Sintered neodymium iron boron diffusion magnet and modification method thereof

Abstract

The invention provides a sintered neodymium iron boron diffusion magnet and a modification method thereof. The modification method comprises the steps that S1, the surface of a sintered neodymium-iron-boron magnet is covered with rare earth alloy powder, and a composite sintered neodymium-iron-boron magnet with the surface coated with a rare earth alloy powder layer is obtained; s2, sequentially performing diffusion heat treatment on the composite sintered neodymium-iron-boron magnet to obtain a sintered neodymium-iron-boron diffusion magnet; wherein the composition of the rare earth alloy powder is Re alpha M beta, Re at least comprises a light rare earth element and a heavy rare earth element, the light rare earth element is selected from any one or more of Ce, Pr, Nd and Gd, and the heavy rare earth element is Dy and / or Tb; m is selected from any one or more of Zn, Ga, Ge, Al, Co, Cu, Ag, Sn and Pd and unavoidable impurities. The sintered neodymium-iron-boron magnet obtained through the modification method has excellent magnetic performance and low cost, and has higher popularization value.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing processes of sintered NdFeB materials, and more particularly, to a sintered NdFeB diffusion magnet and a modification method thereof. Background Art

[0002] Sintered NdFeB materials are a kind of magnetic functional materials that emerged in the 1980s of the last century and are still the permanent magnetic materials with the strongest magnetic properties to date. However, since the manufacture of the materials is inseparable from expensive rare earth raw materials, the price is an important factor restricting the further development of this kind of magnetic functional materials. Especially in recent years, with the strong development of permanent magnet motors, wind turbines, and electric vehicles, higher requirements for the magnetic energy product and higher operating temperature of magnetic materials have been put forward, which are all promoting the innovation of the manufacturing process technology of rare earth permanent magnet materials to achieve the development of magnets with higher magnetic properties while reducing the manufacturing cost of the materials.

[0003] The manufacturing process technology of sintered NdFeB magnets by grain boundary diffusion has been rapidly industrialized under this background, achieving a leap in the performance-price ratio of sintered NdFeB magnets. This technology utilizes the principle of molecular thermal motion. By high temperature, the heavy rare earth compounds or heavy rare earth molecules wrapped on the surface of the sintered NdFeB magnet are given the energy of thermal motion, so that the heavy rare earth molecules enter the Nd-rich phase of the sintered NdFeB magnet, realizing stronger grain boundary magnetic hardening, thus rapidly enhancing the intrinsic coercivity of the magnet and obtaining a sintered NdFeB magnet with a higher performance-price ratio. Therefore, the preparation of the "rare earth alloy or compound used to wrap on the surface of the sintered NdFeB magnet", that is, the diffusion alloy material, has become a key to cost control in the batch production process of this technology.

[0004] As can be seen from the above, how to prepare a diffusion alloy material with relatively low cost and good diffusion effect is one of the keys to further obtaining a sintered NdFeB magnetic steel with a higher performance-price ratio and is also one of the keys to better expanding the application fields of sintered NdFeB magnets. Summary of the Invention

[0005] The main object of the present invention is to provide a sintered NdFeB diffusion magnet and a modification method thereof to solve the problems in the prior art that the preparation method of sintered NdFeB magnets has high preparation cost and limited improvement in the intrinsic coercivity of the prepared sintered NdFeB magnets.

[0006] To achieve the above object, according to one aspect of the present invention, a method for modifying a sintered neodymium-iron-boron diffusion magnet is provided. The modification method includes: Step S1, covering the surface of the sintered neodymium-iron-boron magnet with rare-earth alloy powder to obtain a composite sintered neodymium-iron-boron magnet with a rare-earth alloy powder layer coated on the surface; Step S2, successively performing a diffusion heat treatment step on the composite sintered neodymium-iron-boron magnet to obtain a sintered neodymium-iron-boron diffusion magnet; wherein, the composition of the rare-earth alloy powder is Re α M β , α represents the mass percentage content of Re in Re α M β , β represents the mass percentage content of M in Re α M β , 65 ≤ α ≤ 85, 15 ≤ β ≤ 35; Re includes at least one light rare-earth element and one heavy rare-earth element, and the mass percentage content of the light rare-earth element is 6-25% of the total mass of the rare-earth alloy powder. The light rare-earth element is selected from any one or more of Ce, Pr, Nd, and Gd, and the heavy rare-earth element is Dy and / or Tb; M is selected from any one or more of Zn, Ga, Ge, Al, Co, Cu, Ag, Sn, and Pd and inevitable impurities.

[0007] Further, the above light rare-earth element includes at least Pr, and the mass percentage content of Pr is 40%-100% of the total mass of the light rare-earth elements.

[0008] Further, the above light rare-earth elements include Pr and Nd, and the mass ratio of Pr to Nd is 25:75 to 20:80.

[0009] Further, in the above Step S1, the mass of the rare-earth alloy powder is 0.5-1.2% of the total mass of the sintered neodymium-iron-boron diffusion magnet.

[0010] Further, the average particle size of the above rare-earth alloy powder is 2.5-5 μm.

[0011] Further, the above diffusion heat treatment step includes a sintering step and a tempering step performed successively. Preferably, the sintering temperature in the sintering step is 850-920 °C, and the preferred sintering time is 22-40 h; and / or the tempering temperature in the tempering step is 460-680 °C, and the preferred tempering time is 5-6 h.

[0012] Further, any one or more of a screen printing process, a spraying process, a vapor deposition process, a vacuum coating process, and a chemical coating process are used to cover the surface of the sintered neodymium-iron-boron diffusion magnet with the rare-earth alloy powder.

[0013] Further, the above modification method further includes the preparation process of rare earth alloy powder, and the preparation process includes: Step S3, sequentially performing a batching step, a melting step, and a rapid solidification treatment step according to the element composition of the rare earth alloy powder to obtain rapidly solidified flakes; Step S4, crushing the rapidly solidified flakes to obtain rare earth alloy powder; preferably, the crushing includes a hydrogen crushing step and a jet mill step performed in sequence.

[0014] According to another aspect of the present invention, a sintered Nd-Fe-B diffusion magnet is provided, and the sintered Nd-Fe-B diffusion magnet is prepared by the above modification method.

[0015] Further, the coercivity of the above sintered Nd-Fe-B diffusion magnet is increased by 8-10 kOe.

[0016] Applying the technical solution of the present invention, the present invention prepares a rare earth alloy diffusion material for the grain boundary diffusion process of sintered Nd-Fe-B magnets. Compared with the existing general diffusion materials, since a part of light rare earth elements with relatively low price but relatively high reaction activity replace heavy rare earth elements, the cost is greatly reduced. At the same time, because the activity of light rare earth elements is higher than that of heavy rare earth elements, the light rare earth elements in the rare earth alloy powder react with oxygen preferentially, and the obtained light rare earth element oxides have a certain anti-oxidation protection effect on heavy rare earth elements, thereby reducing the loss of heavy rare earth elements during the high-temperature diffusion process, and further ensuring the full utilization of heavy rare earth elements. However, if the content of light rare earth elements is too high, it is easy to cause a large number of light rare earth elements to undergo oxidation reactions. On the one hand, a large amount of heat is released, activating the reaction of heavy rare earth elements with oxygen and resulting in an increase in the loss of heavy rare earth elements. On the other hand, the oxidation products generated by the oxidation reaction of light rare earth elements extend the diffusion path of heavy rare earth elements, thus hindering the diffusion of heavy rare earth elements into the grain boundaries of sintered Nd-Fe-B magnets through the above two aspects. Therefore, it is necessary to control the mass percentage content of light rare earth elements to be 6-25% of the total mass of the rare earth alloy powder. The addition of M-type metal elements mainly reduces the softening point temperature of the diffusion alloy material after forming an alloy, which is more conducive to the main heavy rare earth elements entering the sintered Nd-Fe-B magnetic steel more effectively in the molten state during the high-temperature diffusion process. The sintered Nd-Fe-B magnet obtained by the above modification method can balance excellent magnetic properties and low cost, and has more promotion value. Detailed Embodiments

[0017] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] As analyzed in the background art, there are problems in the preparation method of sintered Nd-Fe-B magnets in the prior art, such as high preparation cost and limited improvement in the intrinsic coercivity of the prepared sintered Nd-Fe-B magnets. To solve this problem, the present invention provides a sintered Nd-Fe-B diffusion magnet and its modification method.

[0019] In a typical embodiment of the present application, a modification method of a sintered Nd-Fe-B diffusion magnet is provided. The modification method includes: Step S1, covering the surface of the sintered Nd-Fe-B magnet with rare earth alloy powder to obtain a composite sintered Nd-Fe-B magnet with a rare earth alloy powder layer coated on the surface; Step S2, successively performing diffusion heat treatment steps on the composite sintered Nd-Fe-B magnet to obtain a sintered Nd-Fe-B diffusion magnet; wherein, the composition of the rare earth alloy powder is Re α M β , α represents the mass percentage content of Re in Re α M β , β represents the mass percentage content of M in Re α M β , 65 ≤ α ≤ 85, 15 ≤ β ≤ 35; Re includes at least one light rare earth element and one heavy rare earth element, and the mass percentage content of the light rare earth element is 6-25% of the total mass of the rare earth alloy powder. The light rare earth element is selected from any one or more of Ce, Pr, Nd, and Gd, and the heavy rare earth element is Dy and / or Tb; M is selected from any one or more of Zn, Ga, Ge, Al, Co, Cu, Ag, Sn, and Pd and inevitable impurities.

[0020] The present invention prepares a rare earth alloy diffusion material for the grain boundary diffusion process of sintered NdFeB magnets. Compared with the existing general diffusion materials, since a part of light rare earth elements with relatively low price but relatively high reaction activity replaces heavy rare earth elements, the cost is greatly reduced. At the same time, due to the higher activity of light rare earth elements than that of heavy rare earth elements, the light rare earth elements in the rare earth alloy powder preferentially react with oxygen, and the obtained light rare earth element oxides have a certain anti-oxidation protection effect on heavy rare earth elements, thereby reducing the loss of heavy rare earth elements during the high-temperature diffusion process, and further ensuring the full utilization of heavy rare earth elements. However, if the content of light rare earth elements is too high, it is easy to cause a large number of light rare earth elements to undergo oxidation reactions. On the one hand, a large amount of heat is released, activating the reaction of heavy rare earth elements with oxygen and resulting in an increase in the loss of heavy rare earth elements. On the other hand, the oxidation products generated by the oxidation reaction of light rare earth elements extend the diffusion path of heavy rare earth elements, thereby hindering the diffusion of heavy rare earth elements into the grain boundaries of sintered NdFeB magnets through the above two aspects. Therefore, it is necessary to control the mass percentage of light rare earth elements to be 6-25% of the total mass of the rare earth alloy powder. The addition of M-type metal elements mainly reduces the softening point temperature of the diffusion alloy material after forming an alloy, which is more conducive to the high-temperature diffusion process, enabling the main heavy rare earth elements to enter the sintered NdFeB magnetic steel more effectively in the molten state. The sintered NdFeB magnet obtained by the above modification method can balance excellent magnetic properties and low cost, and has more promotion value.

[0021] In some embodiments of the present application, it is preferred that the above light rare earth elements at least include Pr. Based on Pr replacing a part of Nd in the sintered NdFeB magnet during the thermal diffusion process, a Pr-Fe-B phase with a magnetocrystalline anisotropy constant higher than that of the Nd-Fe-B phase is formed, which is more conducive to the improvement of the intrinsic coercivity of the material. And the mass percentage of Pr is 40-100% of the total mass of the light rare earth elements, which is more helpful to exert the effect of the light rare earth elements, and further helps the prepared sintered NdFeB diffusion magnet to balance excellent magnetic properties and low cost. 2 Fe 14 B phase of Pr 2 Fe 14 B phase, which is more conducive to the improvement of the intrinsic coercivity of the material. And the mass percentage of Pr is 40-100% of the total mass of the light rare earth elements, which is more helpful to exert the effect of the light rare earth elements, and further helps the prepared sintered NdFeB diffusion magnet to balance excellent magnetic properties and low cost.

[0022] In some embodiments of the present application, it is preferred that the above light rare earth elements include Pr and Nd, and the mass ratio of Pr to Nd is controlled to be 25:75-20:80, which is more helpful to exert the synergistic effect of Pr and Nd, so as to obtain a sintered NdFeB diffusion magnet with better magnetic properties.

[0023] In an embodiment of the present application, in the above step S1, preferably, the mass of the rare earth alloy powder is 0.5-1.2% of the total mass of the sintered neodymium iron boron diffusion magnet, which helps the heavy rare earth elements to better enter the grain boundaries of the sintered neodymium iron boron magnet, enabling the main phase grains of the sintered neodymium iron boron to have a hard magnetic layer rich in heavy rare earths, effectively increasing the nucleation field of the reverse magnetization domain, thereby significantly increasing the coercivity; at the same time, effectively repairing the integrity and continuity of the grain boundary phase of the material, effectively isolating the magnetic coupling effect between adjacent main phases, and further enhancing the coercivity of the sintered neodymium iron boron magnet material.

[0024] In some embodiments of the present application, in the above step S1, the average particle size of the rare earth alloy powder is controlled to be 2.5-5 μm, which is more conducive to uniformly dispersing the rare earth alloy powder on the surface of the sintered neodymium iron boron diffusion magnet.

[0025] In an embodiment of the present application, the above diffusion heat treatment step includes a sintering step and a tempering step carried out in sequence. Preferably, the sintering temperature in the sintering step is 850-920 °C, and the preferred sintering time is 22-40 h; and / or the tempering temperature in the tempering step is 460-680 °C, and the preferred tempering time is 5-6 h.

[0026] Preferably, the sintering temperature and sintering time in the above sintering step are within the above ranges, which helps the heavy rare earth alloy powder to better enter the grain boundaries of the sintered neodymium iron boron magnet while minimizing the sintering loss of the heavy rare earth alloy powder in the sintering step. Preferably, the temperature and time of the above tempering treatment are within the above ranges, which is more conducive to making the heavy rare earth alloy powder more evenly distributed at the grain boundary phase positions in each region of the sintered neodymium iron boron magnet.

[0027] In some embodiments of the present application, any one or more of the screen printing process, spraying process, chemical vapor deposition process, vacuum coating process, and chemical plating process are used to cover the surface of the sintered neodymium iron boron diffusion magnet with the rare earth alloy powder. These processes are conventional dispersion methods for rare earth alloy powder on the surface of magnet materials in the art and will not be elaborated here.

[0028] In an embodiment of the present application, the above modification method further includes the preparation process of the rare earth alloy powder. The preparation process includes: step S3, sequentially carrying out a batching step, a melting step, and a rapid solidification treatment step according to the element composition of the rare earth alloy powder to obtain a rapidly solidified flake; step S4, crushing the rapidly solidified flake to obtain the rare earth alloy powder; preferably, the crushing includes coarse crushing and fine crushing carried out in sequence. The coarse crushing is mechanical crushing and / or hydrogen crushing, and the fine crushing is jet milling crushing and / or ball milling crushing.

[0029] Manufacture rare earth alloy powder according to the traditional process for preparing sintered Nd-Fe-B alloy. Those skilled in the art can carry out the batching step, melting step, and rapid solidification treatment step according to the conventional conditions in this field, which will not be elaborated here. Preferably, the above-mentioned coarse crushing and fine crushing carried out in sequence contribute to obtaining rare earth alloy powder with a suitable particle size.

[0030] In another typical embodiment of the present application, a sintered Nd-Fe-B diffusion magnet is provided, and the sintered Nd-Fe-B diffusion magnet is prepared by the above-mentioned modification method.

[0031] The sintered Nd-Fe-B diffusion magnet obtained by the above modification method has relatively lower cost and better magnetic properties. Therefore, the above modification method has more promotion value.

[0032] In an embodiment of the present application, the coercivity of the above-mentioned sintered Nd-Fe-B diffusion magnet is increased by 8-10 kOe.

[0033] The coercivity of the sintered Nd-Fe-B diffusion magnet obtained by the above modification method of the present application is increased by 8-10 kOe, thereby ensuring the excellent magnetic properties of the sintered Nd-Fe-B diffusion magnet on the basis of reducing the preparation cost.

[0034] Hereinafter, specific embodiments will be combined to illustrate the beneficial effects of the present application.

[0035] Example 1

[0036] 1. Prepare alloy sheet A of rare earth diffusion alloy with the composition of Nd 4.5 Pr 1.5 Dy 79 Co 5 Cu 6 Al 4 (wt%) by the rapid solidification sheet process;

[0037] 2. After "coarse crushing" A by mechanical crushing, then carry out "fine crushing" on the rare earth diffusion alloy material by the method of jet milling to obtain rare earth diffusion alloy powder A with an average particle size of 2.5 μm;

[0038] 3. Select screen printing technology to attach a layer of rare earth diffusion alloy powder A on the surface of a sintered Nd-Fe-B Φ10×5 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, and the weight gain ratio is 1.0% of the weight of the Φ10×5 (mm) magnetic steel sample block to obtain sintered Nd-Fe-B magnetic steel sample A1;

[0039] 4. Put the sample into a vacuum furnace, carry out vacuum constant temperature diffusion at 920 °C for 22 hours, carry out tempering aging at 510 °C for 6 hours, and cool to obtain diffusion magnet A2 prepared by the grain boundary diffusion process.

[0040] Example 2

[0041] 1. Prepare alloy sheet B made of rare earth diffusion alloy with components Nd 18.75 Pr 6.25 Dy 60 Co 5 Cu 6 Al 4 (wt%) by the rapid solidification flake process;

[0042] 2. After "coarse crushing" B by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain rare earth diffusion alloy powder B with an average particle size of 5.0 μm;

[0043] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder B on the surface of a sintered NdFeB Φ10×5 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium content in the powder is 1.0% of the weight of the Φ10×5 (mm) magnetic steel sample block, and obtain sintered NdFeB magnetic steel sample B1;

[0044] 4. Put the sample into a vacuum furnace, carry out vacuum isothermal diffusion at 920 °C for 22 hours, carry out tempering aging at 510 °C for 6 hours, and obtain diffusion magnet B2 prepared by the grain boundary diffusion process after cooling.

[0045] Example 3

[0046] 1. Prepare alloy sheet C made of rare earth diffusion alloy with components Nd 4.5 Pr 1.5 Dy 59 Co 10 Cu 20 Ga 5 (wt%) by the rapid solidification flake process;

[0047] 2. After "coarse crushing" C by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain rare earth diffusion alloy powder C with an average particle size of 3.0 μm;

[0048] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder C on the surface of a sintered NdFeB Φ10×8 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium content in the powder is 1.0% of the weight of the Φ10×8 (mm) magnetic steel sample block, and obtain sintered NdFeB magnetic steel sample C1;

[0049] 4. Place the sample in a vacuum furnace, conduct vacuum isothermal diffusion at 900 °C for 38 hours, conduct temper aging at 510 °C for 6 hours, and obtain the diffusion magnet C2 prepared by the grain boundary diffusion process after cooling.

[0050] Example 4

[0051] 1. For the rare earth diffusion alloy with the composition of Nd 18.75 Pr 6.25 Dy 40 Co 10 Cu 15 Zn 5 Ga 5 (wt%), use the rapid solidification flake process to obtain the alloy sheet D;

[0052] 2. After "coarse crushing" D by hydrogen crushing, then use the ball milling method to "fine crush" the rare earth diffusion alloy material to obtain the rare earth diffusion alloy powder D with an average particle size of 3.0 μm;

[0053] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder D on the surface of the sintered NdFeB Φ10×6 (mm) magnet sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium content in the powder is 1.0% of the weight of the Φ10×6 (mm) magnet sample block, and obtain the sintered NdFeB magnet sample D1;

[0054] 4. Place the sample in a vacuum furnace, conduct vacuum isothermal diffusion at 920 °C for 28 hours, conduct temper aging at 510 °C for 6 hours, and obtain the diffusion magnet D2 prepared by the grain boundary diffusion process after cooling.

[0055] Example 5

[0056] 1. For the rare earth diffusion alloy with the composition of Pr 15 Dy 60 Co 5 Cu 10 Zn 5 Pd 5 (wt%), use the rapid solidification flake process to obtain the alloy sheet E;

[0057] 2. After "coarse crushing" E by hydrogen crushing, then use the ball milling method to "fine crush" the rare earth diffusion alloy material to obtain the rare earth diffusion alloy powder E with an average particle size of 3.5 μm;

[0058] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder E on the surface of a sintered NdFeB Φ10×6 (mm) magnet sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, achieving a weight gain ratio of dysprosium content in the powder of 1.0% of the weight of the Φ10×6 (mm) magnet sample block, and obtaining a sintered NdFeB magnet sample E1;

[0059] 4. Place the sample in a vacuum furnace, conduct vacuum isothermal diffusion at 920 °C for 26 hours, conduct tempering aging at 510 °C for 6 hours, and obtain a diffusion magnet E2 prepared by the grain boundary diffusion process after cooling.

[0060] Example 6

[0061] 1. Prepare an alloy sheet F from a rare earth diffusion alloy with the composition of Nd 20 Dy 55 Co 10 Cu 10 Al 5 (wt%) by the rapid solidification sheet process;

[0062] 2. After "coarse crushing" F by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain a rare earth diffusion alloy powder F with an average particle size of 4.0 μm;

[0063] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder F on the surface of a sintered NdFeB Φ10×6 (mm) magnet sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, achieving a weight gain ratio of dysprosium content in the powder of 1.0% of the weight of the Φ10×6 (mm) magnet sample block, and obtaining a sintered NdFeB magnet sample F1;

[0064] 4. Place the sample in a vacuum furnace, conduct vacuum isothermal diffusion at 920 °C for 26 hours, conduct tempering aging at 510 °C for 4.5 hours, and obtain a diffusion magnet F2 prepared by the grain boundary diffusion process after cooling.

[0065] Example 7

[0066] 1. Prepare an alloy sheet G from a rare earth diffusion alloy with the composition of Ce 10 Dy 55 Co 15 Cu 15 Pd 5 (wt%) by the rapid solidification sheet process;

[0067] 2. After "coarse crushing" G by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain a rare earth diffusion alloy powder G with an average particle size of 4.5 μm;

[0068] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder G on the surface of a sintered neodymium iron boron Φ10×6 (mm) magnet sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium in the powder is 1.2% of the weight of the Φ10×6 (mm) magnet sample block, and obtain a sintered neodymium iron boron magnet sample G1;

[0069] 4. Put this sample into a vacuum furnace, carry out vacuum isothermal diffusion at 920 °C for 26 hours, carry out tempering aging at 510 °C for 5.5 hours, and obtain a diffusion magnet G2 prepared by the grain boundary diffusion process after cooling.

[0070] Example 8

[0071] 1. Use the rapid solidification sheet process to obtain an alloy sheet H from a rare earth diffusion alloy with components of Gd 20 Tb 50 Co 15 Al 10 Pd 5 (wt%);

[0072] 2. After "coarse crushing" H by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain a rare earth diffusion alloy powder H with an average particle size of 4.2 μm;

[0073] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder H on the surface of a sintered neodymium iron boron Φ10×6 (mm) magnet sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium in the powder is 1.0% of the weight of the Φ10×6 (mm) magnet sample block, and obtain a sintered neodymium iron boron magnet sample H1;

[0074] 4. Put this sample into a vacuum furnace, carry out vacuum isothermal diffusion at 920 °C for 26 hours, carry out tempering aging at 510 °C for 5.5 hours, and obtain a diffusion magnet H2 prepared by the grain boundary diffusion process after cooling.

[0075] Example 9

[0076] 1. Use the rapid solidification sheet process to obtain an alloy sheet I from a rare earth diffusion alloy with components of Pr 25 Dy 60 Co 5 Cu 5 Al 5 (wt%);

[0077] 2. After "coarse crushing" I by hydrogen crushing, then "fine crush" the rare earth diffusion alloy material by ball milling to obtain a rare earth diffusion alloy powder I with an average particle size of 4.5 μm;

[0078] 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder I on the surface of a sintered NdFeB Φ10×6 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium in the powder is 0.8% of the weight of the Φ10×6 (mm) magnetic steel sample block, and obtain the sintered NdFeB magnetic steel sample I1;

[0079] 4. Put this sample into a vacuum furnace, carry out vacuum isothermal diffusion at 920 °C for 26 hours, carry out tempering aging at 480 °C for 5.5 hours, and obtain the diffusion magnet I2 prepared by the grain boundary diffusion process after cooling.

[0080] Example 10

[0081] The difference from Example 9 is that: 1. The rare earth diffusion alloy with the composition of Pr 10 Ce 15 Dy 60 Co 5 Cu 5 Al 5 (wt%) is made into an alloy sheet J by the rapid solidification sheet process, and finally the diffusion magnet J2 is obtained.

[0082] Example 11

[0083] The difference from Example 9 is that: 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder I on the surface of a sintered NdFeB Φ10×6 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium in the powder is 1.2% of the weight of the Φ10×6 (mm) magnetic steel sample block, and obtain the sintered NdFeB magnetic steel sample K1, and finally obtain the diffusion magnet K2.

[0084] Example 12

[0085] The difference from Example 9 is that: 3. Select the spraying technology to attach a layer of rare earth diffusion alloy powder I on the surface of a sintered NdFeB Φ10×6 (mm) magnetic steel sample block with magnetic properties of Br = 14.0 kGs and Hcj = 12.5 kOe, so that the weight gain ratio of dysprosium in the powder is 0.3% of the weight of the Φ10×6 (mm) magnetic steel sample block, and obtain the sintered NdFeB magnetic steel sample L1, and finally obtain the diffusion magnet L2.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that the rare earth diffusion alloy with the composition of Dy 85 Co 5 Cu 6 Al 4 (wt%) is used, and finally the diffusion magnet is obtained.

[0088] Comparative Example 2

[0089] The difference from Example 2 is that a rare earth diffusion alloy with the composition of Dy 85 Co 5 Cu 6 Al 4 (wt%) is used, and finally a diffusion magnet is obtained.

[0090] Comparative Example 3

[0091] The difference from Example 3 is that a rare earth diffusion alloy with the composition of Dy 65 Co 10 Cu 20 Ga 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0092] Comparative Example 4

[0093] The difference from Example 4 is that a rare earth diffusion alloy with the composition of Dy 65 Co 10 Cu 15 Zn 5 Ga 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0094] Comparative Example 5

[0095] The difference from Example 5 is that a rare earth diffusion alloy with the composition of Dy 60 Co 10 Co 5 Cu 10 Zn 5 Pd 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0096] Comparative Example 6

[0097] The difference from Example 6 is that a rare earth diffusion alloy with the composition of Dy 85 Co 10 Cu 10 Al 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0098] Comparative Example 7

[0099] The difference from Example 7 is that a rare earth diffusion alloy with the composition of Dy 65 Co 15 Cu 15 Pd 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0100] Comparative Example 8

[0101] The difference from Example 8 is that a rare earth diffusion alloy with a composition of Tb 70 Co 15 Al 10 Pd 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0102] Comparative Example 9

[0103] The difference from Example 9 is that a rare earth diffusion alloy with a composition of Dy 85 Co 5 Cu 5 Al 5 (wt%) is used, and finally a diffusion magnet is obtained.

[0104] The numerical values of Br (kGs) and Hcj (kOe) of the magnets obtained from the above examples and comparative examples are listed in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] It can be seen from the comparison between the above examples and comparative examples that the performance of the modified sintered Nd-Fe-B magnet obtained by partially adding light rare earth alloy powder in this application is comparable to that of the modified sintered Nd-Fe-B magnet obtained by the scheme of completely using heavy rare earth alloy powder in the comparative example. However, the scheme of this application greatly reduces the cost.

[0109] It can be seen from the above description that the above embodiments of the present invention achieve the following technical effects:

[0110] The present invention prepares a rare earth alloy diffusion material for the grain boundary diffusion process of sintered Nd-Fe-B magnets. Compared with the existing general diffusion materials, since a part of the light rare earth elements with relatively low price but relatively high reaction activity replace the heavy rare earth elements, the cost is greatly reduced. At the same time, due to the higher activity of the light rare earth elements than that of the heavy rare earth elements, the light rare earth elements in the rare earth alloy powder react with oxygen preferentially, and the obtained light rare earth element oxides have a certain anti-oxidation protection effect on the heavy rare earth elements, thus reducing the loss of heavy rare earth elements during the high-temperature diffusion process, and further ensuring the full utilization of heavy rare earth elements. However, if the content of the light rare earth elements is too high, it is easy to cause a large number of light rare earth elements to undergo oxidation reactions. On the one hand, a large amount of heat is released, activating the reaction of heavy rare earth elements with oxygen and resulting in an increased loss of heavy rare earth elements. On the other hand, the oxidation products generated by the oxidation reaction of light rare earth elements extend the diffusion path of heavy rare earth elements, thus hindering the diffusion of heavy rare earth elements into the grain boundaries of sintered Nd-Fe-B magnets through the above two aspects. Therefore, it is necessary to control the mass percentage content of the light rare earth elements to be 6-25% of the total mass of the rare earth alloy powder. The addition of M-type metal elements mainly reduces the softening point temperature of the diffusion alloy material after forming an alloy, which is more conducive to the high-temperature diffusion process, enabling the main heavy rare earth elements to enter the sintered Nd-Fe-B magnetic steel more effectively in the molten state. The sintered Nd-Fe-B magnet obtained by the above modification method can balance excellent magnetic properties and low cost, and has more promotion value.

[0111] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for modifying a sintered neodymium iron boron diffusion magnet, characterized in that, the modification method comprises: Step S1, covering rare earth alloy powder on the surface of the sintered neodymium iron boron magnet to obtain a composite sintered neodymium iron boron magnet with a rare earth alloy powder layer coated on the surface; Step S2, performing a diffusion heat treatment step on the composite sintered neodymium iron boron magnet to obtain the sintered neodymium iron boron diffusion magnet; Among them, the composition of the rare earth alloy powder is Re α M β , α represents the mass percentage content of Re in the Re α M β , β represents the mass percentage content of M in the Re α M β , 65 ≤ α ≤ 85, 15 ≤ β ≤ 35; Re includes at least one light rare earth element and one heavy rare earth element, and the mass percentage content of the light rare earth element is 6-25% of the total mass of the rare earth alloy powder. The light rare earth element is selected from any one or more of Ce, Pr, Nd, and Gd, and the heavy rare earth element is Dy and / or Tb; M is selected from any one or more of Zn, Ga, Ge, Al, Co, Cu, Ag, Sn, and Pd and inevitable impurities.

2. The modification method according to claim 1, characterized in that, the light rare earth element includes at least Pr, and the mass percentage content of Pr is 40%-100% of the total mass of the light rare earth elements.

3. The modification method according to claim 1, characterized in that, the light rare earth element includes Pr and Nd, and the mass ratio of Pr to Nd is 25:75-20:

80.

4. The modification method according to any one of claims 1 to 3, characterized in that, in step S1, the mass of the rare earth alloy powder is 0.5-1.2% of the total mass of the sintered neodymium iron boron diffusion magnet.

5. The modification method according to any one of claims 1 to 4, characterized in that, in step S1, the average particle size of the rare earth alloy powder is 2.5-5 μm.

6. The modification method according to any one of claims 1 to 5, characterized in that, the diffusion heat treatment step includes a sintering step and a tempering step carried out in sequence. Preferably, the sintering temperature in the sintering step is 850-920 °C, and the sintering time is preferably 22-40 h; and / or the tempering temperature in the tempering step is 460-680 °C, and the tempering time is preferably 5-6 h.

7. The modification method according to any one of claims 1 to 6, characterized in that, any one or more of a screen printing process, a spraying process, a vapor deposition process, a vacuum coating process, and a chemical coating process are used to cover the rare earth alloy powder on the surface of the sintered neodymium iron boron diffusion magnet.

8. The modification method according to any one of claims 1 to 7, characterized in that, the modification method further includes the preparation process of the rare earth alloy powder, and the preparation process includes: Step S3, sequentially performing a batching step, a melting step, and a rapid solidification treatment step according to the element composition of the rare earth alloy powder to obtain a rapidly solidified and spun sheet; Step S4, crushing the rapidly solidified and spun sheet to obtain the rare earth alloy powder; preferably, the crushing includes a hydrogenation crushing step and a jet mill step carried out in sequence.

9. A sintered neodymium iron boron diffusion magnet, characterized in that, the sintered neodymium iron boron diffusion magnet is prepared by the modification method according to any one of claims 1 to 8.

10. The sintered Nd-Fe-B diffusion magnet according to claim 9, wherein, the coercivity of the sintered Nd-Fe-B diffusion magnet is increased by 8-10 kOe.

Images