CN113571278A

CN113571278A - Magnetic powder, method for forming magnetic powder, rare earth sintered permanent magnet, and method for producing rare earth sintered permanent magnet

Info

Publication number: CN113571278A
Application number: CN202110829380.XA
Authority: CN
Inventors: 吴树杰; 董义; 张帅; 刁树林; 袁易; 陈雅; 袁文杰
Original assignee: Baotou Tianhe Magnetic Materials Technology Co ltd
Current assignee: Baotou Tianhe Magnetic Materials Technology Co ltd
Priority date: 2021-07-22
Filing date: 2021-07-22
Publication date: 2021-10-29
Anticipated expiration: 2041-07-22
Also published as: CN113571278B

Abstract

The invention discloses a magnetic powder, a forming method of the magnetic powder, a rare earth sintered permanent magnet and a preparation method of the rare earth sintered permanent magnet, wherein the magnetic powder is formed by alloy coarse powder and liquid metal alloy; the content of the liquid metal alloy is 0.02-1 wt% based on the alloy coarse powder; alloy coarse powder comprises R, T, B and M₁R is selected from at least one rare earth element and must contain Nd; t is at least one element selected from the group consisting of Fe and Co, and must contain Fe; b is boron; m₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr and Nb; the liquid metal alloy contains M₂，M₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained; ga accounts for more than 50 wt% of the total amount of the liquid metal alloy. The magnetic powder can ensure that the formed rare earth sintered permanent magnet has higher remanence and coercive forceAnd the dosage of the heavy rare earth can be greatly reduced.

Description

Magnetic powder, method for forming magnetic powder, rare earth sintered permanent magnet, and method for producing rare earth sintered permanent magnet

Technical Field

The invention relates to a magnetic powder, a method for forming the magnetic powder, a rare earth sintered permanent magnet and a method for manufacturing the rare earth sintered permanent magnet.

Background

As a representative example of the high performance permanent magnet, R-T-B based rare earth sintered magnet has a structure containing R as a tetragonal crystal compound₂Fe₁₄The structure of the B-type crystal phase (main phase) and the grain boundary phase can exhibit excellent magnet characteristics. Wherein R is at least one selected from rare earth elements mainly containing Nd and/or Pr, Fe is iron, and B is boron, and a part of these elements may be substituted with other elements.

When a R-T-B-based rare earth sintered magnet is used in various devices such as motors, the sintered magnet is required to have excellent heat resistance and high remanence and coercive force in order to cope with a high-temperature use environment.

In order to improve the coercive force of the R-T-B type rare earth sintered magnet, an alloy in which a light rare earth element RL is blended together with a predetermined amount of a heavy rare earth element RH as a raw material can be used. According to the method, R as the main phase₂Fe₁₄The light rare earth element RL of the B phase is replaced by the heavy rare earth element RH, R₂Fe₁₄The magnetocrystalline anisotropy (the physical quantity that essentially determines the coercivity) of the B phase is improved. However, R₂Fe₁₄Since the magnetic moment of the light rare earth element RL in the B phase is in the same direction as the magnetic moment of Fe and the magnetic moment of the heavy rare earth element RH is opposite to the magnetic moment of Fe, the more the light rare earth element RL is substituted by the heavy rare earth element RH, the lower the remanence (i.e., remanence) Br.The region used in the drive portion of the motor requires a sintered magnet having a high residual magnetism Br and a high coercive force in a region exposed to a high-heat, large diamagnetic field. In addition, due to the limited reserves of Dy and Tb in the world, the use of Dy and Tb in large quantities causes an increase in the price of magnets and accelerated exhaustion of heavy rare earth resources.

Much work has been done in the industry to improve the performance of permanent magnets and reduce the use of heavy rare earths. Among them, improvement of grain boundaries by grain refinement and diffusion penetration are the most important two directions. The small grain size reduces the possibility of nucleation of grain boundary demagnetizing domains and local demagnetizing field, thus improving the coercive force. However, as the crystal grains become finer, the content of impurities such as oxygen and carbon also increases, the proportion of the grain boundary neodymium-rich phase decreases, and the exchange coupling between the grain boundaries cannot be blocked, and the coercivity decreases instead. By diffusion and permeation, heavy rare earth elements enter the crystal boundary of the magnet, so that the coercivity can be greatly improved by using less heavy rare earth, the remanence and the magnetic energy product are not sacrificed, and the cost of the magnet is effectively reduced. CN101404195A, CN101506919A and CN102103916A successively disclose surface coating method, metal vapor method, electrodeposition method, etc. to make heavy rare earth elements reach the surface of the magnet, and then heat it to diffuse into the interior of the magnet along the grain boundary, thereby improving the performance. However, the diffusion infiltration process still needs to use a certain amount of heavy rare earth, and simultaneously increases the production procedures and prolongs the production period.

There are also some reports in the literature of improving the coercivity of a magnet by adjusting the composition or microstructure.

CN103582715B provides an alloy for R-T-B rare earth sintered magnets which can give R-T-B magnets having high coercive force without increasing Dy content contained in the R-T-B alloy. The alloy for R-T-B-based rare earth sintered magnets comprises a rare earth element R, a transition metal T containing Fe as an essential component, a metal element M containing one or more metals selected from Al, Ga and Cu, and B and inevitable impurities, wherein 13 to 15 atomic% of R, 4.5 to 6.2 atomic% of B, 0.1 to 2.4 atomic% of M and the balance of T are contained, and the ratio of Dy in all the rare earth elements is 0 to 65 atomic%, and satisfies 0.0049Dy + 0.34-B/TRE-0.0049 Dy + 0.36. CN104395971B discloses a sintered magnet of a preferred embodiment, which comprises 29.5 to 33.0 mass% of R (R is a rare earth element which should include any one of Nd and Pr), 0.7 to 0.95 mass% of B, 0.03 to 0.6 mass% of Al, 0.01 to 1.5 mass% of Cu, 3.0 mass% or less (excluding 0 mass%) of Co, 0.1 to 1.0 mass% of Ga, 0.05 to 0.3 mass% of C, 0.03 to 0.4 mass% of O, and the balance of Fe and other elements, wherein the total content of heavy rare earth elements is 1.0 mass% or less, and the relationship between Nd, ([ Pr ]/[ Pr ] + [ Pr ] < 0.40 and 0.07 ([ Ga ] + ], [ B ] + ], [ C ]), is satisfied when the numbers of Nd, Pr, B, C and Ga are [ Nd ] < 0.60 ]. There is still a not low heavy rare earth content in this patent document.

CN105190793B discloses by Nd₂Fe₁₄The B-type compound is a main phase, has the main phase, a first grain boundary existing between two main phases, and a second grain boundary existing between three or more main phases, and the first grain boundary having a thickness of 5nm or more and 30nm or less is present in the R-T-B sintered magnet. This patent document controls the number of second crystal boundaries and the thickness of the first crystal boundaries to maintain high remanence and coercive force, and thus has a high requirement for controlling the thickness.

CN103329220A discloses an R-T-B system sintered magnet having R containing a light rare earth element RL (including at least one of Nd and Pr) as a main rare earth element R₂Fe₁₄A R-Fe-B system rare earth sintered magnet in which B type compound crystal grains are a main phase and which contains a heavy rare earth element RH (including at least one of Dy and Tb), wherein a concentrated layer of the rare earth element R is not formed on the surface layer of the R-T-B system rare earth sintered magnet before the surface layer of the R-T-B system rare earth sintered magnet is removed. The patent document still uses heavy rare earth elements.

CN107369512A discloses an R-T-B sintered permanent magnet, the content of impurity elements is controlled in the preparation process; the microstructure of the magnet includes R₂T₁₄B main phase, grain boundary phase and triangular region 1. This magnet structure can improve the coercive force, but the patent document has high requirements on the manufacturing process.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a magnetic powder which can be used to form a rare earth sintered permanent magnet having high remanence and coercive force.

Another object of the present invention is to provide a method of forming the above magnetic powder.

It is still another object of the present invention to provide a rare earth sintered permanent magnet which can maintain a high remanence and simultaneously improve coercive force by reducing the amount of heavy rare earth element RH used even without using heavy rare earth element RH.

Still another object of the present invention is to provide a method for manufacturing a rare earth sintered permanent magnet.

The invention adopts the following technical scheme to achieve the purpose.

The invention provides a magnetic powder, which is formed by alloy coarse powder and liquid metal alloy; the content of the liquid metal alloy is 0.02-1 wt% based on the alloy coarse powder;

alloy coarse powder comprises R, T, B and M₁；

R is selected from at least one rare earth element and must contain Nd;

t is at least one element selected from the group consisting of Fe and Co, and must contain Fe;

b is boron;

M₁at least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr and Nb;

the liquid metal alloy contains M₂，M₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained;

ga accounts for more than 50 wt% of the total amount of the liquid metal alloy.

According to the magnetic powder of the present invention, preferably, the liquid metal alloy further contains Ga₂O₃，Ga₂O₃Is 0.01 to 2 wt% of the total amount of the liquid metal alloy.

The invention also provides a method for forming the magnetic powder, which comprises the following steps: mixing the alloy coarse powder with a liquid metal alloy, and crushing to obtain magnetic powder; wherein the average grain size D50 of the alloy coarse powder is 40-400 μm, and the average grain size D50 of the magnetic powder is 2-5 μm.

The invention also provides a rare earth sintered permanent magnet which is an R-T-B permanent magnet and is R₂Fe₁₄A rare earth sintered permanent magnet having a B-type compound as a main phase,

r is selected from at least one rare earth element and must contain Nd;

b is boron;

containing M, M being derived from M₁And M₂Composition of M₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr and Nb; m₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained;

M₂at R₂T₁₄The content of the B compound main phase grain boundary part accounts for 0.5-5 wt% of the total amount of elements in the grain boundary part, and the Ga in the grain boundary part accounts for M₂40 wt% or more of the total amount.

The rare earth sintered permanent magnet according to the present invention, preferably, M₂At R₂T₁₄The content of the B compound main phase grain boundary part accounts for 0.7-3.5 wt% of the total amount of elements in the grain boundary part, and the Ga in the grain boundary part accounts for M₂More than 50 wt% of the total amount.

According to the rare earth sintered permanent magnet of the present invention, preferably, T is Fe and Co; r does not contain Dy and Tb.

The invention also provides a preparation method of the rare earth sintered permanent magnet,

the rare earth sintered permanent magnet is an R-T-B permanent magnet and is R₂Fe₁₄A rare earth sintered permanent magnet having a B-type compound as a main phase,

r is selected from at least one rare earth element and must contain Nd;

b is boron;

containing M, M being derived from M₁And M₂Composition of M₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr and Nb; m₂At least one element selected from Ga, In, Sn and Zn, and must beContains Ga;

the method comprises the following steps:

(a) r, T, B and M as raw materials for rare earth sintered permanent magnets₁Smelting to obtain a master alloy sheet;

(b) crushing the master alloy sheet into alloy coarse powder under hydrogen pressure; mixing the alloy coarse powder with M₂Mixing the liquid metal alloy, and crushing to obtain magnetic powder;

(c) placing the magnetic powder in a magnetic field for pressing, and then carrying out isostatic pressing treatment to obtain a green body;

(d) and carrying out vacuum heat treatment and two-stage tempering treatment on the green body to obtain the rare earth sintered permanent magnet.

According to the method for producing a rare earth sintered permanent magnet of the present invention, preferably, the liquid metal alloy content is 0.02 to 1 wt% based on the alloy coarse powder; ga accounts for more than 50 wt% of the total amount of the liquid metal alloy.

According to the method for producing a rare earth sintered permanent magnet of the present invention, preferably, the liquid metal alloy further contains Ga₂O₃，Ga₂O₃Accounting for 0.01-2 wt% of the total amount of the liquid metal alloy.

According to the method for producing a rare earth sintered permanent magnet of the present invention, preferably:

in the step (a), the thickness of the master alloy sheet is 0.20-0.45 mm;

in the step (b), the average particle size D50 of the alloy coarse powder is 40-400 μm; the average particle size D50 of the magnetic powder is 2-5 μm;

in the step (c), the strength of the magnetic field is more than or equal to 1.5T, and the density of the green body is 3.5-7 g/cm³；

In the step (d), the degree of vacuum of the vacuum heat treatment is 1.0X 10 or less^-1Pa; the vacuum heat treatment sequentially comprises: preserving the heat for 1-5 h at the temperature of 300-350 ℃; preserving heat for 1-5 h at 500-650 ℃; preserving heat for 3-8 h at 800-900 ℃; preserving heat for 1-10 h at 1020-1120 ℃;

filling inert gas after vacuum heat treatment, and air-cooling to below 150 ℃;

the vacuum degree of the two-stage tempering treatment is less than or equal to 1.0 multiplied by 10^-1Pa; two-stage temperingThe treatment comprises the following steps: keeping the temperature at 850-950 ℃ for 1-4 h, filling inert gas, and air-cooling to below 150 ℃; then preserving the heat for 1.5 to 5 hours at the temperature of 420 to 620 ℃, filling inert gas, and cooling the air to below 70 ℃.

The magnetic powder can be used for forming a rare earth sintered permanent magnet, and the rare earth sintered permanent magnet has higher remanence and coercive force. The rare earth sintered permanent magnet can greatly reduce the use amount of heavy rare earth Dy and Tb, even does not use heavy rare earth Dy and Tb, and has higher remanence and coercive force. The preparation method of the rare earth sintered magnet can greatly reduce the usage amount of heavy rare earth Dy and Tb by adding the Ga-containing low-melting-point liquid metal alloy, and can prepare the rare earth sintered permanent magnet with higher remanence and coercive force. In addition, the preparation method does not need to add an additional heavy rare earth diffusion and permeation process, so that the production cost is effectively reduced; and the operation process is simple, and the method is suitable for large-scale industrial production.

Drawings

Fig. 1 is a microstructure view of a main phase and a grain boundary portion of a rare earth sintered permanent magnet obtained in example 2 of the present invention.

Detailed Description

The present invention will be further described with reference to the following specific examples, but the scope of the present invention is not limited thereto.

The term "remanence" as used herein refers to the value of the magnetic flux density at a zero magnetic field strength on the saturated hysteresis loop, usually expressed as Br or Mr, in Tesla (T) or Gauss (Gs). 1Gs is 0.0001T.

The "coercivity", also referred to as intrinsic coercivity, in the present invention is the magnetic field strength from the saturated magnetization state of the magnet, which is usually referred to as Hcj or MHc in oersted (Oe) or ampere/meter (a/m), when the magnetic field is monotonically decreased to zero and inversely increased so that the magnetization thereof is decreased to zero along the saturation hysteresis loop. 1Oe 79.6A/m.

Hcj is the intrinsic coercivity at room temperature.

In the present invention, the "inert gas" includes helium, neon, argon, krypton and xenon. "inert atmosphere" refers to an atmosphere in which an inert gas is formed and which does not affect the performance of the magnet.

The vacuum in the invention refers to absolute vacuum degree; the smaller the value, the higher the degree of vacuum.

The "average particle size D50" in the present invention represents the equivalent diameter of the largest particle with a cumulative distribution of 50% in the particle size distribution curve.

< magnetic powder >

The magnetic powder of the present invention is formed of alloy coarse powder and a liquid metal alloy. In addition, the magnetic powder may contain inevitable impurities.

Alloy coarse powder comprises R, T, B and M₁。

R is selected from at least one rare earth element and must contain Nd.

Rare earth elements of the present invention include, but are not limited to, neodymium (Nd), praseodymium (Pr), or "heavy rare earth element RH". The heavy rare earth element RH is also called yttrium family element, and comprises nine elements such as yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like. Preferably, the at least one rare earth element comprises Pr, Nd, Y, Tb and Dy. More preferably, R is free of Dy and Tb; r is Nd and Pr. Still more preferably, R is Nd.

T is at least one element selected from Fe and Co, and Fe is essentially contained. According to one embodiment of the invention, T is Fe. According to another embodiment of the invention, T is Fe and Co.

In the present invention, B is boron.

M₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr, and Nb. Preferably, M₁At least one element selected from the group consisting of Ti, Cu, Al, Zr, and Nb. According to one embodiment of the invention, M₁Is composed of Ti, Cu and Al.

The liquid metal alloy contains M₂，M₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained. Preferably, M₂In must also be contained. According to one embodiment of the invention, the liquid metal alloy consists of Ga and In. According to another aspect of the inventionIn a specific embodiment, the liquid metal alloy consists of Ga, In and Sn. The method is favorable for improving the coercive force of the sintered permanent magnet and keeping higher remanence when the formed magnetic powder is used for preparing the rare earth sintered permanent magnet. Preferably, the liquid metal alloy may be Ga₇₅In₂₅Liquid metal alloy, Ga_62.5In_21.5Sn₁₆Liquid metal alloy or Ga₆₁In₂₅Sn₁₃Zn₁A liquid metal alloy. Ga₂O₃The content of the metal alloy is 0.01-2 wt%, preferably 0.02-1.8 wt%, and more preferably 0.05-1.5 wt% of the total amount of the liquid metal alloy.

The liquid metal alloy is contained in an amount of 0.02 to 1 wt%, preferably 0.03 to 1 wt%, and more preferably 0.05 to 1 wt%, based on the alloy coarse powder. The amount of Ga in the liquid metal alloy is more than 50 wt% of the total amount of the liquid metal alloy.

The average particle size D50 of the alloy coarse powder may be 40 to 400 μm, preferably 350 μm or less, and more preferably 100 to 300. mu.m.

The average particle size D50 of the magnetic powder is 2 to 5 μm, preferably 2 to 4 μm, and more preferably 2.5 to 3.5 μm.

In a preferred embodiment, the liquid metal alloy further contains gallium oxide (Ga)₂O₃)，Ga₂O₃The content of the metal alloy is 0.01-2 wt%, preferably 0.02-1.8 wt%, and more preferably 0.05-1.5 wt% of the total amount of the liquid metal alloy. The invention discovers that the existence of trace gallium oxide can obviously improve the adhesion and wettability of the liquid metal alloy, so that the liquid metal can be better coated around the powder, the distribution of liquid metal alloy elements around main phase grains of the sintered magnet is promoted, and the exchange coupling among the grains is blocked.

The magnetic powder obtained by the invention is beneficial to forming a rare earth sintered permanent magnet with a specific structure. In the rare earth sintered permanent magnet, M₂At R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.5-5 wt% of the total amount of elements in the grain boundary part, and the amount of the Ga in the grain boundary part accounts for M₂40 wt% or more of the total amount. The rare earth sintered permanent magnet can keep higher remanence and coercive force.

In the present invention, when the liquid metal alloy is added, an antioxidant and a lubricant are also added, and then the mixture is uniformly mixed with the alloy coarse powder. This facilitates uniform mixing and prevents oxidation of the alloy coarse powder or magnetic powder.

< method for forming magnetic powder >

In the invention, alloy coarse powder and liquid metal alloy are mixed and crushed to obtain magnetic powder. The mixing method is not particularly limited. For example, a liquid metal alloy is added to the alloy coarse powder and mixed uniformly. The details of the alloy coarse powder and the liquid metal alloy are described above and will not be described herein.

In the forming method of the magnetic powder, a mixture formed by the alloy coarse powder and the liquid metal alloy is crushed into the magnetic powder by adopting a ball milling process and/or an air flow milling process. The ball milling process is to adopt a mechanical ball milling device to crush the mixture into magnetic powder. The mechanical ball milling device may be selected from rolling ball milling, vibratory ball milling or high energy ball milling. The jet milling process is to make the mixture to collide with each other and break up after accelerating by the air flow. The gas stream may be a nitrogen stream, preferably a high purity nitrogen stream. N in high purity nitrogen stream₂The content may be 99.0 wt% or more, preferably 99.9 wt% or more. The pressure of the air flow may be 0.1 to 2.0MPa, preferably 0.5 to 1.0MPa, and more preferably 0.6 to 0.7 MPa.

The alloy coarse powder of the invention is prepared by the following steps: r, T, B and M as raw materials for rare earth sintered permanent magnets₁Smelting to obtain a master alloy sheet; crushing the master alloy sheet into alloy coarse powder. For example, master alloy pieces are broken into alloy coarse powder under hydrogen pressure.

According to one embodiment of the present invention, R, T, B raw materials and M for rare earth sintered permanent magnets₁And putting the alloy into a vacuum intermediate-frequency rapid hardening induction furnace, vacuumizing to less than 1Pa, filling argon (Ar), heating and melting under the protection of the argon to form alloy liquid, and pouring the alloy liquid onto a rotating cooling copper roller to prepare a master alloy sheet with the thickness of 0.20-0.45 mm. Wherein the temperature of the alloy liquid is controlled between 1400 ℃ and 1500 ℃. According to one embodiment of the invention, the hydrogen pressure fragmentation process of the invention is preferablyIn a hydrogen fragmentation furnace. The pressure of hydrogen used in the crushing is 0.02 to 0.2MPa, preferably 0.05 to 0.1 MPa. The vacuumizing dehydrogenation temperature is 400-800 ℃, and preferably 500-600 ℃.

< rare earth sintered permanent magnet >

The rare earth sintered permanent magnet of the present invention is an R-T-B type permanent magnet and is R₂Fe₁₄A rare earth sintered permanent magnet having a B-type compound as a main phase.

R is selected from at least one rare earth element and must contain Nd. Rare earth elements of the present invention include, but are not limited to, neodymium (Nd), praseodymium (Pr), or "heavy rare earth element RH". The heavy rare earth element RH is also called yttrium family element, and comprises nine elements such as yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like. Preferably, the at least one rare earth element comprises Pr, Nd, Y, Tb and Dy. More preferably, R is free of Dy and Tb; r is Nd and Pr. Still more preferably, R is Nd.

In the present invention, B is boron.

In the present invention, the rare earth sintered permanent magnet contains M. M is composed of₁And M₂Composition of M₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr, and Nb. Preferably, M₁At least one element selected from the group consisting of Ti, Cu, Al, Zr, and Nb. M₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained. Preferably, M₂In must also be contained.

In the present invention, M is as defined above₂At R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.5-5 wt% of the total amount of elements in the grain boundary part, and the amount of the Ga in the grain boundary part accounts for M₂40 wt% or more of the total amount. Preferably, M is as defined above₂At R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.7-3.5 wt% of the total amount of elements in the grain boundary part, and the amount of the grain boundary part Ga accounts for M₂More than 50 wt% of the total amount. More excellentOptionally, M is₂At R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.8-2.5 wt% of the total amount of elements in the grain boundary part, and the amount of the grain boundary part Ga accounts for M₂Over 55 wt% of the total amount.

Controlling R, T and M within the above range can greatly improve the coercive force Hcj of the obtained sintered permanent magnet while keeping high remanence Br. If either one is not satisfied, the grain boundary phase may be discontinuous, and the iron content may be increased, so that the exchange coupling between the main phase grains cannot be blocked well, and the effect of greatly increasing the coercive force Hcj cannot be achieved.

For the rare earth sintered permanent magnet obtained by the presence of the above features, Dy, Tb, which are heavy rare earths, have a higher remanence and a higher coercive force even without using them. The mechanism of which is not clear. Based on the prior known knowledge, the present inventors have made the following explanation of the mechanism understood. It should be noted that the explanation of the mechanism does not have any limiting effect on the technical scope of the present invention.

It is generally believed that the coercive force of the magnet is closely related to the microstructure and controlled by the nucleation field of the grain boundary anti-magnetization domain, and the grain boundary defects and local demagnetization can reduce the nucleation field, so that the coercive force is reduced, which is also the reason that the coercive force can be improved by refining grains, because the smaller grain size reduces the nucleation probability of the grain boundary reverse magnetic domain and the local demagnetization stray field.

R of rare earth sintered permanent magnet₂Fe₁₄The composition and thickness of the grain boundary phase around the B main phase have great influence on the coercive force of the magnet. Two kinds of interaction exist in the magnet grains, one is magnetostatic coupling among the grains, and the action distance is long; the other is exchange coupling at short distance, about 2.1nm in length. The formation of a non-ferromagnetic neodymium-rich intergranular phase reduces intergranular exchange coupling, while the increased thickness of the neodymium-rich phase reduces intergranular magnetostatic coupling, thereby increasing coercivity, R₂Fe₁₄The reason why the B main phase rare earth sintered permanent magnet has high coercive force is important. However, the coercivity of the currently reported heavy rare earth-free sintered permanent magnet is much lower than R₂Fe₁₄Theoretical limit of B (anisotropy field), at the highestLess than R₂Fe₁₄B anisotropy field 30%. Recent studies have shown that grain boundary phases with iron contents of up to 65 at% or more are ferromagnetic, ferromagnetic coupling exists between grains, and ferromagnetic grain boundary phases (even if diamagnetic nuclei exist) increase coercivity by pinning domain wall motion. If the grain boundary phase is non-ferromagnetic, R₂Fe₁₄The coercivity is higher if complete de-exchange coupling is formed between the B grains.

In order to reduce the ferromagnetism of the grain boundary phase, the iron content of the grain boundary phase can be reduced by increasing the amount of rare earth or penetrating a non-ferromagnetic phase such as Nd-Cu, PrNd-Cu alloy. However, an excess of rare earth causes the neodymium-rich phase to aggregate, and the remanence is lowered.

Therefore, the present invention seeks to reduce the iron content of the grain boundary phase by adding a liquid metal alloy containing Ga while improving the wettability of the grain boundary phase and distributing the grain boundary phase between two grains, rather than enriching the grain boundary corners, to increase the coercivity of the R-T-B sintered magnet while maintaining a high remanence.

In certain embodiments, the rare earth sintered permanent magnet has the following specific composition:

based on all elements of the sintered permanent magnet, the atomic percentage (at%) of R is 13-15.5%; preferably 13-15.2%; more preferably 13.5 to 15%.

T is Fe and Co. Wherein the atomic percent of Co is 0-2.5% based on all elements of the sintered permanent magnet; preferably 0.8-2.0%; more preferably 1.0 to 1.8%.

Based on all elements of the sintered permanent magnet, the atomic percent of B is 5.4-5.8%; preferably 5.5-5.75%; more preferably 5.6 to 5.75%.

Based on all elements of the sintered permanent magnet, the atomic percent of M is 0.2-5%.

The balance being Fe.

According to one embodiment of the invention, M consists of Ga, Cu, Al, Ti, In, Zr and Nb. According to another embodiment of the present invention, M consists of Ga, Cu, Al, Ti, In, Sn, Zr and Nb. According to yet another embodiment of the present invention, M consists of Ga, Cu, Al, Ti, In, Sn and Zn.

According to a preferred embodiment of the present invention, M₁Consists of Cu, Al and Ti. Wherein, based on all elements of the sintered permanent magnet, the atomic percent of Al is 0-1.2%; preferably 0 to 1.0 percent; more preferably 0 to 0.5%. Based on all elements of the sintered permanent magnet, the atomic percent of Cu is 0.08-0.3%; preferably 0.08-0.28%; more preferably 0.08 to 0.25%. Based on all elements of the sintered permanent magnet, the atomic percent of Ti is 0.05-0.2%; preferably 0.08-0.2%; more preferably 0.08 to 0.15%.

According to another preferred embodiment of the present invention, M₁Consisting of Cu, Al and Zr. Wherein, based on all elements of the sintered permanent magnet, the atomic percent of Al is 0-1.2%; preferably 0 to 1.0 percent; more preferably 0 to 0.5%. Based on all elements of the sintered permanent magnet, the atomic percent of Cu is 0.08-0.3%; preferably 0.08-0.28%; more preferably 0.08 to 0.25%. Based on all elements of the sintered permanent magnet, the atomic percent of Zr is 0.05-0.3%; preferably 0.1-0.25%; more preferably 0.1 to 0.15%.

The rare earth sintered magnet provided by the invention can greatly reduce the usage amount of heavy rare earth Dy and Tb, and has high remanence and coercive force.

Method for producing rare earth sintered permanent magnet

The preparation method of the rare earth sintered permanent magnet comprises the following steps: (a) r, T, B and M as raw materials for rare earth sintered permanent magnets₁Smelting to obtain a master alloy sheet; (b) crushing the master alloy sheet into alloy coarse powder; mixing the alloy coarse powder with M₂Mixing the liquid metal alloy, and crushing to obtain magnetic powder; (c) placing the magnetic powder in a magnetic field for pressing, and then carrying out isostatic pressing treatment to obtain a green body; (d) and carrying out vacuum heat treatment and two-stage tempering treatment on the green body to obtain the rare earth sintered permanent magnet.

The rare earth sintered permanent magnet obtained by the preparation method of the invention is an R-T-B permanent magnet with Nd₂Fe₁₄A main phase of the B crystal phase and a grain boundary phase of the rare earth-rich phase.

R is selected from at least one rare earth element and must contain Nd.

T is at least one element selected from Fe and Co, and Fe is essentially contained.

B is boron.

The rare earth sintered permanent magnet contains M, M being M₁And M₂And (4) forming. M₁At least one element selected from the group consisting of Ti, Cu, Al, Bi, Zr and Nb; m₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained.

M₂At R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.5-5 wt% of the total amount of elements in the grain boundary part, and the amount of the Ga in the grain boundary part accounts for M₂40 wt% or more of the total amount.

The details of the rare earth sintered permanent magnet are described in detail above, and are not described herein.

In the step (a), R, T, B and M, which are raw materials for rare earth sintered permanent magnets₁And smelting to obtain the master alloy sheet. In order to prevent the raw material of the sintered permanent magnet and the master alloy made therefrom from being oxidized, the melting is performed in a vacuum or an inert atmosphere. The smelting process preferably adopts an ingot casting process or a rapid hardening and sheet casting process. The ingot casting process is to cool and solidify the raw material of the sintered permanent magnet after melting, and to make an alloy ingot (master alloy). The rapid-hardening cast piece is a raw material of a sintered permanent magnet after melting, is rapidly cooled and solidified, and is thrown into an alloy piece (master alloy piece). According to one embodiment of the invention, the melting process employs a rapid solidification cast sheet process. Compared with an ingot casting process, the rapid hardening and sheet casting process can avoid the generation of alpha-Fe influencing the uniformity of magnetic powder and avoid the generation of lumpy neodymium-rich phase, thereby being beneficial to the master phase Nd of the master alloy₂Fe₁₄And B, refining the grain size. The rapid hardening cast piece process of the invention is preferably carried out in a vacuum melting rapid hardening furnace (such as a vacuum intermediate frequency rapid hardening induction furnace). In the step (a), the thickness of the master alloy sheet is 0.20 to 0.45mm, preferably 0.2 to 0.4mm, and more preferably 0.25 to 0.35 mm.

According to one embodiment of the present invention, R, T, B raw materials and M for rare earth sintered permanent magnets₁Placing into a vacuum intermediate frequency rapid hardening induction furnace, and vacuumizing to a pressure less than 1PaArgon (Ar) is filled downwards, heating and melting are carried out under the protection of the argon to form alloy liquid, then the alloy liquid is poured onto a rotating cooling copper roller, and a master alloy sheet with the thickness of 0.20-0.45 mm is prepared. Wherein the temperature of the alloy liquid is controlled between 1400 ℃ and 1500 ℃.

In some specific embodiments, the raw materials Nd, Co, B and M required for sintering rare earth element into permanent magnet₁(M₁Including Al, Ti, Cu, Zr, and Nb) and the balance Fe. In other specific embodiments, the raw materials Nd, Co, B and M required for sintering rare earth element into permanent magnet₁(M₁Including Al, Ti, and Cu) and the balance Fe.

In the step (b), crushing the master alloy sheet into alloy coarse powder under hydrogen pressure; adding M into alloy coarse powder₂The liquid metal alloy is mixed and crushed to obtain magnetic powder.

M₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained. Preferably, M₂At least one element selected from Ga, In, Sn and Zn, and Ga and In must be contained. Preferably, the liquid metal alloy may be Ga₇₅In₂₅Liquid metal alloy, Ga_62.5In_21.5Sn₁₆Liquid metal alloy or Ga₆₁In₂₅Sn₁₃Zn₁A liquid metal alloy. Ga₂O₃The content of the metal alloy is 0.01-2 wt%, preferably 0.02-1.8 wt%, and more preferably 0.05-1.5 wt% of the total amount of the liquid metal alloy.

The liquid metal alloy is contained in an amount of 0.02 to 1 wt%, preferably 0.03 to 1 wt%, and more preferably 0.05 to 1 wt%, based on the alloy coarse powder. If the amount of the liquid metal alloy added is too small, it becomes difficult to make the grain boundary phase contain the above-mentioned element at a concentration of 0.5 wt% or more; if the proportion of Ga in the liquid metal alloy is less than 50 wt%, it is difficult to ensure that Ga accounts for more than 40 wt% of the element proportion at the grain boundary; and further, the exchange coupling between crystal grains cannot be blocked, and the coercive force of the magnet is improved. If the liquid metal alloy is added in an excessive amount, an excessive nonmagnetic or low magnetic composition is introduced into the magnet, resulting in an excessive decrease in the remanence Br.

In a preferred embodiment, the liquid metal alloyThe gold also contains gallium oxide (Ga)₂O₃) The amount of gallium oxide is 0.01-2 wt%, preferably 0.02-1.8 wt%, and more preferably 0.05-1.5 wt% of the total amount of the liquid metal alloy. The existence of trace gallium oxide can obviously improve the adhesion and wettability of the liquid metal alloy, so that the liquid metal can be better coated around the powder, the distribution of liquid metal alloy elements around main phase grains of the sintered magnet is promoted, and the exchange coupling among the grains is blocked.

In order to prevent oxidation of the master alloy pieces and the alloy coarse powder and magnetic powder produced by crushing the master alloy pieces, the pulverization of the present invention is carried out in vacuum or in an inert atmosphere. The powder preparation process comprises a coarse crushing process and a magnetic powder forming process. The rough crushing step is to crush the master alloy pieces into coarse alloy powder having a large particle size. The magnetic powder forming process is to grind the mixture of the alloy coarse powder and the liquid metal alloy into magnetic powder.

In the coarse crushing procedure, the master alloy sheet is crushed into alloy coarse powder by adopting a mechanical crushing process and/or a hydrogen crushing process. The mechanical crushing process is to crush the master alloy sheets into alloy coarse powder by using a mechanical crushing device. The mechanical crushing means may be selected from a jaw crusher or a hammer crusher. The hydrogen crushing process comprises the following steps: firstly, absorbing hydrogen in a master alloy sheet, reacting the master alloy sheet with hydrogen to initiate volume expansion of crystal lattices of the master alloy sheet to crush the master alloy sheet, and then heating for dehydrogenation to obtain alloy coarse powder. According to a preferred embodiment of the present invention, the hydrogen fragmentation process of the present invention is preferably carried out in a hydrogen fragmentation furnace. The pressure of hydrogen used in the crushing is 0.02 to 0.2MPa, preferably 0.05 to 0.1 MPa. The vacuumizing dehydrogenation temperature is 400-800 ℃, and preferably 500-600 ℃. The average particle size D50 of the alloy coarse powder obtained by the coarse crushing process can be 40-400 μm, preferably 350 μm or less, and more preferably 100-300 μm.

The magnetic powder forming process is described in detail in the magnetic powder forming method, and is not described herein.

According to a preferred embodiment of the present invention, first, the master alloy pieces are crushed into alloy coarse powder by a hydrogen crushing process; then, adding liquid metal alloy into the alloy coarse powder, mixing, and crushing the mixture into magnetic powder by an air flow milling process.

Through a large number of researches and experiments, the invention surprisingly discovers that the melting point of a grain boundary phase can be lower by adding the liquid metal alloy containing Ga, the grain boundary phase has the element distribution characteristics, the iron content of the grain boundary phase can be effectively reduced, the thickness and the continuity of the grain boundary phase are increased, the grain boundary defects are reduced, and the coercive force is improved.

In the invention, when the liquid metal alloy is added, an antioxidant and a lubricant are also added, and then the mixture is uniformly mixed with alloy coarse powder or magnetic powder. This facilitates uniform mixing and prevents oxidation of the alloy coarse powder or magnetic powder.

In the step (c), the magnetic powder is placed in a magnetic field for pressing, and then isostatic pressing treatment is carried out to obtain a green body. In order to prevent the magnetic powder from being oxidized, the pressing and isostatic pressing processes are performed in a vacuum or inert atmosphere. The pressing process preferably employs a press-molding process. The orientation magnetic field direction and the magnetic powder pressing direction are oriented in parallel or perpendicular to each other. The strength of the orienting magnetic field is not particularly limited and may be determined as required. The magnetic field strength is 1.5T or more, preferably 1.75T or more, and more preferably 2.0T or more.

In some embodiments, the molded and pressed blank is taken out and vacuum-packaged, then the molded and pressed blank is put into an isostatic press to be pressurized at 150-250 MPa, and the green blank is taken out after pressure maintaining.

The green compact density is 3.5 to 7g/cm³Preferably 4.0 to 7g/cm³More preferably 4.2 to 5.5g/cm³. This is advantageous in that the rare earth sintered permanent magnet maintains a high remanence.

In the step (d), the green compact is subjected to vacuum heat treatment and two-stage tempering treatment to obtain the rare earth sintered permanent magnet. This is advantageous in that the resulting rare earth sintered permanent magnet maintains high remanence and coercive force. Step (d) is carried out in a vacuum sintering furnace.

Vacuum degree of 1.0X 10 or less in vacuum heat treatment^-1Pa, preferably 1.0X 10 or less^-2Pa, more preferably 5.0X 10^-3Pa. The vacuum heat treatment sequentially comprises: preserving the heat for 1-5 h at the temperature of 300-350 ℃; preserving heat for 1-5 h at 500-650 ℃; keeping the temperature at 800-900 DEG C3-8 h; keeping the temperature for 1-10 h at 1020-1120 ℃. Preferably, the vacuum heat treatment comprises in sequence: preserving heat for 1-3 h at 320-350 ℃; preserving heat for 1-4 h at 550-650 ℃; preserving heat for 3-6 h at 850-900 ℃; and preserving the heat for 1-8 hours at 1050-1120 ℃. More preferably, the vacuum heat treatment comprises in sequence: preserving heat for 1-2 h at 320-350 ℃; preserving heat for 1-2 h at 550-650 ℃; preserving heat for 3-5 h at 850-900 ℃; and preserving the heat for 1-6 h at 1050-1120 ℃.

And filling inert gas after vacuum heat treatment, and air-cooling to below 150 ℃ to obtain the sintered blank block.

And carrying out two-stage tempering treatment on the sintered blank block to obtain the rare earth sintered permanent magnet. The vacuum degree of the two-stage tempering treatment is less than or equal to 1.0 multiplied by 10^-1Pa, preferably 5.0X 10 or less^-2Pa, more preferably not more than 5.0X 10^-3Pa. The two-stage tempering treatment comprises the following steps: keeping the temperature at 850-950 ℃ for 1-4 h, filling inert gas, and air-cooling to below 150 ℃; then preserving the heat for 1.5 to 5 hours at the temperature of 420 to 620 ℃, filling inert gas, and cooling the air to below 70 ℃. Preferably, the two-stage tempering treatment comprises: preserving heat for 1.5-3.5 h at 880-950 ℃, filling argon, and cooling to below 150 ℃; then preserving the heat for 2.5 to 5 hours at the temperature of 450 to 580 ℃, filling argon, and cooling the air to below 70 ℃. More preferably, the temperature is kept at 880-900 ℃ for 2-3 h, argon is filled, and the air is cooled to below 150 ℃; and then preserving the heat for 4-5 h at the temperature of 450-550 ℃, filling argon, and cooling the air to below 70 ℃.

< test methods >

And (3) determination of element content: the microstructure of the main phase and the grain boundary portion was observed using an SU5000 field emission Scanning Electron Microscope (SEM). Further, the content ratio of each element in the grain boundary portion was calculated by analyzing the observed structure by point, line and plane using an X-ray energy analyzer (SEM-EDS) attached to SEM.

Measurement of magnetic properties: and (3) measuring the magnetic properties of the sintered body and the sintered permanent magnet by using a B-H magnetic measuring instrument at room temperature to obtain room-temperature residual magnetism Br and room-temperature coercive force Hcj of the sintered body and the sintered permanent magnet.

EXAMPLE 1 formation of magnetic powders

1) A smelting process: preparing raw materials by atomic percent, 15 percent of Nd, 1.5 percent of Al, 1.0 percent of Co, 0.1 percent of Cu, 0.1 percent of Ti, 5.7 percent of B and the balance of Fe; under the protection of argon, the alloy is melted by medium frequency induction heating in a vacuum melting furnace and then cast on a rotating quenching copper roller at 1450 ℃ to obtain a master alloy sheet with the average thickness of 0.3 mm.

2) The alloy coarse powder and magnetic powder manufacturing process comprises the following steps: the master alloy sheet obtained in the melting step was hydrogen-crushed under 0.1MPa of hydrogen, and then vacuum-dehydrogenated at 550 ℃ to obtain an alloy coarse powder having an average particle size D50 of 300. mu.m.

Adding 0.5 wt% Ga to the alloy coarse powder₇₅In₂₅Liquid metal alloy, Ga₇₅In₂₅The liquid metal alloy contains 1 wt% of gallium oxide, and 1ml/kg of lubricant is added at the same time, mixed uniformly, and pulverized into magnetic powder with the average particle size D50 of 3 μm by jet milling.

Example 2 preparation of rare earth sintered permanent magnet

3) A molding procedure: and pressing the magnetic powder on a forming press with an oriented magnetic field larger than 1.8T under the protection of nitrogen to form a blank, vacuumizing and packaging, and performing isostatic pressing on the packaged blank at the pressure of more than 200MPa for more than 15s to obtain a green body.

4) A sintering process and a tempering process: placing the formed green body in a high vacuum sintering furnace at a vacuum degree of 1 × 10^-2Carrying out vacuum heat treatment under Pa, and specifically sequentially: keeping the temperature at 300 ℃ for 1 h; keeping the temperature at 600 ℃ for 1.5 h; keeping the temperature at 900 ℃ for 5 h; preserving heat for 4 hours at 1060 ℃, then filling argon, air-cooling to below 60 ℃, discharging to obtain a sintered blank block;

sintering the blank block in a vacuum degree of 1X 10^-2Tempering at 900 ℃ for 3h under Pa, filling argon, and air-cooling to below 150 ℃; then, the resultant was tempered at a low temperature of 500 ℃ for 5 hours, and then air-cooled to 70 ℃ or lower by filling argon gas to obtain a rare earth sintered permanent magnet.

The microstructure of the main phase and grain boundary portion of the sintered permanent magnet obtained in example 1 was observed using an SU5000 field emission Scanning Electron Microscope (SEM), as shown in fig. 1.

Example 3

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 0.5 wt% of Ga_62.5In_21.5Sn₁₆A liquid metal alloy.

Example 4

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 0.5 wt% of Ga₆₁In₂₅Sn₁₃Zn₁A liquid metal alloy.

Comparative example 1

The procedure was as in example 2 except for the following differences:

the obtained alloy coarse powder is not added with any liquid metal alloy.

Comparative example 2

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 0.5 wt% of Ga₃₀Sn₆₀In₁₀A liquid metal alloy.

Comparative example 3

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 0.5 wt% of Ga₇₅In₂₅Liquid metal alloy, but Ga₇₅In₂₅The liquid metal alloy does not contain gallium oxide (Ga)₂O₃)。

Comparative example 4

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 0.5 wt% of Ga pure metal.

Comparative example 5

The procedure was as in example 2 except for the following differences:

to the resulting alloy coarse powder was added 2 wt% Ga₇₅In₂₅A liquid metal alloy.

Comparative example 6

The procedure was as in example 2 except for the following differences:

in the smelting process, the raw material also comprises 0.5 wt% of Ga₇₅In₂₅Liquid metal alloy, Ga₇₅In₂₅The liquid metal alloy contains 1 wt% gallium oxide (Ga)₂O₃). The alloy coarse powder is not added with any liquid metal alloy.

TABLE 1

As can be seen from comparison of examples 2 to 4 with comparative example 1, M was not added₂The coercive force of the obtained sintered permanent magnet is greatly reduced. This indicates that M is contained₂The coercive force of the sintered permanent magnet is greatly influenced by the liquid metal alloy.

As is clear from comparison between example 2 and comparative example 2, when the Ga content in the liquid metal alloy is reduced, the coercive force of the obtained sintered permanent magnet is reduced. This means that the Ga content in the liquid metal alloy is to be controlled.

As can be seen from comparison between example 2 and comparative example 3, the coercive force of the obtained sintered permanent magnet is reduced without adding gallium oxide to the liquid metal alloy; m₂The proportion of the grain boundary portion was only 0.4 wt%.

As can be seen from comparison between example 2 and comparative example 4, when only pure metal Ga was added to the alloy coarse powder, and no liquid metal alloy was used, the remanence and coercive force of the obtained sintered permanent magnet were significantly reduced. And M₂The content of Ga in the grain boundary part is only 0.3 wt%, and the content of Ga in the grain boundary part is M₂The ratio of (A) to (B) is 100 wt%.

As can be seen from comparison between example 2 and comparative example 5, if the content of the liquid metal alloy is greater than 1 wt%, the residual magnetism and coercive force of the obtained sintered permanent magnet are reduced. And M₂The proportion of the grain boundary portion was only 0.4 wt%. This indicates that the higher the liquid metal alloy content is, the better, the higher the liquid metal alloy content is, but the liquid metal alloy content is controlled within a certain range so as to contribute to the improvement of the coercive force and the remanence.

As is clear from comparison between example 2 and comparative example 6, when the liquid metal alloy was added to the melting process instead of the alloy coarse powder, the coercive force of the obtained sintered body was lowered. And M₂The proportion of the grain boundary portion was only 0.4 wt%. This demonstrates that the order of addition of the liquid metal alloy has some effect on the properties of the sintered body.

In summary, in the present invention, the addition of a liquid metal alloy containing Ga in a specific ratio in a specific step enables M in the obtained rare earth sintered permanent magnet₂The content of Ga in the grain boundary part is more than 0.5 wt% and less than 5 wt%, and the content of Ga in the grain boundary part is M₂The ratio of (A) to (B) is not less than 50 wt%. So that the residual magnetism of the obtained rare earth sintered permanent magnet is not reduced under the condition of not adding heavy rare earth elements, and the coercive force is obviously improved.

The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.

Claims

1. A magnetic powder, characterized by being formed of alloy coarse powder and a liquid metal alloy; the content of the liquid metal alloy is 0.02-1 wt% based on the alloy coarse powder;

alloy coarse powder comprises R, T, B and M₁；

R is selected from at least one rare earth element and must contain Nd;

b is boron;

ga accounts for more than 50 wt% of the total amount of the liquid metal alloy.

2. The magnetic powder according to claim 1, wherein the liquid metal alloy further contains Ga₂O₃，Ga₂O₃Is 0.01 to 2 wt% of the total amount of the liquid metal alloy.

3. The method of forming a magnetic powder according to claim 1 or 2, comprising the steps of:

mixing the alloy coarse powder with a liquid metal alloy, and crushing to obtain magnetic powder; wherein the average grain size D50 of the alloy coarse powder is 40-400 μm, and the average grain size D50 of the magnetic powder is 2-5 μm.

4. A rare earth sintered permanent magnet which is an R-T-B system permanent magnet and is R₂Fe₁₄A rare earth sintered permanent magnet having a B-type compound as a main phase,

r is selected from at least one rare earth element and must contain Nd;

b is boron;

containing M, M being derived from M₁And M₂Composition of M₁Selected from Ti, Cu, Al, Bi, Zr and Nb; m₂At least one element selected from Ga, In, Sn and Zn, and Ga must be contained;

M₂at R₂T₁₄The amount of the B compound main phase grain boundary part accounts for 0.5-5 wt% of the total amount of elements in the grain boundary part, and Ga in the grain boundary part accounts for M₂40 wt% or more of the total amount.

5. The rare earth sintered permanent magnet as claimed in claim 4, wherein M is₂At R₂T₁₄The content of the B compound main phase grain boundary part accounts for 0.7-3.5 wt% of the total amount of elements in the grain boundary part, and Ga in the grain boundary part accounts for M₂More than 50 wt% of the total amount.

6. The rare earth sintered permanent magnet according to claim 5, wherein T is Fe and Co; r does not contain Dy and Tb.

7. A method for producing a rare earth sintered permanent magnet,

r is selected from at least one rare earth element and must contain Nd;

b is boron;

the method comprises the following steps:

(b) crushing the master alloy sheet into alloy coarse powder; mixing the alloy coarse powder with M₂Mixing the liquid metal alloy, and crushing to obtain magnetic powder;

8. The method of claim 7, wherein:

the content of the liquid metal alloy is 0.02-1 wt% based on the alloy coarse powder;

ga accounts for more than 50 wt% of the total amount of the liquid metal alloy.

9. The method of claim 8, wherein the liquid metal alloy further comprises Ga₂O₃，Ga₂O₃Accounting for 0.01-2 wt% of the total amount of the liquid metal alloy.

10. The method of claim 9, wherein:

in the step (a), the thickness of the master alloy sheet is 0.20-0.45 mm;

the vacuum degree of the two-stage tempering treatment is less than or equal to 1.0 multiplied by 10^-1Pa; the two-stage tempering treatment comprises the following steps: keeping the temperature at 850-950 ℃ for 1-4 h, filling inert gas, and air-cooling to below 150 ℃; then preserving the heat for 1.5 to 5 hours at the temperature of 420 to 620 ℃, filling inert gas, and cooling the air to below 70 ℃.