A heavy rare earth grain boundary diffusion permanent magnet and its preparation method and application

Abstract

The present invention discloses a heavy rare earth grain boundary diffusion permanent magnet and its preparation method and application. The preparation method comprises: mixing a main alloy with an auxiliary alloy source and performing orientation pressing, cold isostatic pressing, sintering, and tempering heat treatment to obtain a base magnet, wherein the magnet main phase grains of the base magnet have a core-shell structure; and applying a heavy rare earth source to the surface of the base magnet and performing diffusion heat treatment to obtain a heavy rare earth grain boundary diffusion permanent magnet, wherein the magnet main phase grains of the heavy rare earth grain boundary diffusion permanent magnet have a double-shell core-shell structure. The heavy rare earth grain boundary diffusion permanent magnet prepared by the present invention effectively reduces the usage of heavy rare earth metal, improves the magnetic properties of the magnet to a certain extent, has good consistency and stability, and is of great significance to the sintered NdFeB industry and the field of rare earth permanent magnet materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth permanent magnet materials, and in particular relates to a heavy rare earth grain boundary diffusion permanent magnet and a preparation method and application thereof. Background Art

[0002] Neodymium iron boron (NdFeB) rare earth permanent magnet materials have become the core functional material for electric motors used in new energy vehicles due to their excellent permanent magnetic properties. Coercivity, which characterizes a magnet's ability to resist external magnetic fields without demagnetization, is an important magnetic parameter that affects the magnet's service life. However, the actual coercivity of currently available NdFeB magnets is still significantly lower than the theoretical value. Further improving coercivity is a common goal in the field of NdFeB rare earth permanent magnets. Studies have shown that under the action of an external reverse magnetic field, the surface layer of the NdFeB main phase grains is prone to preferential magnetization reversal and produces reverse magnetization domains. These reverse magnetization domains are then transferred within the grains and expand throughout the magnet, ultimately causing the magnet to lose its magnetic function. Therefore, strengthening the magnetic hardening effect of the surface layer of the main phase grains of the magnet is the key to improving the coercivity of the magnet. The grain boundary diffusion technology of heavy rare earth can effectively enhance the magnetic hardening effect of the grain surface, thereby greatly improving the coercive force of the magnet. The principle is to attach the diffusion source material containing heavy rare earth elements Dy or Tb to the surface of the magnet, and through a certain heat treatment process, the heavy rare earth in the diffusion source diffuses into the interior of the magnet along the grain boundary channel between the main phase grains, and then enters the epitaxial layer of the main phase grains, and finally forms an anisotropic field on the grain surface that is much higher than that of Nd2Fe 14 B-phase (Nd, Dy / Tb)2Fe 14 The B-phase heavy rare earth magnetic hardening shell can effectively inhibit the nucleation of reverse magnetization domains on the surface of the grains, thereby achieving the goal of improving the coercive force of the magnet. Theoretical calculations show that a heavy rare earth magnetic hardening shell with a thickness of 14 nanometers has reached saturation. However, the heavy rare earth shell observed on the surface of the actual diffusion magnet is too thick and has approached the micron level. This excessively thick shell is a waste of scarce heavy rare earth Dy and Tb resources. How to reduce the thickness of the heavy rare earth magnetic hardening shell during grain boundary diffusion is the key to high-quality utilization of heavy rare earth resources. It is of great significance to the development of heavy rare earth grain boundary diffusion technology and even the NdFeB rare earth permanent magnet industry. Summary of the Invention

[0003] The main purpose of the present invention is to provide a heavy rare earth grain boundary diffusion permanent magnet and its preparation method and application, which effectively compresses the thickness of the heavy rare earth magnetic hardening shell, reduces the amount of heavy rare earth, and satisfies the requirement that the magnetic properties of the diffused magnet have good consistency and stability while ensuring the heavy rare earth diffusion effect and coercive force amplification level.

[0004] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0005] An embodiment of the present invention provides a method for preparing a heavy rare earth grain boundary diffusion permanent magnet, which includes:

[0006] The main alloy and the auxiliary alloy source are mixed and subjected to orientation pressing, cold isostatic pressing, sintering, and tempering heat treatment to obtain a base magnet, wherein the magnet main phase grains of the base magnet have a core-shell structure;

[0007] Furthermore, a heavy rare earth source is applied to the surface of the base magnet and diffusion heat treatment is performed to produce a heavy rare earth grain boundary diffusion permanent magnet, wherein the magnet main phase grains of the heavy rare earth grain boundary diffusion permanent magnet have a double-shell core-shell structure, and the double-shell core-shell structure includes a core and a high-abundance rare earth inner shell layer and a heavy rare earth magnetic hardening outer shell layer formed in sequence on the core surface.

[0008] The embodiment of the present invention also provides a heavy rare earth grain boundary diffusion permanent magnet prepared by the aforementioned preparation method.

[0009] An embodiment of the present invention further provides a method for reducing the content of heavy rare earth elements in a permanent magnet, which comprises: preparing the permanent magnet using the aforementioned preparation method.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] (1) The present invention provides a method for preparing a heavy rare earth grain boundary diffusion permanent magnet. By utilizing the strong main phase forming ability and metallurgical properties of high-abundance rare earth elements, a relatively cheap high-abundance rare earth shell is preferentially formed around the main phase, effectively inhibiting the excessive diffusion of expensive heavy rare earth elements Dy / Tb into the main phase. After the heavy rare earth elements Dy / Tb are diffused, a second shell is formed around the main phase. While ensuring the optimization of magnetic properties, the thickness of the magnetic hardening shell is regulated, thereby reducing the use of expensive heavy rare earth elements Dy / Tb.

[0012] (2) The preparation method of the heavy rare earth grain boundary diffusion permanent magnet provided by the present invention is simple to operate, the raw materials are easily available, and the final product has good consistency and stability, which is of great significance to the rare earth permanent magnet industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 It is a schematic diagram of the principle of preparing heavy rare earth grain boundary diffusion permanent magnets in a typical embodiment of the present invention. DETAILED DESCRIPTION

[0015] In view of the defects of the existing technology, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. It mainly realizes the control of the metallurgical behavior of heavy rare earth elements during the diffusion process by optimizing the design of the matrix magnet structure and the element distribution of the main phase grains, effectively compresses the thickness of the heavy rare earth magnetic hardening shell on the surface of the grains, and improves the magnet diffusion effect and heavy rare earth utilization rate, which is of great significance.

[0016] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Specifically, as one aspect of the technical solution of the present invention, a method for preparing a heavy rare earth grain boundary diffusion permanent magnet includes:

[0018] The main alloy and the auxiliary alloy source are mixed and subjected to orientation pressing, cold isostatic pressing, sintering, and tempering heat treatment to obtain a base magnet, wherein the magnet main phase grains of the base magnet have a core-shell structure;

[0019] Furthermore, a heavy rare earth source is applied to the surface of the base magnet and diffusion heat treatment is performed to produce a heavy rare earth grain boundary diffusion permanent magnet, wherein the magnet main phase grains of the heavy rare earth grain boundary diffusion permanent magnet have a double-shell core-shell structure, and the double-shell core-shell structure includes a core and a high-abundance rare earth inner shell layer and a heavy rare earth magnetic hardening outer shell layer formed in sequence on the core surface.

[0020] In some preferred embodiments, the schematic diagram of the principle of preparing heavy rare earth grain boundary diffusion permanent magnets in the present invention is as follows: Figure 1 shown.

[0021] In some preferred embodiments, the mass ratio of the auxiliary alloy source to the base magnet is 0.5-30:100.

[0022] In some preferred embodiments, the mass ratio of the heavy rare earth source to the base magnet is 1 to 5:100.

[0023] Furthermore, the mass ratio of the heavy rare earth source to the base magnet is 2-4:100.

[0024] Furthermore, the mass ratio of the heavy rare earth source to the base magnet is 3:100.

[0025] In some preferred embodiments, the thickness of the high-abundance rare earth inner shell layer is 1 to 3 μm.

[0026] In some preferred embodiments, the thickness of the heavy rare earth magnetic hardening shell layer is 0.3-1 μm.

[0027] In some preferred embodiments, the general chemical formula of the master alloy is as shown in formula (I):

[0028] RE x B y M z Fe 100-x-y-z Formula (I)

[0029] Wherein, RE is selected from any one or more combinations of Pr, Nd, La, Ce, Sm, and Ho, M is selected from any one or more combinations of Nb, Zr, Cu, Co, Ga, and Al, B is boron, and Fe is iron; x, y, and z are the mass percentage contents of the corresponding elements, respectively, and satisfy 20≤x≤40, 0.5≤y≤1.5, and 1≤z≤5.

[0030] Furthermore, in the formula (I), x is preferably 25 to 35, more preferably 29 to 31, and most preferably 30; y is preferably 0.7 to 1.2, more preferably 0.9 to 1.1, and most preferably 1; wherein, if the rare earth content is too low, it will lead to the formation of impurity phases such as αFe, thereby reducing the coercive force of the key magnetic property of the magnet, while if it is too high, it will lead to a decrease in remanence; if the boron content is too low, it will lead to the inability to form the NdFeB main phase, while if it is too high, it will easily form a non-ferromagnetic phase; long-term practice has shown that only within the preferred scheme can the comprehensive performance of the magnet be maintained at a relatively high level.

[0031] In some preferred embodiments, the general chemical formula of the auxiliary alloy source is as shown in formula (II):

[0032] RE1 a RE2 b RE3 c M 100-a-b-c Formula (II)

[0033] Among them, RE1 is selected from any one or more combinations of Pr, Nd, La, Ce, Sm and Ho, RE2 is selected from any one or more combinations of Y and Gd, RE3 is selected from any one or more combinations of Tb and Dy, M is selected from any one or more combinations of Al, Cu, Ga, Si, Sn, Ge, Ti and Zn, a, b and c are the mass percentage contents of the corresponding elements, and satisfy 20≤a≤60, 20≤b≤60 and 0≤c≤40.

[0034] Furthermore, in formula (II), a is preferably 25-55, more preferably 35-45, and most preferably 40; b is preferably 25-55, more preferably 35-45, and most preferably 40; and c is preferably 15-35, more preferably 20-30, and most preferably 25. The content of RE1 affects the wettability of the auxiliary alloy; too high or too low a content will lead to element segregation; too high a content of RE2 will reduce the anisotropy field of the magnet, thereby deteriorating the magnetic properties, while too low a content will not play a role in grain boundary regulation; RE3 is a heavy rare earth element; too high a content will result in high cost, while too low a content will reduce the magnetic properties of the magnet.

[0035] In some preferred embodiments, the chemical formula of the heavy rare earth source is as shown in formula (III):

[0036] (RE4)H3 Formula (III)

[0037] Wherein, RE4 is selected from Tb and / or Dy, and H is hydrogen.

[0038] In some preferred embodiments, the magnetic field strength used in the orientation pressing process is 1.5-2.5T.

[0039] Furthermore, the orientation pressing is preferably performed by isostatic pressing in a magnetic field, and the isostatic pressing pressure is preferably 150-200 MPa, more preferably 160-190 MPa, and most preferably 170-180 MPa. Too little pressure will result in too low density of the magnet blank and a loose structure; too much pressure will cause the magnet blank to crack.

[0040] In some preferred embodiments, the pressure used in the cold isostatic pressing process is 150-220 MPa, preferably 180-200 MPa, wherein too low a pressure will result in too low a density of the magnet blank and a loose structure; too high a pressure will cause the magnet blank to crack. In the present invention, the cold isostatic pressing is preferably oil-cooled isostatic pressing.

[0041] In the present invention, the sintering is preferably vacuum sintering.

[0042] In the present invention, the sintering temperature is preferably 900-1100°C; the sintering time is preferably 2-8h, more preferably 3-5h, and most preferably 4h. In the present invention, the sintering temperature rise process is preferably continuous and slow temperature rise. In the present invention, the temperature rise time is preferably 5-20h, more preferably 10-18h, and most preferably 15h. If the sintering time is too short, the magnet will lack density, and if the sintering time is too long, the grains will grow. If the temperature rise time is too short, the internal degassing of the magnet will be incomplete, and if the temperature rise time is too long, the magnet preparation efficiency will be reduced.

[0043] In some preferred embodiments, the tempering heat treatment includes a primary tempering treatment and a secondary tempering treatment.

[0044] Furthermore, the temperature of the primary tempering treatment is 800-920°C.

[0045] Furthermore, the temperature of the secondary tempering treatment is 460-560°C.

[0046] Furthermore, the time of the primary tempering treatment and the secondary tempering treatment are independently 0.5 to 2 hours.

[0047] In some preferred embodiments, the preparation method specifically comprises: applying a heavy rare earth source to the surface of the base magnet, and then heating the base magnet at a temperature of 800-1000°C and a vacuum degree of 1×10 -2 Performing diffusion heat treatment for 2 to 10 hours under the condition of less than pa to obtain the heavy rare earth grain boundary diffusion permanent magnet;

[0048] Furthermore, the temperature of the diffusion heat treatment is 850-950°C.

[0049] Furthermore, the diffusion heat treatment time is 4 to 9 hours.

[0050] In some preferred embodiments, the master alloy comprises master alloy powder; the particle size of the master alloy powder is 2 to 5 μm.

[0051] In some preferred embodiments, the auxiliary alloy source includes auxiliary alloy powder; the auxiliary alloy powder has a particle size of 2 to 5 μm.

[0052] In some preferred embodiments, the heavy rare earth source comprises heavy rare earth powder; the particle size of the heavy rare earth powder is 2 to 5 μm.

[0053] In the present invention, the method for preparing the main alloy powder comprises: hydrogen crushing the main alloy flakes and then performing air flow grinding to pulverize the powder.

[0054] In the present invention, the method for preparing the main alloy casting comprises: melting alloy raw materials and then rapidly solidifying them to obtain the main alloy casting.

[0055] In the present invention, the thickness of the master alloy casting is preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.4 mm, and most preferably 0.3 mm. If the master alloy casting is too thick, the internal grain size will be uneven, while if it is too thin, the casting will have a fishbone shape and a discontinuous structure. This will also reduce the yield and waste raw materials.

[0056] The present invention has no special restrictions on the smelting method. The alloy raw materials can be mixed according to the pre-obtained components and then smelted using a smelting method well known to those skilled in the art. In the present invention, the vacuum degree during the rapid solidification process is preferably less than 10 -2 Pa, the copper roller speed is preferably 1.8-3.0 m / s, more preferably 2.0-2.5 m / s; the pouring temperature is preferably 1200-1500°C, more preferably 1300-1400°C, and most preferably 1350°C. Too fast a copper roller speed will result in discontinuous casting, while too slow a speed will cause material to accumulate at the copper roller, resulting in a waste of raw materials; too high a pouring temperature will result in unnecessary waste of electricity and cause the metal with a lower melting point to volatilize prematurely, while too low a pouring temperature will result in incomplete melting of the raw materials.

[0057] In the present invention, the hydrogen pressure during the hydrogen crushing process is preferably 0.1-0.4 MPa, more preferably 0.2-0.3 MPa; the hydrogen absorption time is preferably 2-5 hours, more preferably 3-4 hours; the dehydrogenation temperature is 320-500°C; dehydrogenation is preferably performed in vacuum; and the dehydrogenation time is 4-8 hours. Too low a hydrogen pressure will result in excessively slow hydrogen absorption, while too high a hydrogen pressure will cause unnecessary waste and pose a risk to the equipment's pressure tolerance. Too long a hydrogen absorption time will reduce process efficiency, while too short a hydrogen absorption time will result in insufficient hydrogen absorption saturation.

[0058] In the present invention, the hydrogen content of the coarsely crushed powder obtained after hydrogen crushing is preferably less than 1500 ppm, and the average particle size of the powder is 100 to 250 microns. Excessive hydrogen content in the coarsely crushed powder will reduce the gas release efficiency during the temperature rise process of the sintering process, and excessive hydrogen content will deteriorate the magnetic properties of the final magnet.

[0059] In the present invention, the moisture content of the pulverizer during the airflow milling process is preferably less than 10 ppm, and the rotation frequency of the classifying wheel is preferably 65 to 110 Hz. Too high a moisture content in the airflow mill will deteriorate the magnetic properties of the final magnet.

[0060] In the present invention, the preparation method of the auxiliary alloy powder comprises: hydrogen crushing the auxiliary alloy flakes and then performing air flow mill crushing.

[0061] In the present invention, the method for preparing the auxiliary alloy casting sheet comprises: melting the alloy raw material and then rapidly solidifying it to obtain the auxiliary alloy casting sheet.

[0062] In the present invention, the thickness of the auxiliary alloy casting sheet is preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.4 mm, and most preferably 0.3 mm. The reasons for the preference are the same as those for the main alloy casting sheet preparation process.

[0063] The present invention has no special restrictions on the smelting method. The alloy raw materials can be mixed according to the pre-obtained components and then smelted using a smelting method well known to those skilled in the art. In the present invention, the vacuum degree during the rapid solidification process is preferably less than 10 -2 The speed is preferably 1.8-3.0 m / s, more preferably 2.0-2.5 m / s; the pouring temperature is preferably 900-1500° C., more preferably 1000-1400° C., more preferably 1100-1300° C., and most preferably 1200° C. The reasons for the preference are the same as those for the main alloy casting process.

[0064] In the present invention, the process parameters for hydrogen crushing are selected within the same range as those described in the above-mentioned technical solution and will not be further elaborated here. The hydrogen content of the coarse crushed powder obtained after hydrogen crushing is preferably less than 1500 ppm, and the average particle size of the powder is 100 to 250 microns. The reasons for this preference are the same as those for the main alloy hydrogen crushing process.

[0065] In the present invention, the moisture content of the powder making machine during the airflow milling process is preferably less than 10 ppm, and the rotation frequency of the classifying wheel is 65 to 110 Hz. The reasons for the preference are the same as those for the main alloy airflow milling powder preparation process.

[0066] In the present invention, the preparation method of the heavy rare earth metal powder comprises: hydrogen crushing the heavy rare earth metal block and then performing air flow grinding to pulverize the heavy rare earth metal block.

[0067] In the present invention, the process parameters for hydrogen fracturing are consistent with those described in the aforementioned technical solution and will not be further elaborated here. The hydrogen content of the powder obtained after hydrogen fracturing is preferably less than 1500 ppm, and the average particle size of the powder is 100 to 250 microns. The reasons for this preference are the same as those for the main alloy hydrogen fracturing process.

[0068] In the present invention, the moisture content of the pulverizer during the airflow milling process is preferably less than 10 ppm, and the rotation frequency of the classifying wheel is . The reasons for the preference are the same as those for the main alloy airflow milling powder preparation process.

[0069] The present invention provides a method for preparing heavy rare earth grain boundary diffusion permanent magnets. By leveraging the strong main phase-forming ability and metallurgical properties of high-abundance rare earth elements, a relatively inexpensive high-abundance rare earth shell is preferentially formed around the main phase, effectively inhibiting the excessive diffusion of Dy / Tb heavy rare earth elements into the main phase during subsequent diffusion. A secondary shell is formed around the main phase using a diffusion heat treatment process. While ensuring optimal magnetic properties, the thickness of the magnetically hardened shell is regulated, reducing the amount of Dy / Tb heavy rare earth elements used. The present invention is simple to operate, utilizes readily available raw materials, and produces a final product with good consistency and stability, making it of great significance to the rare earth permanent magnet industry.

[0070] In some more specific embodiments, the method for preparing the heavy rare earth grain boundary diffusion permanent magnet comprises:

[0071] S1: mixing the main alloy powder and the auxiliary alloy powder, and sequentially performing orientation pressing, cold isostatic pressing, sintering and tempering heat treatment to obtain a main phase single shell structure NdFeB permanent magnet material as a base magnet;

[0072] S2: evenly spraying heavy rare earth powder on the surface of the base magnet to obtain a pretreated magnet;

[0073] S3: performing diffusion heat treatment on the pretreated magnet to obtain a main phase double-shell structure diffusion material as a heavy rare earth grain boundary diffusion permanent magnet.

[0074] Another aspect of the embodiments of the present invention further provides a heavy rare earth grain boundary diffusion permanent magnet produced by the aforementioned preparation method.

[0075] Another aspect of the embodiments of the present invention further provides a method for reducing the content of heavy rare earth elements in a permanent magnet, which comprises: preparing a permanent magnet using the aforementioned preparation method, thereby reducing the content of heavy rare earth elements in the permanent magnet.

[0076] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0077] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0078] Example 1

[0079] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0080] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Nd 15.08 Ce 12.54 A 10.15 Co 0.45 Zr 0.21 Ga 0.53 Fe 70.11 B 0.93 , the auxiliary alloy composition and mass percentage are Pr 53.86 Y 33.99 Cu 12.15 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3Pa, the copper roller speed is 2.2m / s, the main alloy pouring temperature is 1350℃, the auxiliary alloy pouring temperature is 1200℃, the average thickness of the main alloy casting is 0.29mm, and the average thickness of the auxiliary alloy casting is 0.30mm.

[0081] (2) The heavy rare earth metal block DyH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 6 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 166 μm, the average particle size of the main coarse crushed powder is 165 μm, and the average particle size of the auxiliary coarse crushed powder is 168 μm.

[0082] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 6.5 ppm, the classification wheel rotation frequency is 100 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 3 μm.

[0083] (4) The main alloy powder and the auxiliary alloy powder obtained in step (3) are weighed separately, lubricant is added and evenly mixed, and orientation pressing is performed in an argon atmosphere, wherein the magnetic field strength is 1.7T and the isostatic pressing pressure is 180MPa. Subsequently, the obtained molded blank is cold isostatically pressed at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0084] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 1000°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0085] (6) Using a spray gun, the heavy rare earth powder obtained in step (3) is evenly sprayed on the surface of the base magnet obtained in step (5), wherein the spraying amount of the heavy rare earth powder is 3% of the mass of the base magnet, to obtain a pretreated magnet.

[0086] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours, to obtain a heavy rare earth grain boundary diffusion sintered permanent magnet.

[0087] In this embodiment, in order to compare the effects of a single heavy rare earth diffusion magnet and a magnet prepared by the method of the present invention, the main alloy powder obtained in step (3) was used to prepare a raw magnet using the same sintering and tempering process. The raw magnet and the heavy rare earth powder obtained in step (3) were used to prepare a single heavy rare earth diffusion magnet using the same spraying and diffusion heat treatment process. Microstructural observation showed that the raw magnet had no shell structure; the average thickness of the high-abundance rare earth inner shell of the magnet of the present invention was 2.2 μm, and the average thickness of the heavy rare earth outer shell was 0.5 μm; the single heavy rare earth diffusion magnet only had a heavy rare earth shell with an average thickness of 1.5 μm. Two magnet samples were randomly selected from each of the raw magnet, the single heavy rare earth diffusion magnet, and the magnet obtained in step (7) of this embodiment for magnetic property testing. The test results are shown in Table 1.

[0088] Table 1 Magnet performance data of Example 1

[0089]

[0090] It can be seen from Table 1 that, compared with a single heavy rare earth diffusion magnet, the magnet prepared by the method of the present invention has improved magnetic properties while ensuring the use of less heavy rare earth powder, and has better consistency and stability.

[0091] Example 2

[0092] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0093] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Pr 4.21 Nd 15.45 Ce 8.97 A 10.52 Cu 0.28 Co 0.11 Zr 0.13 Ga 0.08 Fe 59.34 B 0.91 , the auxiliary alloy composition and mass percentage are Pr 31.15 Y 19.65 Tb 35.14 Cu 14.05 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3 Pa, the copper roller speed is 2.2m / s, the main alloy pouring temperature is 1340℃, the auxiliary alloy pouring temperature is 1100℃, the average thickness of the main alloy casting is 0.29mm, and the average thickness of the auxiliary alloy casting is 0.29mm.

[0094] (2) The heavy rare earth metal block TbH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 6 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 167 μm, the average particle size of the main coarse crushed powder is 164 μm, and the average particle size of the auxiliary coarse crushed powder is 165 μm.

[0095] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 4.1 ppm, the rotation frequency of the classifying wheel is 100 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 3 μm.

[0096] (4) The main alloy powder and the auxiliary alloy powder obtained in step (3) are weighed separately, lubricant is added and evenly mixed, and orientation pressing is performed in an argon atmosphere, wherein the magnetic field strength is 1.7T and the isostatic pressing pressure is 180MPa. Subsequently, the obtained molded blank is cold isostatically pressed at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0097] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 950°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0098] (6) Using a spray gun, the heavy rare earth powder obtained in step (3) is evenly sprayed on the surface of the base magnet obtained in step (5), wherein the spraying amount of the heavy rare earth powder is 3% of the mass of the base magnet, to obtain a pretreated magnet.

[0099] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours, to obtain a heavy rare earth grain boundary diffusion sintered permanent magnet.

[0100] In this embodiment, in order to compare the effects of a single heavy rare earth diffusion magnet and a magnet prepared by the method of the present invention, the main alloy powder obtained in step (3) was used to prepare a raw magnet using the same sintering and tempering process. The raw magnet and the heavy rare earth powder obtained in step (3) were used to prepare a single heavy rare earth diffusion magnet using the same spraying and diffusion heat treatment process. Microstructural observation showed that the raw magnet had no shell structure; the average thickness of the high-abundance rare earth inner shell of the magnet of the present invention was 2.5 μm, and the average thickness of the heavy rare earth outer shell was 0.4 μm; the single heavy rare earth diffusion magnet only had a heavy rare earth shell with an average thickness of 1.7 μm. Two magnet samples were randomly selected from each of the raw magnet, the single heavy rare earth diffusion magnet, and the magnet obtained in step (7) of this embodiment for magnetic property testing. The test results are shown in Table 2.

[0101] Table 2 Magnet performance data of Example 2

[0102]

[0103] It can be seen from Table 2 that, compared with a single heavy rare earth diffusion magnet, the magnet prepared by the method of the present invention has improved magnetic properties while ensuring the use of less heavy rare earth powder, and has better consistency and stability.

[0104] Example 3

[0105] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0106] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Pr 6.11 Nd 20.78 Ce 4.30 Al 0.19 Cu 0.19 Co 0.21 Zr 0.25 Ga 0.09 Fe 66.92 B 0.96 , the auxiliary alloy composition and mass percentage are Pr 24.23 Y 22.93 Dy 41.91 Cu 10.93 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3 Pa, the copper roller speed is 2.2m / s, the main alloy pouring temperature is 1340℃, the auxiliary alloy pouring temperature is 1100℃, the average thickness of the main alloy casting is 0.30mm, and the average thickness of the auxiliary alloy casting is 0.30mm.

[0107] (2) The heavy rare earth metal block DyH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 6 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 166 μm, the average particle size of the main coarse crushed powder is 163 μm, and the average particle size of the auxiliary coarse crushed powder is 165 μm.

[0108] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 5.4 ppm, the rotation frequency of the classifying wheel is 100 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 3 μm.

[0109] (4) The main alloy powder and the auxiliary alloy powder obtained in step (3) are weighed separately, lubricant is added and evenly mixed, and orientation pressing is performed in an argon atmosphere, wherein the magnetic field strength is 1.7T and the isostatic pressing pressure is 180MPa. Subsequently, the obtained molded blank is cold isostatically pressed at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0110] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 950°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0111] (6) Using a spray gun, the heavy rare earth powder obtained in step (3) is evenly sprayed on the surface of the base magnet obtained in step (5), wherein the spraying amount of the heavy rare earth powder is 3% of the mass of the base magnet, to obtain a pretreated magnet.

[0112] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours, to obtain a heavy rare earth grain boundary diffusion sintered permanent magnet.

[0113] In this embodiment, in order to compare the effects of a single heavy rare earth diffusion magnet and a magnet prepared by the method of the present invention, the main alloy powder obtained in step (3) was used to prepare a raw magnet using the same sintering and tempering process. The raw magnet and the heavy rare earth powder obtained in step (3) were used to prepare a single heavy rare earth diffusion magnet using the same spraying and diffusion heat treatment process. Microstructural observation showed that the raw magnet had no shell structure; the average thickness of the high-abundance rare earth inner shell of the magnet of the present invention was 2.0 μm, and the average thickness of the heavy rare earth outer shell was 0.3 μm; the single heavy rare earth diffusion magnet only had a heavy rare earth shell with an average thickness of 1.8 μm. Two magnet samples were randomly selected from each of the raw magnet, the single heavy rare earth diffusion magnet, and the magnet obtained in step (7) of this embodiment for magnetic property testing. The test results are shown in Table 3.

[0114] Table 3 Magnet performance data of Example 3

[0115]

[0116] It can be seen from Table 3 that, compared with a single heavy rare earth diffusion magnet, the magnet prepared by the method of the present invention has improved magnetic properties while ensuring the use of less heavy rare earth powder, and has better consistency and stability.

[0117] Example 4

[0118] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0119] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Pr 9.11 Nd 23.78 Ce 6.88 Al 1.12 Cu 1.65 Co 1.41 Sn 0.98 Ga 0.74 Fe 52.92 B 1.41 , the auxiliary alloy composition and mass percentage are Pr 40.16 Gd 55.83 Cu 4.01 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3 Pa, the copper roller speed is 2.1m / s, the main alloy pouring temperature is 1040℃, the auxiliary alloy pouring temperature is 980℃, the average thickness of the main alloy casting is 0.28mm, and the average thickness of the auxiliary alloy casting is 0.31mm.

[0120] (2) The heavy rare earth metal block TbH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 7 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 165 μm, the average particle size of the main coarse crushed powder is 162 μm, and the average particle size of the auxiliary coarse crushed powder is 164 μm.

[0121] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 2.7 ppm, the rotation frequency of the classifying wheel is 110 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 2 μm.

[0122] (4) The main alloy powder and the auxiliary alloy powder obtained in step (3) are weighed separately, lubricant is added and evenly mixed, and orientation pressing is performed in an argon atmosphere, wherein the magnetic field strength is 1.7T and the isostatic pressing pressure is 180MPa. Subsequently, the obtained molded blank is cold isostatically pressed at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0123] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 920°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0124] (6) Using a spray gun, the heavy rare earth powder obtained in step (3) is evenly sprayed on the surface of the base magnet obtained in step (5), wherein the spraying amount of the heavy rare earth powder is 3% of the mass of the base magnet, to obtain a pretreated magnet.

[0125] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours, to obtain a heavy rare earth grain boundary diffusion sintered permanent magnet.

[0126] In this embodiment, in order to compare the effects of a single heavy rare earth diffusion magnet and a magnet prepared by the method of the present invention, the main alloy powder obtained in step (3) was used to prepare a raw magnet using the same sintering and tempering process. The raw magnet and the heavy rare earth powder obtained in step (3) were used to prepare a single heavy rare earth diffusion magnet using the same spraying and diffusion heat treatment process. Microstructural observation showed that the raw magnet had no shell structure; the average thickness of the high-abundance rare earth inner shell of the magnet of the present invention was 2.8 μm, and the average thickness of the heavy rare earth outer shell was 0.4 μm; the single heavy rare earth diffusion magnet only had a heavy rare earth shell with an average thickness of 1.9 μm. Two magnet samples were randomly selected from each of the raw magnet, the single heavy rare earth diffusion magnet, and the magnet obtained in step (7) of this embodiment for magnetic property testing. The test results are shown in Table 4.

[0127] Table 4 Magnet performance data of Example 4

[0128]

[0129]

[0130] It can be seen from Table 4 that, compared with a single heavy rare earth diffusion magnet, the magnet prepared by the method of the present invention has improved magnetic properties while ensuring the use of less heavy rare earth powder, and has better consistency and stability.

[0131] Example 5

[0132] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0133] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Pr 3.14 Nd 17.43 Ce 1.12 Al 0.14 Cu 0.13 Co 0.11 Ge 0.15 Ti 0.03 Fe 77.2 B 0.55 , the auxiliary alloy composition and mass percentage are Nd 21.23 Gd 22.93 Dy 38.31 Cu 17.53 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3 Pa, the copper roller speed is 2.5m / s, the main alloy pouring temperature is 1480℃, the auxiliary alloy pouring temperature is 1250℃, the average thickness of the main alloy casting is 0.29mm, and the average thickness of the auxiliary alloy casting is 0.29mm.

[0134] (2) The heavy rare earth metal block DyH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 6 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 165 μm, the average particle size of the main coarse crushed powder is 164 μm, and the average particle size of the auxiliary coarse crushed powder is 165 μm.

[0135] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 4.7 ppm, the rotation frequency of the classifying wheel is 110 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 3 μm.

[0136] (4) The main alloy powder and the auxiliary alloy powder obtained in step (3) are weighed separately, lubricant is added and evenly mixed, and orientation pressing is performed in an argon atmosphere, wherein the magnetic field strength is 1.7T and the isostatic pressing pressure is 180MPa. Subsequently, the obtained molded blank is cold isostatically pressed at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0137] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 900°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0138] (6) Using a spray gun, the heavy rare earth powder obtained in step (3) is evenly sprayed on the surface of the base magnet obtained in step (5), wherein the spraying amount of the heavy rare earth powder is 3% of the mass of the base magnet, to obtain a pretreated magnet.

[0139] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours, to obtain a heavy rare earth grain boundary diffusion sintered permanent magnet.

[0140] In this embodiment, in order to compare the effects of a single heavy rare earth diffusion magnet and a magnet prepared by the method of the present invention, the main alloy powder obtained in step (3) was used to prepare a raw magnet using the same sintering and tempering process. The raw magnet and the heavy rare earth powder obtained in step (3) were used to prepare a single heavy rare earth diffusion magnet using the same spraying and diffusion heat treatment process. Microstructural observation showed that the raw magnet had no shell structure; the average thickness of the high-abundance rare earth inner shell of the magnet of the present invention was 1.8 μm, and the average thickness of the heavy rare earth outer shell was 0.2 μm; the single heavy rare earth diffusion magnet only had a heavy rare earth shell with an average thickness of 1.7 μm. Two magnet samples were randomly selected from each of the raw magnet, the single heavy rare earth diffusion magnet, and the magnet obtained in step (7) of this embodiment for magnetic property testing. The test results are shown in Table 5.

[0141] Table 5 Magnet performance data of Example 5

[0142]

[0143] It can be seen from Table 5 that, compared with a single heavy rare earth diffusion magnet, the magnet prepared by the method of the present invention has improved magnetic properties while ensuring the use of less heavy rare earth powder, and has better consistency and stability.

[0144] Comparative Example 1

[0145] Heavy rare earth grain boundary diffusion sintered permanent magnets were prepared according to the following method:

[0146] (1) Prepare the raw materials according to the main alloy composition and auxiliary alloy composition, where the main alloy composition and mass percentage are Nd 15.08 Ce 12.54 A 10.15 Co 0.45 Zr 0.21 Ga 0.53 Fe 70.11 B 0.93 , the auxiliary alloy composition and mass percentage are Pr 53.86 Y 33.99 Cu 12.15 The raw materials are melted and cast into main alloy castings and auxiliary alloy castings by using the rapid solidification process. The vacuum degree during the rapid solidification process is 7*10 -3 Pa, the copper roller speed is 2.2m / s, the main alloy pouring temperature is 1350℃, the auxiliary alloy pouring temperature is 1200℃, the average thickness of the main alloy casting is 0.29mm, and the average thickness of the auxiliary alloy casting is 0.30mm.

[0147] (2) The heavy rare earth metal block DyH3 and the main alloy casting sheet and the auxiliary alloy casting sheet obtained in step (1) are placed in a hydrogen crushing furnace in sequence, wherein the hydrogen pressure during the hydrogen crushing process is 0.3 MPa, the hydrogen absorption time is 3 hours, and the dehydrogenation time is 6 hours. The average particle size of the obtained heavy rare earth coarse crushed powder is 166 μm, the average particle size of the main coarse crushed powder is 165 μm, and the average particle size of the auxiliary coarse crushed powder is 168 μm.

[0148] (3) The heavy rare earth coarse crushed powder, main coarse crushed powder and auxiliary coarse crushed powder obtained in step (2) are placed in a jet mill in sequence for pulverization, wherein the moisture content during the pulverization process is 6.5 ppm, the classification wheel rotation frequency is 100 Hz, and the average particle size of the obtained heavy rare earth powder is 3 μm, the average particle size of the main alloy powder is 3 μm, and the average particle size of the auxiliary alloy powder is 3 μm.

[0149] (4) After weighing the main alloy powder obtained in step (3), add lubricant and shake to mix evenly, carry out orientation pressing in an argon atmosphere, wherein the intensity of the magnetic field is 1.7T and the isostatic pressing pressure is 180MPa. Then, the obtained molded blank is subjected to cold isostatic pressing at a pressure of 190MPa to obtain a double-pressed magnet blank.

[0150] (5) The double-pressed magnet blank obtained in step (4) is placed in a sintering furnace for sintering and tempering heat treatment, wherein the sintering temperature is 1000°C, the sintering time is 4 hours, the first-level tempering temperature is 900°C, the first-level tempering time is 2 hours, the second-level tempering temperature is 500°C, and the second-level tempering time is 2 hours, to obtain a base magnet.

[0151] (6) Mix the auxiliary alloy powder and heavy rare earth powder in a certain proportion and shake them evenly, and use a spray gun to evenly spray the mixed powder on the surface of the base magnet obtained in step (5). The spraying amount of the mixed powder is 3% of the mass of the base magnet to obtain a pretreated magnet.

[0152] (7) The pretreated magnet obtained in step (6) is placed in a sintering furnace for diffusion heat treatment, wherein the diffusion heat treatment temperature is 900° C. and the diffusion heat treatment time is 8 hours to obtain a mixed diffusion sintered permanent magnet.

[0153] Two magnet samples were randomly selected from each of the mixed diffusion sintered permanent magnet obtained in this comparative example (7), the original magnet in Example 1, and the magnet in Example 1 of the present invention for magnetic property testing. The test results are shown in Table 6. Microstructural observation shows that the original magnet in Example 1 has no shell structure; the average thickness of the high-abundance rare earth inner shell layer of the magnet in Example 1 of the present invention is 2.2 μm, and the average thickness of the heavy rare earth outer shell layer is 0.5 μm; the magnet in this comparative example has a high-abundance rare earth shell layer with an average thickness of 1.9 μm, and the heavy rare earth elements are agglomerated in the shallow area of ​​the magnet without forming a shell structure.

[0154] Table 6 Comparative Example Magnet Performance Data

[0155]

[0156] It can be seen from Table 6 that the magnetic properties of the mixed diffusion magnet in this comparative example are significantly inferior to those of the magnet in Example 1 of the present invention. Since the high-abundance elements Y and Gd preferentially occupy the grain boundaries, they block the deep diffusion of heavy rare earth elements, resulting in the agglomeration of heavy rare earth elements on the surface of the magnet. Therefore, the use of mixed powder for diffusion should be avoided in production.

[0157] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0158] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a heavy rare earth grain boundary diffusion permanent magnet, characterized in that: include: The main alloy and the auxiliary alloy source are mixed and subjected to orientation pressing, cold isostatic pressing, sintering, and tempering heat treatment to obtain a base magnet, wherein the magnet main phase grains of the base magnet have a core-shell structure; and applying a heavy rare earth source to the surface of the base magnet and performing a diffusion heat treatment to produce a heavy rare earth grain boundary diffusion permanent magnet, wherein the magnet main phase grains of the heavy rare earth grain boundary diffusion permanent magnet have a double-shell core-shell structure, the double-shell core-shell structure comprising a core and a high-abundance rare earth inner shell layer and a heavy rare earth magnetic hardening outer shell layer sequentially formed on the core surface, wherein the high-abundance element in the high-abundance rare earth inner shell layer is Y; Wherein, the mass ratio of the auxiliary alloy source to the base magnet is 0.5-30:100; the mass ratio of the heavy rare earth source to the base magnet is 1-5:100; The thickness of the high-abundance rare earth inner shell layer is 1-3 μm; the thickness of the heavy rare earth magnetic hardening outer shell layer is 0.3-0.5 μm; The general chemical formula of the main alloy is shown in formula (I): ； Wherein, RE is selected from any one or more combinations of Pr, Nd, La, Ce, Sm, and Ho, M is selected from any one or more combinations of Nb, Zr, Cu, Co, Ga, and Al, B is boron, and Fe is iron; x, y, and z are the mass percentage contents of the corresponding elements, and satisfy 20≤x≤40, 0.5≤y≤1.5, and 1≤z≤5; The general chemical formula of the auxiliary alloy source is shown in formula (II): ； Wherein, RE1 is selected from any one or more combinations of Pr, Nd, La, Ce, Sm and Ho, RE2 is selected from Y, RE3 is selected from any one or more combinations of Tb and Dy, M is selected from any one or more combinations of Al, Cu, Ga, Si, Sn, Ge, Ti and Zn, a, b and c are the mass percentage contents of the corresponding elements, and satisfy 20≤a≤60, 20≤b≤60, and 0≤c≤40; The general chemical formula of the heavy rare earth source is shown in formula (III): ； Wherein, RE4 is selected from Tb and / or Dy, and H is hydrogen.

2. The preparation method according to claim 1, wherein: The mass ratio of the heavy rare earth source to the base magnet is 2-4:

100.

3. The preparation method according to claim 1, wherein: The magnetic field strength used in the orientation pressing process is 1.5-2.5T.

4. The preparation method according to claim 1, wherein: The pressure used in the cold isostatic pressing process is 150-220 MPa.

5. The preparation method according to claim 4, characterized in that: The pressure used in the cold isostatic pressing process is 180-200 MPa.

6. The preparation method according to claim 1, wherein: The sintering temperature is 900-1100°C.

7. The preparation method according to claim 1, wherein: The sintering time is 2 to 8 hours.

8. The preparation method according to claim 7, characterized in that: The sintering time is 3 to 5 hours.

9. The preparation method according to claim 1, wherein: The tempering heat treatment includes a primary tempering treatment and a secondary tempering treatment; wherein, the temperature of the primary tempering treatment is 800-920°C; the temperature of the secondary tempering treatment is 460-560°C; and the time of the primary tempering treatment and the secondary tempering treatment are both independently 0.5-2 hours.

10. The preparation method according to claim 1, characterized in that Specifically include: A heavy rare earth source is applied to the surface of the base magnet, and then the base magnet is heated at a temperature of 800-1000°C and a vacuum degree of 1×10 -2 Performing diffusion heat treatment for 2 to 10 hours under the condition of less than 1% Pa to obtain the heavy rare earth grain boundary diffusion permanent magnet; The temperature of the diffusion heat treatment is 850-950° C., and the time of the diffusion heat treatment is 4-9 hours.

11. The preparation method according to claim 1, characterized in that: The main alloy includes main alloy powder; the particle size of the main alloy powder is 2-5 μm.

12. The preparation method according to claim 1, characterized in that: The auxiliary alloy source includes auxiliary alloy powder; the particle size of the auxiliary alloy powder is 2-5 μm.

13. The preparation method according to claim 1, characterized in that: The heavy rare earth source includes heavy rare earth powder; the particle size of the heavy rare earth powder is 2-5 μm.

14. A heavy rare earth grain boundary diffusion permanent magnet produced by the production method according to any one of claims 1 to 13.

15. A method for reducing the content of heavy rare earth elements in permanent magnets, characterized in that: include: The permanent magnet is prepared by the preparation method according to any one of claims 1 to 13.

Images