Preparation method of sintered neodymium-iron-boron permanent magnet without heavy rare earth

Abstract

The application belongs to the technical field of Nd-Fe-B permanent magnet, and relates to a preparation method of heavy rare earth-free sintered Nd-Fe-B permanent magnet. The application discloses a preparation method of heavy rare earth-free sintered Nd-Fe-B permanent magnet, and the preparation method comprises the following steps: S1, mixing heavy rare earth-free main alloy powder and heavy rare earth-free auxiliary alloy powder mixture to obtain heavy rare earth-free mixed magnetic powder; S2, performing orientation compression on the heavy rare earth-free mixed magnetic powder, and performing isostatic pressing on the heavy rare earth-free auxiliary alloy powder mixture sprayed on the surface of the heavy rare earth-free magnet pre-compacted body when the press is demoulded, so as to obtain a heavy rare earth-free magnet compacted body; and S3, placing the heavy rare earth-free magnet compacted body together with a sintering box in a glove box, and then placing the heavy rare earth-free magnet compacted body into a sintering furnace to perform sintering and tempering heat treatment. The application adopts the mode of grain boundary addition, so that the rare earth elements in the heavy rare earth-free auxiliary alloy are concentrated in the grain boundary phase, the coercive force of the magnet is improved, and the remanence of the magnet is almost not reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of Nd-Fe-B permanent magnets, and relates to a preparation method of a heavy rare earth-free sintered Nd-Fe-B permanent magnet. BACKGROUND

[0002] Sintered Nd-Fe-B is an important magnetic functional material, which is widely used in the fields of sound equipment, communication products, consumer electronics, medical equipment, household appliances, magnetic separation equipment and the like due to its excellent magnetic performance. With the continuous breakthrough of the magnetic performance of sintered Nd-Fe-B magnets, the application fields thereof are becoming more and more wide. In recent years, with the rapid development of emerging industries such as new energy vehicles and wind power generation, new demands for the application of sintered Nd-Fe-B magnets are proposed: the coercivity of the magnets is greatly improved in low-heavy rare earth or heavy rare earth-free magnets.

[0003] At present, there are mainly two methods for improving the coercivity of low-heavy rare earth or heavy rare earth-free sintered Nd-Fe-B magnets. One is to add heavy rare earth elements Dy and Tb to improve the anisotropy field of the magnets and thus improve the coercivity of the magnets. However, the resources of heavy rare earth elements Dy and Tb are scarce and the price is high, which greatly increases the cost of the magnets. Since the coercivity of sintered Nd-Fe-B magnets is a sensitive parameter of microstructure, the other method is to refine the grains to reduce the demagnetization effect between the grains and thus improve the coercivity. However, the process and equipment required for grain refinement are high in cost, which limits the universal application in the industry. In view of this, a new method for improving the coercivity of the magnets is urgently needed.

[0004] Chinese Patent Application (Publication No. CN111696742A) discloses adding auxiliary organic coating to anisotropic magnetic material powder, reducing the grain boundary ferromagnetism and improving the wettability of the grain boundary and the main phase by introducing Ni in the auxiliary organic coating, so as to significantly improve the coercivity of the Nd-Fe-B permanent magnet material. However, there are problems that the improvement of the coercivity is limited, the remanence Br needs to be sacrificed if the improvement of the coercivity is > 3kOe, and the grain boundary phase in the magnet is united, resulting in poor uniformity of the magnet. SUMMARY

[0005] The purpose of the present application is to solve the above-mentioned problems existing in the prior art, and a preparation method of a heavy rare earth-free sintered Nd-Fe-B permanent magnet which significantly improves the coercivity, has little effect on the remanence and is uniform in the magnet is proposed.

[0006] The purpose of the present application can be achieved by the following technical scheme:

[0007] A preparation method of a heavy rare earth-free sintered Nd-Fe-B permanent magnet, characterized in that the preparation method comprises:

[0008] S1, mixing the non-heavy rare earth main alloy powder and the non-heavy rare earth auxiliary alloy powder mixture to obtain a non-heavy rare earth mixed magnetic powder;

[0009] The non-heavy rare earth main alloy powder has the following components in mass percentage: RE a Fe 100-a-b-c M b B c , RE includes at least one of Pr and Nd, M includes at least one of Cu, Al, Zr, Co, Ga and Nb, and satisfies 28<=a<=35, 0.01<=b<=1.0, 0.8<=c<=1.2.

[0010] The non-heavy rare earth auxiliary alloy powder has the following components in mass percentage: R x N y Fe 100-x-y , R includes at least one of Pr and Nd, N includes at least one of Cu and Ga, and satisfies 50<=x<=53, 3<=y<=5.

[0011] S2, orienting and compacting the non-heavy rare earth mixed magnetic powder, spraying the non-heavy rare earth auxiliary alloy powder mixture on the surface of the non-heavy rare earth magnet pre-compacted body when the compacting machine is demoulded, and then isostatic pressing to obtain a non-heavy rare earth magnet compacted body.

[0012] S3, placing the non-heavy rare earth magnet compacted body together with a sintering box in a glove box, and then placing it in a sintering furnace for sintering and tempering heat treatment to obtain a non-heavy rare earth sintered Nd-Fe-B permanent magnet.

[0013] The application adopts two kinds of non-heavy rare earth alloy powders, a double alloy process and a grain boundary adding method to concentrate the rare earth elements in the grain boundary phase in the auxiliary alloy, and mixes the non-heavy rare earth main alloy powder and the non-heavy rare earth auxiliary alloy powder mixture to significantly improve the uniformity of the mixed non-heavy rare earth mixed magnetic powder.

[0014] After the non-heavy rare earth mixed magnetic powder is oriented and compacted, and before isostatic pressing, the non-heavy rare earth auxiliary alloy powder mixture is sprayed, the pressure in the isostatic pressing process is used to uniformly penetrate the non-heavy rare earth auxiliary alloy powder into the magnet compacted body, and the main phase alloy powder reacts in the sintering process to further improve the magnetic properties of the magnet. If the non-heavy rare earth auxiliary alloy powder is directly and uniformly sprinkled on the surface of the pre-compacted body, the uniformity of the surface layer and the internal magnet will be reduced.

[0015] Preferably, the mass of the non-heavy rare earth auxiliary alloy powder in the non-heavy rare earth mixed magnetic powder is 0.1-2wt% of the total mass of the non-heavy rare earth main alloy powder and the non-heavy rare earth auxiliary alloy powder.

[0016] Preferably, the non-heavy rare earth auxiliary alloy powder mixture is a mixture of non-heavy rare earth auxiliary alloy powder and organic solvent, and the mass ratio of non-heavy rare earth auxiliary alloy powder to organic solvent is 1:(5-20).

[0017] During the powder mixing process, too much organic solvent in the non-heavy rare earth auxiliary alloy powder mixture will result in high carbon content in the magnet, affecting the coercivity of the magnet; too little organic solvent will result in agglomeration of the magnetic powder, and poor uniformity in the magnet.

[0018] During the spraying process before isostatic pressing, too much organic solvent in the non-heavy rare earth auxiliary alloy powder mixture will result in surface cracking and oxidation of the magnet; too little organic solvent will result in uneven surface and large deviation in magnetic properties.

[0019] Further preferably, the organic solvent is trifluorotrichloroethane.

[0020] Trifluorotrichloroethane, as a refrigerant, can reduce the surface activity of the magnetic powder particles and prevent the magnetic powder particles from oxidizing and self-igniting.

[0021] Preferably, the non-heavy rare earth main alloy powder has a composition of REaM a Fe 100-a-b- c M b B c , RE includes at least one of Pr and Nd, M includes at least one of Cu, Al, Zr, Co, Ga, and Nb, and satisfies 30≤a≤35, 0.8≤b≤1.0, and 0.9≤c≤1.0.

[0022] The non-heavy rare earth auxiliary alloy powder has a composition of R x N y Fe 100-x-y , R includes at least one of Pr and Nd, N is at least one of Cu and Ga, and satisfies 50≤x≤53 and 3≤y≤5.

[0023] Preferably, RE can also include Ce.

[0024] Preferably, the non-heavy rare earth main alloy powder in step S1 is prepared by melting, rapid solidification, hydrogen crushing, and airflow milling of non-heavy rare earth main alloy raw materials.

[0025] Further preferably, the melting temperature is 1000-1400℃; the rotating speed of the copper roller for rapid solidification is 1.8-5m / s; and the thickness of the non-heavy rare earth main alloy cast sheet obtained after rapid solidification is 100-500 microns.

[0026] The hydrogen pressure in the hydrogen crushing is 0.1-0.3 MPa, the hydrogen absorption is saturated, the dehydrogenation temperature is 300-600 ℃, and the dehydrogenation time is 3-10 h.

[0027] The rotation speed of the jet mill is 3000-6000 rpm.

[0028] Preferably, the average particle size of the heavy rare earth-free main alloy powder in step S1 is 2.3-2.7 microns.

[0029] Preferably, the heavy rare earth-free auxiliary alloy powder in step S1 is prepared from heavy rare earth-free auxiliary alloy raw materials by melting, rapid solidification, hydrogen crushing, and jet milling.

[0030] Further preferably, the melting temperature is 1000-1400 ℃, the rotation speed of the copper roller for rapid solidification is 3-8 m / s, and the thickness of the heavy rare earth-free auxiliary alloy cast sheet after rapid solidification is 100-300 microns.

[0031] The hydrogen pressure in the hydrogen crushing is 0.1-0.3 MPa, the hydrogen absorption is saturated, the dehydrogenation temperature is 300-600 ℃, and the dehydrogenation time is 3-10 h.

[0032] The rotation speed of the jet mill is 3000-6000 rpm.

[0033] Preferably, the average particle size of the heavy rare earth-free auxiliary alloy powder in step S1 is 1.8-2.2 microns.

[0034] Further preferably, the total hydrogen content of the heavy rare earth-free main alloy powder after hydrogen crushing and the heavy rare earth-free auxiliary alloy powder after hydrogen crushing is less than 300 ppm.

[0035] Preferably, the magnetic field strength of the orientation press molding in step S2 is 1.4-2.6 T, and the pressure is 5-30 MPa.

[0036] Preferably, the pressure of the isostatic pressing in step S2 is 130-260 MPa.

[0037] Preferably, the spraying amount of the heavy rare earth-free auxiliary alloy powder mixture in step S2 is 0.1-10 wt% of the weight of the preform.

[0038] Further preferably, the spraying amount of the heavy rare earth-free auxiliary alloy powder mixture in step S2 is 3-10 wt% of the weight of the preform.

[0039] Preferably, the glove box in step S3 is filled with nitrogen, and the standing time is 1-3 h.

[0040] The standing allows the heavy rare earth-free auxiliary alloy powder to adhere to the surface of the magnet after the volatilization of the surface-sprayed heavy rare earth-free auxiliary alloy powder surface trifluorotrichloroethane.

[0041] As preferred, the sintering box in step S3 is a graphite box.

[0042] The sintering box used in the present application is a graphite box, which is smoother than an iron box, can reduce the friction between the magnet and the box during the sintering shrinkage of the magnet, and reduce the case of the magnet corner falling.

[0043] As preferred, the sintering temperature in step S3 is 960-1100℃, and the sintering time is 8-10h.

[0044] As preferred, the tempering in step S3 includes first tempering and second tempering; the first tempering temperature is 680-950℃, and the first tempering time is 2-5h; the second tempering temperature is 400-600℃, and the second tempering time is 2-5h.

[0045] During the tempering process, argon is filled to 80-100kpa, and the fan speed is 3000-8000r / min.

[0046] Further preferably, the first tempering temperature is higher than the second tempering temperature, and the temperature difference between the two is 200-500℃.

[0047] Further preferably, the second tempering time is longer than the first tempering time.

[0048] A heavy rare earth-free sintered Nd-Fe-B permanent magnet, in which the rare earth elements R in the heavy rare earth-free auxiliary alloy are concentrated in the grain boundary phase.

[0049] As preferred, compared with the heavy rare earth-free sintered Nd-Fe-B permanent magnet prepared without spraying the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet pre-compacted body, the coercive force of the heavy rare earth-free sintered Nd-Fe-B permanent magnet prepared by spraying the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet pre-compacted body is increased by >4kOe, and the remanence change is ≤0.2kGs.

[0050] Further preferably, compared with the heavy rare earth-free sintered Nd-Fe-B permanent magnet prepared without spraying the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet pre-compacted body, the coercive force of the heavy rare earth-free sintered Nd-Fe-B permanent magnet prepared by spraying the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet pre-compacted body is increased by 5-10kOe.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] 1. The present application adopts a double alloy process, adopts a grain boundary adding method, compared with adding rare earth elements during smelting, can make the rare earth elements in the heavy rare earth-free auxiliary alloy more concentrated in the grain boundary phase, and can diffuse into the main phase as little as possible, so as to maximize the formation of a high-magnetic crystal anisotropy shell of light rare earth elements at the grain boundary of the magnet, improve the coercive force of the magnet, and ensure that the remanence of the magnet is almost not reduced.

[0053] 2、The present application separates the preparation of the heavy rare earth-free main alloy powder and the heavy rare earth-free auxiliary alloy powder, avoids the substitution of elements at the grain boundaries into the main phase, thereby causing the decline of the magnetic properties.

[0054] 3、The rare earth elements of the heavy rare earth-free auxiliary alloy of the present application are concentrated in the grain boundary phase, the formation of the grain boundary phase not only can improve the coercivity of the magnet, but also can improve the wettability of the rare earth-rich phase, and the synergistic effect of the light rare earth elements can further improve the coercivity of the magnet.

[0055] 4、The present application adopts the low-temperature long-time sintering process, so that the heavy rare earth-free auxiliary alloy can be more uniformly distributed around the main phase grain, and reacts with the main phase in the low-temperature long-time sintering process, so that the elements in the heavy rare earth-free auxiliary alloy form a rare earth thin shell layer with higher magnetic crystal anisotropy field at the edge of the main phase grain, further improving the coercivity of the magnet.

[0056] 5、The present application sprays the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet compact during the demolding of the press, and then performs isostatic pressing, which can utilize the pressure in the isostatic pressing process to uniformly penetrate the heavy rare earth-free auxiliary alloy powder into the magnet compact, and react with the main phase alloy powder in the sintering process, further improving the magnetic properties of the magnet.

[0057] 6、The heavy rare earth-free main alloy powder and the heavy rare earth-free auxiliary alloy powder of the present application do not contain heavy rare earth elements, effectively saving heavy rare earth resources, reducing production costs, and being applicable to industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 SEM and mapping diagrams of the heavy rare earth-free sintered neodymium-iron-boron permanent magnet of the present application embodiment 1.

[0059] Figure 2 SEM and mapping diagrams of the heavy rare earth-free sintered neodymium-iron-boron permanent magnet of the present application embodiment 2. DETAILED DESCRIPTION

[0060] The following are specific embodiments of the present application, which further describe the technical solutions of the present application, but the present application is not limited to these embodiments.

[0061] Unless otherwise specified, the materials used in the present application are conventional commercially available products, and the methods used are conventional technical means.

[0062] Embodiment 1

[0063] (1) According to the heavy rare earth-free main alloy composition and the heavy rare earth-free auxiliary alloy composition, the raw materials are configured, wherein the heavy rare earth-free main alloy is Nd 32.5 Al 0.02Cu 0.1 Co 0.6 Zr 0.1 Fe 65.76 B 0.92 , the non-heavy rare earth auxiliary alloy is Pr 50 Cu3Fe 47 , respectively, after smelting and rapid solidification, to obtain non-heavy rare earth main alloy castings and non-heavy rare earth auxiliary alloy castings, the rotating speed of the copper roller for rapid solidification is 2.0 m / s and 5.0 m / s, respectively, the pouring temperature of the non-heavy rare earth main alloy is 1350℃, and the pouring temperature of the non-heavy rare earth auxiliary alloy is 1250℃, the thickness of the obtained non-heavy rare earth main alloy castings is 300 microns, and the thickness of the obtained non-heavy rare earth auxiliary alloy castings is 100 microns.

[0064] (2) The non-heavy rare earth main alloy castings and the non-heavy rare earth auxiliary alloy castings are respectively subjected to hydrogen crushing to obtain non-heavy rare earth main alloy coarse powder and non-heavy rare earth auxiliary alloy coarse powder, wherein the hydrogen pressure in the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, the dehydrogenation time is 6 hours, and the total hydrogen content of the non-heavy rare earth coarse powder is 260 ppm.

[0065] (3) The non-heavy rare earth main alloy coarse powder and the non-heavy rare earth auxiliary alloy coarse powder are respectively subjected to airflow milling to obtain non-heavy rare earth main alloy powder and non-heavy rare earth auxiliary alloy powder, the non-heavy rare earth auxiliary alloy powder is mixed with trifluorotrichloroethane at a mass ratio of 1:10 to prepare a non-heavy rare earth auxiliary alloy powder mixture, then the non-heavy rare earth auxiliary alloy powder mixture is mixed with the non-heavy rare earth main alloy powder, stirred and dried to obtain non-heavy rare earth mixed magnetic powder; the mass of the non-heavy rare earth auxiliary alloy powder in the non-heavy rare earth mixed magnetic powder is 1 wt% of the total mass of the non-heavy rare earth main alloy powder and the non-heavy rare earth auxiliary alloy powder.

[0066] (4) The non-heavy rare earth mixed magnetic powder is subjected to orientation molding in an argon atmosphere, wherein the strength of the magnetic field is 1.6 T, the molding pressure is 20 MPa, and isostatic pressing is performed after spraying 5 wt% of the non-heavy rare earth auxiliary alloy powder mixture on the surface of the non-heavy rare earth magnet pre-compacted body during demolding of the press, and the isostatic pressing pressure is 170 MPa, to obtain a non-heavy rare earth magnet compacted body.

[0067] (5) The non-heavy rare earth magnet compacted body is placed together with a sintering box in a glove box filled with nitrogen for 2 hours, the sintering box is a graphite box, and low-temperature long-time sintering and tempering heat treatment are performed in a sintering furnace to obtain a non-heavy rare earth sintered neodymium-iron-boron permanent magnet. The sintering temperature is 980℃, the sintering time is 10h, the first-stage tempering temperature is 800℃, the first-stage tempering time is 3 hours, the second-stage tempering temperature is 600℃, the second-stage tempering time is 3 hours, argon gas is filled to 90 kpa during tempering, and the fan speed is 5000 revolutions per minute, to obtain a non-heavy rare earth sintered neodymium-iron-boron permanent magnet.

[0068] The properties of the prepared heavy rare earth-free sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0069] Figure 1 The SEM and mapping images of the heavy rare earth-free sintered Nd-Fe-B permanent magnet of the present embodiment are shown in Figures 1 and 2. Figure 1 It can be seen that the Pr element of Example 1 forms a shell layer, which is thick and concentrated.

[0070] Example 2

[0071] (1) The raw materials were prepared according to the heavy rare earth-free main alloy composition and the heavy rare earth-free auxiliary alloy composition, wherein the heavy rare earth-free main alloy composition and the mass percentage are as follows: Nd 67.5%, Al 0.5%, Cu 0.5%, Co 0.5%, Zr 0.5%, Fe 29.5%, and B 0.5%. 32.5 Al 0.02 Cu 0.1 Co 0.6 Zr 0.1 Fe 65.76 B 0.92 The heavy rare earth-free auxiliary alloy composition and the mass percentage are as follows: Pr 5%, Cu 1%, Ga 2%, and Fe 92%. 50 Cu1Ga2Fe 47 After melting and rapid solidification, the heavy rare earth-free main alloy cast sheet and the heavy rare earth-free auxiliary alloy cast sheet were obtained, and the rotating speed of the copper roller was 3.0 m / s and 4.0 m / s, respectively. The pouring temperature of the heavy rare earth-free main alloy was 1400°C, and the pouring temperature of the heavy rare earth-free auxiliary alloy was 1150°C. The thickness of the heavy rare earth-free main alloy cast sheet was 200 microns, and the thickness of the heavy rare earth-free auxiliary alloy cast sheet was 150 microns.

[0072] (2) The heavy rare earth-free main alloy cast sheet and the heavy rare earth-free auxiliary alloy cast sheet were subjected to hydrogen crushing, and the heavy rare earth-free main alloy coarse powder and the heavy rare earth-free auxiliary alloy coarse powder were obtained, respectively. The hydrogen pressure during the hydrogen crushing process was 0.2 MPa, the hydrogen absorption time was 4 hours, and the dehydrogenation time was 8 hours. The total hydrogen content of the heavy rare earth-free coarse powder was 220 ppm.

[0073] (3) The heavy rare earth-free main alloy coarse powder and the heavy rare earth-free auxiliary alloy coarse powder were subjected to airflow milling, and the heavy rare earth-free main alloy powder and the heavy rare earth-free auxiliary alloy powder were obtained, respectively. The heavy rare earth-free auxiliary alloy powder was mixed with trifluorotrichloroethane at a mass ratio of 1:10 to prepare a heavy rare earth-free auxiliary alloy powder mixture, and then the heavy rare earth-free auxiliary alloy powder mixture was mixed with the heavy rare earth-free main alloy powder. After stirring and drying, the heavy rare earth-free mixed magnetic powder was obtained.

[0074] (4) The heavy rare earth-free mixed magnetic powder was subjected to orientation molding in an argon atmosphere, wherein the strength of the magnetic field was 1.8 T, and the molding pressure was 14 MPa. After the mold was demolded, isostatic pressing was performed after spraying 5 wt% of the heavy rare earth-free auxiliary alloy powder mixture on the surface of the heavy rare earth-free magnet pre-compacted body. The isostatic pressing pressure was 220 MPa, and the heavy rare earth-free magnet compacted body was obtained.

[0075] (5) The green compact of the heavy rare earth-free magnet is placed in a glove box filled with nitrogen for 1 h together with a sintering box, which is a graphite box, and is put into a sintering furnace for low-temperature long-time sintering and tempering heat treatment to obtain a heavy rare earth-free sintered Nd-Fe-B permanent magnet. The sintering temperature is 1020°C, the sintering time is 8 h, the first-stage tempering temperature is 860°C, the first-stage tempering time is 2 h, the second-stage tempering temperature is 400°C, the second-stage tempering time is 4 h, argon is filled to 90 kPa during the tempering process, and the fan speed is 5000 rpm, thereby obtaining the heavy rare earth-free sintered Nd-Fe-B permanent magnet.

[0076] The properties of the heavy rare earth-free sintered Nd-Fe-B permanent magnet prepared are shown in Table 1.

[0077] Figure 2 The SEM and mapping images of the heavy rare earth-free sintered Nd-Fe-B permanent magnet of the present example are shown in Figures 1 and 2, respectively. Figure 2 It can be seen that, after the addition of Ga, the Pr distribution of the shell layer of the heavy rare earth-free sintered Nd-Fe-B permanent magnet of the present example is more uniform than that of Example 1.

[0078] Example 3

[0079] (1) The raw materials are prepared according to the composition of the heavy rare earth-free main alloy and the composition of the heavy rare earth-free auxiliary alloy, wherein the heavy rare earth-free main alloy is Nd 31 Al 0.1 Co 0.8 Zr 0.1 Fe 67 B 0.9 , and the heavy rare earth-free auxiliary alloy is: Nd 50 Cu1Ga3Fe 46 , respectively. After melting and rapid solidification, heavy rare earth-free main alloy cast sheets and heavy rare earth-free auxiliary alloy cast sheets are obtained. The copper roller speed for rapid solidification is 3.0 m / s and 3.0 m / s, respectively. The pouring temperature of the heavy rare earth-free main alloy is 1380°C, and the pouring temperature of the heavy rare earth-free auxiliary alloy is 1220°C. The thickness of the heavy rare earth-free main alloy cast sheet is 260 microns, and the thickness of the heavy rare earth-free auxiliary alloy cast sheet is 180 microns.

[0080] (4) The heavy rare earth-free main alloy cast sheets and the heavy rare earth-free auxiliary alloy cast sheets are subjected to hydrogen crushing, respectively, to obtain heavy rare earth-free main alloy coarse powder and heavy rare earth-free auxiliary alloy coarse powder, respectively. The hydrogen pressure during hydrogen crushing is 0.3 MPa, the hydrogen absorption time is 4 hours, and the dehydrogenation time is 5 hours. The total hydrogen content of the heavy rare earth-free coarse powder is 270 ppm.

[0081] (3) The non-heavy rare earth main alloy coarse powder and the non-heavy rare earth auxiliary alloy coarse powder are respectively subjected to airflow milling to obtain non-heavy rare earth main alloy powder and non-heavy rare earth auxiliary alloy powder. The non-heavy rare earth auxiliary alloy powder is mixed with trifluorotrichloroethane at a mass ratio of 1:8 to prepare a non-heavy rare earth auxiliary alloy powder mixture, and then the non-heavy rare earth auxiliary alloy powder mixture is mixed with the non-heavy rare earth main alloy powder, stirred and dried to obtain non-heavy rare earth mixed magnetic powder.

[0082] (4) The non-heavy rare earth mixed magnetic powder is subjected to orientation molding in an argon atmosphere, wherein the strength of the magnetic field is 1.8T, the molding pressure is 18MPa, and the surface of the non-heavy rare earth magnet pre-compacted body is sprayed with 8wt% non-heavy rare earth auxiliary alloy powder mixture during demolding of the press, followed by isostatic pressing at a pressure of 200MPa to obtain a non-heavy rare earth magnet compacted body.

[0083] (5) The non-heavy rare earth magnet compacted body is placed together with a sintering box in a glove box filled with nitrogen for 2h, and the sintering box is a graphite box. The non-heavy rare earth magnet compacted body is subjected to low-temperature long-time sintering and tempering heat treatment in a sintering furnace to obtain a non-heavy rare earth sintered Nd-Fe-B permanent magnet. The sintering temperature is 1035℃, the sintering time is 8h, the first-stage tempering temperature is 880℃, the first-stage tempering time is 2h, the second-stage tempering temperature is 560℃, the second-stage tempering time is 4h, the argon gas pressure during tempering is 90kPa, and the fan speed is 5000r / min.

[0084] The properties of the prepared non-heavy rare earth sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0085] Comparative Example 1

[0086] Compared with Example 1, the difference is that in (4), the surface of the non-heavy rare earth magnet compacted body is not sprayed with non-heavy rare earth auxiliary alloy powder mixture during demolding of the press.

[0087] The properties of the prepared non-heavy rare earth sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0088] Comparative Example 2

[0089] Compared with Example 2, the difference is that in (4), the surface of the non-heavy rare earth magnet compacted body is not sprayed with non-heavy rare earth auxiliary alloy powder mixture during demolding of the press.

[0090] The properties of the prepared non-heavy rare earth sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0091] Comparative Example 3

[0092] Compared with Example 3, the difference is that in (4), the surface of the non-heavy rare earth magnet compacted body is not sprayed with non-heavy rare earth auxiliary alloy powder mixture during demolding of the press.

[0093] The properties of the prepared heavy rare earth-free sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0094] Comparative Example 4

[0095] Compared with Example 1, the difference is that in (4), 20wt% of the heavy rare earth-free auxiliary alloy powder mixture is sprayed on the pre-surface of the heavy rare earth-free magnet compact at the time of the press demolding.

[0096] The properties of the prepared heavy rare earth-free sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0097] Comparative Example 5

[0098] Compared with Example 1, the difference is that in (5), the sintering temperature is 3h.

[0099] The properties of the prepared heavy rare earth-free sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0100] Comparative Example 6

[0101] Compared with Example 1, the difference is that in (5), only one-stage tempering is used.

[0102] The properties of the prepared heavy rare earth-free sintered Nd-Fe-B permanent magnet are shown in Table 1.

[0103] Table 1, Performance Test Table of Heavy Rare Earth-Free Sintered Nd-Fe-B Permanent Magnet

[0104]

[0105]

[0106] From the above table, by spraying the heavy rare earth-free auxiliary alloy powder mixture after the orientation compaction of the heavy rare earth-free mixed magnetic powder and before the isostatic pressing, combined with the low-temperature long-time sintering process and the tempering heat treatment process, the coercive force of the magnet is improved, and the remanence of the magnet is almost not reduced. And by adjusting the composition of the heavy rare earth-free auxiliary alloy powder, the distribution of rare earth elements in the shell layer of the heavy rare earth-free sintered Nd-Fe-B permanent magnet is more uniform, and the magnetic properties are further improved.

[0107] In Comparative Example 4, the heavy rare earth-free auxiliary alloy powder mixture sprayed on the pre-surface of the heavy rare earth-free magnet compact is excessive, which reduces the magnetic properties.

[0108] In summary, the present application adopts a double alloy process, uses a grain boundary addition method, introduces metals in the heavy rare earth-free auxiliary alloy, so that the rare earth elements in the auxiliary alloy are concentrated in the grain boundary phase, and can be diffused into the main phase as little as possible, so that the light rare earth elements form a high-magnetic crystal anisotropy shell at the grain boundary of the magnet, improve the coercive force of the magnet, and ensure that the remanence of the magnet is almost not reduced.

[0109] The specific embodiments described herein are merely illustrative of the spirit of the application. Various modifications or changes in the specific embodiments described herein can occur to those skilled in the art to which the application pertains without departing from the spirit of the application, and it is understood that such modifications or changes are to be considered as within the scope of the application as defined by the appended claims.

Claims

1. A method for preparing a heavy rare earth-free sintered NdFeB permanent magnet, characterized in that, The preparation method includes: S1. Mix the heavy rare earth main alloy powder and the heavy rare earth auxiliary alloy powder mixture to obtain heavy rare earth mixed magnetic powder. In the heavy rare earth-free mixed magnetic powder, the mass of the heavy rare earth-free auxiliary alloy powder is 0.1~2wt% of the total mass of the heavy rare earth-free main alloy powder and the heavy rare earth-free auxiliary alloy powder; The heavy rare earth auxiliary alloy powder mixture is a mixture of heavy rare earth auxiliary alloy powder and organic solvent, and the mass ratio of heavy rare earth auxiliary alloy powder to organic solvent is 1:(5~20). The heavy rare earth-free main alloy powder, by mass percentage, has the following composition: RE a Fe 100-a-b-c M b B c RE includes at least one of Pr and Nd, M includes at least one of Cu, Al, Zr, Co, Ga and Nb, and satisfies 28≤a≤35, 0.01≤b≤1.0, and 0.8≤c≤1.2; The heavy rare earth-free auxiliary alloy powder, by mass percentage, has the following composition: R x N y Fe 100-x-y R includes at least one of Pr and Nd, N includes at least one of Cu and Ga, and satisfies 50≤x≤53 and 3≤y≤5; S2. Orient and press the heavy rare earth mixed magnetic powder. When demolding the pre-pressed blank, spray the surface of the heavy rare earth magnet pre-pressed blank with a mixture of heavy rare earth auxiliary alloy powders and then perform isostatic pressing to obtain the heavy rare earth magnet pre-pressed blank. The amount of the heavy rare earth auxiliary alloy powder mixture sprayed is 0.1~10wt% of the weight of the pre-pressed blank. S3. After the heavy rare earth-free magnet blank and sintering box are placed in a glove box for static treatment, they are placed in a sintering furnace for sintering and tempering heat treatment. The sintering temperature is 960~1100℃ and the sintering time is 8~10h. The tempering heat treatment includes primary tempering and secondary tempering. The primary tempering temperature is 680~950℃ and the primary tempering time is 2~5h. The secondary tempering temperature is 400~600℃ and the secondary tempering time is 2~5h. Heavy rare earth-free sintered NdFeB permanent magnets are obtained.

2. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, The average particle size of the heavy rare earth main alloy powder in step S1 is 2.3~2.7 micrometers.

3. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, The average particle size of the heavy rare earth auxiliary alloy powder in step S1 is 1.8~2.2 micrometers.

4. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, In step S1, the rare earth-free main alloy powder also contains Ce (RE).

5. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, The organic solvent in step S1 is trifluorotrichloroethane.

6. The preparation method according to claim 1, characterized in that, In step S2, the magnetic field strength of the orientation compression type is 1.4~2.6T, and the pressure is 5~30MPa.

7. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, The static pressure in step S2 is 130~260MPa.

8. The method for preparing heavy rare earth-free sintered NdFeB permanent magnets according to claim 1, characterized in that, In step S3, the first-stage tempering temperature is greater than the second-stage tempering temperature, and the temperature difference between the two is 200~500℃.

9. A heavy rare earth-free sintered NdFeB permanent magnet, characterized in that, It is prepared by the method for preparing heavy rare earth sintered NdFeB permanent magnets as described in any one of claims 1 to 8.

10. The heavy rare earth-free sintered NdFeB permanent magnet according to claim 9, characterized in that, The rare earth element R in the heavy rare earth-free auxiliary alloy is concentrated in the grain boundary phase.

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