A method for manufacturing a heavy rare earth-free high coercivity RTB magnet

Abstract

The present invention discloses a method for manufacturing a heavy rare earth-free high-coercivity R-T-B magnet, which relates to the technical field of magnets. The technical scheme includes raw materials and diffusion materials composed of 27.5-35.0wt% of an R component, 0.8-0.95wt% of a B component, 0-3wt% of an M component and a balance of a T component in percentage by mass; the M component consists of 0-2wt% of M1 and 0-1wt% of M2, and B and M2 satisfy the following formula (1): 0.8>B-M2>0.2 (1); and M1 is at least one of Cu, Al and Ga, and M2 is at least one of Nb, Zr and Ti; wherein the diffusion material is PrX, and X is at least one element; the manufacturing method includes preparing a R-T-B sintered magnet raw material from the raw material, coating the diffusion material on the surface of the magnet raw material, and obtaining the heavy rare earth-free high-coercivity R-T-B magnet after heat treatment and diffusion. The present invention has the effect of obtaining a heavy rare earth-free high-coercivity R-T-B magnet with a coercivity HcJ greater than 23 kOe without adding heavy rare earth.

Description

Technical Field

[0001] The present invention relates to the technical field of magnets, and more particularly to a method for manufacturing a heavy rare earth-free high-coercivity RTB magnet. Background Art

[0002] RTB-based sintered magnets, in which R is at least one rare earth element and necessarily includes Nd; T is Fe or Fe and Co; and B is boron. RTB-based sintered magnets, the highest-performance permanent magnets, are currently used in various motors and home appliances, including voice coil motors (VCMs) for hard disk drives, electric vehicle motors (EVs, HVs, PHVs, etc.), and motors for industrial machinery. RTB-based sintered magnets are composed of a main phase, primarily composed of an R2T14B compound, and a grain boundary phase located at the grain boundaries of this main phase. The R2T14B compound, as the main phase, is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field, and is the foundation of the properties of RTB-based sintered magnets. At high temperatures, the coercivity (HcJ) of RTB-based sintered magnets decreases, leading to irreversible thermal demagnetization. Therefore, RTB-based sintered magnets used in electric vehicle motors are particularly required to have a high coercivity (HcJ).

[0003] In the RTB-based sintered magnets, if a portion of the light rare earth elements RL (such as Nd and Pr) contained in R in the R2T14B compound is replaced by heavy rare earth elements RH (Dy and Tb), the coercive force HcJ is improved. As the replacement amount of RH increases, the coercive force HcJ increases. However, when RL in the R2T14B compound is replaced by RH, although the coercive force HcJ of the RTB-based sintered magnet is improved, the residual magnetic flux density Br is reduced. In addition, heavy rare earth elements RH, such as Dy in particular, have problems such as unstable supply and large price fluctuations due to the fact that the resources are scarce and the production areas are limited. Therefore, in recent years, there has been a demand for high-coercive force RTB magnets that do not use heavy rare earths.

[0004] International patent application publication number WO2013008756A1 discloses an alloy for RTB-based rare earth sintered magnets, a method for preparing the alloy, an RTB-based rare earth ground magnet alloy material, an RTB-based rare earth welding magnet, and an RTBB production method. Compared to commonly used RTB-based alloys, the composition of the sintered magnet is limited to a relatively small, specific range of boron content and contains one or more metal elements (M) selected from Al, Ga, and Cu. As a result, R2T17 phases form at grain boundaries. Due to the increased volume fraction of the transition metal-rich phase (R6T13M) formed by this R2T17 phase at the grain boundaries, the coercivity (HcJ) increases. Therefore, after grain boundary modification, the coercivity (Hcj) of the magnet can reach 19-21 kOe.

[0005] Chinese Patent Publication No. CN107077965B discloses a method for producing RTB-based sintered magnets. The method comprises a sintered magnet raw material containing 27.5-35.0 mass% R (R is at least one rare earth element, including Nd), 0.80-0.99 mass% B, 0-0.8 mass% Ga, 0-2 mass% M (including at least one of Cu, Al, Nb, and Zr), and the remainder T (T is at least one transition metal element, including Fe, with up to 10% of Fe being replaced by Co), and unavoidable impurities. [T] represents the T content (mass%), and [B] represents the B content (mass%), satisfying the relationship [T] / 55.85>14[B] / 10.8. At least a portion of the surface of the sintered magnet raw material is brought into contact with at least a portion of a Pr-Ga alloy, and a first heat treatment is performed at a temperature exceeding 600°C and below 950°C. The second heat treatment is performed at a temperature lower than the first heat treatment temperature and at a temperature between 450° C. and 750° C. Therefore, by adopting the grain boundary diffusion PrGa process, the maximum coercive force Hcj of the magnetic steel can reach 21 kOe.

[0006] Therefore, it is extremely technically difficult to obtain a magnetic steel with a coercive force Hcj greater than 23kOe or even greater than 25kOe by using only light rare earth elements such as Pr, Nd, La, Ce, etc. without using heavy rare earth elements such as Dy, Tb, Gd, Ho, etc., which affects the scope of use and effect of the magnetic steel and needs to be improved. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for manufacturing a heavy rare earth-free high coercivity RTB magnet, which has the effect of significantly improving the coercivity Hcj.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for manufacturing a heavy rare earth-free high-coercivity RTB magnet includes raw materials and a diffusion material composed of 27.5-35.0 wt% of an R component, 0.8-0.95 wt% of a B component, 0-3 wt% of an M component, and a balance of a T component; the M component is composed of 0-2 wt% of M1 and 0-1 wt% of M2, and B and M2 satisfy the following formula (1):

[0010] 0.8>B-M2>0.2 (1);

[0011] M1 is at least one of Cu, Al and Ga, and M2 is at least one of Nb, Zr and Ti; wherein:

[0012] The diffusion material is PrX, where X is at least one element;

[0013] The manufacturing method comprises the following steps: preparing raw materials to obtain RTB-based sintered magnet raw materials, coating diffusion material on the surface of the magnet raw materials, and obtaining heavy rare earth-free high coercivity RTB magnets after heat treatment and diffusion.

[0014] Preferably, the single-side coating amount of the diffusion material is not less than 2% of the mass percentage of the magnet raw material.

[0015] Preferably, the heat treatment includes a first stage heat treatment and a second stage heat treatment, and the temperature of the first stage heat treatment is 600-950°C and the heat treatment time is 1-4h; the temperature of the second stage heat treatment is 440-550°C and the heat treatment time is 2-8h.

[0016] Preferably, the R component includes Pr and Nd or Pr, Nd and at least one rare earth element.

[0017] Preferably, the T component is Fe or Fe and Co.

[0018] Preferably, the magnet raw material is prepared by a thin strip continuous casting method, and the R component, B component, M component and T component are crushed to 1-10 μm in a jet mill, and then sintered at a temperature of 900-1100° C.

[0019] Preferably, the PrX is PrHx, Pr2O3, Pr-Al or Pr-Cu; wherein the mass percentage of Al in Pr-Al is 40%; the mass percentage of Cu in Pr-Cu is 40%.

[0020] Preferably, the coercive force HcJ of the heavy rare earth-free high-coercive force RTB magnet is greater than 23 kOe.

[0021] It can be seen from the above scheme that the present application provides a method for manufacturing a heavy rare earth-free high-coercive force RTB magnet, and the method for manufacturing a heavy rare earth-free high-coercive force RTB magnet has the following beneficial effects: by using RTB raw materials based on the 0.8>B-M2>0.2 formula and more than 2wt% of PrX diffusion material to achieve a heavy rare earth-free high-coercive force RTB magnet after heat treatment, the coercive force HcJ of the obtained heavy rare earth-free high-coercive force RTB magnet is greater than 23kOe. DETAILED DESCRIPTION

[0022] To make the technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the embodiments. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] The following is a detailed description of a method for manufacturing a heavy rare earth-free high coercivity RTB magnet of the present application.

[0024] A method for manufacturing a heavy rare earth-free, high-coercivity RTB magnet includes raw materials and a diffusion material composed of 27.5-35.0 wt% of an R component, 0.8-0.95 wt% of a B component, 0-3 wt% of an M component, and the balance of a T component. In an embodiment of the present application, the M component is composed of 0-2 wt% of M1 and 0-1 wt% of M2. M1 is at least one of Cu, Al, and Ga, and M2 is at least one of Nb, Zr, and Ti. The R component includes Pr and Nd, or Pr, Nd, and at least one rare earth element. The T component is Fe, or Fe and Co.

[0025] It should be mentioned that B and M2 in the embodiment of the present application satisfy the following formula (1):

[0026] 0.8>B-M2>0.2 (1);

[0027] Meanwhile, the diffusion material is PrX, and X is at least one element.

[0028] The method for manufacturing the heavy rare earth-free high coercivity RTB magnet comprises preparing raw materials to obtain RTB-based sintered magnet raw materials, coating diffusion material on the surface of the magnet raw materials, and obtaining the heavy rare earth-free high coercivity RTB magnet after heat treatment and diffusion.

[0029] To effectively increase the coercivity (HcJ), the diffusion material coating on a single surface in the embodiments of the present application is no less than 2% by mass of the magnet raw material. The heat treatment includes a first-stage heat treatment at a temperature of 600-950°C for 1-4 hours and a second-stage heat treatment at a temperature of 440-550°C for 2-8 hours.

[0030] The raw materials for the magnets are prepared by a thin strip continuous casting method, and the R, B, M, and T components are ground to 1-10 μm in a jet mill and then sintered at a temperature of 900-1100°C. When the volume center value = D50, as measured by the airflow dispersion laser diffraction method, of the crushed particle size of each component is less than 1 μm, the manufacturing difficulty will be significantly increased, resulting in a significant reduction in production efficiency. When the crushed particle size of each component is greater than 10 μm, the crystal grain size of the heavy rare earth-free high coercivity RTB magnet will be too large, resulting in a reduction in the coercivity HcJ and making it difficult to effectively improve it.

[0031] According to tests, the coercive force HcJ of the heavy rare earth-free high-coercive force RTB magnet in the embodiment of the present application is greater than 23 kOe.

[0032] Example 1

[0033] In Example 1 of the present application, the R component is 31.5wt% PrNd and 1.5wt% Co, the B component is B and accounts for 0.9wt%, M1 is 0.4wt% Al, 0.3wt% Cu and 0.3wt% Ga, and M2 is Ti and accounts for 0.18wt%.

[0034] The remainder of T is Fe.

[0035] Meanwhile, the diffusion material in Example 1 of this application is PrHx, and the single-sided coating amount of the diffusion material is controlled to 2%. The temperature of the first stage heat treatment is 900°C and the heat treatment time is 2 hours. The temperature of the second stage heat treatment is 500°C and the heat treatment time is 4 hours.

[0036] Example 2

[0037] The difference between Example 2 and Example 1 is that the single-side coating amount of the diffusion material in Example 2 is 3%.

[0038] Example 3

[0039] The difference between Example 3 and Example 1 is that the single-side coating amount of the diffusion material in Example 3 is 4%.

[0040] Example 4

[0041] The difference between Example 4 and Example 1 is that the single-side coating amount of the diffusion material in Example 4 is 5%.

[0042] Example 5

[0043] The difference between Example 5 and Example 3 is that the diffusion material in Example 5 is Pr2O3.

[0044] Example 6

[0045] The difference between Example 6 and Example 3 is that the diffusion material in Example 6 is Pr-Al.

[0046] Example 7

[0047] The difference between Example 7 and Example 3 is that the diffusion material in Example 7 is Pr-Cu.

[0048] Example 8

[0049] The difference between Example 8 and Example 3 is that the R component in Example 8 is 30.5wt% of PrNd and 1.5wt% of Co, the B component is B and accounts for 0.9wt%, M1 is 0.4wt% of Al, 0.3wt% of Cu and 0.3wt% of Ga, and M2 is Ti and accounts for 0.18wt%.

[0050] The remainder of T is Fe.

[0051] Embodiment 9

[0052] The difference between Example 9 and Example 3 is that the temperature of the first stage heat treatment in Example 9 is 600° C. and the heat treatment time is 4 hours, and the temperature of the second stage heat treatment is 440° C. and the heat treatment time is 8 hours.

[0053] Example 10

[0054] The difference between Example 10 and Example 3 is that the temperature of the first stage heat treatment in Example 10 is 950° C. and the heat treatment time is 1 hour, and the temperature of the second stage heat treatment is 550° C. and the heat treatment time is 2 hours.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 3 is that the R component in Comparative Example 1 is 30.5wt% of PrNd and 0.5wt% of Co, the B component is B and accounts for 0.98wt%, M1 is 0.7wt% of Al, 0.3wt% of Cu and 0.3wt% of Ga, and M2 is Ti and accounts for 0.12wt%.

[0057] The remainder of T is Fe.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 3 is that the R component in Comparative Example 2 is 31 wt% of PrNd and 0.5 wt% of Co, the B component is B and accounts for 0.93 wt%, M1 is 0.7 wt% of Al, 0.3 wt% of Cu and 0.3 wt% of Ga, and M2 is Ti and accounts for 0.05 wt%.

[0060] The remainder of T is Fe.

[0061] Comparative Example 3

[0062] The difference between Comparative Example 3 and Example 1 is that the single-side coating amount of the diffusion material in Comparative Example 3 is 1%.

[0063] test:

[0064] The heavy rare earth-free high coercivity RTB magnets in Examples 1 to 8 and Comparative Examples 1 and 3 were cut into 7*7*5 mm square pieces. After the diffusion material was sprayed on the surface and heat treated, the corresponding residual magnetic flux density Br and coercivity HcJ were tested. The test results are shown in Table 1 below.

[0065] Table 1 Performance test results

[0066]

[0067] Of course, the corresponding residual magnetic flux density Br and coercivity HcJ of the heavy rare earth-free high coercivity RTB magnets in the corresponding embodiments are also tested. The test results are shown in Table 2 below.

[0068] Table 2 Test results of heavy rare earth-free high coercivity RTB magnets

[0069]

[0070] As can be seen from Tables 1 and 2 above, in Comparative Example 1, the Hcj of the substrate is too low (14.62 kOe), so even after diffusion, it is difficult to reach the target of >23 kOe. In Comparative Example 2, although the initial Hcj can reach (17.35 kOe), the large amount of Pr diffusion does not increase the Hcj to >23 kOe. The excess diffusion material forms reverse magnetization cores, thereby inhibiting the growth of Hcj.

[0071] Therefore, when the formula of 0.8>B-M2>0.2 is met, and diffusion materials such as ≥2wt% PrHx are used, it is a necessary condition to achieve a heavy rare earth-free high coercive force RTB magnet with a strength greater than 23kOe. Then, combined with the corresponding manufacturing method, mass production of heavy rare earth-free high coercive force RTB magnets with a strength greater than 23kOe will be achieved.

[0072] In summary, the present application provides a method for manufacturing a heavy rare earth-free high-coercive force RTB magnet. The method for manufacturing a heavy rare earth-free high-coercive force RTB magnet achieves a heavy rare earth-free high-coercive force RTB magnet after heat treatment by using an RTB raw material based on a formula of 0.8>B-M2>0.2 and a PrX diffusion material greater than 2wt%, thereby achieving a coercive force HcJ of greater than 23kOe for the obtained heavy rare earth-free high-coercive force RTB magnet.

[0073] References to "first," "second," "third," "fourth," and the like (if any) herein are intended to distinguish similar objects and are not necessarily intended to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions, e.g., a process, method, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, or apparatus.

[0074] It should be noted that the descriptions of "first", "second", etc. in this application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0075] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for manufacturing a heavy rare earth-free high coercivity RTB magnet, characterized by: The invention comprises a raw material and a diffusion material composed of 27.5-35.0 wt% of an R component, 0.8-0.95 wt% of a B component, 0-3 wt% of an M component, and a balance of a T component; the M component is composed of 0-2 wt% of M1 and 0-1 wt% of M2, and B and M2 satisfy the following formula (1): 0.8>B-M2>0.2 (1); M1 is at least one of Cu, Al and Ga, M2 is at least one of Nb, Zr and Ti; the R component includes Pr and Nd; the T component is Fe or Fe and Co; in: The diffusion material is PrX, where X is at least one element; The manufacturing method comprises preparing raw materials to obtain RTB-based sintered magnet raw materials, then coating the surface of the magnet raw materials with diffusion material, wherein the single-side coating amount of the diffusion material is not less than 2% of the mass percentage of the magnet raw materials, and obtaining a heavy rare earth-free high-coercivity RTB magnet after heat treatment and diffusion.

2. The method for manufacturing a heavy rare earth-free high coercivity RTB magnet according to claim 1, wherein: The heat treatment includes a first stage heat treatment and a second stage heat treatment, wherein the temperature of the first stage heat treatment is 600-950° C. and the heat treatment time is 1-4 hours; the temperature of the second stage heat treatment is 440-550° C. and the heat treatment time is 2-8 hours.

3. The method for manufacturing a heavy rare earth-free high coercivity RTB magnet according to claim 1, wherein: The magnet raw material is prepared by a thin strip continuous casting method, and the R component, B component, M component and T component are crushed to 1-10 μm in a jet mill, and then sintered at a temperature of 900-1100° C.

4. The method for manufacturing a heavy rare earth-free high coercivity RTB magnet according to claim 1, wherein: The PrX is PrHx, Pr2O3, Pr-Al or Pr-Cu; wherein the mass percentage of Al in Pr-Al is 40%; the mass percentage of Cu in Pr-Cu is 40%.

5. The method for manufacturing a heavy rare earth-free high coercivity RTB magnet according to claim 1, wherein: The coercive force HcJ of the heavy rare earth-free high-coercive force RTB magnet is greater than 23 kOe.

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