A high-throughput process for preparing sintered NdFeB magnets with different target element contents

Abstract

The present invention provides an NdFeB magnet intermediate, which is obtained by infiltration and sintering an NdFeB compact and a low-melting-point alloy sheet composited onto the NdFeB compact. Compared with the prior art, the present invention uses the NdFeB magnet compact as the starting material. Through specific infiltration of the compact, a concentration gradient is formed in the alloy melt along the infiltration direction. As a result, a content gradient of the target element in the alloy is also formed in the compact. After segmentation and block formation, tempering heat treatment is used to uniformly distribute the elements within each magnet block. This ensures that the target element content is distributed in a gradient between the magnet blocks after a single process, and that the composition and structure of each magnet block are uniform. This allows for the efficient production of large quantities of sintered NdFeB magnets with different target element contents in a short period of time, thus achieving high-throughput production of sintered NdFeB magnets with different target element contents.

Description

Technical Field

[0001] The present invention belongs to the technical field of sintered NdFeB magnet preparation, and relates to a NdFeB magnet intermediate and a preparation method of sintered NdFeB magnets with different target element contents, and in particular to a high-throughput process for preparing sintered NdFeB magnets with different target element contents. Background Art

[0002] Sintered NdFeB permanent magnet material, known as the "King of Magnets", has become a core functional material in the fields of electricity, telecommunications, automobiles, computers, biomedicine and household appliances. It is being used to manufacture generators and motors for electric (or hybrid electric) vehicles with hundreds of kilowatts, as well as to manufacture megawatt-level permanent magnet motors for wind power generation.

[0003] The composition of sintered NdFeB permanent magnets is crucial. Many of their intrinsic magnetic properties, such as magnetic polarization, magnetocrystalline anisotropy field (HA), magnetocrystalline anisotropy constant (K1), and Curie temperature (TC), are determined by the material's composition. Composition is fundamental to the performance of sintered NdFeB permanent magnets and also influences their microstructure to a certain extent. Therefore, rare earth permanent magnet material researchers have always carefully and scientifically designed the composition of permanent magnets, prioritizing material composition design.

[0004] In the formation of RE2Fe 14 Based on B, the composition (mass ratio) of sintered NdFeB permanent magnet material can be expressed as follows:

[0005] (Nd 1-x RE x ) 29.08+ω (Fe 1-y My )69.89 B 1.03 (1)

[0006] Where RE is the other rare earth element, and x is the amount (mass fraction) of other rare earth elements replacing Nd. Of the 29.08% rare earth metal, 26.68% is required to form the 2:14:1 phase, and 2.4% is added to ensure sufficient rare earth-rich phase in the sintered NdFeB permanent magnet. This ensures that each 2:14:1 phase grain is surrounded by the rare earth-rich phase, which de-exchanges and increases coercivity, and acts as a sintering agent to achieve magnet densification. ω is the amount of additional rare earth element added, which depends on the control of oxygen content during magnet production. The value of ω is typically 1.8. M is the other metal element, and y is the amount of other metal substituted for metallic iron. Research has found that adding small amounts of other metal elements can significantly alter the properties of sintered NdFeB permanent magnets. So far, most rare earth permanent magnet scholars have studied most of the metal elements on the periodic table and have a preliminary understanding of the role of some metal elements in sintered NdFeB permanent magnet materials. For example, Tb, Dy and other elements can replace Nd to form Tb2Fe with higher anisotropy field. 14 B、Dy2Fe 14 B, etc., can significantly improve the coercive force of the magnet, Co can significantly increase the Curie temperature of the magnet, Al, Cu, Nb, Ga, Ti, W, Mo and other elements can effectively improve the coercive force and temperature stability of the magnet, but at the same time, the addition of these elements will reduce the remanence of the magnet. However, these understandings are only qualitative rather than quantitative preliminary understandings. The addition of these elements does not act on the magnet individually, but is the result of a combined effect. Some non-metallic elements have not yet been included in the research, and the influence of each element on the coercive force mechanism is not yet clear. The phase characteristics of different elements at the grain boundaries of the magnet also need to be studied. Due to the role of each element, researchers are eager to develop ternary sintered NdFeB into quaternary, quinary, hexavalent and even septenary sintered NdFeB, pursuing magnets with comprehensive properties of high coercive force and high remanence. This requires scholars to accurately understand the influence of each element and the combined effect of several elements on the magnet structure and properties.

[0007] At present, scholars study the influence of various elements on the performance of sintered NdFeB permanent magnet materials mainly through experimental methods. The current experimental method mainly mixes other elements into the materials during the batching and powder making stages of the sintered NdFeB production process. Each experiment can only study the influence of a certain amount of one or a small amount of several target elements on the performance of sintered NdFeB permanent magnet materials. The test repeatability is poor and comparison is difficult. The test is time-consuming and the operation is cumbersome, which greatly increases the test cycle and error. A comprehensive and in-depth study of the combined effects of each element or several elements and the influence of the types and contents of other metal elements in magnets with different rare earth element contents will be a long and complex task.

[0008] Therefore, how to find a suitable method to obtain a sintered NdFeB magnet that is convenient for scholars to use for research, which can easily obtain magnets with different contents of target elements and have better repeatability and comparability has become one of the urgent problems to be solved by researchers in the industry. Summary of the Invention

[0009] In view of this, the technical problem to be solved by the present invention is to provide a NdFeB magnet intermediate and a method for preparing sintered NdFeB magnets with different target element contents, particularly a process for high-throughput preparation of sintered NdFeB magnets with different target element contents. The method provided by the present invention can simply achieve high-throughput preparation of sintered NdFeB magnets with different target element contents. Moreover, the method has a short test cycle, simple operation, and high test reproducibility, which is of great significance to the sintered NdFeB industry and the field of rare earth permanent magnet materials, especially magnet research.

[0010] The invention provides a NdFeB magnet intermediate. The NdFeB magnet intermediate is obtained by subjecting a NdFeB compact and a low-melting-point alloy sheet composited on the NdFeB compact to infiltration and sintering treatment.

[0011] Preferably, the NdFeB compact is obtained by orienting and pressing NdFeB raw material;

[0012] The density of the NdFeB compact is 3.2-4.2 g / cm 3 ;

[0013] The thickness of the compact is 5 to 50 mm.

[0014] Preferably, the NdFeB compact is not subjected to densification treatment;

[0015] The NdFeB compact is a loose green body with micropores;

[0016] The densification treatment includes one or more of densification sintering, semi-densification sintering and pre-sintering.

[0017] Preferably, the melting point of the low-melting-point alloy sheet is less than or equal to 900°C;

[0018] The low melting point alloy sheet is an alloy diffusion source for infiltration;

[0019] The mass ratio of the low melting point alloy sheet to the pressed green sheet is 5% to 10%.

[0020] Preferably, the sintering process further includes a cutting process;

[0021] The cutting direction is perpendicular to the diffusion direction of the NdFeB magnet.

[0022] The present invention also provides a method for preparing sintered NdFeB magnets with different target element contents, comprising the following steps:

[0023] 1) Alloying a multi-element raw material containing a target element to obtain a low-melting-point alloy sheet;

[0024] The NdFeB raw material powder is oriented and pressed, and then cold isostatically pressed to obtain NdFeB compacts;

[0025] 2) placing the low melting point alloy sheet obtained in the above step on one side of the NdFeB compact to obtain a combined compact;

[0026] 3) subjecting the combined green sheets obtained in the above steps to infiltration and sintering to obtain an initial magnet;

[0027] 4) Cutting the initial magnet obtained in the above step into segments to obtain a plurality of magnet intermediates;

[0028] 5) The plurality of magnet intermediates obtained in the above steps are subjected to tempering treatment to obtain sintered NdFeB magnets with different target element contents.

[0029] Preferably, the melting point of the low-melting-point alloy sheet is less than or equal to 900°C;

[0030] The density of the NdFeB compact is 3.2-4.2 g / cm 3 ;

[0031] The thickness of the compact is 5 to 20 μm;

[0032] The mass ratio of the low melting point alloy sheet to the pressed green sheet is 5% to 10%.

[0033] Preferably, the heating rate of the diffusion process is 2 to 10°C / min;

[0034] The oxygen content in the diffusion process is less than or equal to 0.1 ppm;

[0035] The diffusion method includes pressure diffusion;

[0036] The pressure is 50kPa~5Mpa;

[0037] The sintering temperature is 1050-1100°C.

[0038] Preferably, the holding time of the sintering treatment is 2 to 5 hours;

[0039] The vacuum degree of the sintering process is less than or equal to 10 -3 Pa;

[0040] The direction of the cutting and segmenting is perpendicular to the diffusion direction of the NdFeB magnet;

[0041] The vacuum degree of the tempering treatment is less than or equal to 10 -3 Pa;

[0042] The sintered NdFeB magnets with different target element contents are multiple NdFeB magnets with different target element contents.

[0043] Preferably, the tempering treatment includes a first tempering treatment stage and a second tempering treatment stage;

[0044] The temperature of the first tempering treatment is 850-950°C;

[0045] The first tempering treatment time is 3 to 5 hours;

[0046] The temperature of the second tempering treatment is 450-600°C;

[0047] The second tempering treatment lasts for 3 to 5 hours.

[0048] The present invention provides a neodymium iron boron magnet intermediate, which is obtained by infiltration and sintering a neodymium iron boron compact and a low-melting-point alloy sheet composited on the neodymium iron boron compact. Compared with the prior art, the present invention aims to address the problems of long test cycles, large errors, poor test repeatability and comparability, and cumbersome operation in existing research on the effects of various elements on the properties of sintered neodymium iron boron permanent magnet materials, and to prepare sintered neodymium iron boron magnets with different target element contents. The present invention specifically begins with the study of neodymium iron boron magnet compacts, using the compacts as the starting material and, through specific infiltration of the compacts, creatively obtaining a neodymium iron boron magnet intermediate. The present invention can form a concentration gradient in the alloy melt along the diffusion direction, so the target element in the alloy will also form a content gradient in the compact. After segmented cutting, the elements of each magnetic block are evenly distributed through tempering heat treatment. This ensures that the target element content between the magnetic blocks is distributed in a gradient after one process, and that the composition and structure of each magnetic block are uniform. A large number of sintered NdFeB magnets with different target element contents can be efficiently produced in a short period of time, that is, high-throughput preparation of sintered NdFeB magnets with different target element contents is achieved.

[0049] The present invention discloses a high-throughput process for preparing sintered NdFeB magnets with different target element contents. The process comprises the following steps: a low-melting-point alloy sheet containing the target element is laid on the top of the NdFeB compact, and a sintering heat treatment is performed and an alloy diffusion infiltration effect is performed to form a content gradient of the target element inside the NdFeB compact. After sintering and densification, the NdFeB compact is segmented and cut into pieces along the alloy diffusion infiltration direction. Each piece is then uniformly subjected to a long-term tempering heat treatment to make the composition and structure of each magnetic block uniform, thereby simultaneously obtaining multiple NdFeB magnets with different target element contents. Compared with the sample preparation performed by the traditional method, many preparation processes that require different components to affect the material system require a lot of time. On this basis, the present invention analyzes the structure and performance of magnets with different target element contents, and can efficiently and accurately study the influence of each element or the combined effect of several elements on the structure and performance of the sintered NdFeB magnet. The test cycle is short, the operation is simple, and the test repeatability is strong. The process is of great significance to the sintered NdFeB industry and the field of rare earth permanent magnet materials, especially magnet research.

[0050] Experimental results show that the preparation method provided by the present invention can be used to efficiently prepare magnets with different target element contents in batches. Moreover, according to the control of the covering amount of low-melting-point alloy sheets and the heat treatment process during the implementation process, the concentration content of the target element among the prepared multiple magnets can be distributed in a relatively gentle gradient. The relatively gentle concentration gradient ensures the effective collection of samples with specific content of the target element and related data. At the same time, each magnet has a uniform composition and organizational structure, which ensures the repeatability of the sample and the reliability of related research. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic diagram showing the movement of target elements in the diffusion and sintering treatments provided by the present invention;

[0052] Figure 2 A schematic diagram of the key process for high-throughput preparation of NdFeB magnets with different target element contents provided by the present invention. DETAILED DESCRIPTION

[0053] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the patent claims of the present invention.

[0054] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0055] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials with conventional purity in the field of NdFeB magnet diffusion treatment.

[0056] All raw materials of the present invention, their sources and abbreviations are conventional sources and abbreviations in the field, and are clear and unambiguous in the field of their relevant uses. Those skilled in the art can purchase them from commercial sources or prepare them by conventional methods based on the abbreviations and corresponding uses.

[0057] The invention provides a NdFeB magnet intermediate. The NdFeB magnet intermediate is obtained by subjecting a NdFeB compact and a low-melting-point alloy sheet composited on the NdFeB compact to infiltration and sintering treatment.

[0058] In the present invention, the NdFeB compact is preferably obtained by orienting and pressing NdFeB raw material.

[0059] In the present invention, the density of the NdFeB compact is preferably 3.2 to 4.2 g / cm 3 , more preferably 3.4 to 4.0 g / cm 3 , more preferably 3.6 to 3.8 g / cm 3 .

[0060] In the present invention, the thickness of the green compact is preferably 5 to 50 mm, more preferably 10 to 40 mm, and even more preferably 20 to 30 mm.

[0061] In the present invention, the NdFeB compact is preferably not subjected to densification treatment.

[0062] In the present invention, the NdFeB compact is preferably a loose green body with micropores.

[0063] In the present invention, the densification treatment preferably includes one or more of densification sintering, semi-densification sintering, and pre-sintering, and more preferably includes multiple of these. It should be noted that the matrix material subjected to diffusion in the present invention is a compact, a loose, porous body, i.e., a green body, rather than a cooked body that has undergone treatment that facilitates magnet densification.

[0064] In the present invention, the melting point of the low-melting-point alloy sheet is preferably equal to or less than 900°C, more preferably equal to or less than 880°C, and even more preferably equal to or less than 870°C.

[0065] In the present invention, the low melting point alloy sheet is preferably an alloy diffusion source for infiltration.

[0066] In the present invention, the mass ratio of the low melting point alloy sheet to the green compact is preferably 5% to 10%, more preferably 6% to 9%, and even more preferably 7% to 8%.

[0067] In the present invention, the diffusion and sintering treatment is a continuous process of continuously heating to the sintering temperature and keeping the temperature.

[0068] It should be pointed out that the diffusion in the present invention is different from the traditional grain boundary diffusion. It is not diffusion, but a combination of infiltration and diffusion. In the present invention, the low melting point alloy melts under the condition of heating to 500-800℃. Under the action of gas pressure and continuous heating, the target element begins to penetrate into the magnet green body. Due to the use of loose and porous green body, the penetration depth is quite large, but the overall elements are unevenly distributed in the green body. After the temperature reaches 900℃, the green body has a considerable density (6.0g / cm 3 Above), the pores are filled with liquid phase, and the target elements begin to diffuse (i.e., diffuse) in the liquid phase (grain boundary phase) with the help of the liquid phase, so that the elements are relatively evenly distributed on the surface perpendicular to the diffusion direction. After all heat treatments (including the sintering process) are completed, the concentration of the target elements is gradiently distributed along the diffusion direction.

[0069] See also Figure 1 , Figure 1 This is a simplified diagram showing the movement of target elements in the diffusion and sintering treatments provided by the present invention.

[0070] In the present invention, between 900° C. and the sintering temperature, the original pressure can be maintained or the sintering can be carried out in a vacuum state.

[0071] In the present invention, the sintering process preferably includes a dicing process.

[0072] In the present invention, the cutting direction is preferably perpendicular to the diffusion direction of the NdFeB magnet.

[0073] In the present invention, the slicing produces sintered NdFeB magnets with different target element contents. Specifically, the target element content in the sintered NdFeB magnets with different target element contents varies in a gradient. More specifically, the gradient variation is preferably a step-like, decreasing gradient variation in the target element content along the diffusion direction.

[0074] The present invention provides a method for preparing sintered NdFeB magnets with different target element contents, comprising the following steps:

[0075] 1) Alloying a multi-element raw material containing a target element to obtain a low-melting-point alloy sheet;

[0076] The NdFeB raw material powder is oriented and pressed, and then cold isostatically pressed to obtain NdFeB compacts;

[0077] 2) placing the low melting point alloy sheet obtained in the above step on one side of the NdFeB compact to obtain a combined compact;

[0078] 3) subjecting the combined green sheets obtained in the above steps to infiltration and sintering to obtain an initial magnet;

[0079] 4) Cutting the initial magnet obtained in the above step into segments to obtain a plurality of magnet intermediates;

[0080] 5) The plurality of magnet intermediates obtained in the above steps are subjected to tempering treatment to obtain sintered NdFeB magnets with different target element contents.

[0081] In the present invention, the initial magnet is the above-mentioned NdFeB magnet intermediate.

[0082] The present invention first alloys a multi-element raw material containing a target element to obtain a low-melting-point alloy sheet;

[0083] The NdFeB raw material powder is oriented and pressed, and then cold isostatically pressed to obtain the NdFeB compact.

[0084] In the present invention, the melting point of the low-melting-point alloy sheet is preferably less than or equal to 900° C., more preferably less than or equal to 800° C., and even more preferably less than or equal to 600° C. Specifically, the melting point of the low-melting-point alloy sheet can be 500-800° C., 550-750° C., or 600-700° C.

[0085] In the present invention, the density of the NdFeB compact is preferably 3.2 to 4.2 g / cm 3 , more preferably 3.4 to 4.0 g / cm 3 , more preferably 3.6 to 3.8 / cm 3 .

[0086] In the present invention, the thickness of the green compact is preferably 5 to 20 m, more preferably 8 to 17 m, and even more preferably 13 to 14 m.

[0087] The present invention further places the low melting point alloy sheet obtained in the above steps on one surface of the NdFeB compact to obtain a combined compact.

[0088] In the present invention, the mass ratio of the low melting point alloy sheet to the green compact is preferably 5% to 10%, more preferably 6% to 9%, and even more preferably 7% to 8%.

[0089] The present invention then performs diffusion and sintering on the combined green sheets obtained in the above steps to obtain an initial magnet. Specifically, the initial magnet is the aforementioned NdFeB magnet intermediate.

[0090] In the present invention, the heating rate of the diffusion process is preferably 2-10°C / min, more preferably 3-9°C / min, more preferably 4-8°C / min, and more preferably 5-7°C / min.

[0091] In the present invention, the oxygen content in the diffusion process is preferably less than or equal to 0.1 ppm, more preferably less than or equal to 0.09 ppm, and more preferably less than or equal to 0.08 ppm.

[0092] In the present invention, the diffusion method preferably includes pressure diffusion.

[0093] In the present invention, the pressure is preferably 50 kPa to 5 MPa, more preferably 0.1 to 4 MPa, and even more preferably 1 to 3 MPa.

[0094] In the present invention, during the infiltration process, the temperature of the infiltration process is less than or equal to 900°C, more preferably 500-900°C, and more preferably 600-800°C. Specifically, the starting temperature of the infiltration is when the low-melting-point alloy sheet reaches the melting temperature.

[0095] In the present invention, the temperature of the sintering treatment is preferably 1050-1100°C, more preferably 1060-1090°C, and even more preferably 1070-1080°C.

[0096] In the present invention, the holding time of the sintering treatment is preferably 2 to 5 hours, more preferably 2.5 to 4.5 hours, and even more preferably 3 to 4 hours.

[0097] In the present invention, the vacuum degree of the sintering process is preferably less than or equal to 10 -3 Pa, more preferably less than or equal to 10 - 4 Pa, more preferably less than or equal to 10 -5 Pa.

[0098] In the present invention, the sintering process is carried out directly after the diffusion process. The oxygen content is strictly controlled to be less than 0.1ppm during the diffusion process. Pressure diffusion can be used. Most preferably, argon is used as the gas with a pressure between 50kPa and 5Mpa. After the temperature is raised to the sintering temperature, the sintering process is carried out under vacuum and kept warm for 2 to 5 hours. The vacuum degree is less than 10 -3 Pa.

[0099] The present invention then cuts the initial magnet obtained in the above steps into pieces and segments to obtain a plurality of magnet intermediates.

[0100] In the present invention, the direction of cutting and segmenting is preferably perpendicular to the diffusion direction of the NdFeB magnet.

[0101] Finally, the present invention subjects the plurality of magnet intermediates obtained in the above steps to tempering treatment to obtain sintered NdFeB magnets with different target element contents.

[0102] Specifically, the sintered NdFeB magnets of the present invention are preferably not sintered NdFeB magnets for practical applications, but are used for magnet performance research, especially magnet composition design research, and contain single or multiple target elements with different contents of parallel magnet samples.

[0103] In the present invention, the vacuum degree of the tempering treatment is preferably less than or equal to 10 -3 Pa, more preferably less than or equal to 10 - 4 Pa, more preferably less than or equal to 10 -5 Pa.

[0104] In the present invention, the sintered NdFeB magnets with different target element contents are preferably multiple NdFeB magnets with different target element contents.

[0105] In the present invention, the tempering treatment preferably includes a first tempering treatment stage and a second tempering treatment stage.

[0106] In the present invention, the temperature of the first tempering treatment is preferably 850-950°C, more preferably 870-930°C, and even more preferably 890-910°C.

[0107] In the present invention, the time of the first tempering treatment is preferably 3 to 5 hours, more preferably 3.4 to 4.6 hours, and even more preferably 3.8 to 4.2 hours.

[0108] In the present invention, the temperature of the second tempering treatment is preferably 450-600°C, more preferably 480-570°C, and even more preferably 510-540°C.

[0109] In the present invention, the second tempering treatment time is preferably 3 to 5 hours, more preferably 3.4 to 4.6 hours, and even more preferably 3.8 to 4.2 hours.

[0110] The present invention discloses a high-throughput process for preparing sintered NdFeB magnets with different target element contents, which belongs to the field of rare earth permanent magnet materials and comprises the following steps: (1) laying a prepared low-melting-point alloy containing the target element on top of the NdFeB compact, accompanying the sintering heat treatment and forming a target element content gradient within the NdFeB compact through alloy diffusion; (2) after sintering and densification, the NdFeB compact is segmented and cut into pieces along the alloy diffusion direction; (3) each piece is uniformly subjected to a long-term tempering heat treatment to make the composition and structure of each magnetic block uniform, thereby simultaneously obtaining multiple NdFeB magnets with different target element contents. A large number of sintered NdFeB magnets with different target element contents can be efficiently produced in a short period of time, and the influence of different target element contents on the structure and properties of NdFeB magnets can be tested in a high-throughput manner, which is of great significance to the sintered NdFeB industry and the field of rare earth permanent magnet materials.

[0111] The present invention is to better complete and refine the overall technical solution, better improve the magnet's targetability, stability and repeatability. The above-mentioned high-throughput process for preparing sintered NdFeB magnets with different target element contents can specifically be the following steps:

[0112] The high-throughput process for preparing sintered NdFeB magnets with different target element contents comprises laying a prepared low-melting-point alloy sheet containing the target element on top of a NdFeB compact, forming a target element content gradient inside the NdFeB compact through sintering heat treatment and alloy diffusion, cutting the NdFeB compact into segments along the alloy diffusion direction after sintering and densification, and then uniformly subjecting each segment to a long-term tempering heat treatment to make the composition and structure of each magnet segment uniform, thereby simultaneously obtaining multiple NdFeB magnets with different target element contents.

[0113] Specifically, the following steps are included:

[0114] Step 1: preparing an alloy sheet containing the target element: alloying the target element with other elements to obtain a low-melting-point alloy sheet;

[0115] Step 2: preparing NdFeB compacts: orienting and pressing NdFeB powder and performing cold isostatic pressing to obtain compacts;

[0116] Step 3: Placing alloy sheets: evenly placing the alloy sheets obtained in step 1 on top of the compact obtained in step 2 to obtain a composite compact;

[0117] Step 4: Infiltration and sintering: Infiltration and high vacuum sintering of the above-mentioned combined blank in a low-oxygen environment to obtain an initial magnet;

[0118] Step 5: Cutting: Cut the initial magnet into segments from the top to the bottom to obtain a series of magnets;

[0119] Step 6: Homogenization and tempering: The above series of magnets are uniformly subjected to high vacuum tempering to obtain the final magnet.

[0120] Specifically, the low-melting-point alloy sheet is obtained by solid casting or other alloying technology, the target elements are evenly distributed in the alloy, and the melting point of the alloy is not higher than 900°C.

[0121] Specifically, the green compact described in step 2 has a thickness of 5 mm to 20 mm and a density of 3.2 g / cm 3 ~4.2g / cm 3 .

[0122] Specifically, the amount of the alloy sheet covered in step 3 is 5% to 10% of the mass of the green compact.

[0123] Specifically, in the diffusion and high vacuum sintering process described in step 4, the temperature is raised to 1050-1100° C. at a heating rate of 2° C. / min-10° C. / min, and the temperature is kept at the highest temperature for 2-5 hours.

[0124] Specifically, in step six, the series of magnets are tempered in high vacuum at 850-950° C. and 450-600° C. for 3-5 hours respectively.

[0125] See also Figure 2 , Figure 2 A schematic diagram of the key process for high-throughput preparation of NdFeB magnets with different target element contents provided by the present invention.

[0126] The first step is to co-sinter and diffuse the NdFeB compact with the diffusion source; the second step is to cut the diffused magnet into small pieces of uniform size; and the third step is to homogenize and temper the cut small pieces of magnet.

[0127] The above steps of the present invention provide a process for high-throughput preparation of sintered NdFeB magnets with different target element contents. The present invention starts with NdFeB magnet compacts and conducts research. Using the compacts as the starting material, the compacts are diffused through a specific compact to creatively obtain a NdFeB magnet intermediate. The present invention can form a concentration gradient in the alloy melt along the diffusion direction, so that the target element in the alloy will also form a content gradient in the compact. After segmentation and block cutting, tempering heat treatment is used to uniformly distribute the elements of each magnet block. This ensures that the target element content between the magnet blocks is distributed in a gradient after one process, and also ensures that the composition and structure of each magnet block are uniform. A large number of sintered NdFeB magnets with different target element contents can be efficiently produced in a short period of time, that is, high-throughput preparation of sintered NdFeB magnets with different target element contents is achieved.

[0128] The present invention discloses a high-throughput process for preparing sintered NdFeB magnets with different target element contents. The process comprises the following steps: a low-melting-point alloy sheet containing the target element is laid on the top of the NdFeB compact, and a sintering heat treatment is performed and an alloy diffusion infiltration effect is performed to form a content gradient of the target element inside the NdFeB compact. After sintering and densification, the NdFeB compact is segmented and cut into pieces along the alloy diffusion infiltration direction. Each piece is then uniformly subjected to a long-term tempering heat treatment to make the composition and structure of each magnetic block uniform, thereby simultaneously obtaining multiple NdFeB magnets with different target element contents. Compared with the sample preparation performed by the traditional method, many preparation processes that require different components to affect the material system require a lot of time. On this basis, the present invention analyzes the structure and performance of magnets with different target element contents, and can efficiently and accurately study the influence of each element or the combined effect of several elements on the structure and performance of the sintered NdFeB magnet. The test cycle is short, the operation is simple, and the test repeatability is strong. The process is of great significance to the sintered NdFeB industry and the field of rare earth permanent magnet materials, especially magnet research.

[0129] Experimental results show that the preparation method provided by the present invention can be used to efficiently prepare magnets with different target element contents in batches. Moreover, according to the control of the covering amount of low-melting-point alloy sheets and the heat treatment process during the implementation process, the concentration content of the target element among the prepared multiple magnets can be distributed in a relatively gentle gradient. The relatively gentle concentration gradient ensures the effective collection of samples with specific content of the target element and related data. At the same time, each magnet has a uniform composition and organizational structure, which ensures the repeatability of the sample and the reliability of related research.

[0130] To further illustrate the present invention, a method for preparing a NdFeB magnet intermediate and a sintered NdFeB magnet with different target element contents provided by the present invention are described in detail below in conjunction with the examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The scope of protection of the present invention is not limited to the following examples.

[0131] Example 1

[0132] The rare earth metal Pr, metal Cu and metal Al were mixed in an atomic ratio of 36:32:32 and smelted in vacuum homogenization. The smelted alloy ingot was spun into alloy flakes at a linear speed of 10 m / s by vacuum spinning. Under oxygen-controlled conditions, NdFeB powder particles with a particle size of 3-5 μm and a composition of Nd27.5Fe71.3B1.2 were oriented and pressed in a 1.8 T magnetic field and cold isostatically pressed at 180 MPa to obtain 10×10×25 mm 3 Green compact, green compact density is 4.0g / cm 3 550 mg of alloy flakes were evenly spread on the top of the green sheet and placed in a vacuum heat treatment furnace. The temperature was raised to 1060°C at a rate of 5°C / min and kept at that temperature for 3 hours. The green sheet was then rapidly cooled to obtain a sintered green sheet. The green sheet was cut into 5 pieces of 10×10×5 mm in parallel to the surface covered with the alloy flakes. 3 magnet; the magnet was high vacuum tempered at 900℃ and 500℃ for 2h respectively; 5 sintered NdFeB magnets with different target element contents were obtained.

[0133] According to ICP measurement, the Pr element content in the five magnets was 30.2%, 15.0%, 8.3%, 2.1% and 0.3% (wt.%), respectively; the Cu element content was 18.6%, 10.4%, 5.7%, 2.6% and 0.8% (wt.%), respectively; the Al element content was 7.9%, 4.5%, 2.4%, 0.9% and 0.5% (wt.%), respectively. The content of the target elements showed a gradient change, and the microstructure of each magnet block was uniform after observation.

[0134] Example 2

[0135] The rare earth metal Pr, rare earth metal Tb, metal Cu and metal Zr were mixed in an atomic ratio of 30:20:25:25 and smelted in vacuum homogenization; the smelted alloy ingot was spun into alloy flakes at a linear speed of 8m / s by vacuum spinning; NdFeB powder particles with a particle size of 3-5μm and a composition of Nd28.8Fe70.2B1.0 were oriented and pressed in a 1.8T magnetic field and cold isostatically pressed at 220MPa under an oxygen-controlled environment to obtain 15×15×40mm 3 Green compact, green compact density is 4.1g / cm 3 1900 mg of alloy flakes were evenly spread on the top of the green compact and placed in a vacuum heat treatment furnace. The temperature was raised to 1080°C at a rate of 4°C / min and kept at that temperature for 3 hours. The green compact was then rapidly cooled to obtain a sintered green compact. The green compact was cut into 8 pieces of 15×15×5 mm in parallel to the surface of the alloy flakes. 3 magnet; the magnet was tempered in high vacuum at 920℃ and 510℃ for 2h respectively; 8 sintered NdFeB magnets with different target element contents were obtained.

[0136] According to ICP measurement, the Pr element contents in the 8 magnets were 25.6%, 13.5%, 6.9%, 4.1%, 3.0%, 2.2%, 1.3% and 0.3% (wt.%), respectively; the Tb element contents were 15.5%, 9.8%, 6.5%, 3.7%, 2.5%, 1.5%, 0.6% and 0.2% (wt.%), respectively; the Cu element contents were 11.9%, 6.2%, 3.5%, 2.4%, 1.7%, 1.2%, 0.4% and 0.1% (wt.%), respectively; the Zr element contents were 18.2%, 9.5%, 5.5%, 3.5%, 2.4%, 1.4%, 0.5% and 0.1% (wt.%), respectively. The target element contents varied gradiently, and the microstructure of each magnet block was uniform after observation.

[0137] Example 3

[0138] The rare earth metal Pr, rare earth metal Tb, metal Cu and metal Al were mixed in an atomic ratio of 40:20:25:15 and smelted in vacuum homogenization; the smelted alloy ingot was spun into alloy flakes at a linear speed of 8 m / s by vacuum spinning; NdFeB powder particles with a particle size of 3-5 μm and a composition of Nd28.8Fe70.2B1.0 were oriented and pressed in a 1.8 T magnetic field and cold isostatically pressed at 200 MPa under an oxygen-controlled environment to obtain 10×10×30 mm 3 Green compact, green compact density is 4.0g / cm 3600 mg of alloy flakes were evenly spread on the top of the green sheet and placed in a vacuum heat treatment furnace. The temperature was raised to 1070°C at a rate of 6°C / min and kept at that temperature for 3 hours. The green sheet was then rapidly cooled to obtain a sintered green sheet. The green sheet was cut into 6 pieces of 10×10×5 mm in parallel to the surface covered with the alloy flakes. 3 magnet; the magnet was high vacuum tempered at 890℃ and 500℃ for 2h respectively; 6 sintered NdFeB magnets with different target element contents were obtained.

[0139] According to ICP measurement, the Pr element contents in the six magnets were 32.6%, 18.5%, 9.9%, 3.1%, 1.0% and 0.4% (wt.%), respectively; the Tb element contents were 16.5%, 9.8%, 4.5%, 1.5%, 0.5% and 0.2% (wt.%), respectively; the Cu element contents were 12.3%, 6.6%, 2.4%, 1.9%, 1.2% and 0.2% (wt.%), respectively; and the Al element contents were 5.5%, 2.8%, 1.6%, 0.7%, 0.2% and 0.1% (wt.%), respectively. The target element contents showed a gradient change, and the microstructure of each magnet block was uniform after observation.

[0140] The above is a detailed introduction to a high-throughput process for preparing sintered NdFeB magnets with different target element contents provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be noted that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the literal wording of the claims, or if they include equivalent structural elements that are not substantially different from the literal wording of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing sintered NdFeB magnets with different target element contents, characterized in that: The following steps are involved: 1) Alloying a multi-element raw material containing a target element to obtain a low-melting-point alloy sheet; The NdFeB raw material powder is oriented and pressed, and then cold isostatically pressed to obtain NdFeB compacts; 2) placing the low melting point alloy sheet obtained in the above step on one side of the NdFeB compact to obtain a combined compact; 3) subjecting the combined green sheets obtained in the above steps to infiltration and sintering to obtain an initial magnet; The diffusion method includes pressure diffusion; 4) Cutting the initial magnet obtained in the above step into segments to obtain a plurality of magnet intermediates; 5) The plurality of magnet intermediates obtained in the above steps are subjected to tempering treatment to obtain sintered NdFeB magnets with different target element contents.

2. The preparation method according to claim 1, characterized in that The density of the NdFeB compact is 3.2-4.2 g / cm 3 ; The thickness of the compact is 5 to 50 mm.

3. The preparation method according to claim 1, characterized in that The NdFeB compact is not subjected to densification treatment; The NdFeB compact is a loose green body with micropores; The densification treatment includes one or more of densification sintering, semi-densification sintering and pre-sintering.

4. The preparation method according to claim 1, characterized in that The melting point of the low-melting-point alloy sheet is less than or equal to 900° C. The low melting point alloy sheet is an alloy diffusion source for infiltration; The mass ratio of the low melting point alloy sheet to the pressed green sheet is 5% to 10%.

5. The preparation method according to claim 1, characterized in that The heating rate of the diffusion process is 2 to 10°C / min; The oxygen content in the diffusion process is less than or equal to 0.1 ppm.

6. The preparation method according to claim 1, characterized in that The pressure is 50kPa~5Mpa; The sintering temperature is 1050-1100°C.

7. The preparation method according to claim 1, characterized in that The holding time of the sintering treatment is 2 to 5 hours; The vacuum degree of the sintering process is less than or equal to 10 -3 Pa.

8. The preparation method according to claim 1, characterized in that The direction of the cutting and segmenting is perpendicular to the diffusion direction of the NdFeB magnet.

9. The preparation method according to claim 1, characterized in that The vacuum degree of the tempering treatment is less than or equal to 10 -3 Pa; The sintered NdFeB magnets with different target element contents are multiple NdFeB magnets with different target element contents.

10. The preparation method according to claim 1, characterized in that The tempering treatment includes a first tempering treatment stage and a second tempering treatment stage; The temperature of the first tempering treatment is 850-950°C; The first tempering treatment time is 3 to 5 hours; The temperature of the second tempering treatment is 450-600°C; The second tempering treatment lasts for 3 to 5 hours.

Images