taken out.
  • the residual heavy rare earth source layer on the surface of the magnet is removed by machining, which is convenient for magnet performance detection.
  • Comparative Example 3-1 The only difference between Comparative Example 3-1 and Example 3 was that the first stage heat treatment was carried out by conventional heat source heating for 120 minutes.
  • Comparative Example 3-2 The difference between Comparative Example 3-2 and Comparative Example 3-1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • Comparative Example 3-3 The difference between Comparative Example 3-3 and Example 3 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • H k is the value of the applied magnetic field when the magnet's magnetic induction is equal to 90% remanence.
  • the sintered NdFeB billet magnet was prepared by a conventional process (but not including the tempering step), and the magnet composition (wt.%) was (PrNd) 30.5 Al 0.25 Co 1.0 Cu 0.1 Ga 0.1 Fe bal B 0.97 , and the magnet size was ⁇ 7 mm ⁇ 3.3. Mm, the orientation direction is parallel to the axial direction.
  • the surface of the magnet is uniformly coated with a slurry by a smear coating method, and the coating thickness of the upper and lower end faces of the magnet is preferably 0.2 mm; the sample is placed in a vacuum environment and subjected to normal temperature dealcoholization for 30 minutes;
  • the magnet coated with the slurry is placed in a vacuum microwave oven for microwave heating treatment, the microwave frequency is 2450 MHz, the heating temperature is set to 920 ° C, the heat is kept for 3 min, and the microwave emission is stopped after the completion of the heat preservation.
  • the sample was cooled by air cooling, and after the sample temperature was below 100 ° C, the sample was taken out.
  • the second-stage heat treatment is performed, and the first-stage heat-treated sample is placed in a conventional vacuum heat source heating furnace for vacuum heat treatment at 500 ° C for 150 minutes, and then the sample is cooled to 100 ° C by furnace or air cooling, and the magnet is taken out.
  • the residual heavy rare earth source layer on the surface of the magnet is removed by machining, which is convenient for magnet performance detection.
  • Comparative Example 4-1 The only difference between Comparative Example 4-1 and Example 4 was that the first stage heat treatment was carried out by conventional heat source heating for 115 minutes.
  • Comparative Example 4-2 The difference between Comparative Example 4-2 and Comparative Example 4-1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • Comparative Example 4-3 The difference between Comparative Example 4-3 and Example 4 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • H k is the value of the applied magnetic field when the magnet's magnetic induction is equal to 90% remanence.
  • the sintered NdFeB billet magnet was prepared by a conventional process (but not including the tempering step), and the magnet composition (wt.%) was (PrNd) 30.5 Al 0.25 Co 1.0 Cu 0.1 Ga 0.1 Fe bal B 0.97 , and the magnet size was ⁇ 7 mm ⁇ 3.3. Mm, the orientation direction is parallel to the axial direction.
  • the surface of the magnet is uniformly coated with a slurry by a smear coating method, and the coating thickness of the upper and lower end faces of the magnet is preferably 0.2 mm; the sample is placed in a vacuum environment and subjected to normal temperature dealcoholization for 30 minutes;
  • the magnet coated with the slurry is placed in a vacuum microwave oven for microwave heating treatment, the microwave frequency is 2450 MHz, the heating temperature is set to 910 ° C, the heat is kept for 3 min, and the microwave emission is stopped after the completion of the heat preservation.
  • the sample was cooled by air cooling, and after the sample temperature was below 100 ° C, the sample was taken out.
  • the second-stage heat treatment is performed, and the first-stage heat-treated sample is placed in a conventional vacuum heat source heating furnace for vacuum heat treatment at 480 ° C for 150 minutes, and then the sample is cooled to 100 ° C by furnace or air-cooling, and the magnet is taken out.
  • the residual heavy rare earth source layer on the surface of the magnet is removed by machining, which is convenient for magnet performance detection.
  • Comparative Example 5-1 The only difference between Comparative Example 5-1 and Example 5 was that the first stage heat treatment was carried out by conventional heat source heating for 150 minutes.
  • Comparative Example 5-2 The difference between Comparative Example 5-2 and Comparative Example 5-1 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • Comparative Example 5-3 The difference between Comparative Example 5-3 and Example 5 was that there was no surface coating process before the magnet was subjected to heat treatment.
  • H k is the value of the applied magnetic field when the magnet's magnetic induction is equal to 90% remanence.
  • the invention combines the microwave heat treatment with the grain boundary thermal diffusion, improves the grain boundary anisotropy field of the main phase grain surface layer by improving the grain boundary characteristics and the interaction with the main phase crystal grains, thereby improving the sintered ferroniobium
  • the intrinsic coercive force Hcj of the boron magnet has little effect on the remanence Br and the maximum magnetic energy product (BH)max.
  • the demagnetization curve in Fig. 2 is a comparison of the magnetic properties of the sample after microwave diffusion treatment and heat treatment in Table 1, and the performance of the as-sintered sample.
  • the results of Fig. 2 illustrate the improvement of the magnetic properties of the product after microwave treatment.
  • the "sintered sample” of Fig. 2 refers to the magnet after the completion of the preparation of the step 1.
  • the demagnetization curve in Fig. 3 is a comparison of the magnetic properties of the sample after microwave diffusion treatment and heat treatment in Table 2 with that of the as-sintered sample, and the results of Fig. 3 illustrate the improvement of the magnetic properties of the product after microwave treatment.
  • the "sintered sample” of Fig. 3 refers to the magnet after the completion of the preparation of the step 1.
  • Table 1 lists the magnetic properties of the magnets of Example 1, Comparative Example 1-1, Comparative Example 1-2, and Comparative Example 1-3. performance. among them:
  • Embodiment 1 adopts the method of the present invention, using Tb-Cu as a heavy rare earth raw material, and using microwave heating technology to carry out grain boundary thermal diffusion of heavy rare earth elements.
  • Comparative Example 1-1 the conventional material was used to diffuse the same material.
  • Comparative Example 1-2 and Comparative Example 1-3 are comparative heat treatment samples of the original sintered sample which has not been surface-coated, and Comparative Example 1-2 is the same as the heat treatment process of Comparative Example 1-1, Comparative Example 1 3 is in accordance with the heat treatment step of the first embodiment.
  • the magnetic properties of the uncoated sintered samples were substantially the same whether they were subjected to microwave treatment (Comparative Examples 1-3) or conventional heat treatment (Comparative Examples 1-2).
  • the coercive force after microwave heat treatment is increased by about 3.5kOe compared with the uncoated sample, and the residual magnetization is basically unchanged, although the coercivity is not as good as the effect.
  • Proportion 1-1 but because the holding time is only 3 minutes, far less than the holding time of Comparative Example 1-1, there is obvious industrial application value.
  • the volume diffusion depth of Comparative Example 1-1 was smaller than that of Example 1, which was about 25 ⁇ m.
  • the detection depth exceeded 200 ⁇ m, it was difficult to detect a significant Tb content (Fig. 7). It is shown that under the same maximum heat treatment temperature, the effect of the diffusion reaction is better due to the activation of the microwave heat treatment. No significant volume diffusion zone is seen in Figure 7.
  • the microwave emission power, frequency, heat treatment temperature, and holding time By changing the microwave emission power, frequency, heat treatment temperature, and holding time, the microstructure and magnetic properties of the inside of the magnet after diffusion can be adjusted.
  • Example 2 lists the magnetic properties of Example 2, Comparative Example 2-1, Comparative Example 2-2, and Comparative Example 2-3 magnets, where:
  • Example 2 employs the method of the present invention, using Dy-F as a heavy rare earth source material, using micro Wave heating technology for grain boundary thermal diffusion of heavy rare earth elements,
  • Comparative Example 2-1 the conventional material was used to diffuse the same material.
  • Comparative Example 2-2 and Comparative Example 2-3 are comparative heat treatment samples of the original sintered sample which was not surface-coated, and Comparative Example 2-2 was consistent with the heat treatment process of Comparative Example 2-1, Comparative Example 2 3 is in accordance with the heat treatment step of the second embodiment.
  • the coercivity of the sintered samples after microwave heat treatment is about 2.5kOe higher than that of the uncoated samples, and the residual magnetization is basically unchanged, although the coercivity improvement effect is not as good as The ratio is 2-1, but since the holding time is only 3 minutes, which is far less than the holding time of Comparative Example 1, there is a significant industrial application value.

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Abstract

本发明公开了一种稀土永磁体及稀土永磁体的制备方法，该稀土永磁体所述材料由磁体表面沿磁场取向方向至磁体内部5μm～100μm深度存在重稀土元素体积扩散现象，形成体积扩散层区；将体积扩散区划分为体积10*100*5um的磁体单元，体积扩散层内各个位置磁体单元的重稀土元素的浓度差在0.5at％以下。本发明提供了一种在不影响产品剩磁Br和最大磁能积(BH)max的前提下，具有高内禀矫顽力Hcj的烧结钕铁硼磁体。在稀土永磁体的制备方法中，将涂覆重稀土源浆料的毛坯磁体在真空条件下进行微波热处理。该方法能够有效地提高加热效率，缩短热处理时间，降低能量的消耗，削减磁体的生产成本。

Description

稀土永磁体及稀土永磁体的制备方法 技术领域
本发明属于稀土永磁体制备技术领域，特别是涉及一种在基本不损失剩磁的前提下提高磁体的内禀矫顽力的稀土永磁体的制备方法，以及利用这种方法制备的稀土永磁体。
背景技术
目前，烧结钕铁硼最大磁能积的实验室水平已经非常接近其理论极限值。生产水平与该极限值的差别也不大，但其内禀矫顽力则远远低于理论极限值，存在很大的提升空间。随着钕铁硼磁体应用领域的不断发展，更高的矫顽力也成为业内人士追求的重点。于是，如何充分发挥钕铁硼主相的内在特性，提高烧结钕铁硼的内禀矫顽力Hcj，就成了当前热点研究的问题。
多年的基础研究和生产实践表明，在磁体生产过程中加入Dy(元素镝)、Tb(铽)等重稀土元素，使其置换磁体中的部分Nd以提高烧结NdFeB磁体的矫顽力已经成了一种众所周知的有效方法。
主要原因是Dy2Fe14B或Tb2Fe14B晶体具有比Nd2Fe14B晶体更高的磁晶各向异性场，也就是具有更大的理论内禀矫顽力。
Dy、Tb部分取代主相Nd2Fe14B中的Nd后，生成的固溶相(Nd，Dy)2Fe14B或(Nd，Tb)2Fe14B的磁晶各向异性场比Nd2Fe14B大，因而可以明显提高烧结磁体的矫顽力。
Dy、Tb的加入方法通常有：合金熔炼过程直接加入Dy、Tb；或富Dy/Tb合金与钕铁硼合金双合金方法。但是，这两种方法的弊端就是会明显降低磁体的饱和磁化强度，特别是直接熔炼的方法，从而导致了磁体的剩磁和最大磁能积的降低。因为在Nd2Fe14B主相中，Nd与Fe的磁矩正向平行排列，两者的磁矩是同向叠加；而Dy/Tb与Fe为反铁磁耦合，Dy/Tb的磁矩与Fe磁矩反向叠加，导致了总磁矩的削弱。
另外，相对于Nd而言，含Dy、Tb的矿藏储量稀少且主要分布在少数几个地域，Dy、Tb金属的价格远高于Nd金属，这种导致了磁体生产成本的显著增加。
近几年，晶界热扩散工艺被用来有效提高烧结钕铁硼磁体的内禀矫顽力，且很少降低磁体的剩磁和磁能积。该工艺首先通过涂覆、沉积、镀覆、溅射、粘覆等方法使磁体外部覆盖含有重稀土元素的物质层，如Dy或Tb的金属粉末或化合物，通过热处理使重稀土元素沿着富Nd的液态晶界相扩散到磁体内部。热处理过程中，晶界中Dy/Tb扩散的速度比晶界中Dy/Tb向主相晶粒内部扩散的速度快得多。
利用该扩散速度差，调整热处理温度和时间，将在烧结体主相和富稀土相之间产生一个很薄的、连续的、含重稀土元素的壳层。
由于NdFeB烧结磁体矫顽力由主相粒子的各向异性决定，因此在主相晶粒外，包覆高浓度重稀土元素壳层的NdFeB烧结磁体具有高矫顽力。而这种浓度较高的区域仅限于各主相晶粒的表层，其体积与主相晶粒的体积比很低，因此磁体的剩磁(Br)和最大磁能积基本上不会变化。
例如，日本信越化学株式会社的专利申请公开的CN1898757A给出了一种磁体表面的渗镀技术。将烧结毛坯加工成薄的磁体，用由重稀土微米级细粉分散于水或有机溶剂中所形成的浆液，来浸涂磁体，然后在真空或惰性气体气氛下，在不高于烧结温度下对磁体进行热处理。结果使矫顽力有较多提高，而剩磁基本不降低。这种方法既节约了重稀土的使用，又抑制了剩磁的下降。
以上方法可以在一定程度上提高Hcj，而且都需要一个在900℃左右、为时数小时的晶界热扩散处理过程，以使得磁体表面的重稀土元素向磁体内部移动，并在磁体主相晶粒表面形成高含量壳层，最终达到提高磁体矫顽力的目的。
然而，由于采用的是常规加热方式(普遍为电阻加热)，加热机制以辐射、传导为主，加热效率低。同时，由于真正发生重稀土金属元素晶界热扩散的区域只集中在磁体表层一定范围内，因此，对磁体芯部不参与扩散过程的部分加热就意味着能量的浪费，进而提高了生产成本。
如果能够有效地提高加热效率，同时有选择的进行局域性加热，就可以简化工艺，缩短热处理时间，降低能量的消耗，削减磁体的生产成本。
发明内容
本发明的第一目的是提供一种稀土永磁体。
本发明的第二目的是提供一种稀土永磁体的制备方法。
为了实现上述第一目的，本发明提供一种稀土永磁体，所述材料由磁体表面沿磁场取向方向至磁体内部5μm～100μm深度存在重稀土元素体积扩散现象，形成体积扩散层区；将体积扩散区划分为体积10*100*5um的磁体单元，体积扩散层内各个位置磁体单元的重稀土元素的浓度差在0.5at％以下。本发明中，at％为原子数百分含量。
本发明如上所述的稀土永磁体，优选地，所述重稀土元素为Tb和Dy。
本发明如上所述的稀土永磁体，优选地，在磁体的体积扩散区和内部磁体之间存在晶界扩散区，所述内部磁体中重稀土含量与未扩散前磁体中重稀土含量差不大于0.1at％；所述晶界扩散区中至少有70％数量的晶粒具有壳-芯结构，其中所述芯部重稀土元素的含量低于所述壳部重稀土元素的含量，二者至少相差1at％，优选相差1～4at％。所述磁体由外至内依次为体积扩散区、晶界扩散区和内部磁体。
为了实现上述第二目的，本发明提供一种如上所述稀土永磁体的制备方法，包括以下步骤：
步骤1，制备出毛坯磁体；
步骤2，制备重稀土源浆料：将重稀土元素金属的粉末、含有重稀土元素的合金、含有重稀土元素的固溶体、含有重稀土元素的化合物的任意一种或一种以上，与有机溶剂混合均匀制成重稀土源浆料；
步骤3，将重稀土源浆料涂覆到毛坯磁体的至少一个表面上形成涂覆层；
步骤4，微波热处理：对涂覆后的毛坯磁体在真空条件下进行微波热处理；热处理温度为650℃～1000℃，保温时间为1分钟～60分钟。
本发明如上所述的稀土永磁体的制备方法，进一步，在步骤4之后还包括步骤5，对步骤4微波热处理后获得的毛坯磁体进行常规热处理，常规热处理的温度为400℃～600℃，保温时间为60分钟～300分钟。
本发明如上所述的稀土永磁体的制备方法，进一步，所述毛坯磁体在最小厚度方向上，厚度不超过10mm。
本发明如上所述的稀土永磁体的制备方法，进一步，所述重稀土元素包括但不限于Dy、Tb和Ho；所述重稀土元素的金属粉末中至少含有一种重稀土元素，粉末平均颗粒度为1μm～100μm。
本发明如上所述的稀土永磁体的制备方法，进一步，含有重稀土元素的化合物包括：稀土金属的氢化物、稀土金属的氟化物、稀土金属的氧化物、稀土金属的硝酸盐水合物中的至少一种。
本发明如上所述的稀土永磁体的制备方法，进一步，含有重稀土元素的合金表示为Ra-Mb或者表示为RxTyMz；
其中R选自重稀土元素中的至少一种；M选自Al、Si、C、P、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Ge、Zr、Nb、Mo、Ag、In、Sn、Sb、Hf、Ta、W、Pb和Bi中的至少一种元素，T是选自Fe和Co中的至少一种；
a和b；x，y和z为对应元素的原子百分数，并且：15＜b≤99，余量为a；5≤x≤85，15＜z≤95，余量为y，并且y大于0。
本发明如上所述的稀土永磁体的制备方法，进一步，所述有机溶剂为醇类、酯类和烷烃中的至少一种。
本发明如上所述的稀土永磁体的制备方法，进一步，所述涂覆层的厚度小于或等于0.5mm。
本发明如上所述的稀土永磁体的制备方法，进一步，在步骤3之前，还包括对毛坯磁体进行表面处理的步骤，以清除表面的氧化层。
本发明如上所述的稀土永磁体的制备方法，进一步，在步骤3之后，还包括对涂覆后的毛坯磁体进行干燥挥发处理的步骤，以去除涂覆层中的有机溶剂。优选地，干燥挥发处理的步骤中，干燥温度为20℃～200℃，干燥时间至少为1分钟。
本发明如上所述的稀土永磁体的制备方法，进一步，，步骤5完成后，采取快速冷却或随炉冷却的方式将毛坯磁体冷却至100℃以下，然后对毛坯磁体进行表面处理，以去除毛坯磁体表面的涂覆层。
本发明的有益效果是：
本发明在不影响产品剩磁Br和最大磁能积(BH)max的前提下，提高烧结钕铁硼磁体的内禀矫顽力Hcj，并且能够有效地提高加热效率，缩短热处理时间，降低能量的消耗，削减磁体的生产成本。
本发明通过将微波热处理与晶界热扩散相结合，通过改善晶界的边界特征及其与主相晶粒的相互作用，提高主相晶粒表面层的磁晶各向异性场，进而提高烧结钕铁硼磁体的内禀矫顽力Hcj，同时，对剩磁Br和最大磁能积(BH)max影响很小。
传统工艺在进行晶界热扩散时所采用的常规热源加热，加热主要机制为辐射和传导，加热从外向内进行，加热时间长；本发明中在进行晶界热扩散时，采用的加热方式为冷源加热，主要利用微波与样品作用产生吸波效果，并通过调节微波发射频率，可以使趋肤深度与扩散深度相匹配。进而将电磁 能转化为热能，实现加热的目的，属于体加热范畴，这种方式具有加热速度快、加热均匀的特点。而且近期的研究表明，在某些化学反应中采用微波加热技术，可以有效降低化学反应活化能，从而降低化学反应的温度，并提高化学反应的速度，属于活化热处理的一种。因此，扩散时间较常规热源加热而言大为减少。
附图说明
图1为电磁波波谱图；
图2为实施例1及对比例1-1、1-2、1-3中磁体的退磁曲线；
图3为实施例2及对比例2-1、2-2、2-3中磁体的退磁曲线；
图4a为实施例1磁体抛光截面边缘处的背散射照片；图4b为对比例1-1磁体抛光截面边缘处的背散射照片；
图5a为实施例2磁体抛光截面边缘处的背散射照片；图b为对比例2-1磁体抛光截面边缘处的背散射照片；
图6a为实施例1磁体抛光截面边缘处能谱分析；
图6b为为实施例1磁体抛光截面边缘处的区域特征电镜照片；
图7为对比例1-1磁体抛光截面边缘处能谱分析。
具体实施方式
下面将结合实施例对本发明的实施方案进行详细描述，实施例中未注明具体条件者，按照常规条件或制造商建议的条件进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
本发明是通过将微波热处理工艺与晶界热扩散技术相结合，通过改善晶界特性及其与主相晶粒的相互作用，提高主相晶粒表面层的磁晶各向异性场，进而在几乎不降低剩磁及磁能积的前提下提高烧结钕铁硼磁体的内禀矫顽力。
微波是介于无线电波与红外线之间的电磁波，波长1mm～1m，频率为300MHz-300GHz(由于微波的频率很高，也叫做超高频电磁波)，如图1所示。微波与其它波段的电磁波相比，具有波长短、频率高、穿透能力强、量子特性明显等特点。其波长范围与地球上的一般物体的尺寸相比处于同一个数量级或更小，与其它可见光一样(除激光外)，微波是极化和相干波，遵 循光的物理定律，它与物质的相互作用根据物理性质不同，可以被透过、吸收或反射，即具有选择性。同时，微波具有渡越时间效应、辐射效应和趋肤效应。
由于微波对于金属来讲存在趋肤效应，因此吸波深度不深，而对于晶界热扩散而言，扩散也发生在样品表面一定深度(宏观磁体及单个晶粒)，因此，可以通过改变微波发射频率使吸波深度与晶界热扩散深度相匹配。
即使趋肤深度不深，在传导作用下，被微波加热的磁体样品也能够快速的实现整体升温，这就即实现了加热，又很大程度上避免了未发生晶界热扩散的磁体内部(宏观磁体及单个晶粒)的加热损失，节约了能量，降低了成本。
对于非金属材料的烧结，如在陶瓷烧结领域，微波加热的应用已经比较广泛，这些尝试和应用主要是利用了微波热处理的活化机理和体积效应以及某些材料的高的吸波效率。然而，对于近实密度的金属块体材料而言，由于存在吸波趋肤效应，大量微波被反射，作用深度不足，块体内部存在明显的温度梯度，所以，传统的技术思维认为微波加热不能直接用于传统意义上的均匀热处理环节。然而，对于本发明所面临的晶界热扩散(GBD)而言，由于渗透元素是从样品表面向块体内部移动，所以主要反应在块体表面发生，因此，内部的高温对促进反应并无实质性的贡献，这就为本发明采用微波热处理提供了相当的创新空间。
下面，详细说明本发明所述稀土永磁体的制备方法的基本过程。
a，制备出毛坯磁体；所谓常规工序，通常是：配料-合金熔炼-条带制备-粉碎制粉-成形-烧结，以制备出毛坯磁体。
优选地，所述毛坯磁体在最小厚度方向上，厚度不超过10mm。
b，制备重稀土源浆料：将重稀土元素金属的粉末、含有重稀土元素的合金、含有重稀土元素的固溶体、含有重稀土元素的化合物、稀土金属的硝酸盐水合物的任意一种或一种以上，与有机溶剂混合均匀制成重稀土源浆料；
所述重稀土元素包括但不限于Dy、Tb和Ho；所重稀土元素的金属粉末中至少含有一种重稀土元素，粉末平均颗粒度为1μm～100μm。
含有重稀土元素的化合物包括：稀土金属的氢化物、稀土金属的氟化物、稀土金属的氧化物中的至少一种。
含有重稀土元素的合金表示为Ra-Mb或者表示为RxTyMz；
其中R选自重稀土元素中的至少一种；M选自Al、Si、C、P、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Ge、Zr、Nb、Mo、Ag、In、Sn、Sb、Hf、Ta、W、Pb和Bi中的至少一种元素，T是选自Fe和Co中的至少一种；
a和b；x，y和z为对应元素的原子百分数，并且：15＜b≤99，余量为a；5≤x≤85，15＜z≤95，余量为y，并且y大于0。
所述有机溶剂为醇类、酯类和烷烃中的至少一种。例如，乙醇、丙醇、乙酸乙酯、正己烷。
c，对毛坯磁体进行表面处理，以清除表面的氧化层。
d，将重稀土源浆料涂覆到毛坯磁体的至少一个表面上形成涂覆层；
优选地，所述涂覆层的厚度小于或等于0.5mm。
e，对涂覆后的毛坯磁体进行干燥挥发处理，以去除涂覆层中的有机溶剂。更优选地，干燥挥发处理的步骤中，干燥温度为20℃～200℃，干燥时间至少为1分钟。
f，微波热处理：对涂覆后的毛坯磁体在真空条件下进行微波热处理；热处理温度为650℃～1000℃，保温时间为1分钟～60分钟；微波热处理后，采取快速冷却或随炉冷却的方式将毛坯磁体冷却至100℃以下；
优选地，微波热处理过程中，微波频率为2450±50MHz，功率在0～10kW之间。在微波热处理过程中，通过调节微波发射频率使趋肤深度与扩散深度相匹配。
g，对微波热处理后获得的毛坯磁体进行常规热处理，常规热处理的温度为400℃～600℃，保温时间为60分钟～300分钟。常规热处理后，采取快速冷却或随炉冷却的方式将毛坯磁体冷却至100℃以下。
h，对毛坯磁体进行表面处理，以去除毛坯磁体表面的涂覆层。
以上步骤，可以根据具体的工作环境或要求，做出适当的调整或者改变。
实施例1
采取常规工序但不包括回火处理步骤制备烧结钕铁硼毛坯磁体，磁体成分(wt.％)为(PrNd)30.5Al0.25Co1.0Cu0.1Ga0.1FebalB0.97，磁体尺寸Φ7mm×3.3mm，取向方向与轴向平行。
将5g平均粒度为5μm的TbCu粉末与20ml无水乙醇搅拌，形成浆料。
采用蘸涂的方式将磁体表面均匀涂覆浆料，磁体上下端面的涂覆厚度为0.2mm。将样品放入真空环境中进行常温脱醇处理30分钟；
然后对表面涂有浆料的磁体进行两级热处理。
第一级是将表面涂有浆料的磁体放入真空微波处理炉内进行微波加热处理，微波频率2450MHz，加热温度设定为920℃，保温3min，保温完成后停止微波发射；
采用风冷方式进行样品冷却，至样品温度低于100℃后，取出样品。
然后进行第二级热处理，将一级热处理后的样品放入常规真空热源加热炉内进行480℃真空热处理150分钟，然后采用随炉或风冷方式将样品冷却至100℃一下，将磁体取出；
采用机加工方式将磁体表面残余重稀土源层去掉，进行磁体性能检测。
对比例1-1
对比例1-1与实施例1的唯一区别是第一级热处理采用常规热源加热，保温120分钟。
对比例1-2
对比例1-2与对比例1-1的区别是磁体进行热处理前没有表面涂覆工艺。
对比例1-3
对比例1-3与实施例1的区别是磁体进行热处理前没有表面涂覆工艺。
表1实施例1与对比例1的磁性能
  Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk/Hcj
实施例1 13.76 18.83 46.28 0.958
对比例1-1 13.70 22.06 45.8 0.931
对比例1-2 13.72 15.23 46.18 0.977
对比例1-3 13.72 15.37 46.24 0.973
注：Hk为当磁体磁感强度等于90％剩磁时的外加磁场值。
实施例2
准备常规工序但不包括回火处理步骤制备烧结钕铁硼毛坯磁体，磁体成分(wt.％)为(PrNd)30.5Al0.25Co1.0Cu0.1Ga0.1FebalB0.97，磁体尺寸Φ7mm×3.3mm， 取向方向与轴向平行。
将5g粒度为5μm的DyF3粉末与20ml无水乙醇搅拌，形成浆料。
采用蘸涂的方式将磁体表面均匀涂覆浆料，样品两个端面的涂覆厚度为0.15mm。
将样品放在开放环境中进行常温脱醇处理120分钟；
然后对表面涂有浆料的磁体进行两级热处理；
第一级是将表面涂有浆料的磁体放入真空微波处理炉内进行微波加热处理，发射功率2450MHz，加热温度设定为900℃，保温3min，保温完成后停止微波发射，随炉冷却至样品温度低于100℃后，取出样品。
然后进行第二级热处理，将一级热处理后的样品放入常规真空热源加热炉内进行490℃真空热处理160分钟，然后采用随炉或风冷方式将样品冷却至100℃以下，将磁体取出；
采用机加工方式将磁体表面残余重稀土源层去掉，进行磁体性能检测。
对比例2-1
对比例2-1与实施例2的唯一区别是第一级热处理采用常规热源加热，保温150分钟。
对比例2-2
对比例2-2与对比例2-1的区别是磁体进行热处理前没有表面涂覆工艺。
对比例2-3
对比例2-3与实施2的区别是磁体进行热处理前没有表面涂覆工艺。
表2实施例2与对比例2的磁性能
  Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk/Hcj
实施例2 13.75 17.80 46.63 0.934
对比例2-1 13.58 18.32 45.41 0.950
对比例2-2 13.72 15.23 46.18 0.977
对比例2-3 13.72 15.37 46.24 0.973
注：Hk为当磁体磁感强度等于90％剩磁时的外加磁场值。
实施例3
采取常规工序(但不包括回火处理步骤)制备烧结钕铁硼毛坯磁体，磁体成分(wt.％)为(PrNd)30.5Al0.25Co1.0Cu0.1Ga0.1FebalB0.97，磁体尺寸Φ7mm×3.3mm，取向方向与轴向平行。
将5克50wt％氧化铽、30wt％具有MgCu2型结构的金属间化合物(其成分为2％Ce-22％Nd-16％Dy-15％Tb-2％Ho-40.8％Fe-1％Co-0.1％Cu-0.5％Ni-0.2％Ga-0.2％Cr-0.2％Ti)和20wt％六水硝酸铽的混合粉末与20ml无水乙醇搅拌，形成浆料。
采用蘸涂的方式将磁体表面均匀涂覆浆料，磁体上下端面的涂覆厚度优选为0.2mm；将样品放入真空环境中，进行常温脱醇处理30分钟；
之后，对表面涂有浆料的磁体进行两级热处理：
第一级热处理，是将表面涂有浆料的磁体放入真空微波处理炉内进行微波加热处理，微波频率2450MHz，加热温度设定为900℃，保温3min，保温完成后停止微波发射，
采用风冷方式进行样品冷却，至样品温度低于100℃后，取出样品。
然后，进行第二级热处理，将一级热处理后的样品放入常规真空热源加热炉内进行480℃真空热处理150分钟，然后采用随炉或风冷方式将样品冷却至100℃一下，将磁体取出，
采用机加工方式将磁体表面残余重稀土源层去掉，便于进行磁体性能检测。
对比例3-1
对比例3-1与实施例3的唯一区别是第一级热处理采用常规热源加热，保温120分钟。
对比例3-2
对比例3-2与对比例3-1的区别是磁体进行热处理前没有表面涂覆工艺。
对比例3-3
对比例3-3与实施例3的区别是磁体进行热处理前没有表面涂覆工艺。
表3实施例3与第三组对比例的磁性能
  Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk/Hcj
实施例3 13.72 17.07 46.26 0.952
对比例3-1 13.68 17.15 45.5 0.933
对比例3-2 13.72 15.23 46.18 0.977
对比例3-3 13.72 15.37 46.24 0.973
注：Hk为当磁体磁感强度等于90％剩磁时的外加磁场值。
实施例4
采取常规工序(但不包括回火处理步骤)制备烧结钕铁硼毛坯磁体，磁体成分(wt.％)为(PrNd)30.5Al0.25Co1.0Cu0.1Ga0.1FebalB0.97，磁体尺寸Φ7mm×3.3mm，取向方向与轴向平行。
将5g平均粒度为15μm的60wt％氧化镝、20wt％五水硝酸钬和20wt％DyHx的混合粉末与20ml无水乙醇搅拌，形成浆料。
采用蘸涂的方式将磁体表面均匀涂覆浆料，磁体上下端面的涂覆厚度优选为0.2mm；将样品放入真空环境中，进行常温脱醇处理30分钟；
之后，对表面涂有浆料的磁体进行两级热处理：
第一级热处理，是将表面涂有浆料的磁体放入真空微波处理炉内进行微波加热处理，微波频率2450MHz，加热温度设定为920℃，保温3min，保温完成后停止微波发射，
采用风冷方式进行样品冷却，至样品温度低于100℃后，取出样品。
然后，进行第二级热处理，将一级热处理后的样品放入常规真空热源加热炉内进行500℃真空热处理150分钟，然后采用随炉或风冷方式将样品冷却至100℃一下，将磁体取出，
采用机加工方式将磁体表面残余重稀土源层去掉，便于进行磁体性能检测。
对比例4-1
对比例4-1与实施例4的唯一区别是第一级热处理采用常规热源加热，保温115分钟。
对比例4-2
对比例4-2与对比例4-1的区别是磁体进行热处理前没有表面涂覆工艺。
对比例4-3
对比例4-3与实施例4的区别是磁体进行热处理前没有表面涂覆工艺。
表4实施例4与第四组对比例的磁性能
  Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk/Hcj
实施例4 13.73 15.93 46.25 0.955
对比例4-1 13.70 16.72 45.8 0.938
对比例4-2 13.72 15.23 46.18 0.977
对比例4-3 13.72 15.37 46.24 0.973
注：Hk为当磁体磁感强度等于90％剩磁时的外加磁场值。
实施例5
采取常规工序(但不包括回火处理步骤)制备烧结钕铁硼毛坯磁体，磁体成分(wt.％)为(PrNd)30.5Al0.25Co1.0Cu0.1Ga0.1FebalB0.97，磁体尺寸Φ7mm×3.3mm，取向方向与轴向平行。
将5g平均粒度为5μm的60wt％DyFe和40wt％PrNdHx混合粉末与20ml无水乙醇搅拌，形成浆料。
采用蘸涂的方式将磁体表面均匀涂覆浆料，磁体上下端面的涂覆厚度优选为0.2mm；将样品放入真空环境中，进行常温脱醇处理30分钟；
之后，对表面涂有浆料的磁体进行两级热处理：
第一级热处理，是将表面涂有浆料的磁体放入真空微波处理炉内进行微波加热处理，微波频率2450MHz，加热温度设定为910℃，保温3min，保温完成后停止微波发射，
采用风冷方式进行样品冷却，至样品温度低于100℃后，取出样品。
然后，进行第二级热处理，将一级热处理后的样品放入常规真空热源加热炉内进行480℃真空热处理150分钟，然后采用随炉或风冷方式将样品冷却至100℃一下，将磁体取出，
采用机加工方式将磁体表面残余重稀土源层去掉，便于进行磁体性能检测。
对比例5-1
对比例5-1与实施例5的唯一区别是第一级热处理采用常规热源加热，保温150分钟。
对比例5-2
对比例5-2与对比例5-1的区别是磁体进行热处理前没有表面涂覆工艺。
对比例5-3
对比例5-3与实施例5的区别是磁体进行热处理前没有表面涂覆工艺。
表5实施例5与第五组对比例的磁性能
  Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk/Hcj
实施例5 13.70 15.63 45.60 0.951
对比例5-1 13.70 16.17 45.8 0.947
对比例5-2 13.72 15.23 46.18 0.977
对比例5-3 13.72 15.37 46.24 0.973
注：Hk为当磁体磁感强度等于90％剩磁时的外加磁场值。
本发明通过将微波热处理与晶界热扩散相结合，通过改善晶界特征及其与主相晶粒的相互作用，提高主相晶粒表面层的磁晶各向异性场，进而提高烧结钕铁硼磁体的内禀矫顽力Hcj，同时，对剩磁Br和最大磁能积(BH)max影响很小。
图2中的退磁曲线是表1中的经过微波扩散处理、热处理后样品磁性能与烧结态样品的性能比较，通过图2的结果说明经过微波处理后产品磁性能的提高。其中，图2种的“烧结态样品”是指步骤1制备完成后的磁体。
图3中的退磁曲线是表2中的经过微波扩散处理、热处理后样品磁性能与烧结态样品的性能比较，通过图3的结果说明经过微波处理后产品磁性能的提高。其中，图3种的“烧结态样品”是指步骤1制备完成后的磁体。
表1列出了实施例1、对比例1-1、对比例1-2和对比例1-3磁体的磁 性能。其中：
实施例1采用了本发明中的方法，以Tb-Cu作为重稀土原材料，采用微波加热技术进行重稀土元素的晶界热扩散，
而对比例1-1则采用了常规的加热方法进行了相同材料的扩散。
对比例1-2和对比例1-3都是对未进行表面涂覆的原始烧结样品进行的同步热处理对比样，对比例1-2与对比例1-1的热处理工序一致，对比例1-3与实施例1的热处理工序一致。
从表1中展示的数据可以看出，对于未涂覆的烧结态样品，无论经过微波处理(对比例1-3)还是常规热处理(对比例1-2)，其磁性能基本相同。而对于经过表面重稀土源涂覆的烧结态样品，经过微波热处理后，其矫顽力较没有涂覆的样品提高了3.5kOe左右，而且剩磁基本没有变化，虽然矫顽力提高效果不如对比例1-1，但是由于保温时间只有3分钟，远远小于对比例1-1的保温时间，因此存在明显的工业应用价值。
从图4a的显微结构照片看，在实施例1的样品边缘位置Tb元素渗透效果明显，扩散量明显大于对比例1-1样品(图4b)。图6a中区域1为经过微波扩散处理后的实施1样品表面残留的涂覆层，由于微波源使用功率偏高，实施例1样品边缘沿磁体取向深度方向存在体积扩散区，厚度约为70μm，从图6a中区域2和3的能谱分析结果看，此区域中Tb的含量分别为8at％和7.5at％，二者相差0.5at％，可见体积扩散区内扩散的重稀土元素浓度差较小。当检测深度提高到100-200μm时(图6a的区域4和5)，Tb的含量分别为2.19at％和0.45at％。区域4和5中70％以上晶粒体现出明显的壳一芯结构。检测深度超过350μm后，如图6a的区域6，则很难检测到明显的Tb含量。图6b标示出了实施1中样品体积扩散区和晶界扩散区的范围。
而对比例1-1的体积扩散深度则较实施例1小，大概为25μm，当检测深度超过200μm后，则很难检测到明显的Tb含量(图7)。说明在相同最高热处理温度的条件下，由于微波热处理的活化作用，扩散反应的效果更佳明显。图7中未看到明显的体积扩散区。
通过改变微波的发射功率、频率及热处理温度、保温时间，可以对扩散后磁体内部的显微结构及磁性能进行调整。
表2列出了实施例2、对比例2-1、对比例2-2和对比例2-3磁体的磁性能，其中：
实施例2采用了本发明中的方法，以Dy-F作为重稀土源材料，采用微 波加热技术进行重稀土元素的晶界热扩散，
而对比例2-1则采用了常规的加热方法进行了相同材料的扩散。
对比例2-2和对比例2-3都是对未进行表面涂覆的原始烧结样品进行的同步热处理对比样，对比例2-2与对比例2-1的热处理工序一致，对比例2-3与实施例2的热处理工序一致。
从表2中展示的数据可以看出，对于未涂覆的烧结态样品，无论经过微波处理(对比例2-3)还是常规热处理(对比例2-2)，其磁性能基本相同。
而对于经过表面重稀土源涂覆的烧结态样品，经过微波热处理后，其矫顽力较没有涂覆的样品提高了2.5kOe左右，而且剩磁基本没有变化，虽然矫顽力提高效果不如对比例2-1，但是由于保温时间只有3分钟，远远小于对比例1的保温时间，因此存在明显的工业应用价值。
从图5a的显微结构照片看，在实施例2的样品边缘位置Dy元素渗透效果明显，与对比例2-1样品(图5b)相当，由此可以得知，可以通过微波加热温度和加热时间调整，对样品的性能进行优化。
以上实施例仅为本发明的示例性实施例，不用于限制本发明，本发明的保护范围由权利要求书限定。本领域技术人员可以在本发明的实质和保护范围内，对本发明做出各种修改或等同替换，这种修改或等同替换也应视为落在本发明的保护范围内。

Claims (15)

  1. 一种稀土永磁体，其特征在于，所述材料由磁体表面沿磁场取向方向至磁体内部5μm～100μm深度存在重稀土元素体积扩散现象，形成体积扩散层区；将体积扩散区划分为体积10*100*5um的磁体单元，体积扩散层内各个位置磁体单元的重稀土元素的浓度差在0.5at％以下。
  2. 根据权利要求2所述的稀土永磁体，其特征在于，重稀土元素为Tb和Dy。
  3. 根据权利要求1或2所述的稀土永磁体，其特征在于，在磁体的体积扩散区和内部磁体之间存在晶界扩散区；所述内部磁体中重稀土含量与未扩散前磁体中重稀土含量差不大于0.1at％；所述晶界扩散区中至少有70％数量的晶粒具有壳-芯结构，其中所述芯部重稀土元素的含量低于所述壳部重稀土元素的含量，二者至少相差1at％。
  4. 权利要求1-3任一项所述稀土永磁体的制备方法，其特征在于，包括以下步骤：
    步骤1，制备出毛坯磁体；
    步骤2，制备重稀土源浆料：将重稀土元素金属的粉末、含有重稀土元素的合金、含有重稀土元素的固溶体、含有重稀土元素的化合物的任意一种或一种以上，与有机溶剂混合均匀制成重稀土源浆料；
    步骤3，将重稀土源浆料涂覆到毛坯磁体的至少一个表面上形成涂覆层；
    步骤4，微波热处理：对涂覆后的毛坯磁体在真空条件下进行微波热处理；热处理温度为650℃～1000℃，保温时间为1分钟～60分钟。
  5. 根据权利要求1所述的稀土永磁体的制备方法，其特征在于，在步骤4之后还包括步骤5，对步骤4微波热处理后获得的毛坯磁体进行常规热处理，常规热处理的温度为400℃～600℃，保温时间为60分钟～300分钟。
  6. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于， 所述毛坯磁体在最小厚度方向上，厚度不超过10mm。
  7. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，所述重稀土元素包括但不限于Dy、Tb和Ho；所述重稀土元素的金属粉末中至少含有一种重稀土元素，粉末平均颗粒度为1μm～100μm。
  8. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，含有重稀土元素的化合物包括：稀土金属的氢化物、稀土金属的氟化物、稀土金属的氧化物、稀土金属的硝酸盐水合物中的至少一种。
  9. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，含有重稀土元素的合金表示为Ra-Mb或者表示为RxTyMz；
    其中R选自重稀土元素中的至少一种；M选自Al、Si、C、P、Ti、V、Cr、Mn、Ni、Cu、Zn、Ga、Ge、Zr、Nb、Mo、Ag、In、Sn、Sb、Hf、Ta、W、Pb和Bi中的至少一种元素，T是选自Fe和Co中的至少一种；
    a和b；x，y和z为对应元素的原子百分数，并且：15＜b≤99，余量为a；5≤x≤85，15＜z≤95，余量为y，并且y大于0。
  10. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，所述有机溶剂为醇类、酯类和烷烃中的至少一种。
  11. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，所述涂覆层的厚度小于或等于0.5mm。
  12. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，在步骤3之前，还包括对毛坯磁体进行表面处理的步骤，以清除表面的氧化层。
  13. 根据权利要求4或5所述的稀土永磁体的制备方法，其特征在于，在步骤3之后，还包括对涂覆后的毛坯磁体进行干燥挥发处理的步骤，以去 除涂覆层中的有机溶剂。
  14. 根据权利要求13所述的稀土永磁体的制备方法，其特征在于，干燥挥发处理的步骤中，干燥温度为20℃～200℃，干燥时间至少为1分钟。
  15. 根据权利要求5所述的稀土永磁体的制备方法，其特征在于，步骤5完成后，采取快速冷却或随炉冷却的方式将毛坯磁体冷却至100℃以下，然后对毛坯磁体进行表面处理，以去除毛坯磁体表面的涂覆层。
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