Manufacturing method of heavy-rare-earth-free high-coercivity R-T-B magnet

Abstract

The invention discloses a manufacturing method of a heavy-rare-earth-free high-coercive-force R-T-B magnet, and relates to the technical field of magnets, and the manufacturing method is characterized in that the magnet comprises the following raw materials and diffusion materials in percentage by mass: 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; the component M is composed of 0-2 wt% of M1 and 0-1 wt% of M2, and B and M2 meet the following formula (1): 0.8 > B-M2 > 0.2 (1); 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 comprises the steps that raw materials are prepared into an R-T-B series sintered magnet raw material, then the surface of the magnet raw material is coated with a diffusion material, and the heavy-rare-earth-free high-coercivity R-T-B magnet is obtained after heat treatment diffusion. The method has the effect that the heavy-rare-earth-free high-coercive-force R-T-B magnet with the coercive force HcJ larger than 23 kOe is obtained on the basis that heavy rare earth is not added.

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 R-T-B magnet. Background Art

[0002] The R-T-B sintered magnet, where R is at least one of rare-earth elements and necessarily contains Nd; T is Fe or Fe and Co, and B is boron. The R-T-B sintered magnet, being the magnet with the highest performance among permanent magnets, is currently used in various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), and motors for industrial machines, as well as in household electrical appliances. The R-T-B sintered magnet is composed of a main phase mainly composed of R2T14B compound and a grain boundary phase located at the grain boundary part of the main phase. The R2T14B compound as the main phase is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field, which forms the basis of the characteristics of the R-T-B sintered magnet. At high temperatures, the coercivity HcJ of the R-T-B sintered magnet decreases, resulting in irreversible thermal demagnetization. Therefore, in particular, the R-T-B sintered magnet used in motors for electric vehicles is required to have a high coercivity HcJ.

[0003] In the selected R-T-B sintered magnet, if a part of the light rare-earth element RL (such as Nd, Pr) contained in R in the R2T14B compound is replaced with a heavy rare-earth element RH (Dy, Tb), the coercivity HcJ increases. Along with the increase in the replacement amount of RH, the coercivity HcJ increases. However, when RL in the R2T14B compound is replaced with RH, although the coercivity HcJ of the R-T-B sintered magnet increases, the residual magnetic flux density Br decreases. In addition, in particular, heavy rare-earth elements RH such as Dy have problems such as unstable supply and large price fluctuations due to the small amount of resource availability and limited production areas. Therefore, in recent years, there has been a demand for high-coercivity R-T-B magnetic steel without using heavy rare earths.

[0004] The international patent application document with publication number WO2013008756A1 discloses an alloy for RTB-based rare earth sintered magnets, a method for preparing RTB-based rare earth sintered magnet alloys, RTB-based rare earth grounding magnet alloy materials, RTB-based rare earth welding magnets, and RTBB production methods. Compared with the commonly used RTB-based alloys, the composition of the sintered magnet is limited to a relatively small specific range of B content and contains one or more metal elements M selected from Al, Ga, and Cu. As a result, R2T17 phases are generated at the grain boundaries. Since the volume ratio of the transition metal-rich phase (R6T13M) formed by the R2T17 phase at the grain boundaries increases, the coercive force HcJ increases. Therefore, after the grain boundary modification method, the coercive force Hcj of the magnetic steel can reach 19-21kOe.

[0005] The Chinese patent with the publication number CN107077965B discloses a method for manufacturing an RTB-based sintered magnet, wherein the sintered magnet raw material contains R: 27.5-35.0 mass % (R is at least one of the rare earth elements, including Nd), B: 0.80-0.99 mass %, Ga: 0-0.8 mass %, M: 0-2 mass % (M is at least one of Cu, Al, Nb, Zr), the remainder T (T is at least one of the transition metal elements, including Fe, and less than 10% of Fe can be replaced by Co) and inevitable impurities. When the content (mass %) of T is [T] and the content (mass %) of B is [B], [T] / 55.85>14[B] / 10.8 is satisfied. At least a portion of the surface of the sintered magnet raw material is brought into contact with at least a portion of the 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 of 450° C. to 750° C. Therefore, by adopting the grain boundary diffusion PrGa process method, 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: A manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet, comprising raw materials and diffusion materials composed of an R component of 27.5-35.0 wt%, a B component of 0.8-0.95 wt%, an M component of 0-3 wt%, and a T component as the balance by mass percentage; the M component consists 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); and M1 is at least one of Cu, Al, and Ga, and M2 is at least one of Nb, Zr, and Ti; where: the diffusion material is PrX, and X is at least one element; this manufacturing method includes preparing R-T-B series sintered magnet raw materials from the raw materials, then coating the diffusion material on the surface of the magnet raw materials, and obtaining a heavy-rare-earth-free high coercivity R-T-B magnet after heat treatment diffusion.

[0009] Preferably: the single-sided coating amount of the diffusion material is not less than 2% of the mass percentage of the magnet raw materials.

[0010] 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 1-4 h; the temperature of the second-stage heat treatment is 440-550 °C, and the heat treatment time is 2-8 h.

[0011] Preferably: the R component includes Pr and Nd or Pr, Nd, and at least one rare earth element.

[0012] Preferably: the T component is Fe or Fe and Co.

[0013] Preferably: the magnet raw materials are prepared by a thin strip continuous casting method, and the R component, B component, M component, and T component are pulverized to 1-10 μm in a jet mill, and then sintered at a temperature of 900-1100 °C.

[0014] Preferably: the PrX is PrHx, Pr2O3, Pr-Al, or Pr-Cu; where, the mass percentage of Al in Pr-Al is 40%; the mass percentage of Cu in Pr-Cu is 40%.

[0015] Preferably: the coercivity HcJ of the heavy-rare-earth-free high coercivity R-T-B magnet is greater than 23 kOe.

[0016] As can be seen from the above solution, the present application provides a method for manufacturing a heavy-rare-earth-free high-coercivity R-T-B magnet. The method for manufacturing the heavy-rare-earth-free high-coercivity R-T-B magnet has the following beneficial effects: a heavy-rare-earth-free high-coercivity R-T-B magnet after heat treatment is realized by using an R-T-B raw material based on a formula of 0.8 > B - M2 > 0.2 and a PrX diffusion material with a content greater than 2 wt%, so that the coercivity HcJ of the obtained heavy-rare-earth-free high-coercivity R-T-B magnet is greater than 23 kOe. Detailed implementation manners

[0017] To make the technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0018] The following will specifically describe a method for manufacturing a heavy-rare-earth-free high-coercivity R-T-B magnet of the present application.

[0019] A method for manufacturing a heavy-rare-earth-free high-coercivity R-T-B magnet includes a raw material and a diffusion material composed of an R component of 27.5 - 35.0 wt% by mass percentage, a B component of 0.8 - 0.95 wt%, an M component of 0 - 3 wt%, and a T component as the balance. In the embodiments 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.

[0020] It should be noted that B and M2 in the embodiments of the present application satisfy the following formula (1): 0.8 > B - M2 > 0.2 (1); At the same time, the diffusion material is PrX, and X is at least one element.

[0021] The method for manufacturing the heavy-rare-earth-free high-coercivity R-T-B magnet includes preparing an R-T-B series sintered magnet raw material from the raw material, then coating the diffusion material on the surface of the magnet raw material, and obtaining a heavy-rare-earth-free high-coercivity R-T-B magnet after heat treatment diffusion.

[0022] In order to effectively increase the coercivity HcJ, the single-sided coating amount of the diffusion material in the embodiments of the present application is not less than 2% of the mass percentage of the magnet raw material. The heat treatment includes a first-stage heat treatment and a second-stage heat treatment. The temperature of the first-stage heat treatment is 600 - 950 °C, and the heat treatment time is 1 - 4 h; the temperature of the second-stage heat treatment is 440 - 550 °C, and the heat treatment time is 2 - 8 h.

[0023] The magnet raw material is prepared by strip casting, and the R component, B component, M component, and T component are pulverized to 1 - 10 μm in a jet mill and then sintered at a temperature of 900 - 1100 °C. Since when the volume median diameter = D50 of the pulverized particle size of each component measured by the air-flow dispersion laser diffraction method is less than 1 μm, the manufacturing difficulty will be significantly increased, resulting in a significant reduction in production efficiency. When the pulverized particle size of each component is greater than 10 μm, it will cause the crystal particle size of the heavy-rare-earth-free high-coercivity R-T-B magnet to be too large, resulting in a decrease in coercivity HcJ and difficulty in effectively improving it.

[0024] After testing, the coercivity HcJ of the heavy-rare-earth-free high-coercivity R-T-B magnet in the embodiments of the present application is greater than 23 kOe.

[0025] Example 1 In Example 1 of the present application, the R component is 31.5 wt% PrNd and 1.5 wt% Co, the B component is B and accounts for 0.9 wt%, M1 is 0.4 wt% Al, 0.3 wt% Cu, and 0.3 wt% Ga, and M2 is Ti and accounts for 0.18 wt%.

[0026] The balance of T is all Fe.

[0027] Meanwhile, the diffusion material in Example 1 of the present application is PrHx, and the single-sided coating amount of the diffusion material is controlled to be 2%. The temperature of the first-stage heat treatment is 900 °C, and the heat treatment time is 2 h. The temperature of the second-stage heat treatment is 500 °C, and the heat treatment time is 4 h.

[0028] Example 2 The difference between Example 2 and Example 1 is that the single-sided coating amount of the diffusion material in Example 2 is 3%.

[0029] Example 3 The difference between Example 3 and Example 1 is that the single-sided coating amount of the diffusion material in Example 3 is 4%.

[0030] Example 4 The difference between Example 4 and Example 1 is that the single-sided coating amount of the diffusion material in Example 4 is 5%.

[0031] Example 5 The difference between Example 5 and Example 3 is that the diffusion material in Example 5 is Pr2O3.

[0032] Example 6 The difference between Example 6 and Example 3 is that the diffusion material in Example 6 is Pr - Al.

[0033] Example 7 The difference between Example 7 and Example 3 is that the diffusion material in Example 7 is Pr - Cu.

[0034] Example 8 The difference between Example 8 and Example 3 is that in Example 8, the R component is 30.5 wt% PrNd and 1.5 wt% Co, the B component is B and accounts for 0.9 wt%, M1 is 0.4 wt% Al, 0.3 wt% Cu, and 0.3 wt% Ga, and M2 is Ti and accounts for 0.18 wt%.

[0035] The balance of T is all Fe.

[0036] Example 9 The difference between Example 9 and Example 3 is that in Example 9, the temperature of the first - stage heat treatment is 600 °C and the heat - treatment time is 4 h. The temperature of the second - stage heat treatment is 440 °C and the heat - treatment time is 8 h.

[0037] Example 10 The difference between Example 10 and Example 3 is that in Example 10, the temperature of the first - stage heat treatment is 950 °C and the heat - treatment time is 1 h. The temperature of the second - stage heat treatment is 550 °C and the heat - treatment time is 2 h.

[0038] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that in Comparative Example 1, the R component is 30.5 wt% PrNd and 0.5 wt% Co, the B component is B and accounts for 0.98 wt%, M1 is 0.7 wt% Al, 0.3 wt% Cu, and 0.3 wt% Ga, and M2 is Ti and accounts for 0.12 wt%.

[0039] The balance of T is all Fe.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, the R component is 31 wt% PrNd and 0.5 wt% Co, the B component is B and accounts for 0.93 wt%, M1 is 0.7 wt% Al, 0.3 wt% Cu, and 0.3 wt% Ga, and M2 is Ti and accounts for 0.05 wt%.

[0041] The balance of T is all Fe.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the single-sided coating amount of the diffusion material in Comparative Example 3 is 1%.

[0043] Test: The heavy-rare-earth-free high coercivity R-T-B magnets in Examples 1 to 8, Comparative Example 1 and Comparative Example 3 were cut into 7*7*5 mm square pieces. After spraying the diffusion material on the surface and heat treatment, the corresponding residual magnetic flux density Br and coercivity HcJ were tested, and the test results are shown in Table 1 below.

[0044] Table 1 Performance test results

[0045] Of course, it also includes testing the corresponding residual magnetic flux density Br and coercivity HcJ of the heavy-rare-earth-free high coercivity R-T-B magnets under the corresponding examples, and the test results are shown in Table 2 below.

[0046] Table 2 Test results of heavy-rare-earth-free high coercivity R-T-B magnets

[0047] As can be seen from Table 1 and Table 2 above, in Comparative Example 1, due to the too low Hcj of the substrate (14.62 kOe), it is difficult to reach the target of >23 kOe even after diffusion. Although the initial Hcj in Comparative Example 2 can reach (17.35 kOe), the large amount of Pr diffusion did not achieve the effect of increasing Hcj to >23 kOe. The excessive diffusion material formed reverse magnetization nuclei, thus suppressing the growth of Hcj.

[0048] Therefore, when the heavy-rare-earth-free high coercivity R-T-B magnet with a 0.8 > B-M2 > 0.2 formula and diffusion materials such as ≥2 wt% PrHx are satisfied, it is a necessary condition to achieve a heavy-rare-earth-free high coercivity R-T-B magnet greater than 23 kOe. Furthermore, combined with the corresponding manufacturing method, the mass production of a heavy-rare-earth-free high coercivity R-T-B magnet greater than 23 kOe will be realized.

[0049] In summary, the present application provides a manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet. The manufacturing method of the heavy-rare-earth-free high coercivity R-T-B magnet realizes the heavy-rare-earth-free high coercivity R-T-B magnet after heat treatment through R-T-B raw materials based on a 0.8 > B-M2 > 0.2 formula and PrX diffusion materials greater than 2 wt%, so as to achieve a coercivity HcJ of the obtained heavy-rare-earth-free high coercivity R-T-B magnet greater than 23 kOe.

[0050] The "first", "second", "third", "fourth", etc. (if any) involved in this application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments described herein can be implemented in an order other than that described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, or devices.

[0051] It should be noted that the descriptions involving "first", "second", etc. in this application are only for descriptive purposes, and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. Additionally, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0052] Specific examples are used herein to elaborate on the principles and implementation manners of this application. The descriptions of the above embodiments are only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet, characterized in that: It includes raw materials and diffusion materials composed of an R component at 27.5 - 35.0 wt% by mass percentage, a B component at 0.8 - 0.95 wt%, an M component at 0 - 3 wt%, and a T component as the balance; 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); and M1 is at least one of Cu, Al, and Ga, and M2 is at least one of Nb, Zr, and Ti; where: the diffusion material is PrX, and X is at least one element; This manufacturing method includes preparing raw materials to obtain R - T - B system sintered magnet raw materials, then coating the surface of the magnet raw materials with the diffusion material, and obtaining a heavy - rare - earth - free high - coercivity R - T - B magnet after heat - treatment diffusion.

2. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The single - side coating amount of the diffusion material is not less than 2% of the mass percentage of the magnet raw materials.

3. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The heat - treatment includes a first - stage heat - treatment and a second - stage heat - treatment. The temperature of the first - stage heat - treatment is 600 - 950 °C, and the heat - treatment time is 1 - 4 h; the temperature of the second - stage heat - treatment is 440 - 550 °C, and the heat - treatment time is 2 - 8 h.

4. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The R component includes Pr and Nd or Pr, Nd, and at least one rare - earth element.

5. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The T component is Fe or Fe and Co.

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

7. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The PrX is PrHx, Pr2O3, Pr - Al, or Pr - Cu; among them, the mass percentage of Al in Pr - Al is 40%; the mass percentage of Cu in Pr - Cu is 40%.

8. The manufacturing method of a heavy-rare-earth-free high coercivity R-T-B magnet according to claim 1, characterized in that: The coercivity HcJ of the heavy - rare - earth - free high - coercivity R - T - B magnet is greater than 23 kOe.

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