Heavy-rare-earth-free high-performance neodymium-iron-boron magnet and preparation method thereof
By covering the surface of the fine powder of NdFeB alloy, the thickness of the grain boundary diffusion layer is controlled, and the problems of degradation of magnetic properties of rare earth NdFeB magnets and low reserves of heavy rare earth elements at high temperatures are solved, and the effects of high coercive force and high temperature stability are achieved.
Patent Information
- Application Number
- CN202510165494.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-14
- Publication Date
- 2025-05-09
AI Technical Summary
The existing rare earth neodymium iron boron magnets have reduced magnetic properties at high temperatures, low reserves of heavy rare earth elements, and expensive prices. The improvement effect of grain boundary diffusion technology is restricted by the thickness of the magnet.
Before sintering, the heavy-free rare earth diffusion source coated on the surface of the fine powder of NdFeB alloy is added to enhance the coercive force effect of the heavy-free rare earth material by controlling the thickness of the grain boundary diffusion layer.
Through uniform and controllable diffusion source diffusion, the coercive force and high temperature stability of the neodymium iron boron magnet are significantly improved, the amount of diffusion source is reduced, and the reserve and price problems of heavy rare earth elements are overcome.
Abstract
Description
Technical Field
[0001] The invention relates to the field of rare earth permanent magnetic materials, and in particular to a heavy rare earth-free high-performance neodymium iron boron magnet and a preparation method thereof. Background Art
[0002] Rare earth NdFeB material is the most representative permanent magnet material with the best comprehensive performance. It is widely used in manufacturing industry and electronic technology. Among them, sintered NdFeB material has the most mature technology. Sintered NdFeB magnets have very high remanence and maximum magnetic energy, but low Curie temperature and coercive force. Therefore, people take various methods to improve the stability of its magnetic properties.
[0003] Reducing the grain size can increase the coercivity of NdFeB magnets at room temperature, but its grains are more likely to grow, and the magnetic properties decrease rapidly with increasing temperature; while adding heavy rare earth elements such as Ty and Db can greatly increase the coercivity and high temperature stability of the magnet, but it will reduce the remanence. Furthermore,
[0004] Using grain boundary diffusion technology to diffuse heavy rare earth elements on the surface of magnets is currently the most mature and optimal magnet modification method, which can greatly improve the intrinsic coercivity of NdFeB magnets and has a small side effect of reducing remanence. However, heavy rare earth elements such as Ty and Db have low reserves and are expensive. For this reason, some studies have pointed out that some light rare earth element alloys have similar effects of improving the coercivity of magnets, such as the combination of Pr with Fe, Al, Cu, Co, Ga and other metals, but their overall effect is somewhat different from that of heavy rare earth elements. In addition, in grain boundary diffusion technology, the depth of the diffusion layer is usually limited to hundreds of microns, which means that the effect of improving coercivity is also restricted by the thickness of the magnet. Summary of the invention
[0005] The purpose of the present invention is to provide a heavy rare earth-free high-performance NdFeB magnet and a preparation method thereof, wherein a heavy rare earth-free diffusion source coated on the surface of NdFeB alloy fine powder is added before sintering, thereby increasing and controlling the thickness of the grain boundary diffusion layer, thereby enhancing the effect of the heavy rare earth-free material on improving the coercive force of the magnet, and overcoming the shortcomings and prejudices of the prior art.
[0006] The present invention provides a method for preparing a heavy rare earth-free high-performance neodymium iron boron magnet, comprising the following steps:
[0007] S1: NdFeB alloy is subjected to hydrogen explosion and air flow grinding in sequence to obtain NdFeB alloy fine powder;
[0008] S2: Under the protection of inert gas, a portion of NdFeB alloy fine powder is dispersed in alkaline oxygen-free water containing a reducing agent, and a diffusion source metal salt solution is gradually added. After the reaction, the mixture is washed and dried to obtain a diffusion source-wrapped NdFeB alloy;
[0009] S3: Under the protection of inert gas, the remaining NdFeB alloy fine powder is subjected to primary orientation molding to obtain a rough embryo, the diffusion source-wrapped NdFeB alloy is uniformly coated on the surface of the rough embryo, and after drying, secondary orientation molding is carried out along the same magnetizing direction and pressing direction as the primary one, and isostatic pressing is performed to obtain a green embryo;
[0010] S4: The green embryo is subjected to microwave vacuum sintering and tempering treatment to obtain a heavy rare earth-free high-performance NdFeB magnet;
[0011] The mass fraction of the diffusion source alloy in the diffusion source-wrapped NdFeB alloy is 5 to 20%;
[0012] The mass fraction of the diffusion source-wrapped NdFeB alloy in the green embryo is 0.5-10%;
[0013] The diffusion source alloy composition is Pr 100-a-b-c La a Fe b Co c , wherein a, b, and c represent atomic percentages, and 0≤a≤3, 5≤b≤20, and 0≤c≤15.
[0014] The present invention also provides a heavy rare earth-free high-performance neodymium iron boron magnet prepared by the above preparation method.
[0015] The technical solution of the present invention has the following beneficial effects:
[0016] 1. In the preparation method of the heavy rare earth-free high-performance NdFeB magnet of the present invention, the diffusion source is wrapped on the surface of the NdFeB alloy fine powder suspended in water by reduction deposition, and the powder is coated on the rough blank as a whole, so that the diffusion of the diffusion source is more uniform within a certain depth, the diffusion layer thickness is larger and controllable, and the effect of improving the coercive force is enhanced while reducing the amount of diffusion source.
[0017] 2. In the preparation method of the heavy rare earth-free high-performance NdFeB magnet described in the present invention, the diffusion source wrapped with the NdFeB alloy fine powder is added to the magnet green body before sintering, and a low-temperature microwave vacuum method is used for rapid sintering and forming, and tempering is combined with the grain boundary diffusion process to achieve a better grain boundary diffusion modification effect, overcoming the technical prejudice that the diffusion source will excessively enter the main phase when sintering with the green body. DETAILED DESCRIPTION
[0018] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the specific implementation of the present invention is further described below. Obviously, the embodiments described therein are only part of the implementation of the present invention, which is an explanation of the technical solution of the present invention rather than a limitation.
[0019] The present invention provides a method for preparing a heavy rare earth-free high-performance neodymium iron boron magnet, comprising the following steps:
[0020] S1: The NdFeB alloy is subjected to hydrogen explosion and air flow grinding in sequence to obtain NdFeB alloy fine powder.
[0021] S2: Under the protection of inert gas, a portion of NdFeB alloy fine powder is dispersed in alkaline oxygen-free water containing a reducing agent, and a diffusion source metal salt solution is gradually added. After the reaction, the powder is washed and dried to obtain a diffusion source-wrapped NdFeB alloy.
[0022] S3: Under the protection of inert gas, the remaining NdFeB alloy fine powder is subjected to primary orientation molding to obtain a rough embryo, and the diffusion source-wrapped NdFeB alloy is uniformly coated on the surface of the rough embryo. After drying, secondary orientation molding is carried out along the same magnetizing direction and pressing direction as the initial one, and isostatic pressing is performed to obtain a green embryo.
[0023] S4: The green embryo is subjected to microwave vacuum sintering and tempering treatment to obtain a heavy rare earth-free high-performance NdFeB magnet.
[0024] The mass fraction of the diffusion source alloy in the diffusion source-wrapped NdFeB alloy is 5-20%.
[0025] The mass fraction of the diffusion source-wrapped NdFeB alloy in the green embryo is 0.5-10%.
[0026] The diffusion source alloy composition is Pr 100-a-b-c La a Fe b Co c , wherein a, b, and c represent atomic percentages, and 0≤a≤3, 5≤b≤20, and 0≤c≤15.
[0027] Preferably, the reducing agent is hydrazine hydrate, and the alkaline oxygen-free water is an ammonia / ammonium salt buffer solution with a pH between 9 and 11 and dissolved oxygen below 20 ppb. Hydrazine hydrate and ammonia buffer solutions introduce fewer impurities.
[0028] Preferably, the diffusion source metal salt is Pr 3+ ,La 3+ , Fe 2+ and / or Co 2+ The salt is a composition configured according to the molar ratio of the diffusion source alloy. The metal salts are all low-valent salts of the corresponding metals.
[0029] Furthermore, the magnetic induction intensity of the primary orientation molding is 0.2-0.5 T, and the magnetic induction intensity of the secondary orientation molding is 1.5-2.0 T. The primary orientation molding is only to roughly shape the NdFeB rough blank and determine the magnetization direction and the pressing direction, so weak processing conditions are used.
[0030] Furthermore, in the microwave vacuum sintering, the sintering temperature is 900-950°C, the sintering time is 20-40 minutes, and the microwave power is 2.0-4.0 kW. Optionally, in the microwave vacuum sintering, there is also a magnetic field with a magnetic induction intensity of 3-6T.
[0031] The primary sintering temperature of the green embryo in general technical means is above 1050°C, which will cause the diffusion source to seriously invade the main phase, resulting in a magnetic dilution effect; microwave sintering can reduce this temperature to below 950°C and significantly shorten the sintering time, which is consistent with other technical improvements of the present invention. Optionally, the microwave vacuum sintering is replaced by spark plasma sintering.
[0032] Furthermore, the tempering is divided into primary tempering and secondary tempering; the primary tempering is heating from room temperature to 800-900°C and maintaining at this temperature for 4-12 hours; the secondary tempering is heating from room temperature to 450-550°C and maintaining at this temperature for 2-6 hours.
[0033] Furthermore, the uniform coating on the rough blank surface at least includes uniformly coating the diffusion source-wrapped NdFeB alloy on all surfaces that are not perpendicular to the magnetization direction and the pressing direction. In particular, for the hexahedral magnet rough blank, the surface includes at least two surfaces that are not perpendicular to the magnetization direction and the pressing direction.
[0034] Furthermore, the NdFeB alloy may be any commercial heavy rare earth-free NdFeB alloy, preferably a NdFeB alloy having the following composition:
[0035] R x Fe 100-x-y-z M y B z ,
[0036] Wherein R is selected from at least one of Rd, La and Ce, and at least includes Rd; M is selected from at least one of Cu, Al, Co, Ga and Z; x, y, z represent atomic percentages, and 28≤x≤32, 0.5≤y≤1.5, 0.94≤z≤1.00.
[0037] Preferably, the particle size of the NdFeB alloy fine powder is 1-4 μm.
[0038] The present invention is described in detail below with reference to the embodiments. The experimental methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified; the order of the described implementation steps does not strictly represent the order of specific implementation, except for those with logical associations.
[0039] Example 1
[0040] (1) Prepare NdFeB alloy according to the following raw material ratio:
[0041] Nd 29.6 Fe 68.34 Co 0.5 Al 0.2 Ga 0.2 Cu 0.1 Zr 0.1 B 0.96 ,
[0042] The raw materials were melted and cast into 0.3 mm thick alloy sheets at 1400°C by rapid solidification method, and then hydrogenated, dehydrogenated and crushed, and finally ground into NdFeB alloy fine powder with an average particle size of 2.4 μm in a nitrogen-protected air flow mill.
[0043] (2) Under nitrogen protection, 100 g of the obtained NdFeB alloy fine powder was dispersed in 2 L of an oxygen-free ammonia-ammonium chloride buffer solution containing 70 mmol of hydrazine hydrate and a pH of 10; stirred and heated to 60°C, and 80 mmol of metal ions of Pr 0.84 La 0.01 Fe 0.12 Co 0.04 The chloride solution was dripped in 30 minutes, the reaction was kept warm for 3 hours, and precipitated at room temperature; the precipitate was filtered, washed with ultrapure water, and dried at 80°C to obtain a diffusion source-wrapped NdFeB alloy (the diffusion source accounted for 10wt%).
[0044] (3) Under nitrogen protection, the NdFeB alloy fine powder obtained in (1) was added to a magnetic field forming machine with an oxygen content of less than 10 ppm and pressed to 4.8 g / cm at a magnetic induction intensity of 0.3 T. 3 A hexahedral rough blank is formed; then 3wt% of the diffusion source wrapped NdFeB alloy is uniformly sprayed on the two surfaces of the rough blank that are not perpendicular to the magnetization direction and the pressing direction, and the rough blank is pressed to 4.4g / cm in the same orientation under the magnetic induction intensity of 2.0T in the magnetic field forming machine. 3 , and finally isostatic pressing is performed to obtain the green embryo.
[0045] (4) The green embryo is subjected to microwave magnetic field vacuum sintering: vacuum degree 0.5 Pa, temperature 950°C, time 20 min, microwave power 2.0 kW, magnetic field intensity 3.0 T, and after completion, it is cooled by argon air and then taken out of the furnace to cool to room temperature; tempered in a 850°C vacuum sintering furnace for 8 h, cooled by argon air and then taken out of the furnace to cool to room temperature; tempered in a 500°C vacuum sintering furnace for 2 h, cooled by argon air and then taken out of the furnace to cool to room temperature, to obtain a heavy rare earth-free high-performance NdFeB magnet.
[0046] Example 2
[0047] The only difference between the steps of preparing NdFeB magnets in this embodiment and in Embodiment 1 is that in step (2), 35 mmol of hydrazine hydrate and 40 mmol of metal ions are used, i.e., the diffusion source accounts for 5 wt%; meanwhile, in step (3), the diffusion source wrapping the NdFeB alloy accounts for 8 wt%.
[0048] Example 3
[0049] The only difference between the steps of preparing NdFeB magnets in this embodiment and in Embodiment 1 is that in step (2), the amount of hydrazine hydrate used is 130 mmol, and the amount of metal ions used is 160 mmol, that is, the diffusion source accounts for 18 wt%; and at the same time, in step (3), the diffusion source wrapping the NdFeB alloy accounts for 0.5 wt%.
[0050] Example 4
[0051] The only difference between the steps of preparing NdFeB magnets in this embodiment and in embodiment 1 is that the composition of the NdFeB alloy is Nd 29 Ce2Fe 67.16 Co 0.1 Cu 0.3 Ga 0.5 B 0.94 .
[0052] Example 5
[0053] The only difference between the steps of preparing NdFeB magnets in this embodiment and in embodiment 1 is that the cation composition of the metal chloride salt solution is Pr 0.76 La 0.02 Fe 0.10 Co 0.12 .
[0054] Comparative Example 1
[0055] The only difference between the steps of preparing NdFeB magnets in this comparative example and Example 1 is that microwave vacuum sintering is not used, but sintering is carried out at 1060° C. for 6 hours in an ordinary vacuum sintering furnace; the subsequent tempering remains unchanged.
[0056] Comparative Example 2
[0057] The only difference between the steps of preparing NdFeB magnets in this comparative example and Example 1 is that step (2) of preparing diffusion source-wrapped NdFeB alloy is not performed, and in step (3) 5 wt % of Pr 0.84 La 0.01 Fe 0.12 Co 0.04 alloy.
[0058] Comparative Example 3
[0059] The only difference between the steps of preparing NdFeB magnets in this comparative example and Example 1 is that in step (2), the diffusion source-wrapped NdFeB alloy is not prepared, but 100 g of the obtained NdFeB alloy fine powder is directly mixed with 10 g of Pr 0.84 La 0.01 Fe 0.12 Co 0.04 The alloy powder is mixed for the next step; the alloy powder is obtained by the same hydrogen explosion and air flow milling process.
[0060] The magnetic properties of the NdFeB magnets obtained in the above embodiments and comparative examples are tested, including their remanence and intrinsic coercive force. The results are shown in Table 1.
[0061] Table 1 Comparison of magnetic properties of NdFeB magnets
[0062] Group Remanence(kGs) Intrinsic coercivity (kOe) Example 1 14.1 16.4 Example 2 13.8 17.1 Example 3 14.4 16.2 Example 4 12.5 14.5 Example 5 13.6 15.7 Comparative Example 1 8.7 11.4 Comparative Example 2 13.1 16.0 Comparative Example 3 10.4 13.5
[0063] In addition, the maximum magnetic energy product and the maximum operating temperature of the NdFeB magnet obtained in Example 1 were tested, which were 50.8 MGOe and 107.4°C, respectively, reaching the N52-H grade standard and having high performance.
[0064] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and the obvious changes or modifications derived therefrom should still be considered as the protection scope of the present invention.
Claims
1. A method for preparing a heavy rare earth-free high-performance neodymium iron boron magnet, characterized in that: The steps include: S1: NdFeB alloy is subjected to hydrogen explosion and air flow grinding in sequence to obtain NdFeB alloy fine powder; S2: Under the protection of inert gas, a portion of NdFeB alloy fine powder is dispersed in alkaline oxygen-free water containing a reducing agent, and a diffusion source metal salt solution is gradually added. After the reaction, the mixture is washed and dried to obtain a diffusion source-wrapped NdFeB alloy; S3: Under the protection of inert gas, the remaining NdFeB alloy fine powder is subjected to primary orientation molding to obtain a rough embryo, the diffusion source-wrapped NdFeB alloy is uniformly coated on the surface of the rough embryo, and after drying, secondary orientation molding is carried out along the same magnetizing direction and pressing direction as the primary one, and isostatic pressing is performed to obtain a green embryo; S4: The green embryo is subjected to microwave vacuum sintering and tempering treatment to obtain a heavy rare earth-free high-performance NdFeB magnet; in, The mass fraction of the diffusion source alloy in the diffusion source-wrapped NdFeB alloy is 5 to 20%; The mass fraction of the diffusion source-wrapped NdFeB alloy in the green embryo is 0.5-10%; The diffusion source alloy composition is Pr 100-a-b-c La a Fe b Co c , wherein a, b, and c represent atomic percentages, and 0≤a≤3, 5≤b≤20, and 0≤c≤15.
2. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The reducing agent is hydrazine hydrate, and the alkaline oxygen-free water is an ammonia / ammonium salt buffer solution with a pH between 9 and 11 and dissolved oxygen less than 20 ppb.
3. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The diffusion source metal salt is Pr 3+ ,La 3+ , Fe 2+ and / or Co 2+ The salt is a composition configured according to the molar ratio of the diffusion source alloy composition.
4. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The magnetic induction intensity of the primary orientation molding is 0.2-0.5T, and the magnetic induction intensity of the secondary orientation molding is 1.5-2.0T.
5. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: In the microwave vacuum sintering, the sintering temperature is 900-950° C., the sintering time is 20-40 minutes, and the microwave power is 2.0-4.0 kW.
6. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The tempering is divided into primary tempering and secondary tempering. The primary tempering is heating from room temperature to 800-900°C and maintaining the temperature for 4-12 hours, and the secondary tempering is heating from room temperature to 450-550°C and maintaining the temperature for 2-6 hours.
7. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The uniform coating on the rough surface at least includes uniformly coating the diffusion source on all surfaces of the NdFeB alloy that are not perpendicular to the magnetizing direction and the pressing direction.
8. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The NdFeB alloy has the following composition: R x Fe 100-x-y-z M y B z , Wherein R is selected from at least one of Rd, La and Ce, and at least includes Rd; M is selected from at least one of Cu, Al, Co, Ga and Zr; x, y, z represent atomic percentages, and 28≤x≤32, 0.5≤y≤1.5, 0.94≤z≤1.
00.
9. The method for preparing a heavy rare earth-free high-performance NdFeB magnet according to claim 1, characterized in that: The particle size of the NdFeB alloy fine powder is 1-4 μm.
10. A heavy rare earth-free high-performance NdFeB magnet prepared by the preparation method according to any one of claims 1 to 9.