阅读说明：本技术 SmFeN永磁体及其制备方法、电机 (SmFeN permanent magnet, preparation method thereof and motor ) 是由 赖彬 王子京 景遐明 郑精武 车声雷 于 2021-07-20 设计创作，主要内容包括：本申请提供一种SmFeN永磁体,包括多个SmFeN晶粒和位于所述多个SmFeN晶粒之间的晶界相。所述晶界相包括SmFeXN,其中X为来自熔点低于800℃的金属单质或合金的元素；所述晶界相在所述SmFeN永磁体的至少一外表面的含量大于所述晶界相在所述SmFeN永磁体的中心的含量。本申请还提供该SmFeN永磁体的制备方法和应用该SmFeN永磁体的电机。晶界相除了能够消除SmFeN磁粉加工过程中形成的表面缺陷外,还会在SmFeN晶粒间形成去磁耦合作用的无磁晶界层,从而实现SmFeN磁体的矫顽力的提升。(Provided is a SmFeN permanent magnet including a plurality of SmFeN grains and a grain boundary phase between the plurality of SmFeN grains. The grain boundary phase comprises SmFeXN, wherein X is an element from a metal simple substance or an alloy with a melting point lower than 800 ℃; the content of the grain boundary phase on at least one outer surface of the SmFeN permanent magnet is greater than that of the grain boundary phase in the center of the SmFeN permanent magnet. The application also provides a preparation method of the SmFeN permanent magnet and a motor using the SmFeN permanent magnet. The grain boundary phase can eliminate surface defects formed in the SmFeN magnetic powder processing process, and a nonmagnetic grain boundary layer with the demagnetization coupling effect is formed among SmFeN grains, so that the coercive force of the SmFeN magnet is improved.)

1. A SmFeN permanent magnet, comprising:

a plurality of SmFeN grains;

a grain boundary phase positioned among the plurality of SmFeN grains, wherein the grain boundary phase comprises SmFeXN, and X is an element of a metal simple substance or an alloy with a melting point lower than 800 ℃; the content of the grain boundary phase on at least one outer surface of the SmFeN permanent magnet is greater than that of the grain boundary phase in the center of the SmFeN permanent magnet.

2. A SmFeN permanent magnet as claimed in claim 1 wherein the content of grain boundary phases in the SmFeN permanent magnet becomes smaller from at least one outer surface of the SmFeN permanent magnet toward the center of the SmFeN permanent magnet.

3. A SmFeN permanent magnet as claimed in claim 1 or 2 wherein X is an element of a simple metal having a melting point of less than 600 ℃ or an element of an alloy having a melting point of less than 600 ℃.

4. A SmFeN permanent magnet as claimed In any one of claims 1 to 3 wherein, when X is an element of a simple metal having a melting point of less than 800 ℃, X is Zn, Al, Sn, Mg, Ga, Bi, Pt or In.

5. A SmFeN permanent magnet as claimed In any one of claims 1 to 3 wherein when X is an element of an alloy having a melting point below 800 ℃, the X comprises a rare earth metal element which is one or more of La, Ce, Pr, Nd, Sm, Y and a further metal element which is one or more of Fe, Cu, Zn, Al, Mg, Ga, Co, Zr, Mo, V, Sn, Bi, Pt, In, Nb.

6. A SmFeN permanent magnet according to any one of claims 1 to 5, wherein the grain boundary phase further comprises a simple metal or alloy having a melting point below 800 ℃.

7. A SmFeN permanent magnet according to any one of claims 1 to 6, wherein the crystal structure of the SmFeN grains comprises Th2Zn17 type and TbCu7 type, wherein the volume fraction of TbCu7 type structure grains in the SmFeN grains is 10%.

8. A SmFeN permanent magnet according to claim 7, wherein the TbCu7 type structure grains are present in the SmFeN grains at a volume fraction of less than 5%.

9. A SmFeN permanent magnet according to any one of claims 1 to 8, wherein the grain boundary phase surrounds SmFeN grains to a thickness of greater than 1nm and less than 500 nm.

10. A SmFeN permanent magnet as claimed in any one of claims 1 to 9 having a density of 7.2g/cm³-7.7g/cm³The maximum magnetic energy product is more than or equal to 25 MGOe.

11. A method for preparing a SmFeN permanent magnet is characterized by comprising the following steps:

providing SmFeN magnetic powder with the average grain size less than or equal to 10 mu m;

carrying out magnetic field orientation and pressing on the SmFeN magnetic powder under the environment of protective atmosphere or organic solvent, and then carrying out isostatic pressing to prepare a cold blank magnet;

preparing a metal simple substance or alloy with a melting point lower than 800 ℃ and in a flake or powder shape;

covering at least one surface of the cold blank magnet with the metal simple substance or the alloy, and carrying out thermal diffusion densification treatment at the temperature lower than 600 ℃.

12. A method of producing a SmFeN permanent magnet as claimed in claim 11 wherein the SmFeN magnetic powder has an oxygen content of less than 5000 ppm.

13. A method of producing a SmFeN permanent magnet as claimed in claim 11 or 12 wherein the step of providing a SmFeN magnetic powder having an average particle size of 10 μm or less is providing a SmFeN magnetic powder having an average particle size of 5 μm or less.

14. A SmFeN permanent magnet as claimed in any one of claims 11 to 13 wherein said cold blank magnet has a density of 4.0g/cm³-5.0g/cm³。

15. A SmFeN permanent magnet as claimed in any one of claims 11 to 14 wherein said SmFeN magnetic powder is oriented using a magnetic field having a strength of 1.0T to 2.0T.

16. A SmFeN method for producing a permanent magnet as claimed in any one of claims 11 to 15, wherein the production of the elemental metal or alloy having a melting point of less than 800 ℃ and being in a form of a flake or powder comprises: preparing a powdery metal simple substance or alloy with the average grain diameter of 1-1000 mu m.

17. A SmFeN method for producing a permanent magnet as claimed in any one of claims 11 to 16, wherein the coating of the elemental metal or alloy on the surface of the cold blank magnet comprises: adding a powdery metal simple substance or alloy directly to the surface of the cold blank magnet, or forming the metal simple substance or alloy on the surface of the cold blank magnet by at least one of a chemical coating method, a vapor deposition method, a magnetron sputtering method, and an ion spraying method.

18. A SmFeN permanent magnet production method according to any one of claims 11 to 17 wherein said step of covering at least one surface of said cold blank magnet with said element metal or alloy is carried out in an amount of 25% by weight or less relative to the weight of said cold blank magnet.

19. A SmFeN method of producing as claimed in any one of claims 11 to 18 wherein said coating of said elemental metal or alloy on at least one surface of said cold blank magnet comprises: and respectively covering the two opposite surfaces of the cold blank magnet with the metal simple substance or the alloy, wherein the distance between the two opposite surfaces is less than or equal to 20 mm.

20. A SmFeN method as claimed in any one of claims 11 to 19 wherein the pressure of the thermal diffusion densification process is 0.1GPa to 10GPa for a period of time equal to or less than 5 min.

21. A method of making a SmFeN permanent magnet as claimed in any one of claims 11 to 20 wherein said thermal diffusion densification process comprises one of spark plasma sintering, hot pressing, hot isostatic pressing, current assisted sintering; the melting point of the metal simple substance or the alloy is lower than 600 ℃.

22. A method of producing a SmFeN permanent magnet as claimed in any one of claims 11 to 21 wherein said thermal diffusion densification is by impact compression.

23. An electrical machine comprising a rotor, further comprising a SmFeN permanent magnet as claimed in any one of claims 1 to 10 disposed on the rotor.

Technical Field

The application relates to a SmFeN (samarium-iron-nitrogen) permanent magnet, a preparation method thereof and a motor using the SmFeN permanent magnet.

Background

The rare earth permanent magnet is widely applied to the fields of aerospace, information communication, electronic information, automobile industry, medical equipment and the like with high remanence and high coercivity. The new energy automobile industry is rising, and the development of the rare earth permanent magnet industry is greatly promoted. The neodymium iron boron magnet is a permanent magnet which is most widely applied and accounts for more than 90% of the market of rare earth permanent magnets, but the neodymium iron boron has the defects of low working temperature, large temperature coefficient, high cost and the like. With the sharp rise of the price of the rare earth, the cost and price of the neodymium iron boron magnet are also increased. The SmFeN permanent magnet has intrinsic magnetic performance equivalent to that of neodymium iron boron, higher working temperature and lower raw material cost, becomes the most probable alternative scheme of the neodymium iron boron, and is an important candidate of a fourth-generation rare earth permanent magnet. However, the SmFeN permanent magnet is decomposed at a temperature of more than 600 ℃, so that the SmFeN permanent magnet cannot be produced by adopting a high-temperature sintering process similar to the sintered NdFeB permanent magnet, and the preparation process and the application field of the SmFeN permanent magnet are seriously influenced. At present, SmFeN permanent magnets exist mainly in the form of bonded magnets, and have low magnetic performance.

Disclosure of Invention

A first aspect of an embodiment of the present application provides a SmFeN permanent magnet, including:

a plurality of SmFeN grains;

a grain boundary phase positioned among the plurality of SmFeN grains, wherein the grain boundary phase comprises SmFeXN, and X is an element of a metal simple substance or an alloy with a melting point lower than 800 ℃; the content of the grain boundary phase on at least one outer surface of the SmFeN permanent magnet is greater than that of the grain boundary phase in the center of the SmFeN permanent magnet.

The grain boundary phase can eliminate surface defects formed in the SmFeN magnetic powder processing process, and can also form a nonmagnetic grain boundary layer with a demagnetizing coupling effect among SmFeN grains, so that the coercive force of the SmFeN magnet is improved; in addition, according to the preparation process of the SmFeN permanent magnet, a metal simple substance or alloy is initially placed on the outer surface of a cold blank magnet, then the metal simple substance or alloy diffuses and permeates towards the inside of the cold blank magnet, the permeated metal simple substance or alloy reacts with the surface layer of SmFeN grains to form a product SmFeXN, the product SmFeXN forms the main component of a grain boundary phase, and meanwhile, the preparation process causes the uneven distribution of the grain boundary phase in the SmFeN permanent magnet, which shows that the content of the grain boundary phase on at least one outer surface of the SmFeN permanent magnet is higher, and the content of the grain boundary phase in the center of the SmFeN permanent magnet is lower.

In the present embodiment, the content of the grain boundary phase in the SmFeN permanent magnet becomes smaller from at least one outer surface of the SmFeN permanent magnet toward the center of the SmFeN permanent magnet.

In the embodiment of the application, X is an element of a simple metal with a melting point lower than 600 ℃ or an element of an alloy with a melting point lower than 600 ℃.

For elemental metals or alloys with melting points below 600 ℃, they can be introduced between SmFeN grains by one of spark plasma sintering, hot pressing, hot isostatic pressing, current assisted sintering. When some special preparation process is adopted to introduce the grain boundary phase between SmFeN grains, such as an explosive impact method, the grain boundary phase may include a metal simple substance or an alloy with a melting point higher than 600 ℃ and lower than 800 ℃, specifically because: the explosion impact method forms larger pressure or impact energy, so that the requirement on the melting point of the metal simple substance or the alloy of the grain boundary phase can be reduced.

In the embodiment of the application, when the X is an element of a simple metal with a melting point lower than 800 ℃, the X is Zn, Al, Sn, Mg, Ga, Bi, Pt or In.

In the embodiment of the present application, when X is an element of an alloy having a melting point lower than 800 ℃, the X includes a rare earth metal element and another metal element, wherein the rare earth metal element is one or more of La, Ce, Pr, Nd, Sm, and Y, and the another metal element is one or more of Fe, Cu, Zn, Al, Mg, Ga, Co, Zr, Mo, V, Sn, Bi, Pt, In, and Nb.

In the embodiment of the application, the grain boundary phase further comprises a metal simple substance or an alloy with a melting point lower than 800 ℃.

The metal simple substance or the alloy permeates among SmFeN grains in a mode of grain boundary diffusion in the SmFeN grains, meanwhile, the metal simple substance or the alloy reacts with the surface layer of the SmFeN grains to form a product SmFeXN, and when the residual metal simple substance or the alloy does not react with the SmFeN grains, the grain boundary phase can also comprise the metal simple substance or the alloy with the melting point lower than 800 ℃.

In the embodiment of the application, the crystal structure of the SmFeN crystal grains comprises a Th2Zn17 type and a TbCu7 type, wherein the volume percentage of the TbCu7 type structure crystal grains in the SmFeN crystal grains is less than or equal to 10%.

In the embodiment of the application, the volume percentage of the TbCu7 type structural crystal grains in the SmFeN crystal grains is less than 5%.

The Th2Zn17 type is anisotropic, the TbCu7 type is isotropic, and the anisotropic SmFeN magnetic powder can be oriented in a magnetic field, so that high orientation degree is realized, and the magnetic performance of the product is greatly improved.

In the embodiment of the application, the thickness of SmFeN crystal grains wrapped by the grain boundary phase is more than 1nm and less than 500 nm.

In the embodiment of the application, the density of the SmFeN permanent magnet is 7.2g/cm³-7.7g/cm³The maximum magnetic energy product is more than or equal to 25 MGOe.

A second aspect of the embodiments of the present application provides a method for preparing a SmFeN permanent magnet, including:

providing SmFeN magnetic powder with the average grain size less than or equal to 10 mu m;

orienting and pressing the SmFeN magnetic powder in a protective atmosphere or in an organic solvent environment, and then carrying out isostatic pressing to prepare a cold blank magnet;

preparing a metal simple substance or alloy with a melting point lower than 800 ℃ and in a flake or powder shape;

covering at least one surface of the cold blank magnet with the metal simple substance or the alloy, and carrying out thermal diffusion densification treatment at the temperature lower than 600 ℃.

The preparation method of the SmFeN permanent magnet reduces the powder mixing process, avoids the problems of magnetic powder oxidation and low-melting-point phase non-uniform distribution when the magnetic powder is mixed with low-melting-point metal simple substance or alloy powder, and is suitable for preparing the high-performance SmFeN magnet; the mode of low-melting-point metal simple substance or alloy phase permeation is adopted, so that air gaps among magnetic powder can be eliminated, the density of the magnet can be improved, the interface structure among the magnetic powder can be improved, and the coercive force and the magnetic energy product of the final magnet can be improved; the cold blank magnet is coated with metal simple substance or alloy phase and then is subjected to thermal densification, so that the difficulty of coating magnetic powder and the process cost are greatly reduced, the production efficiency is improved, and the method is suitable for large-scale mass production.

In the embodiment of the application, the step of providing SmFeN magnetic powder with the average grain size less than or equal to 10 mu m is to provide SmFeN magnetic powder with the average grain size less than or equal to 5 mu m.

In the embodiment of the application, the oxygen content of the SmFeN magnetic powder is less than 5000 ppm.

The preparation method of the SmFe binary alloy mainly comprises a powder metallurgy method, a reduction diffusion method, a rapid quenching method, a mechanical alloying method, a gas atomization method and the like; after the alloy is prepared, mechanically crushing the alloy to a certain particle size, for example, the particle size is less than 10mm, and nitriding the alloy in the atmosphere of nitrogen or ammonia gas to form a SmFeN phase; further crushing the nitrided magnetic powder by jet milling or ball milling to ensure that the average particle size of the SmFeN magnetic powder is less than or equal to 10 mu m, wherein the crushed magnetic powder is easy to oxidize and the jet milling or ball milling is generally carried out in protective gas or organic solvent; in order to obtain a high-performance magnet, the oxygen content of the SmFeN magnetic powder needs to be less than 5000 ppm.

In the embodiment of the application, the density of the cold blank magnet is 4.0g/cm³-5.0g/cm³。

In the embodiment of the application, the intensity of an orientation magnetic field for orienting the SmFeN magnetic powder is 1.0T-2.0T.

After orientation and pressing, the easy magnetization directions of the SmFeN magnetic powder are uniformly arranged along the direction of a magnetic field; then, isostatic pressing is carried out, and a compact cold blank magnet is obtained.

In the embodiment of the application, the preparation of the metal simple substance or the alloy which has the melting point lower than 800 ℃ and is in the form of thin sheet or powder comprises the following steps: preparing a powdery metal simple substance or alloy with the average grain diameter of 1-1000 mu m.

In an embodiment of the present application, the coating the metal simple substance or the alloy on the surface of the cold blank magnet includes: adding a powdery metal simple substance or alloy directly to the surface of the cold blank magnet, or forming the metal simple substance or alloy on the surface of the cold blank magnet by at least one of a chemical coating method, a vapor deposition method, a magnetron sputtering method, and an ion spraying method.

In the embodiment of the application, in the step of covering at least one surface of the cold blank magnet with the metal simple substance or the alloy, the weight percentage of the metal simple substance or the alloy relative to the cold blank magnet is less than or equal to 25%.

In an embodiment of the present application, the coating the elemental metal or the alloy on at least one surface of the cold blank magnet includes: and respectively covering the two opposite surfaces of the cold blank magnet with the metal simple substance or the alloy, wherein the distance between the two opposite surfaces is less than or equal to 20 mm.

In the embodiment of the application, the pressure of the thermal diffusion densification treatment is 0.1 GPa-10 GPa, and the time is less than or equal to 5 min.

Due to Sm₂Fe₁₇N_xDecomposition occurs at a temperature of 600 ℃ or higher, and therefore, the same sintering process as that of NdFeB magnets cannot be used, and the temperature of thermal densification needs to be lower than 600 ℃. For example, the temperature of thermal densification is above 300 ℃ and below 600 ℃. In order to obtain a densified high performance SmFeN magnet, it is necessary to complete the rapid densification work by high stress in a short time.

In the embodiment of the application, the thermal diffusion densification treatment mode comprises one of spark plasma sintering, hot pressing, hot isostatic pressing and current-assisted sintering; the melting point of the metal simple substance or the alloy is lower than 600 ℃.

In the embodiment of the present application, the thermal diffusion densification process is performed by an impact compression method.

A third aspect of embodiments of the present application provides an electric machine comprising a rotor and a SmFeN permanent magnet as defined in the first aspect of embodiments of the present application disposed on the rotor.

Drawings

Fig. 1 is a schematic microstructure diagram of a SmFeN permanent magnet according to an embodiment of the present application.

Fig. 2 is a flow chart of the preparation of SmFeN permanent magnets of the embodiments of the present application.

Fig. 3 is a schematic diagram of a process for preparing a SmFeN permanent magnet according to an embodiment of the present application.

Description of the main elements

SmFeN permanent magnet 100

SmFeN grains 10

Grain boundary phase 30

SmFeN magnetic powder 20

Magnetic field orientation forming press 200

Magnet 40

Cold billet magnet 60

Elemental metal or alloy 80

Die 400

Permanent magnet blank 62

Detailed Description

The embodiments of the present application will be described below with reference to the drawings. The data ranges referred to in this application are to be understood as being inclusive, unless specifically stated otherwise.

In the existing method for preparing SmFeN rare earth permanent magnet, SmFeN magnetic powder and low-melting-point metal simple substance or alloy are mixed or low-melting-point metal or alloy is added into SmFeN magnetic powder in a form of coating a layer of low-melting-point metal or alloy phase on the surface of SmFe alloy powder. However, SmFeN magnetic powder is fine, the particle size is generally in the range of 1-10 mu m, and oxidation is easy to occur; meanwhile, the two modes also have the defects that the distribution of low-melting-point metal or alloy powder is not uniform, the coating efficiency is low, and the fine metal or alloy powder is easy to oxidize.

Therefore, the embodiment of the application provides a high-performance SmFeN permanent magnet and a preparation method thereof, and by means of covering a layer of powder or thin sheet of a low-melting-point metal simple substance or alloy on the surface of a SmFeN precursor magnet, the powder mixing or covering process is avoided, and meanwhile, the requirement on the form of metal or alloy powder is reduced.

As shown in fig. 1, the SmFeN permanent magnet 100 includes a plurality of SmFeN grains 10 and a grain boundary phase 30 located around the SmFeN grains 10. The grain boundary phase 30 is located between the plurality of SmFeN grains 10. The grain boundary phase 30 mainly includes a product of a reaction of SmFeN with a simple metal having a melting point of less than 800 ℃ or an alloy having a melting point of less than 800 ℃. In the present application, the grain boundary phase 30 includes a product represented as a SmFeXN phase, where X is an element from a simple metal or an alloy having a melting point of less than 800 ℃. The grain size of each SmFeN crystal grain 10 is 1-10 μm. In one embodiment, the grain boundary phase 30 includes a Zn-rich SmFeZnN phase formed by reacting SmFeN with elemental metal Zn having a melting point less than 800 ℃. The grain boundary phase 30 is extremely low magnetic or non-magnetic compared to the SmFeN grains 10.

In some embodiments, the elemental metal or alloy having a melting point below 800 ℃ is an elemental metal having a melting point below 600 ℃ or an alloy having a melting point below 600 ℃. In some embodiments, the elemental metal with a melting point below 600 ℃ is Zn, Al, Sn, Mg, Ga, Bi, Pt, or In, i.e., X is Zn, Al, Sn, Mg, Ga, Bi, Pt, or In. In some embodiments, the alloy having a melting point below 600 ℃ is an alloy of a rare earth metal and another metal, i.e., X comprises the rare earth metal element and at least one additional metal element, wherein the rare earth metal is one or more (including two) of La, Ce, Pr, Nd, Sm, Y, and the additional metal is one or more of Fe, Cu, Zn, Al, Mg, Ga, Co, Zr, Mo, V, Sn, Bi, Pt, In, Nb. For example, the low melting point alloy may be SmCu, PrCu, smcecual, or the like.

In the embodiment of the present application, the grain boundary phase 30 includes SmFeXN, which is a product of a reaction between a simple metal or an alloy with a melting point lower than 800 ℃ added in the preparation process of the SmFeN permanent magnet 100 and the surface layer of the SmFeN crystal grain 10. The simple metal substance or the alloy permeates among the SmFeN crystal grains 10 in a mode of grain boundary diffusion in the SmFeN crystal grains 10, and simultaneously the simple metal substance or the alloy reacts with the surface layers of the SmFeN crystal grains 10 to form the grain boundary phase 30. The grain boundary phase 30 may also include elemental metals or alloys that do not react with SmFeN grains. That is, the grain boundary phase 30 may or may not selectively include a simple metal or an alloy.

The preparation process of the SmFeN permanent magnet 100 is that a metal simple substance or alloy is initially placed on the outer surface of a cold blank magnet, then the metal simple substance or alloy diffuses and permeates towards the inside of the cold blank magnet, the permeated metal simple substance or alloy reacts with the surface layer of SmFeN crystal grains to form a product SmFeXN, the product SmFeXN forms the main component of a grain boundary phase 30, and meanwhile, the preparation process causes the uneven distribution of the grain boundary phase 30 in the SmFeN permanent magnet 100. The grain boundary phase 30 is present in a greater amount in at least one outer surface of the SmFeN permanent magnet 100 than in the center of the SmFeN permanent magnet 100. The grain boundary phase 30 is present in the SmFeN permanent magnet 100 in a reduced amount from at least one outer surface of the SmFeN permanent magnet 100 toward the center of the SmFeN permanent magnet 100. In one example, the grain boundary phase 30 is present in a progressively decreasing amount from at least an outer surface of the SmFeN permanent magnet 100 toward the center of the SmFeN permanent magnet 100.

The content of the grain boundary phase 30 in the SmFeN permanent magnet 100 can be characterized by the thickness of the wrapped SmFeN crystal grains 10, and the distribution of the thickness of the grain boundary phase 30 from the surface of the permanent magnet to the center of the permanent magnet is changed along the permeation direction, wherein the closer the grain boundary phase 30 is to the center of the permanent magnet, the smaller the thickness of the grain boundary phase 30 is; the farther from the center of the permanent magnet, the greater the thickness of the grain boundary phase 30. As shown in fig. 1, the thickness of the grain boundary phase 30 gradually increases from the center of the SmFeN permanent magnet 100 toward the outer surface of the SmFeN permanent magnet 100. For example, the SmFeN permanent magnet has a thickness of 200nm in the grain boundary phase at the outer surface and a thickness of 20nm in the central region 3mm from the outer surface. For example, if the magnet has opposite surfaces on which the simple metal or alloy is initially placed and then the simple metal or alloy is diffusion-infiltrated toward the inside of the magnet, if the distance between the two surfaces is greater than 10mm, there may be no low-melting-point grain boundary phase or very few grain boundary phases present in the central portion of the permanent magnet. The variation in thickness of the grain boundary phase 30 is represented by a variation in concentration of an element in the low-melting-point metal simple substance or alloy in the permeation direction, and the concentration is higher at the surface of the permanent magnet and lower at the center of the permanent magnet.

In one embodiment, the grain boundary phase 30 is formed by introducing metallic Zn into the SmFeN crystal grains 10, the concentration of Zn decreases from at least one outer surface of the SmFeN permanent magnet 100 to the center, and the mass percentage content of Zn at the outer surface of the SmFeN permanent magnet 100 is measured as W_maxAnd the mass percentage of Zn at the center of the SmFeN permanent magnet 100 is measured to be W_min，W_maxGreater than W_min. In one embodiment, W_max-W_min≥10％。

Since the grain boundary phase 30 is formed by disposing a simple metal substance or an alloy on the outer surface of the cold blank magnet and diffusing and permeating the simple metal substance or the alloy toward the inside of the magnet, that is, the content of the grain boundary phase 30 as a whole tends to decrease from at least one outer surface (the surface on which the simple metal substance or the alloy was originally disposed) of the SmFeN permanent magnet 100 to the center due to the manufacturing process. It will be understood that the present application also does not exclude the following: the content of the grain boundary phase 30 is equal in at least a partial region of the SmFeN permanent magnet 100 and at different positions along the permeation direction of the simple metal or the alloy.

For elemental metals having a melting point below 600 c or alloys having a melting point below 600 c, they may be introduced between the SmFeN grains 10 by one of spark plasma sintering, hot pressing, hot isostatic pressing, current assisted sintering. When the grain boundary phase 30 is introduced between the SmFeN grains 10 by using some special preparation process, such as an impact compression method, a simple metal or alloy having a melting point higher than 600 ℃ and lower than 800 ℃ may be introduced between the SmFeN grains 10. The specific reason is as follows: the higher pressure or impact energy generated by the impact compression method can reduce the requirement on the melting point of the metal simple substance or the alloy of the grain boundary phase 30. The impact compression method may be an explosive impact method, but is not limited thereto.

The crystal structure of the SmFeN crystal grains comprises a Th2Zn17 type and a TbCu7 type, the Th2Zn17 type is anisotropic, and the TbCu7 type is isotropic. The volume percentage of TbCu7 type structure crystal grains in the SmFeN crystal grains is less than or equal to 10 percent. In some embodiments, the volume fraction of the TbCu7 type structure grains is less than 5%. In still other embodiments, the TbCu7 type structure grains have a volume fraction of 0%, i.e., preferably include only anisotropic SmFeN grains. The anisotropic SmFeN magnetic powder can complete orientation in a magnetic field, and high orientation degree is realized, so that the magnetic property of the product is greatly improved.

Metallic Zn is an additive used for low temperature sintering of SmFeN magnets. In one embodiment, Sm₂Fe₁₇N_xThe surface layer of the crystal grains and the metal Zn form a Zn-rich SmFeZnN phase after heat treatment. In one embodiment, the weight ratio of Sm, Fe, Zn, and N in the SmFeZnN phase in the grain boundary phase 30 may be 11.6: 2.3: 19.6: 6.5.

the grain boundary phase 30 can eliminate surface defects formed by SmFeN grains in the SmFeN magnetic powder processing process, and can also form a nonmagnetic grain boundary layer with a demagnetizing coupling effect among the SmFeN grains, so that the coercive force of the SmFeN magnet is improved. The thickness of the SmFeN crystal grains 10 wrapped by the grain boundary phase 30 is generally more than 1nm and less than 500nm, and in some embodiments, the thickness of the SmFeN crystal grains 10 wrapped by the grain boundary phase 30 is 10nm-50 nm.

With reference to fig. 2, the present application further provides a method for preparing a SmFeN permanent magnet, including:

providing SmFeN magnetic powder with the average grain size less than or equal to 10 mu m;

orienting and pressing the SmFeN magnetic powder in a protective atmosphere or in an organic solvent environment, and then carrying out isostatic pressing to prepare a cold blank magnet;

providing a metal simple substance or alloy with a melting point lower than 800 ℃ and in a flake or powder shape;

covering at least one surface of the cold blank magnet with the metal simple substance or the alloy, and performing thermal diffusion densification treatment at the temperature lower than 600 ℃ to prepare a blank of the permanent magnet.

It can be understood that the blank of the permanent magnet can be cut, ground and the like according to the requirement to obtain a SmFeN permanent magnet product with the required shape and size.

The SmFeN magnetic powder can be purchased directly or prepared. The preparation method of the SmFeN magnetic powder comprises the following steps: preparing SmFe binary alloy; crushing the SmFe binary alloy into powder; nitriding the powdery SmFe binary alloy. The preparation method of the SmFe binary alloy mainly comprises a powder metallurgy method, a reduction diffusion method, a rapid quenching method, a mechanical alloying method, a gas atomization method and the like. After the alloy is prepared, mechanically crushed to a certain particle size, for example, a particle size of less than 10mm, preferably 1mm to 2mm, and nitrided in a nitrogen or ammonia atmosphere to form Sm₂Fe₁₇N_xAnd (4) phase(s).

The nitrided magnetic powder needs to be further crushed by an air flow mill or a ball mill, and the average particle size of the crushed SmFeN magnetic powder is less than or equal to 10 mu m. In some embodiments, the SmFeN magnetic powder has an average particle size of less than or equal to 5 μm. Because the crushed magnetic powder is fine and easy to oxidize, the jet milling or ball milling is generally carried out in protective gas or organic solvent. In order to obtain a high-performance magnet, the oxygen content of the SmFeN magnetic powder needs to be less than 5000 ppm. In some embodiments, the SmFeN magnetic powder has an oxygen content of less than 1000 ppm.

As shown in fig. 3, SmFeN magnetic powder 20 satisfying the particle size requirement is pressed in a magnetic field orientation molding press 200, and the SmFeN magnetic powder 20 is oriented by magnetic fields formed by the magnets 40 on the left and right sides while being pressed up and down, and the strength of the magnetic field is generally 1.0T to 2.0T. After orientation and pressing, the easy magnetization directions of the SmFeN magnetic powder are uniformly arranged along the direction of a magnetic field. Then the mixture is subjected to oil cold isostatic pressing to obtain the product with the density of 4.0g/cm³-5.0g/cm³The cold blank magnet 60. The cold blank magnet 60 is a precursor for grain boundary diffusion, that is, the aforementioned precursor magnet. In some embodiments, the density of the cold blank magnet 60 is 4.5g/cm³-5.0g/cm³. In the present embodiment, as shown in fig. 3, the manufactured cold blank magnet 60 is in the shape of a rectangular parallelepiped block, but not limited thereto, and may be in various shapes such as a cylinder, a prism, and the like. Wherein the isostatic pressing treatment is to place the processed object in a closed container filled with liquid and to gradually carry out the treatment through a pressurization systemThe pressurizing applies equal pressure to each surface of the object, so that the distance between molecules is reduced and the density is increased without changing the appearance shape, thereby improving the physical properties of the substance.

In the application, the metal simple substance or the alloy covering the cold blank magnet can have various forms, and can be powder of the metal simple substance or the alloy; it can also be made into thin strip or thin slice of quick quenching metal simple substance or alloy. For the powder of the metal simple substance or the alloy, the average grain diameter is 1 μm to 1000 μm, for example, 800 mesh Zn powder. The powder of the metal simple substance or the alloy can be directly added to the surface of the cold blank magnet, and the metal simple substance or the alloy can be formed on the surface of the cold blank magnet by a chemical coating method, a vapor deposition method, a magnetron sputtering method, an ion spraying method and the like.

As shown in fig. 3, in the present embodiment, the rectangular parallelepiped block-shaped cold blank magnet 60 is covered with a simple metal or alloy 80 on its opposite surfaces, respectively. It is to be understood that the surface of the cold blank magnet 60 on which the elemental metal or alloy 80 is placed is not limited to that shown in fig. 3, and that alternative placement may be possible, such as placement on only one surface of the cold blank magnet 60, or placement on all surfaces of the cold blank magnet 60, or placement as desired.

Because the powder of the metal simple substance or the alloy is easy to oxidize, the preparation process is complex, the cost is high, the application also provides a way of using a quick quenching thin strip or sheet to cover the surface of the cold blank magnet, so that the preparation difficulty of the metal simple substance or the alloy is greatly reduced, and the oxidation resistance is greatly improved.

The metal simple substance or alloy expresses the adding amount thereof in the magnet through a weight gain ratio, and the weight gain ratio refers to the percentage of the weight of the added metal simple substance or alloy relative to the weight of the body of the cold blank magnet. The weight gain ratio of the metal simple substance or the alloy is less than or equal to 25 percent. In some embodiments, the weight gain ratio of the metal element or alloy is less than or equal to 10%. Since the distance of atomic diffusion is limited, in this embodiment, the distance between two opposite surfaces of the cold blank magnet on which the metal simple substance or alloy is placed cannot be too large, and is generally less than or equal to 20 mm. In some embodiments, the distance is less than 10 mm; in other embodiments, the distance is less than 5 mm. The smaller the penetration distance is, the more sufficient the penetration is, and the more uniform the distribution of the coercive force of the magnet is, whereas if the penetration distance is larger, the coercive force inside the magnet is obviously lower than that of the surface layer of the magnet.

After the metal simple substance or the alloy covers the surface of the cold blank magnet, thermal densification treatment is carried out at a certain temperature and under a certain pressure, so that the metal simple substance or the alloy is diffused and permeated among crystal grains. As shown in fig. 3, the cold-rolled magnet 60 having opposite surfaces covered with the simple metal substance or alloy 80 is placed in a mold 400, and the cold-rolled magnet 60 is pressed by applying pressure from both sides having the simple metal substance or alloy 80, respectively, while maintaining a high temperature (e.g., higher than 300 ℃ and lower than 600 ℃) in the mold 400, so that the simple metal substance or alloy 80 gradually diffuses and permeates from the surface of the magnet toward the center of the magnet, and finally, a blank 62 of the permanent magnet is produced.

Due to Sm₂Fe₁₇N_xDecomposition occurs above 600 ℃, so that the same sintering process as an NdFeB magnet cannot be adopted for treatment, and the temperature of thermal densification needs to be lower than 600 ℃; in some embodiments, the temperature of the thermal densification is less than 500 ℃. For example, the temperature of thermal densification is above 300 ℃ and below 600 ℃. In order to obtain a high-performance densified SmFeN magnet, rapid densification needs to be performed in a short time by high stress, and thermal densification methods including Spark Plasma Sintering (SPS), hot pressing, hot isostatic pressing, current-assisted Sintering, blast impact method, and the like are used. The highest pressure of thermal densification is 0.1 GPa-10 GPa; the time for thermal densification is less than or equal to 5min, and in some embodiments, the time for thermal densification is less than or equal to 1 min. The density of the SmFeN magnet is 7.2g/cm after thermal densification³-7.7g/cm³The maximum magnetic energy product (BH) m is more than or equal to 25 MGOe.

For the thermal densification treatment by the impact compression method such as the blast impact method, the melting point of the simple metal or alloy covering the surface of the cold blank magnet can be suitably relaxed to more than 600 ℃ and less than 800 ℃. The specific principle is as follows: the impact compression method forms larger pressure or impact energy, so that the requirement on the melting point of the metal simple substance or the alloy of the grain boundary phase can be reduced.

The preparation method of the SmFeN permanent magnet has the following advantages.

(1) The problems of oxidation and uneven distribution when SmFeN magnetic powder is mixed with low-melting-point metal simple substance or alloy phase powder are solved.

The SmFeN magnetic powder has small granularity, high activity and easy oxidation, and the preparation method reduces the powder mixing process, avoids the problems of magnetic powder oxidation and low-melting-point phase non-uniform distribution when the magnetic powder is mixed with low-melting-point metal simple substance or alloy powder, and is suitable for preparing high-performance SmFeN magnets.

(2) The interface structure of the magnetic powder is improved, and the performance is improved.

The mode of low-melting-point metal simple substance or alloy phase permeation is adopted, so that air gaps among magnetic powder can be eliminated, the density of the magnet can be improved, the interface structure among the magnetic powder can be improved, and the coercive force and the magnetic energy product of the final magnet can be improved.

(3) The process difficulty is low, and the method is suitable for mass production.

The cold blank magnet is coated with metal simple substance or alloy phase and then is subjected to thermal densification, so that the difficulty of coating magnetic powder and the process cost are greatly reduced, the production efficiency is improved, and the method is suitable for large-scale mass production.

The SmFeN permanent magnet can be used in motors, sensors, loudspeakers, instruments and meters, medical equipment and the like. The present application also provides an electric machine (not shown) comprising a rotor and the above-described SmFeN permanent magnet disposed on the rotor.

The technical solution of the embodiments of the present application is further described below by specific examples.

Examples 1 to 12

The raw material of the magnet is SmFeN coarse powder which is commercially available for Sumitomo, the grain structure of the magnetic powder is Th2Zn17 type, and the grain diameter of the magnetic powder is about 23 mu m. SmFeN coarse powder is prepared into SmFeN fine powder with oxygen content of about 3000ppm through ball milling in gasoline to reach average grain size of about 5 micron. Transferring the fine powder containing gasoline into a glove box of a magnetic field forming press, and filtering and vacuumizing to remove gasoline to obtain dry magnet powder. Weighing the powder and adding it into a magnetic fieldAnd (3) carrying out orientation and pressing in a die in a mould press, wherein the orientation magnetic field is 1.5T. After pressing, the magnet is encapsulated in a vacuum bag and then is further pressed in an oil-cooled isostatic press under 200MPa to obtain the magnet with the density of 4.8g/cm³The cold-rolled magnet of (1).

Commercial 325-mesh Zn powder is used as a low-melting-point alloy, the Zn powder, acetone and resin are weighed according to the mass ratio of 20:80:1, the mixture is continuously stirred until the resin is completely dissolved, and the Zn powder is uniformly mixed to obtain the coating liquid. After weighing m0 of the cold-rolled magnet by balance, the coating liquid was put into a glove box having an oxygen content of less than 100ppm together with the cold-rolled magnet, the coating liquid was applied to the upper and lower surfaces of the cold-rolled magnet, the coating amount (different weight ratio) of the cold-rolled magnet was changed by the number of times of coating, and then dried at 60 ℃ for 2 hours to remove acetone, to obtain a coated dry cold-rolled magnet. The coated dry cold-blank magnet was weighed to give a weight m1, and the weight gain ratio was verified by calculation.

And (3) putting the cold blank magnet with the coating into a pressure-resistant die of SPS equipment, loading current to quickly raise the temperature of the magnet to 480 ℃, pressing (different loads) under different pressures after the temperature is stable, and keeping the pressure for 2 min. The cold blank is rapidly densified under the pressure action of the punch, and blank magnets with different densities are obtained. The density of the blank magnet was measured by the drainage method, and the properties of the blank were measured using a magnetic property measuring instrument.

2 variables were designed in the above preparation of SmFeN magnets.

The first group was fixed pressed at a load of 700MPa, the weight gain ratio of Zn powder was changed, and the results of magnet performance tests for different weight gain ratios were shown in examples 1 to 5.

The second group was that the weight gain ratio of fixed Zn powder was 10%, the load of pressing was changed, and the results of the performance test of magnets prepared under different loads were shown in examples 7 to 11.

Using the cold-rolled magnet prepared in the same manner as above, the magnetic properties obtained by changing the addition of Zn powder from chemical coating to physical filling were as shown in example 6. The physical filling method is that in SPS equipment, a layer of 325-mesh Zn powder is filled at the bottom of a mold, the Zn powder is placed into a cold blank magnet after being distributed evenly, and then a layer of Zn powder is covered on the cold blank magnet. Thermal densification was then carried out under the same temperature and pressure conditions as in example 4. The properties of the blanks were tested using a magnetic properties tester to give example 6. The table one shows the effect of different weight gain ratios of Zn powder on SmFeN magnet performance.

Watch 1

Item	Metal	Weight ratio of	Remanence (T)	Coercive force (kA/m)	Maximum magnetic energy product (kJ/m)3)
						Magnetic powder property (Fine powder)	/	/	1.32	680	285
Example 1	325 mesh Zn powder	25％	0.81	1416.9	118.7
						Example 2	325 mesh Zn powder	20％	0.88	1202.0	140.1
Example 3	325 mesh Zn powder	15％	0.93	1010.9	156.5
						Example 4	325 mesh Zn powder	10％	0.98	811.9	173.7
Example 5	325 mesh Zn powder	5％	1.05	764.2	188.2
						Example 6	325 mesh Zn powder	10％	1.00	823.5	176.5

As can be seen from table one, as the content of Zn powder increases, the content of the nonmagnetic phase in the magnet increases, and the remanence of the SmFeN magnet gradually decreases, but the coercive force gradually increases. Example 6 has a smaller improvement in performance than example 4, because the direct use of Zn powder can reduce the oxygen content.

Magnetic properties obtained by using cold-rolled magnets prepared by the methods of examples 7 to 11 and the same chemical coating method of Zn powder, changing the pressing method, using a hot pressing process different from the SPS process of examples 7 to 11, at a pressure of 900MPa or 1000MPa, at a pressing temperature and a dwell time the same as those of examples 7 to 11, were as shown in examples 12 and 13. Table two shows the effect of different pressing pressures on SmFeN magnet performance.

Watch two

As can be seen from table two, for the SPS process or the hot pressing process, the density of the magnet is gradually increased and the magnetic performance of the magnet is gradually improved as the pressing pressure is increased. Examples 12 and 13 showed a slight improvement in performance over examples 9 and 10 because the temperature rise time of the SPS process was longer than that of the hot-press process.

The green magnet of example 13 was subjected to composition analysis by plasma spectroscopy (ICP). The blank magnet size was 25mm 20mm 6mm, the coated face was 2 faces of 25mm 20mm, and the diffusion direction was 6mm thick. 1.0mm flakes were cut out from the sample at different positions in the diffusion direction, and the Zn contents of these flakes were measured to obtain the following Zn content distributions, as shown in Table III, of the Zn element in the magnet in the diffusion direction. It can be seen that the Zn element has the highest Zn content in the surface layer of the magnet and the lowest Zn content in the middle of the magnet.

Watch III

Position of	0-1mm	1-2mm	2-3mm	3-4mm	4-5mm	5-6mm
							Zn content (wt.%)	16.1	2.1	1.9	1.8	2.2	16.1

Examples 13 to 18

The selection of the magnetic powder and the preparation of the cold-blank magnet are the same as those in the specific example 1, and the SmFeN coarse powder which is commercially available for Sumitomo is selected as the raw material of the magnet, and the particle size of the magnetic powder is about 23 μm. The SmFeN coarse powder is ball-milled to reduce the average grain diameter to about 5 mu m, and then SmFeN fine powder is prepared, wherein the oxygen content of the fine powder is about 3000 ppm. And transferring the fine powder belt with gasoline into a glove box of a magnetic field forming press for vacuum drying treatment to obtain dry magnet powder. The powder was weighed into a die in a magnetic field forming press and then oriented and pressed in a 1.5T orientation magnetic field. After pressing, the magnet is packaged in a vacuum bag and then is further pressed in an oil-cooling isostatic press under 200MPa to obtain the magnet with the density of 4.8g/cm³The cold-rolled magnet of (1).

The low-melting-point alloy is a SmCuFeAl rapid quenching belt. HeadFirstly, Sm is proportioned₆₀Cu₂₅Fe₆Al₁₁Weighing pure samarium (99.9%), pure copper (99.0%), pure iron (99.99%) and pure aluminum (99.99%), and then smelting for multiple times in a crucible of a medium-frequency induction furnace to prepare alloy ingots with uniform components. And (3) coarsely crushing the cast ingot, putting the cast ingot into a vacuum induction quick quenching furnace for remelting, and spraying the melt onto a water-cooled copper roller under the pressure action of inert gas to obtain the SmCuFeAl quick quenching belt.

And (3) primarily crushing the SmCuFeAl rapid quenching belt, and sieving by using a sieve with 10 meshes to obtain alloy rapid quenching powder. And (3) putting the cold blank magnet and the alloy quick quenching powder into SPS equipment for preparing thermal densification treatment. The weight increasing ratio of the added alloy rapid quenching powder is 10 wt%, and the physical filling is carried out according to the weight increasing ratio design, and the specific mode is that in the SPS equipment, a layer of alloy rapid quenching powder with the weight of 5 wt% is filled at the bottom of a mould, so that the powder is evenly distributed, then the cold blank magnet is placed, and then a layer of alloy rapid quenching powder with the weight of 5 wt% is covered on the cold blank magnet. After the filling is finished, current is applied to rapidly raise the temperature of the magnet to a specified temperature, and after the temperature is stable, pressing is carried out under the pressure of 1000MPa, and the pressure maintaining time is 2 min. And (3) rapidly densifying the cold blank under the action of the pressure and the temperature of the punch to obtain a blank magnet, and measuring the performance of the blank by using a magnetic characteristic measuring instrument. The magnetic properties obtained at 400 c, 420 c, 450 c, 480 c, 500 c for the thermal densification temperatures were examples 14-18, respectively, and the effects of different thermal densification temperatures on SmFeN magnet performance are shown in table four.

Watch four

As can be seen from table four, after the low melting point SmCuFeAl alloy is added, the remanence and the maximum energy product of the smcen magnet increase first with the increase of the thermal densification temperature, because the density is increased and the coercivity of the magnet tends to be stable at temperatures below 500 ℃.

It should be noted that the above is only a specific embodiment of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present application, and all should be covered by the scope of the present application; in the present invention, the embodiments and features of the embodiments may be combined with each other without conflict. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.