High-remanence cerium-rich mixed rare earth permanent magnet material and preparation method thereof

Abstract

The invention discloses a high-remanence cerium-rich mixed rare earth permanent magnet material and a preparation method thereof, and belongs to the field of rare earth permanent magnet materials. The preparation method of the high-remanence cerium-rich mischmetal permanent magnet material comprises the following steps: (1) preparing magnetic powder, and preparing a sintered cerium-rich mischmetal permanent magnet base material magnet through a sintering process; (2) carrying out grain boundary diffusion treatment on the base material magnet by using a diffusant obtained by mixing rare earth hydrogenated powder and metal elementary substance / alloy nano powder in proportion; and (3) carrying out multi-step heat treatment on the diffused magnet to finally obtain the high-remanence cerium-rich mixed rare earth permanent magnet material. By redesigning a base material magnet and a grain boundary diffusion source and innovating a heat treatment process after diffusion, the residual magnetism of the cerium-rich mixed rare earth permanent magnet material is greatly improved, so that the comprehensive magnetic performance is improved, and the industrial application of high-abundance rare earth cerium and mixed rare earth in the rare earth permanent magnet material is promoted.

Description

Technical Field

[0001] The invention relates to the field of rare earth permanent magnet materials, and in particular to a high remanence cerium-rich mixed rare earth permanent magnet material and a preparation method thereof. Background Art

[0002] NdFeB rare earth permanent magnet materials have the advantages of high remanence, high coercivity and high magnetic energy product. They are key materials in important fields of national defense and national economy such as aerospace, information and energy. In recent years, the rapid development of new energy vehicles and other fields has brought huge market demand for NdFeB permanent magnet materials. Traditional NdFeB rare earth permanent magnet materials consume a large amount of rare earth elements such as neodymium (Nd), praseodymium (Pr), dysprosium (Dy) and terbium (Tb) with low abundance and scarce resources, while high-abundance rare earths such as cerium (Ce) and lanthanum (La) have not been effectively utilized, and a large backlog has caused serious waste of resources. China is a country with a large number of rare earth resources. The rare earth content in the Bayan Obo co-existing rare earth ore in Baotou ranks first in the world. In the mixed rare earth metal MM enriched in the ore, the proportion of rare earth Ce exceeds 50%, and the proportion of rare earth La exceeds 20%. If mixed rare earths can be directly applied to rare earth permanent magnet materials, it will have significant economic advantages due to the reduction of a large number of separation and purification processes. It is also expected to alleviate the backlog of Ce and La, and the shortage of Nd, Pr, Dy and Tb, and contribute to the balanced utilization of rare earth resources.

[0003] Mixed rare earth metal MM is a rare earth alloy composed of La, Ce, Pr and Nd. Due to the high content of Ce and La in MM, Ce2Fe 14 B and La2Fe 14 The intrinsic magnetic properties of phase B are poor, for example, the saturation magnetization M s and the magnetocrystalline anisotropy field H A Both are significantly lower than (Nd,Pr)2Fe 14 B phase. This results in the magnetic properties of rare earth permanent magnet materials prepared directly using mixed rare earths being much lower than those of traditional NdFeB magnets prepared with neodymium-praseodymium alloys, making it difficult to meet the needs of commercial applications. In addition, for cerium-rich mixed rare earth permanent magnets, the large amount of precipitation of REFe2 grain boundary phase will seriously reduce the magnetic properties of the magnet, especially the precipitation of large blocks of triple grain boundary phase will seriously deteriorate the remanence of the magnet. In order to improve the comprehensive performance of the magnet, the method of increasing the coercive force of the magnet is usually adopted, while less attention is paid to how to improve the remanence of the magnet. In traditional sintered NdFeB magnets, the method of increasing the volume proportion of hard magnetic main phase grains and increasing the orientation degree of grains along the C-axis direction is often used to increase the remanence of the magnet. For cerium-rich mixed rare earth permanent magnet materials, how to achieve their high remanence is the key to improving the magnetic energy product and obtaining excellent comprehensive magnetic properties, and it is still a major problem facing the industry. Summary of the invention

[0004] The object of the present invention is to solve the deficiencies of the prior art and provide a high remanence cerium-rich rare earth permanent magnet material and a preparation method thereof. The preparation method of the present invention comprises the following steps:

[0005] (1) Prepare magnetic powder, and prepare a sintered cerium-rich rare earth permanent magnet base magnet through a sintering process;

[0006] (2) Perform grain boundary diffusion treatment on the base magnet using a diffusing agent obtained by mixing rare earth hydride powder and metal single element / alloy nano powder in a certain proportion, and the dosage of the diffusing agent is less than 3% of the mass of the selected base magnet;

[0007] (3) Perform multi-step heat treatment on the diffused magnet to finally obtain a high remanence cerium-rich rare earth permanent magnet material.

[0008] Further, the magnetic powder in step (1) has a composition of [R 1-a-b (Ce 1-x MM x ) a R’ b c Fe bal T d B e , where R is one or two of the rare earth elements Nd and Pr, R’ is one or several of the rare earth elements Gd, Tb, Dy, Ho, Sm, Y, Ce is the rare earth element cerium, MM is mixed rare earth, and its mass ratio is: Ce: 50 - 60%, La: 20 - 35%, Pr: 5 - 10%, Nd: 10 - 20%, other elements and inevitable impurities ≤ 2%; Fe is the iron element, T is one or more of the alloy elements Co, Ni, Al, Cu, Cr, Ga, Mn, Nb, Zr, Ti and V, B is the boron element, and in terms of mass percentage, 0.4 ≤ a ≤ 1, 0 ≤ x ≤ 0.8, 0 ≤ b ≤ 0.15, 28 ≤ c ≤ 34, 0.2 ≤ d ≤ 5, 0.85 ≤ e ≤ 1.

[0009] Further, in the sintering process of step (1), the sintering temperature used is 980 - 1080 °C, the sintering time is 2 - 10 h, and the vacuum degree in the chamber is lower than 10 -2 Pa.

[0010] Further, the rare earth hydride powder in step (2) has a composition of A 1-f H f , where A is one or more of the rare earth elements Nd, Pr, La, Ce, Gd, Tb, Dy, Ho, the total mass ratio of Nd and Pr elements in A is higher than 60%, H is the hydrogen element, and in terms of atomic percentage, 0 < f ≤ 0.75; the metal nano powder has a composition of A’ 1-g U g ​, wherein A' is one or more of the rare earth elements Nd, Pr, La, Ce, Gd, Tb, Dy, and Ho, U is one or more of Cu, Zn, Ti, and Zr, the size of the nanopowder is 5 to 500 nm, and in terms of mass percentage, 0.4≤g≤1, wherein when g=1, the nanopowder is a metal element nanopowder; in the diffusing agent obtained by mixing the rare earth hydride and the metal nanopowder, the mass proportion of the rare earth hydride powder is not less than 50%; the temperature of the grain boundary diffusion treatment is 800 to 950°C, and the diffusion time is 2 to 10 hours.

[0011] Furthermore, the multi-step heat treatment in step (3) includes: firstly performing high-temperature heat treatment at a temperature of 960-1050°C and a heat preservation time of 0.5-2h; and then performing low-temperature heat treatment at a temperature of 300-700°C and a heat preservation time of 0.5-10h.

[0012] The present invention also provides a high remanence cerium-rich mixed rare earth permanent magnet material prepared by any of the above methods.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The present invention uses Ce with high abundance and mixed rare earth to prepare cerium-rich mixed rare earth permanent magnet materials, which significantly reduces the production cost of magnets. A small amount of medium and heavy rare earth elements are further introduced into the magnet composition design to improve the comprehensive performance of the magnet and improve the cost performance. The present invention ensures that while using a large amount of high-abundance Ce and La rare earth elements, higher comprehensive magnetic properties can still be obtained, alleviating the large backlog of rare earth Ce and La, and achieving balanced utilization of rare earth resources.

[0015] (2) The present invention adopts grain boundary diffusion technology to design a diffusion agent that is a mixture of rare earth hydrogenated powder and metal nanopowder in proportion. The introduction of rare earth hydrogenated powder can form a magnetically hardened main phase shell in the cerium-rich mixed rare earth substrate magnet, thereby improving the coercive force and remanence of the magnet. Metal nanopowders have high specific surface area and surface energy. By optimizing the composition of metal single substance nanopowders and alloy nanopowders, the nanopowders are more likely to interact with the rare earth hydrogenated powder during the diffusion process, thereby improving the diffusion efficiency and uniformity; at the same time, the introduction of elements such as Cu, Zn, Ti, and Zr can regulate the grain size of the main phase, improve the composition and distribution of the grain boundary phase, and reduce the content of REFe2 grain boundary phase in the magnet, thereby greatly improving the remanence of the magnet.

[0016] (3) The present invention redesigns the grain boundary diffusion process. To address the common problem that REFe2 blocks the diffusion channel after grain boundary diffusion of cerium-rich magnets, resulting in the inability of the diffusion source rare earth to efficiently enter the main phase to form a hard magnetic shell layer, and the inability of the alloying elements to efficiently enter the interior of the diffused magnet to form a continuous grain boundary phase, the present invention performs a short-term high-temperature heat treatment on the magnet after the grain boundary diffusion treatment, so that the rare earth elements accumulated in the grain boundary phase enter the interior of the main phase, reducing the Ce / La content in the main phase, thereby further improving the remanence of the magnet. On this basis, a low-temperature heat treatment is performed to achieve the precipitation of the alloying elements that have been dissolved into the main phase during the high-temperature heat treatment into the grain boundary phase, and Ce and La are further segregated into the grain boundary phase, thereby continuing to improve the remanence of the magnet, and finally achieving the preparation of high remanence cerium-rich mixed rare earth permanent magnet materials. DETAILED DESCRIPTION

[0017] The present invention is further described and illustrated below in conjunction with specific examples, which are merely exemplary of the present disclosure and do not limit the scope of the present invention. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other:

[0018] Embodiment 1:

[0019] The preparation composition is [(Pr 0.2 Nd 0.8 ) 0.25 (Ce 0.9 MM 0.1 ) 0.75 ] 32 Fe bal Co 0.2 Cu 0.2 Al 0.1 Nb 0.15 Ga 0.3 B 0.95 (wt.%) magnetic powder was used to prepare sintered cerium-rich mixed rare earth permanent magnet substrate magnets by sintering process, the sintering temperature was 1020℃, and the sintering time was 3h. 0.25 H 0.75 The powder is uniformly mixed with nano Cu powder (size is about 50nm) in a mass ratio of 80:20 to prepare a diffusing agent, and a grain boundary diffusion treatment is performed. The amount of diffusing agent powder is 2% of the mass of the selected sintered cerium-rich mixed rare earth permanent magnet substrate magnet. The diffusion temperature is 920℃ and the diffusion time is 4h. The above-mentioned magnet is subjected to high-temperature heat treatment at a heat treatment temperature of 1020℃ and kept warm for 1h. Subsequently, the magnet is subjected to low-temperature heat treatment at a heat treatment temperature of 650℃ and kept warm for 2.5h to obtain a high remanence cerium-rich mixed rare earth permanent magnet material. The test results of the NIM6500C permanent magnet property measuring instrument show that the properties of the sintered magnet before diffusion are: remanence B r =10.12kG, coercive force H cj=4.50kOe, maximum magnetic energy product (BH) max =20.74MGOe; the performance of the magnet after diffusion is: B r =10.80kG,H cj =9.95kOe,(BH) max =27.80MGOe.

[0020] Comparative Example 1:

[0021] The difference between Comparative Example 1 and Example 1 is that the diffusant components used for grain boundary diffusion are different. 0.25 H 0.75 Powder, no nano Cu powder was added. The test results of NIM6500C permanent magnet property measuring instrument show that the performance of the magnet after diffusion is: B r =10.17kG,H cj =9.04kOe,(BH) max =22.08MGOe, the remanence of the magnet is significantly lower than that in Example 1.

[0022] Comparative Example 2:

[0023] The difference between Comparative Example 2 and Example 1 is that after the grain boundary diffusion treatment, the magnet is not subjected to high temperature heat treatment, but directly subjected to low temperature heat treatment. The test results of the NIM6500C permanent magnet property measuring instrument show that the performance of the magnet after diffusion is: B r =10.16kG,H cj =6.15kOe,(BH) max =21.85MGOe, the remanence of the magnet is significantly lower than that in Example 1.

[0024] Embodiment 2:

[0025] The preparation composition is [(Pr 0.2 Nd 0.8 ) 0.35 (Ce 0.8 MM 0.2 ) 0.60 G 0.05 ] 30 Fe bal Co 0.5 Cu 0.15 Al 0.2 Zr 0.2 Ga 0.5 B 0.93 (wt.%) magnetic powder was used to prepare sintered cerium-rich mixed rare earth permanent magnet substrate magnets by sintering process. The sintering temperature was 1040℃ and the sintering time was 3h. 80 Pr 20 ) 0.25 H 0.75Powder and nano Cu 65 Zn 35 The powder (size is about 100nm) is uniformly mixed in a mass ratio of 70:30 to prepare a diffusant, and a grain boundary diffusion treatment is performed. The amount of diffusant powder is 2.5% of the mass of the selected sintered cerium-rich mixed rare earth permanent magnet substrate magnet. The diffusion temperature is 890°C and the diffusion time is 6h. The above-mentioned magnet is subjected to high-temperature heat treatment at a heat treatment temperature of 1020°C and kept warm for 0.5h. Subsequently, the magnet is subjected to low-temperature heat treatment at a heat treatment temperature of 630°C and kept warm for 2h to obtain a high remanence cerium-rich mixed rare earth permanent magnet material. The test results of the NIM6500C permanent magnet property measuring instrument show that the properties of the sintered magnet before diffusion are: remanence B r =10.71kG, coercive force H cj =9.20kOe, maximum magnetic energy product (BH) max =25.66MGOe; the performance of the magnet after diffusion is: B r =11.13kG,H cj =13.68kOe,(BH) max =32.82MGOe.

[0026] Comparative Example 3:

[0027] The difference between Comparative Example 3 and Example 2 is that the proportion of the diffusing agent used is different. 80 Pr 20 ) 0.25 H 0.75 Powder and Nano Cu 65 Zn 35 The powder was uniformly mixed in a mass ratio of 40:60 to obtain a diffusing agent for grain boundary diffusion treatment. The test results of the NIM6500C permanent magnet property measuring instrument showed that the performance of the magnet after diffusion was: B r =10.66kG,H cj =7.14kOe,(BH) max =23.83MGOe, the remanence of the magnet is significantly lower than that in Example 2.

[0028] Embodiment 3:

[0029] The preparation composition is [(Pr 0.2 Nd 0.8 ) 0.50 (Ce 0.7 MM 0.3 ) 0.50 ] 31.5 Fe bal Cu 0.1 Al 0.35 Ti 0.25 Ga 0.5 B 0.98(wt.%) magnetic powder was used to prepare sintered cerium-rich mixed rare earth permanent magnet substrate magnets by sintering process, the sintering temperature was 1045℃, and the sintering time was 3h. 80 Dy 20 ) 0.25 H 0.75 Powder and nano Pr 20 (Cu 65 Zn 35 ) 80 The powder (size is about 100nm) is uniformly mixed in a mass ratio of 85:15 to prepare a diffusant, and a grain boundary diffusion treatment is performed. The amount of diffusant powder is 2.5% of the mass of the selected sintered cerium-rich mixed rare earth permanent magnet substrate magnet. The diffusion temperature is 900℃ and the diffusion time is 6h. The above-mentioned magnet is subjected to high-temperature heat treatment at a heat treatment temperature of 1025℃ and kept warm for 1h. Subsequently, the magnet is subjected to low-temperature heat treatment at a heat treatment temperature of 620℃ and kept warm for 3h to obtain a high remanence cerium-rich mixed rare earth permanent magnet material. The test results of the NIM6500C permanent magnet property measuring instrument show that the properties of the sintered magnet before diffusion are: remanence B r =11.20kG, coercive force H cj =7.54kOe, maximum magnetic energy product (BH) max =30.26MGOe; the performance of the magnet after diffusion is: B r =11.63kG,H cj =15.37kOe,(BH) max =35.84MGOe.

[0030] Comparative Example 4:

[0031] The difference between Comparative Example 4 and Example 3 is that the diffusant components used for grain boundary diffusion are different. 20 (Cu 65 Zn 35 ) 80 Powder, not used (Pr 80 Dy 20 ) 0.25 H 0.75 The test results of NIM6500C permanent magnet property measuring instrument show that the performance of the magnet after diffusion is: B r =11.18kG,H cj =10.31kOe,(BH) max =31.85MGOe, the remanence of the magnet is significantly lower than that in Example 3.

[0032] Comparative Example 5:

[0033] The difference between Comparative Example 5 and Example 3 is that the high temperature heat treatment process selected for the magnet after grain boundary diffusion is different, the heat treatment temperature is 1025°C, and the heat preservation is 3h. The test results of NIM6500C permanent magnet property measuring instrument show that the performance of the magnet after diffusion is: B r =11.38kG,H cj =11.25kOe,(BH) max =33.82MGOe, the remanence of the magnet is significantly lower than that in Example 3.

[0034] In summary, the present invention aims at the bottleneck problem of low comprehensive magnetic properties caused by low remanence of cerium-rich mixed rare earth permanent magnet materials, and innovates the design of substrate magnets, grain boundary diffusion sources and diffusion process technology. In terms of diffusion substrate, the remanence of the matrix is ​​improved by co-adding Ce and MM; in terms of grain boundary diffusion sources, rare earth hydrogenated powder and metal single substance / alloy nanopowders such as Cu, Ti, and Zn are introduced to broaden the temperature window of subsequent high-temperature heat treatment, regulate the grain size of the main phase, and improve the composition and distribution of the grain boundary phase, thereby reducing the content of REFe2 grain boundary phase in the magnet. In terms of diffusion process, different from the traditional grain boundary diffusion method, a short-time high-temperature heat treatment process is added to allow the rare earth elements accumulated in the grain boundary phase to enter the main phase, reduce the Ce / La content in the main phase, and combine with the low-temperature heat treatment process to achieve the segregation of different rare earth and alloy elements, thereby greatly improving the remanence of the magnet, and finally preparing a high remanence cerium-rich mixed rare earth permanent magnet material.

[0035] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A high remanence cerium-rich mixed rare earth permanent magnet material and a preparation method thereof, characterized in that: include: (1) preparing magnetic powder, and preparing a sintered cerium-rich mixed rare earth permanent magnet substrate magnet by a sintering process; (2) using a diffusing agent obtained by mixing rare earth hydrogenated powder and metal element / alloy nanopowder in proportion to perform grain boundary diffusion treatment on the base magnet, and the amount of the diffusing agent used is less than 3% of the mass of the selected base magnet; (3) The diffused magnet is subjected to a multi-step heat treatment to finally obtain a high remanence cerium-rich mixed rare earth permanent magnet material.

2. The preparation method according to claim 1, characterized in that: The magnetic powder component in step (1) is [R 1-a-b (Ce 1-x MM x ) a R' b ] c Fe bal T d B e , wherein R is one or two of the rare earth elements Nd and Pr, R' is one or more of the rare earth elements Gd, Tb, Dy, Ho, Sm, and Y, Ce is the rare earth element cerium, MM is mixed rare earth, and the mass proportions thereof are: Ce: 50-60%, La: 20-35%, Pr: 5-10%, Nd: 10-20%, and other elements and unavoidable impurities ≤ 2%; Fe is iron, T is one or more of the alloying elements Co, Ni, Al, Cu, Cr, Ga, Mn, Nb, Zr, Ti, and V, and B is boron. In terms of mass percentage, 0.4≤a≤1, 0≤x≤0.8, 0≤b≤0.15, 28≤c≤34, 0.2≤d≤5, and 0.85≤e≤1.

3. The preparation method according to claim 1, characterized in that: The sintering temperature used in the sintering process in step (1) is 980-1080°C, the sintering time is 2-10 hours, and the vacuum degree in the chamber is less than 10 -2 Pa.

4. The preparation method according to claim 1, characterized in that: The rare earth hydride powder described in step (2) has a composition of A 1-f H f , where A is one or more of the rare earth elements Nd, Pr, La, Ce, Gd, Tb, Dy, Ho. The total mass percentage of Nd and Pr elements in A is higher than 60%. H is hydrogen element, and in atomic percentage, 0 < f ≤ 0.

75. The metal nanopowder has a composition of A' 1-g U g , where A' is one or more of the rare earth elements Nd, Pr, La, Ce, Gd, Tb, Dy, Ho, and U is one or more of Cu, Zn, Ti, Zr. The size of the nanopowder is 5 - 500 nm, and in mass percentage, 0.4 ≤ g ≤ 1. Among them, when g = 1, the nanopowder is a metal single - element nanopowder. In the diffusing agent obtained by mixing the rare earth hydride and the metal nanopowder, the mass percentage of the rare earth hydride powder is not less than 50%. The temperature of the grain - boundary diffusion treatment is 800 - 950 °C, and the diffusion time is 2 - 10 h.

5. The preparation method according to claim 1, characterized in that: The multi-step heat treatment in step (3) includes: firstly, high-temperature heat treatment at a temperature of 960-1050°C for a holding time of 0.5-2h; and then, low-temperature heat treatment at a temperature of 300-700°C for a holding time of 0.5-10h.

6. A high remanence cerium-rich mixed rare earth permanent magnet material, characterized in that: The high remanence cerium-rich mixed rare earth permanent magnet material is prepared by the method described in any one of claims 1-5.