CN116525281A - A neodymium iron boron magnet with ultra-high coercive force and its preparation method and application - Google Patents

Abstract

The invention discloses a neodymium-iron-boron magnet with ultrahigh coercivity, and a preparation method and application thereof. The preparation method comprises the following steps: providing a neodymium iron boron pressed compact; and performing liquid phase sintering treatment on the neodymium iron boron compact to obtain a neodymium iron boron magnet with ultrahigh coercivity; wherein the liquid phase sintering treatment comprises pre-sintering, pre-diffusion, densification sintering and grain boundary diffusion treatment; the main phase crystal grain of the magnet in the pre-diffusion magnet obtained by the pre-diffusion treatment has a core-shell structure, and the main phase crystal grain of the magnet in the neodymium-iron-boron magnet with the ultrahigh coercivity has an inner-outer double-layer heavy rare earth magnetic hardening shell structure. The invention utilizes the sectional process control of the liquid phase sintering process, optimizes the sintering and diffusion processes, realizes the high-quality utilization of heavy rare earth, prepares the neodymium-iron-boron magnet with ultrahigh coercivity, and has simple operation and convenient production.

Description

A neodymium iron boron magnet with ultra-high coercive force and its preparation method and application

technical field

The invention belongs to the technical field of rare earth permanent magnet materials, and in particular relates to a neodymium-iron-boron magnet with ultra-high coercive force and its preparation method and application.

Background technique

As the third-generation rare earth permanent magnet material, NdFeB has the characteristics of high coercive force, high remanence and high magnetic energy product, and is the permanent magnet material with the highest comprehensive magnetic properties discovered so far. The rapid development of emerging fields such as new energy vehicles, maglev trains, wind power and energy-saving home appliances has put forward higher requirements for the magnetic properties of NdFeB permanent magnet materials, especially for their anti-demagnetization ability. However, the current ternary NdFeB The actual value of the coercive force of the magnet is less than half of the theoretical value, which requires NdFeB magnets to further increase their coercive force. The grain boundary diffusion technology of heavy rare earth is an effective means to increase the coercive force of magnets. The boundary enters the interior of the magnet, and forms a magnetically hardened shell with a higher anisotropic field on the surface of the grain, which inhibits the nucleation of the reverse magnetization domain (reverse magnetic domain) on the surface of the grain, thereby increasing the coercive force of the magnet. After years of development, the forms of diffusion sources in diffusion technology have become various, including simple substances of heavy rare earths, oxides, fluorides, hydrides, alloys, etc. , spraying method, magnetron sputtering method, evaporation method, etc. Although the diffusion process is gradually diversified, it has been found in practice that the coercive force of the conventional heavy rare earth grain boundary diffusion technology is limited, and the coercive force increase after diffusion is usually difficult to exceed 10kOe. Therefore, it is an urgent problem to provide an NdFeB magnet with ultra-high coercive force and its preparation method.

Contents of the invention

The main purpose of the present invention is to provide a neodymium-iron-boron magnet with ultra-high coercive force and its preparation method and application, so as to overcome the deficiencies of the prior art.

In order to realize the aforementioned object of the invention, the technical solutions adopted in the present invention include:

An embodiment of the present invention provides a method for preparing a neodymium-iron-boron magnet with ultra-high coercive force, which includes:

Provide NdFeB compacts;

And, performing liquid-phase sintering treatment on the NdFeB compact to obtain an NdFeB magnet with ultra-high coercive force;

Wherein, the liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the main phase grains of the magnet in the pre-diffusion magnet obtained by the pre-diffusion treatment have a core-shell structure, and the super The main phase grains of the high-coercivity NdFeB magnets have a double-layer heavy rare-earth magnetically hardened shell structure inside and outside.

The embodiment of the present invention also provides the NdFeB magnet with ultra-high coercive force obtained by the aforementioned preparation method. The main phase grains of the magnet in the NdFeB magnet with ultra-high coercive force include sequentially formed in The inner heavy rare earth magnetically hardened shell and the outer heavy rare earth magnetically hardened shell on the surface of the core structure.

The embodiment of the present invention also provides the application of the above-mentioned NdFeB magnet with ultra-high coercive force in the fields of new energy vehicles, maglev trains, wind power generation or energy-saving home appliances.

In the high-performance NdFeB magnet prepared by the traditional grain boundary diffusion technology, the magnetically hardened shell layer rich in heavy rare earth only exists on the surface of the grain. The inversion and transmission of domains have a certain pinning effect, but it is easier to nucleate the reverse magnetization inside the grain. Once the volume fraction of the reverse magnetization domain inside the grain reaches a certain proportion, the magnetic hardening effect of the shell on the surface of the grain will not be enough. Continue to block the magnetic exchange coupling between grains, which means that the traditional intergranular diffusion technology has a limited effect on improving the coercive force. The present invention is based on a large number of practical researches, combined with the growth characteristics of NdFeB main phase grains, and utilizing the segmented process control (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion) of the liquid phase sintering process to realize the magnet The main phase grains have a typical structure of inner and outer double-layer heavy rare earth magnetically hardened shells. The inner shell can effectively inhibit the nucleation of reverse magnetization in the weak area inside the grain, and the outer shell can effectively block the transfer of reverse magnetization domains between grains. Finally achieve the purpose of preparing ultra-high coercive force NdFeB magnets

Compared with prior art, the beneficial effect of the present invention is:

(1) The present invention successfully prepares NdFeB grains with double-layer heavy rare earth shells, and simultaneously forms magnetic hardening strengthening structural units on the surface and inside of the magnet grains, effectively inhibiting the nucleation and migration of reverse magnetization domains, optimizing and Improve the coercivity of NdFeB magnets;

(2) The inner and outer double-layer heavy rare earth magnetically hardened shells possessed by the magnet main phase grains of the NdFeB magnets with ultra-high coercive force in the present invention, the thickness of the inner shell and the heavy rare earth content can be obtained by pre-diffusion The process (heavy rare earth pre-diffusion source composition and dosage) is controlled to achieve controllable adjustment, which can realize the expected design of raw material cost and coercivity improvement effect;

(3) The present invention not only realizes the advantages of grain boundary diffusion technology to save heavy rare earth consumption and production cost, but also achieves the characteristics of traditional heavy rare earth alloying smelting and adding method to strengthen the overall anti-demagnetization ability of NdFeB main phase grains, and is practical and creativity;

(4) The preparation method provided by the present invention is simple and easy to operate, and the prepared product has good consistency and stability, and can prepare ultra-high coercive force NdFeB magnets, which are suitable for mass production.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments described in the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic diagram of the principle of preparing an NdFeB magnet with ultra-high coercive force in a typical embodiment of the present invention.

Detailed ways

In view of the defects of the prior art, the inventor of this case has been able to propose the technical solution of the present invention through long-term research and extensive practice. The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are a part of the present invention Examples, not all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Specifically, as an aspect of the technical solution of the present invention, a method for preparing a neodymium-iron-boron magnet with ultra-high coercive force includes:

Provide NdFeB compacts;

And, performing liquid-phase sintering treatment on the NdFeB compact to obtain an NdFeB magnet with ultra-high coercive force;

Wherein, the liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the main phase grains of the magnet in the pre-diffusion magnet obtained by the pre-diffusion treatment have a core-shell structure, and the super The main phase grains of the high-coercivity NdFeB magnets have a double-layer heavy rare-earth magnetically hardened shell structure inside and outside.

In some preferred embodiments, the schematic diagram of the principle of preparing NdFeB magnets with ultra-high coercive force in the present invention is shown in FIG. 1 .

In some preferred embodiments, the preparation method of the NdFeB magnet with ultra-high coercive force includes: preparing raw materials according to the composition of the final sintered NdFeB magnet, performing alloy smelting, and obtaining NdFeB alloy flakes, The NdFeB alloy flakes are hydrogen crushed to obtain hydrogen crushed coarse powder; the hydrogen crushed coarse powder is jet milled to obtain NdFeB fine powder with uniform particle size distribution; Compact: Liquid-phase sintering of NdFeB compacts, including pre-sintering, pre-diffusion, densification sintering and grain boundary diffusion treatment; firstly, pre-sintering of NdFeB compacts to obtain a relatively dense pre-sintered state Magnet; then pre-diffusion treatment is carried out on the pre-sintered magnet, so that the main phase grains of the magnet form a core-shell structure; the above-mentioned magnet is sintered and densified, and finally the grain boundary is diffused to obtain the main phase grains of the magnet. Ultra-high coercive force NdFeB magnets with rare earth hardened shell.

In some preferred embodiments, the preparation method includes: pre-sintering the NdFeB compact at 900-1020°C for 2-5 hours to obtain a pre-sintered magnet; wherein, the crystal grains in the pre-sintered magnet The size is 3-5 μm.

Further, the purpose of the pre-sintering is to prevent excessive grain growth, and the grain size is 3-5 μm at this time.

In some preferred embodiments, the preparation method includes: coating the pre-diffusion source on the surface of the pre-sintered magnet and performing a pre-diffusion treatment for 2-8 hours under vacuum conditions at a temperature of 800-950°C to obtain a pre-diffusion A magnet; wherein the pre-diffusion treatment at least makes the main phase grains of the obtained pre-diffusion magnet form a core-shell structure.

Further, the pre-diffusion source includes a rare earth alloy diffusion source, and the general chemical formula of the rare earth alloy diffusion source is H _x R _y M _100-xy , wherein, H is selected from any one of Tb, Dy, Ho or A combination of two or more, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, La, and M is selected from any of Cu, Al, Fe, Ga, Zn, Mg, Mn A combination of two or more, x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30, and y is 20-80.

Further, the raw materials are prepared according to the composition of the pre-diffusion source, and the required pre-diffusion source is prepared through processes such as arc melting, wire cutting, hydrogen breaking, and jet milling.

In some preferred embodiments, the preparation method includes: densifying and sintering the pre-diffusion magnet at 1000-1100°C for 2-10 hours to obtain a densified sintered magnet; wherein, the crystals in the densified sintered magnet The particle size is 5-10 μm.

Furthermore, the densification and sintering process is to increase the temperature to allow the grains to grow.

In some preferred embodiments, the preparation method includes: covering the surface of the densified sintered magnet with a diffusion source, performing a diffusion treatment at 800-950°C for 2-8h, and then tempering at 400-600°C for 2 -4h, to obtain NdFeB magnets with ultra-high coercive force.

Further, the diffusion source includes a rare earth alloy diffusion source, and the general chemical formula of the rare earth alloy diffusion source is H _x R _y M _100-xy , wherein, H is selected from any one or both of Tb, Dy, Ho A combination of more than one, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, La, and M is selected from any of Cu, Al, Fe, Ga, Zn, Mg, Mn Or a combination of two or more, x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30, and y is 20-80.

Further, the raw materials are prepared according to the composition of the diffusion source, and the required diffusion source is prepared by processes such as arc melting, wire cutting, hydrogen breaking, and jet milling.

In some preferred embodiments, the preparation method comprises:

Provide raw materials for preparing NdFeB compacts and carry out alloy melting treatment to obtain NdFeB alloy flakes;

Perform hydrogen crushing treatment on the NdFeB alloy flakes to obtain hydrogen crushed coarse powder;

Carrying out jet milling to the hydrogen crushing coarse powder to obtain NdFeB fine powder;

And, performing orientation pressing molding and isostatic pressing treatment on the NdFeB fine powder to obtain NdFeB compact.

Further, the general chemical formula of the composition of the NdFeB compact is R _x Fe _y M _z B _α ; wherein, R is selected from La, Ce, Tb, Dy, Ho, Y, Gd, Nd, Pr Any one or a combination of two or more, M is selected from any one or a combination of two or more of Cu, Al, Ga, Mg, Ni, Ti, Co, Zr, x is 28-33wt%, y is 60 -75 wt%, z is 0-5 wt%, α is 0.9-1.2 wt%, x+y+z+α=100.

Further, the thickness of the NdFeB alloy sheet is 200-300 μm.

Further, the grinding gas pressure used in the jet mill treatment is 0.5-0.7 MPa, and the rotating speed of the classifying wheel is 3500-5000 rpm.

Further, the average particle diameter D50 of the NdFeB fine powder is 1 μm≤D50≤2 μm.

The pre-diffusion source and the diffusion source in the present invention may be the same or different.

In some more specific embodiments, the preparation method of the neodymium-iron-boron magnet with ultra-high coercive force includes:

(1) Prepare raw materials according to the composition of the final required sintered NdFeB magnet, carry out alloy smelting, obtain NdFeB alloy flakes, and hydrogen crush the NdFeB alloy flakes to obtain hydrogen broken coarse powder;

(2) Carry out jet milling to hydrogen broken coarse powder, make the neodymium-iron-boron fine powder with uniform particle size distribution;

(3) carrying out isostatic pressing treatment after carrying out oriented press molding, obtains neodymium-iron-boron compact;

(4) Pre-sintering the NdFeB compact to obtain a relatively dense pre-sintered magnet;

(5) Pre-diffusion treatment is performed on the pre-sintered magnet, so that the main phase grains of the magnet form a core-shell structure;

(6) Sintering and densifying the above-mentioned magnet, and finally performing grain boundary diffusion to obtain an ultra-high coercive force NdFeB magnet with an inner and outer double-layer heavy rare earth magnetically hardened shell.

Further, the NdFeB alloy flakes are obtained by flake flakes in a quick-setting furnace, with a thickness of 200-300 μm.

Another aspect of the embodiment of the present invention also provides the NdFeB magnet with ultra-high coercive force prepared by the aforementioned preparation method, the main phase crystal grain of the magnet in the NdFeB magnet with ultra-high coercive force Including the inner heavy rare earth magnetic hardening shell and the outer heavy rare earth magnetic hardening shell formed sequentially on the surface of the core structure;

Further, the thickness of the inner heavy rare earth magnetically hardened shell layer is 0.5-3 μm.

Further, the outer heavy rare earth magnetically hardened shell layer has a thickness of 0.2-0.5 μm.

Another aspect of the embodiment of the present invention also provides the use of the above-mentioned NdFeB magnet with ultra-high coercive force in the field of new energy vehicles, maglev trains, wind power generation or energy-saving home appliances.

The present invention designs a method for preparing an ultra-high coercive force NdFeB magnet. Through the optimization and improvement of the base magnet preparation process and the later diffusion process, NdFeB crystal grains with double-layer heavy rare earth shells are prepared. The magnetically hardened strengthening structural unit is formed on the surface and inside of the grain at the same time, which effectively inhibits the nucleation and migration of the reverse magnetization domain, which has far-reaching significance for improving the coercive force of NdFeB magnets and promoting the rapid development of NdFeB industry and rare earth permanent magnets.

The technical solution of the present invention will be described in further detail below in conjunction with several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and detailed implementation methods and specific operating procedures are provided. However, the present invention The scope of protection is not limited to the examples described below.

The experimental materials used in the following examples can be purchased from conventional biochemical reagent companies unless otherwise specified.

Example 1:

According to the composition of the matrix alloy as Nd _30.5 Fe _68.42 Al _0.1 Cu _0.2 Co _0.5 Zr _0.2 Ga _0.1 B _0.98 , the raw materials were smelted and poured onto copper rollers by quick-setting process to obtain cast sheets with an average thickness of 0.3mm, and the cast sheets were placed In a hydrogen furnace, charge hydrogen to crush and hold at 450°C for 10 hours for dehydrogenation treatment to obtain coarsely crushed powder, and then grind the coarsely crushed powder in a jet mill protected by a nitrogen atmosphere to obtain an average particle size of 2.0 μm The airflow grinding fine magnetic powder; the NdFeB fine powder is oriented and pressed to obtain the NdFeB green body. The NdFeB green body forms a grain structure with an inner and outer double-layer heavy rare earth magnetically hardened shell through the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion); the pre-sintering process is to press the NdFeB The blank is placed in a vacuum heat treatment furnace at a heating rate of 10°C/min to 1020°C for 4 hours, then gas quenched and air cooled. The pre-diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Prepare the diffusion source Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ multi-element alloy block material, put the raw material in a vacuum induction melting furnace for melting, and make the melted alloy ingot by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. The diffusion sheet Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ was pasted on the sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 900 ° C for 8 hours. After pre-sintering and pre-diffusion, the magnet is heated up to 1080° C. for 8 hours. After the heating is completed, after the vacuum heat treatment furnace is cooled to room temperature, the diffusion magnet is taken out, and the above-mentioned diffusion sheet is pasted on the upper and lower surfaces of the diffusion magnet, and then the diffusion process is carried out at 900°C for 8 hours and the tempering treatment at 500°C for 2 hours to obtain a super High coercivity NdFeB magnets.

Comparative example 1

According to the composition of the matrix alloy Nd _30.5 Fe _68.42 Al _0.1 Cu _0.2 Co _0.5 Zr _0.2 Ga _0.1 B _0.98 , the raw materials were smelted and poured onto the copper roller by the quick-setting process to obtain a cast sheet with an average thickness of 0.3mm, and the cast sheet was placed in In the hydrogen crushing furnace, hydrogen-filled crushing and dehydrogenation treatment at 450 ° C for 10 hours to obtain coarse crushed powder, and then the coarse crushed powder is milled in a jet mill protected by a nitrogen atmosphere to obtain a powder with an average particle size of 2.0 μm Jet milling fine magnetic powder; Orienting and pressing the NdFeB fine powder to obtain NdFeB green body. Place the NdFeB green body in a vacuum heat treatment furnace at a heating rate of 10 °C/min to 1080 °C for 8 hours, then gas quenching and air cooling. Grain boundary diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Prepare the diffusion source Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ multi-element alloy block material, put the raw material in a vacuum induction melting furnace for melting, and make the melted alloy ingot by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. Paste the diffusion sheet Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ on the sintered NdFeB magnet, put it in a crucible and place it in a vacuum heat treatment furnace to carry out the diffusion process at 900°C for 8 hours and the tempering treatment at 500°C for 2 hours to obtain High coercivity NdFeB magnets.

Observation of the backscattering structure of the above two samples of Example 1 and Comparative Example 1 found that the main phase grains of the magnet in the sample of Example 1 formed an inner and outer double-layer heavy rare earth magnetically hardened shell, and the thickness of the inner shell was 1.2 μm , the thickness of the outer shell is 0.4 μm, and the sample in Comparative Example 1 has no such inner and outer double-layer structure grains. Its performance data of embodiment 1 and comparative example 1 are compared as shown in table 1:

Table 1 Performance data table of NdFeB magnets prepared in different ways

magnet type Coercivity (kOe) Remanence(kGs) Magnetic energy product (MGOe) Example 1 25.85 14.13 48.44 Comparative example 1 22.32 14.17 48.57

It can be known by comparison that the present invention has obvious advantages, the coercive force of the embodiment is obviously higher than that of the comparative example, through the subsection process control of liquid phase sintering (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion), the main phase of the magnet The crystal grains form an inner and outer double-layer heavy rare earth magnetically hardened shell, and the thickness and heavy rare earth content of the inner shell can be adjusted by controlling the composition and dosage of the heavy rare earth pre-diffusion source, which can realize the improvement of raw material cost and coercive force The expected design of the effect can reduce the production cost while improving the coercive force.

Example 2:

According to the composition of the matrix alloy Nd _25.5 Tb _5.5 Fe _66.33 Cu _0.15 Co ₁ Zr _0.1 Ga _0.5 B _0.92 , the raw materials were smelted and poured onto the copper roller by the quick-setting process to obtain a cast sheet with an average thickness of 0.3mm, and the cast sheet was placed in In the hydrogen crushing furnace, hydrogen-filled crushing and dehydrogenation treatment at 450 ° C for 12 hours to obtain coarse crushed powder, and then the coarse crushed powder is milled in a jet mill protected by a nitrogen atmosphere to obtain a powder with an average particle size of 1.5 μm Jet milling fine magnetic powder; Orienting and pressing the NdFeB fine powder to obtain NdFeB green body. The NdFeB green body forms a grain structure with an inner and outer double-layer heavy rare earth magnetically hardened shell through the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion); the pre-sintering process is to press the NdFeB The blank is placed in a vacuum heat treatment furnace at a heating rate of 10°C/min to 1020°C for 4 hours, then gas quenched and air cooled. The pre-diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Prepare the diffusion source Tb ₁₅ Pr ₅₅ Al ₁₅ Ga ₁₅ multi-element alloy block material, put the raw material in a vacuum induction melting furnace for melting, and cut the melted alloy ingot by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. The diffusion sheet Tb ₁₅ Pr _s5 Al ₁₅ Ga ₁₅ was pasted on the sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 900 ° C for 8 hours. After pre-sintering and pre-diffusion, the magnet is heated up to 1080° C. for 8 hours. After the heating is completed, after the vacuum heat treatment furnace is cooled to room temperature, the diffusion magnet is taken out, and the above-mentioned diffusion sheet is pasted on the upper and lower surfaces of the diffusion magnet, and then the diffusion process is carried out at 900°C for 8 hours and the tempering treatment at 500°C for 2 hours to obtain a super High coercivity NdFeB magnets.

Comparative example 2:

In order to compare the advantages of the present invention, comparative example 2 uses jet-milled magnetic powder with an average particle diameter of 4.0 μm; liquid phase sintering treatment (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion) is carried out after orientation compression molding to obtain high The coercive force sintered NdFeB magnet was tested for magnetic properties after the treatment. The performance data comparison between Example 2 and Comparative Example 2 is shown in Table 2:

Table 2 Performance data table of NdFeB magnets prepared in different ways

magnet type Coercivity (kOe) Remanence(kGs) Magnetic energy product (MGOe) Example 2 42.08 12.42 37.59 Comparative example 2 39.27 12.51 37.71

After comparison, it can be known that the present invention has obvious advantages, the coercive force of the embodiment is obviously higher than that of the comparative example, and the coercive force is greatly improved by using the jet-milled magnetic powder, the process flow is simple, the operation is convenient, and it is suitable for industrial production. Ideal ultra-high coercivity NdFeB magnets can be prepared.

Example 3:

According to the matrix alloy composition Pr _16.43 Nd _5.47 Ce _8.6 Fe _65.94 Gd _1.5 Al _0.5 Cu _0.2 Co _0.2 Zr _0.12 Ga _0.12 B _0.92 , the raw materials were smelted and poured onto copper rollers by quick-setting process to obtain cast sheets with an average thickness of 0.2mm. Place the cast piece in a hydrogen breaking furnace, fill it with hydrogen and hold it at 430°C for 12 hours for dehydrogenation treatment to obtain a coarsely crushed powder, and then grind the coarsely crushed powder in a jet mill protected by a nitrogen atmosphere to obtain an average particle size Airflow milled magnetic powder with a diameter of 2.0 μm; Orientation and pressing of NdFeB fine powder to obtain NdFeB green body. The NdFeB green body forms a grain structure with an inner and outer double-layer heavy rare earth magnetically hardened shell through the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion); the pre-sintering process is to press the NdFeB The blank is placed in a vacuum heat treatment furnace at a heating rate of 10°C/min to 1020°C for 4 hours, then gas quenched and air cooled. The pre-diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Diffusion source Dy ₂₅ Pr ₄₅ Cu ₁₅ Ga ₁₅ multi-element alloy bulk material is prepared, the raw material is melted in a vacuum induction melting furnace, and the melted alloy ingot is made by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. Paste the diffusion sheet Tb ₁₅ Pr ₅₅ Cu ₁₅ Ga ₁₅ on the sintered NdFeB magnet, place it in a crucible and place it in a vacuum heat treatment furnace for a diffusion process at 950°C for 10h. After pre-sintering and pre-diffusion, the magnet is heated up to 1080° C. for 8 hours. After the heating is completed, after the vacuum heat treatment furnace is cooled to room temperature, the diffusion magnet is taken out, and the above-mentioned diffusion sheet is pasted on the surface of the diffusion magnet, and then the diffusion process is carried out at 950°C for 10 hours and the tempering treatment at 500°C for 2 hours, to obtain ultra-high Coercivity NdFeB magnets.

Comparative example 3:

In order to compare the advantages of the present invention, comparative example 3 uses the jet mill fine magnetic powder with an average particle diameter of 2.0 μm, and the jet mill fine magnetic powder carries out the subsection process (pre-sintering, pre-diffusion, densification) of liquid phase sintering after orientation compression molding sintering, grain boundary diffusion), in which the diffusion source used in the pre-diffusion and grain boundary diffusion process is Dy ₂₅ Pr ₁₀ Cu ₃₀ Ga ₃₅ , and finally a high coercivity sintered NdFeB magnet is obtained. After the treatment, the magnetic performance test is carried out. The performance data comparison of Example 3 and Comparative Example 3 is shown in Table 3:

Table 3 Performance data table of NdFeB magnets prepared in different ways

magnet type Coercivity (kOe) Remanence(kGs) Magnetic energy product (MGOe) Example 3 24.97 11.95 35.88 Comparative example 3 20.84 12.03 35.93

It can be known by comparison that the present invention has obvious advantages, the coercive force of the embodiment is obviously higher than that of the comparative example, the content of heavy rare earths is reduced, the high-quality utilization of heavy rare earths is realized, and the production cost is reduced. The coercive force has been greatly improved, the process is simple, the operation is convenient, and it can be applied to industrial production.

Example 4

According to the composition of the matrix alloy as Nd _30.5 Fe _68.42 Al _0.1 Cu _0.2 Co _0.5 Zr _0.2 Ga _0.1 B _0.98 , the raw materials were smelted and poured onto copper rollers by quick-setting process to obtain cast sheets with an average thickness of 0.3mm, and the cast sheets were placed In a hydrogen furnace, charge hydrogen to crush and hold at 450°C for 10 hours for dehydrogenation treatment to obtain coarsely crushed powder, and then grind the coarsely crushed powder in a jet mill protected by a nitrogen atmosphere to obtain an average particle size of 2.0 μm The airflow grinding fine magnetic powder; the NdFeB fine powder is oriented and pressed to obtain the NdFeB green body. The NdFeB green body forms a grain structure with an inner and outer double-layer heavy rare earth magnetically hardened shell through the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion); the pre-sintering process is to press the NdFeB The blank is placed in a vacuum heat treatment furnace at a heating rate of 10°C/min to 1020°C for 4 hours, then gas quenched and air cooled. The pre-diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Prepare the diffusion source Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ multi-element alloy block material, put the raw material in a vacuum induction melting furnace for melting, and make the melted alloy ingot by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. The diffusion sheet Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ was pasted on the sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 800°C for 8h. After pre-sintering and pre-diffusion, the magnet is heated up to 1080° C. for 8 hours. After the heating is completed, after the vacuum heat treatment furnace is cooled to room temperature, the diffusion magnet is taken out, and the above-mentioned diffusion sheet is pasted on the upper and lower surfaces of the diffusion magnet, and then the diffusion process is carried out at 800°C for 8 hours and the tempering treatment at 400°C for 2 hours to obtain a super High coercivity NdFeB magnets.

Table 4 Performance data table of NdFeB magnets prepared in different ways

magnet type Coercivity (kOe) Remanence(kGs) Magnetic energy product (MGOe) Example 4 24.05 14.23 48.64

Example 5

According to the composition of the matrix alloy as Nd _30.5 Fe _68.42 Al _0.1 Cu _0.2 Co _0.5 Zr _0.2 Ga _0.1 B _0.98 , the raw materials were smelted and poured onto copper rollers by quick-setting process to obtain cast sheets with an average thickness of 0.3mm, and the cast sheets were placed In a hydrogen furnace, charge hydrogen to crush and hold at 450°C for 10 hours for dehydrogenation treatment to obtain coarsely crushed powder, and then grind the coarsely crushed powder in a jet mill protected by a nitrogen atmosphere to obtain an average particle size of 2.0 μm The airflow grinding fine magnetic powder; the NdFeB fine powder is oriented and pressed to obtain the NdFeB green body. The NdFeB green body forms a grain structure with an inner and outer double-layer heavy rare earth magnetically hardened shell through the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion); the pre-sintering process is to press the NdFeB The blank is placed in a vacuum heat treatment furnace at a heating rate of 10°C/min to 1020°C for 4 hours, then gas quenched and air cooled. The pre-diffusion treatment is to cut the sintered NdFeB magnet into cylinder. Prepare the diffusion source Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ multi-element alloy block material, put the raw material in a vacuum induction melting furnace for melting, and make the melted alloy ingot by wire cutting /> Remove the surface scale, keep the surface flat and rinse and dry with alcohol. The diffusion sheet Tb ₁₅ Pr ₆₀ Cu ₁₅ Al ₁₀ was pasted on the sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 950°C for 8 hours. After pre-sintering and pre-diffusion, the temperature of the magnet was raised to 1110° C. for 8 hours. After the heating is completed, after the vacuum heat treatment furnace is cooled to room temperature, the diffusion magnet is taken out, and the above-mentioned diffusion sheet is pasted on the upper and lower surfaces of the diffusion magnet, and then the diffusion process is carried out at 950°C for 8 hours and the tempering treatment at 600°C for 2 hours to obtain a super High coercivity NdFeB magnets.

Table 5 Performance data table of NdFeB magnets prepared in different ways

magnet type Coercivity (kOe) Remanence(kGs) Magnetic energy product (MGOe) Example 5 24.21 14.11 47.73

In addition, the inventors of the present case also conducted experiments with reference to the foregoing examples, using other raw materials, process operations, and process conditions mentioned in this specification, and obtained satisfactory results.

It should be understood that the technical solution of the present invention is not limited to the limitations of the above-mentioned specific implementation examples, and any technical deformation made according to the technical solution of the present invention falls within the scope of the present invention without departing from the scope of protection of the present invention and the claims. within the scope of protection of the invention.

Claims (10)

1. The preparation method of the neodymium-iron-boron magnet with the ultrahigh coercivity is characterized by comprising the following steps of:

providing a neodymium iron boron pressed compact;

and performing liquid phase sintering treatment on the neodymium iron boron compact to obtain a neodymium iron boron magnet with ultrahigh coercivity;

wherein the liquid phase sintering treatment comprises pre-sintering, pre-diffusion, densification sintering and grain boundary diffusion treatment; the main phase crystal grain of the magnet in the pre-diffusion magnet obtained by the pre-diffusion treatment has a core-shell structure, and the main phase crystal grain of the magnet in the neodymium-iron-boron magnet with the ultrahigh coercivity has an inner-outer double-layer heavy rare earth magnetic hardening shell structure.

2. The preparation method according to claim 1, characterized by comprising: presintering the neodymium iron boron pressed compact for 2-5 hours at 900-1020 ℃ to obtain a presintered magnet; wherein the grain size in the pre-sintered magnet is 3-5 μm.

3. The preparation method according to claim 2, characterized by comprising: coating a pre-diffusion source on the surface of the pre-sintered magnet and carrying out pre-diffusion treatment for 2-8 hours under the vacuum condition of 800-950 ℃ to obtain a pre-diffusion magnet; wherein the pre-diffusion treatment forms at least the main phase grains of the obtained pre-diffusion magnet into a core-shell structure;

preferably, the pre-diffusion source comprises a rare earth alloy diffusion source having the chemical formula H _x R _y M _100-x-y Wherein H isAny one or more than two of Tb, dy and Ho, R is any one or more than two of Pr, nd, Y, ce, la, M is any one or more than two of Cu, al, fe, ga, zn, mg, mn, x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30, and y is 20-80.

4. A production method according to claim 3, characterized by comprising: performing densification sintering treatment on the pre-diffusion magnet at 1000-1100 ℃ for 2-10 hours to obtain a densified sintered magnet; wherein the grain size in the densified sintered magnet is 5 to 10 μm.

5. The preparation method according to claim 4, characterized by comprising: coating a diffusion source on the surface of the densified sintered magnet, performing diffusion treatment at 800-950 ℃ for 2-8 hours, and tempering at 400-600 ℃ for 2-4 hours to obtain a neodymium-iron-boron magnet with ultrahigh coercivity;

preferably, the diffusion source comprises a rare earth alloy diffusion source having the chemical formula H _x R _y M _100-x-y Wherein H is selected from any one or more than two of Tb, dy and Ho, R is selected from any one or more than two of Pr, nd, Y, ce, la, M is selected from any one or more than two of Cu, al, fe, ga, zn, mg, mn, x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30 and y is 20-80.

6. The preparation method according to claim 1, characterized by comprising:

providing raw materials for preparing a neodymium iron boron pressed compact, and carrying out alloy smelting treatment to obtain a neodymium iron boron alloy sheet;

carrying out hydrogen crushing treatment on the neodymium iron boron alloy sheet to obtain hydrogen crushing coarse powder;

carrying out air current grinding treatment on the hydrogen-broken coarse powder to obtain neodymium iron boron fine powder;

and carrying out orientation press forming and isostatic pressing treatment on the neodymium iron boron fine powder to obtain a neodymium iron boron pressed compact.

7. The method of manufacturing according to claim 6, wherein: the chemical general formula of the components of the neodymium iron boron compact is R _x Fe _y M _z B _α The method comprises the steps of carrying out a first treatment on the surface of the Wherein R is selected from any one or more than two of La, ce, tb, dy, ho, Y, gd, nd, pr, M is selected from any one or more than two of Cu, al, ga, mg, ni, ti, co, zr, x is 28-33wt%, y is 60-75wt%, z is 0-5wt%, alpha is 0.9-1.2wt%, and x+y+z+alpha=100.

8. The method of manufacturing according to claim 6, wherein: the thickness of the neodymium iron boron alloy sheet is 200-300 mu m;

and/or the grinding gas pressure adopted in the jet mill treatment is 0.5-0.7MPa, and the rotating speed of the classifying wheel is 3500-5000 rpm;

and/or the average particle diameter D50 of the neodymium iron boron fine powder is not less than 1 mu m and not more than 2 mu m.

9. A neodymium-iron-boron magnet with ultra-high coercivity produced by the production method according to any one of claims 1 to 8, characterized in that: the main phase crystal grain of the magnet in the neodymium-iron-boron magnet with the ultrahigh coercivity comprises an inner heavy rare earth magnetic hardening shell layer and an outer heavy rare earth magnetic hardening shell layer which are sequentially formed on the surface of the core structure;

preferably, the thickness of the inner heavy rare earth magnetic hardening shell layer is 0.5-3 mu m; preferably, the thickness of the outer heavy rare earth magnetic hardening shell layer is 0.2-0.5 mu m.

10. The use of the neodymium-iron-boron magnet with ultrahigh coercivity in the fields of new energy automobiles, maglev trains, wind power generation or energy-saving household appliances.