CN112053824B - Sintered NdFeB permanent magnet and preparation method thereof - Google Patents

Abstract

The present invention provides a method for preparing sintered NdFeB permanent magnets, which includes the steps of batching, smelting, hydrogen crushing, jet milling, molding, sintering, machining, coating and heat treatment. The sintered NdFeB permanent magnet prepared by the method comprises: 29-33wt% of R, 5-20wt% of Co, 0.8-1.0wt% of B, greater than 0 and less than or equal to 2wt% of M, and the rest is Fe and not Impurities to avoid; wherein R is composed of the second rare earth element and the first rare earth element, and M is selected from one or more elements of Cu, Al, Zr, Nb, Ti and Ga. The invention not only has high cobalt content and high Curie temperature, but also achieves balance between coercive force and remanence, reduces heavy rare earth content and reduces production cost.

Description

A kind of sintered NdFeB permanent magnet and its preparation method

technical field

The invention relates to the technical field of magnetic materials, in particular to a sintered NdFeB permanent magnet and a preparation method thereof.

Background technique

Sintered NdFeB permanent magnet material has excellent characteristics of high remanence, high magnetic energy product and high coercive force. It is the strongest permanent magnet today and is known as the king of permanent magnet materials. As a new generation of rare earth permanent magnet materials, NdFeB magnets are widely used in computer technology, automobile industry, aerospace military industry, automation technology, instrument technology, microwave communication technology and wind power generation. NdFeB magnets are cost-effective and have good mechanical properties; but the disadvantage is that the Curie temperature is low, the Curie temperature is only about 320 ° C, and the temperature characteristics are poor. Generally, they can only work at temperatures below 150 ° C. The application of NdFeB permanent magnet materials in high temperature field.

In order to increase the Curie temperature Tc and improve the use in high-temperature environments, it is generally necessary to adjust the amount of cobalt Co added in the sintered NdFeB permanent magnet material, but with the increase of Co content, the intrinsic coercive force Hcj of the permanent magnet material also increases. It will deteriorate sharply with the increase of Co element addition, and the lower intrinsic coercive force limits the application of NdFeB permanent magnet materials in high temperature fields. Therefore, in the existing commercial sintered NdFeB permanent magnets, the mass percentage content of Co element is often controlled below 5wt%. The percentage of expensive rare earth metal elements Dy and Tb is more than 4wt% to increase the intrinsic coercive force Hcj, but the Curie temperature of the magnet is only about 340 ° C; and adding a large amount of expensive heavy rare earth metal elements Dy and Tb will not only Increase the production cost of the enterprise. At the same time, heavy rare earth Dy or Tb is generally added in smelting, which will form a large number of main phase grains Dy2Fe14B or Tb2Fe14B, resulting in a significant decrease in remanence Br and maximum energy product (BH) _max , which is also limited to Applications in high-end market fields such as industrial motors, rail transit, and aerospace.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing a sintered NdFeB permanent magnet, and the sintered NdFeB permanent magnet prepared by the method has better comprehensive performance.

In view of this, the application provides a method for preparing a sintered NdFeB permanent magnet, comprising the following steps:

A) According to the following composition and weight percentage of the sintered NdFeB permanent magnet: the content of R is 29-33wt%, the content of Co is 5-20wt%, the content of B is 0.8-1.0wt%, and the content of M is greater than 0 and less than or equal to 2wt%, the balance is Fe, R is composed of a first rare earth element and a second rare earth element, and the first rare earth element is selected from one or more of Ce, Pr, Nd, Gd, Ho and Y The second rare earth element is selected from one or both of Dy and Tb, and the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from Cu, Al, Zr, Nb, Ti and One or more of Ga;

B) melting the raw materials after the batching to obtain the quick-setting sheet alloy;

C) jet milling the quick-setting sheet alloy with hydrogen to obtain fine alloy powder;

D) forming, sintering and machining the alloy fine powder in sequence to obtain NdFeB semi-finished products;

E) Coating a slurry containing the second rare earth element and M on the surface of the NdFeB semi-finished product, and obtaining a sintered NdFeB permanent magnet after heat treatment.

Preferably, in step B), the raw material for smelting includes the second rare earth element and M, or the raw material does not include the second rare earth element but includes M, or the raw material does not include the rare earth element and M.

Preferably, the average particle size of the hydrogen crushed powder is 10-30 μm, and the average particle size of the jet-milled powder is 1.8-3 μm.

Preferably, the grain size of the NdFeB semi-finished product is 3-8 μm.

Preferably, the slurry also includes a solvent, the mass ratio of the powder formed by the second rare earth element to the solvent is 1:1, and the solvent is selected from one of alcohol solvents and lipid solvents or Various.

Preferably, the heat treatment includes high-temperature treatment and low-temperature treatment in sequence, the temperature of the high-temperature treatment is 700-900°C, the holding time is 6-10h, the temperature of the low-temperature treatment is 480-580°C, and the holding time is 4～10h.

Preferably, the process of said sintering is specifically:

The formed green body is sintered at 1000-1090°C for 6-16 hours under vacuum condition, then tempered to 850-950°C for 1.5-3 hours, then kept at 400-600°C for 1.5-5 hours and then cooled.

Preferably, during the smelting process, the thickness of the quick-setting sheet alloy is 1.5-4mm, and the pouring temperature is 1350-1450°C.

The present application also provides the sintered NdFeB permanent magnet prepared by the preparation method, including:

R is composed of a second rare earth element and a first rare earth element, the first rare earth element is selected from one or more of Ce, Pr, Nd, Gd, Ho and Y, and the second rare earth element is selected from Dy and One or two of Tb, the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from one or more of Cu, Al, Zr, Nb, Ti and Ga.

Preferably, the content of the second rare earth element is 0.8-2wt%; the content of R is 29.5-32.5wt%.

The present application provides a method for preparing sintered NdFeB permanent magnets, which includes the preparation steps of batching, smelting, hydrogen crushing, jet milling, molding, sintering, machining, coating and heat treatment. In the above preparation process, One or both of the second rare earth elements Dy and Tb in this application is coated on the surface of the high-Co magnet by coating, and then undergoes heat treatment, so that one or both of the second rare earth elements Dy and Tb The species diffuses into the interior of the magnet, thereby improving the coercive force of the high-Co magnet, while hardly reducing the remanence Br, and finally making the comprehensive performance of the sintered NdFeB permanent magnet high.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention.

In view of the fact that in the prior art, it is difficult for NdFeB permanent magnets with high Co content to achieve a balance between intrinsic coercivity and remanence, this application provides a preparation method for sintered NdFeB permanent magnets. When it is high, the intrinsic coercive force and remanence are still well balanced, and the overall performance is high. Specifically, the embodiment of the present invention discloses a method for preparing a sintered NdFeB permanent magnet, including the following steps:

A) According to the following composition and weight percentage of the sintered NdFeB permanent magnet: the content of R is 29-33wt%, the content of Co is 5-20wt%, the content of B is 0.8-1.0wt%, and the content of M is 0.8-1.0wt%. Greater than 0 and less than or equal to 2wt%, the balance is Fe, R is composed of a second rare earth element and a first rare earth element, and the first rare earth element is selected from one of Ce, Pr, Nd, Gd, Ho and Y or Multiple, the second rare earth element is selected from one or both of Dy and Tb, the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from Cu, Al, Zr, Nb, Ti and one or more of Ga;

B) melting the raw materials after the batching to obtain the quick-setting sheet alloy;

C) jet milling the quick-setting sheet alloy with hydrogen to obtain fine alloy powder;

D) forming, sintering and machining the alloy fine powder in sequence to obtain NdFeB semi-finished products;

E) coating the slurry containing the second rare earth element and M on the surface of the NdFeB semi-finished product, and heat-treating to obtain a sintered NdFeB permanent magnet.

In the above-mentioned process of preparing sintered NdFeB permanent magnets, the applicant first carried out batching according to the composition and content of the sintered NdFeB permanent magnets. It is necessary to ensure that the final composition meets the composition requirements of sintered NdFeB permanent magnets.

After batching, the raw materials after batching are smelted to obtain a quick-setting sheet alloy with a thickness of 1.5 mm to 4 mm; , B, M and Fe formed of raw materials, can also include the first rare earth element, Co, B, M and Fe formed raw material; can also include the first rare earth element, Co, B and Fe formed raw material; can also It is a raw material composed of the first rare earth element, the second rare earth element, Co, B and Fe; the smelting is carried out in a smelting furnace, the pouring temperature of the smelting is 1350-1450°C, and the specific operation process of the smelting is according to It is carried out in a manner well known to those skilled in the art, and the present application is not particularly limited thereto.

According to the present invention, after the quick-setting sheet alloy is obtained, it is subjected to jet milling after hydrogen crushing to obtain alloy fine powder, the average particle size of the powder after hydrogen crushing is 10-30 μm, and the average particle size of the alloy fine powder is The particle size is 1.8～3μm. Both the hydrogen crushing and the jet mill are technical methods well known to those skilled in the art, and the application does not impose any special restrictions on their specific operation methods.

In the present application, the alloy fine powder is then formed, sintered and machined in sequence to obtain a NdFeB semi-finished product. The forming specifically involves mixing the alloy fine powders in a mixer for 0.5-5 hours, and pressing them into a green body by using a mold under the protection of an inert gas in a constant magnetic field environment. In the sintering process, this application is preferably carried out under vacuum conditions. The specific sintering process is: sintering the formed green body at 1000-1090°C for 6-16h under vacuum conditions, and then tempering to 850-950°C Keep warm for 1.5-3 hours, then keep warm at 400-600°C for 1.5-5 hours and then cool. After sintering, the blank obtained is cut to obtain semi-finished products. In this application, the grain size of the sintered blank is 3-8 μm, and the grain size will affect the coercive force of the magnet. The dimension in the thickness direction of the semi-finished product is ≤8mm.

According to the present invention, after the above-mentioned semi-finished product is obtained, the slurry containing the second rare earth element and M is coated on the surface of the NdFeB semi-finished product, so as to coat a coating film on the surface of the NdFeB semi-finished product . The above-mentioned slurry also includes a solvent, which is a solvent well known to those skilled in the art, specifically, it can be selected from one or more of alcohol solvents and lipid solvents, more specifically, selected from ethanol, ethylene glycol Alcohol or epoxy resin. The mass ratio of the powder formed by the second rare earth element to the solvent is 1:1. In the above slurry, when the second rare earth element and M element are contained, the above two raw materials in the slurry are added in the form of alloy powder. In addition to adding the second rare earth element and M raw materials in the application, they can also be added during the smelting process, but it is necessary to ensure that the content of the two in the final sintered NdFeB permanent magnet complies with the element composition of the application content.

The applicant then heat-treats the semi-finished product coated with a film on the surface. The heat treatment is preferably carried out in a sintering furnace, preferably filled with argon in the sintering furnace. High-temperature treatment followed by low-temperature treatment, the temperature of the high-temperature treatment is 700-900° C., the holding time is 6-10 hours, the temperature of the low-temperature treatment is 480-580° C., and the holding time is 4-10 hours. During the above heat treatment, one or both of Dy and Tb are distributed at the grain boundaries, and the main phase grains Dy2Fe14B or Tb2Fe14B that greatly reduce the remanence Br will not be formed, thereby ensuring the comprehensive performance.

The present application also provides a sintered NdFeB magnet prepared by the preparation method described in the above scheme, including:

R is composed of a second rare earth element and a first rare earth element, the first rare earth element is selected from one or more of Ce, Pr, Nd, Gd, Ho and Y, and the second rare earth element is selected from Dy and One or two of Tb, the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from one or more of Cu, Al, Zr, Nb, Ti and Ga.

In the above sintered NdFeB magnet, the content of R is 29.5-32.5wt%, the content of Co is 8-18wt%, the content of M is 0.6-1.5wt%, and the content of the second rare earth element 0.8 to 2 wt%.

The present invention obtains a high-performance NdFeB permanent magnet by improving the sintered NdFeB permanent magnet and its manufacturing method, which not only has high cobalt content but also has a high Curie temperature, effectively solving the problem of existing sintered NdFeB permanent magnets. The problem of low Curie temperature of boron permanent magnet materials reduces the content of heavy rare earths and reduces production costs.

The present invention has greatly improved the chemical composition and weight percentage of the sintered NdFeB permanent magnet, increased the Co content, greatly increased the Curie temperature of the sintered NdFeB permanent magnet, and made the sintered NdFeB permanent magnets can be used in high-temperature environments, expanding their scope of use. In the manufacturing process, the coating method and the coating mixed with heavy rare earth alloy and solvent can effectively improve the coercive force of the magnet, ensure that the high-Co permanent magnet has higher performance, and the application environment is wider.

In order to further understand the present invention, the sintered NdFeB permanent magnet provided by the present invention and its preparation method will be described in detail below in conjunction with the examples, and the protection scope of the present invention is not limited by the following examples.

Example 1

The manufacturing method of the high-performance sintered NdFeB permanent magnet of the present embodiment comprises the following steps:

1) Ingredients: NdFeB magnetic material is prepared according to the chemical composition and weight percentage of high-performance sintered NdFeB permanent magnets, and the composition and weight percentage of the FeB magnetic material are weighed for use;

The weight percentage test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in the column of Example 1 in Table 1, wherein R is Ce, Pr, Nd, Tb, Dy and Y , M is Cu, Al, Zr and Ga, and the rest are Fe and unavoidable impurities;

2) Smelting: first put the sintered NdFeB magnetic material into the melting furnace for melting to obtain a quick-setting sheet alloy with a thickness of 1.5mm to 4mm, and the pouring temperature is 1380°C;

3) Hydrogen crushing: put the quick-setting sheet alloy into the hydrogen crushing device, and the quick-setting sheet alloy is processed by hydrogen crushing to obtain coarse powder, and the average particle size of the coarse powder is 20.8 μm;

4) Milling: the hydrogen-crushed coarse powder is pulverized by jet mill, and crushed into fine powder, the average particle size of fine powder is 1.86 μm;

5) Molding: Mix the above fine powder in a mixer for 1 hour, protect it with an inert gas, and press it into a green body with a mold in a constant magnetic field environment;

7) Sintering: The green body is sintered at a high temperature of 1000°C for 16 hours under vacuum conditions, then tempered to 900°C for 1.5 hours, and then kept at 500°C for 4 hours and cooled to obtain a blank. The grain size of the blank is 6.5 μm;

8) Mechanical processing: cutting the blank into semi-finished products of a certain size, and the size of the semi-finished product in the thickness direction is 6.01mm;

9) Coating: After the semi-finished product is pretreated by degreasing, the semi-finished permanent magnet with no impurities on the surface is obtained. The surface of the semi-finished permanent magnet is uniformly coated with a layer of coating film and dried. The coating is TbDyAl alloy powder and solvent The mixture of ethanol, the weight ratio of TbDyAl alloy powder and solvent is 1:1;

10) Heat treatment: Place the coated permanent magnet semi-finished product in the sintering box, put the sintering box with the permanent magnet semi-finished product into the sintering furnace, evacuate to below 10 ^-2 Pa, and fill the argon gas with a pressure of 0.02 Mpa, high-temperature treatment first, and then low-temperature heat treatment to obtain sintered NdFeB permanent magnets. The temperature of high-temperature treatment is 880°C, the holding time of high-temperature treatment is 10h, the temperature of low-temperature treatment is 500°C, and the holding time of low-temperature treatment is 4h.

Example 2

The test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in the column of Example 2 in Table 1, where R is Pr, Nd, Gd, Ho, Tb, M For Cu, Al and Nb, the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 2 of Example 2 in Table 2.

Example 3

The test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 3 of Example 1 in Table 1, wherein R is Pr, Nd, Tb, and M is Cu and Ti. , Al, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 3 of Example 2 in Table 2.

Example 4

The weight percentage test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 4 of Example 1 in Table 1, wherein R is Pr, Nd, Dy, Tb, and M is Cu , Zr, Al, Ga, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 4 of Example 2 in Table 2.

Example 5

The weight percent content test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 5 of Example 1 in Table 1, wherein R is Pr, Nd, Dy, Tb, and M is Al, Cu, Zr, Ga, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 5 of Example 2 in Table 2.

Example 6

The test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 6 of Example 1 in Table 1, wherein R is Pr, Nd, Ho, Tb, and M is Nb. , Cu, Zr, Ga, Al, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 6 of Example 2 in Table 2.

Example 7

The test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 7 of Example 1 in Table 1, wherein R is Pr, Nd, Tb, and M is Ga, Al , Cu, Ti, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 7 of Example 2 in Table 2.

Example 8

The test results of the main chemical components in the high-performance sintered NdFeB permanent magnet of this embodiment are shown in column 8 of Example 1 in Table 1, wherein R is Nd, Tb, Dy, and M is Ti, Al , Cu, and the rest are Fe and unavoidable impurities.

The manufacturing method of the high-performance sintered NdFeB permanent magnet of this embodiment has similar process steps to that of Example 1, and the specific process parameters different from that of Example 1 are shown in column 8 of Example 2 in Table 2.

The properties of the sintered NdFeB permanent magnets prepared in Examples 1 to 8 were tested, and the test results are shown in Table 3.

Table 1 Example 1-8 High-performance sintered NdFeB permanent magnet main chemical components and weight percentage comparison table

Table 2 Example 1-8 High-performance sintered NdFeB permanent magnet manufacturing method parameter comparison table

Table 3 Comparison table of performance parameters of high-performance sintered NdFeB permanent magnets in Examples 1-8

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A preparation method of sintered NdFeB permanent magnet, comprising the following steps: A) According to the following composition and weight percentage of the sintered NdFeB permanent magnet: the content of R is 29.5-33wt%, the content of Co is 10-20wt%, the content of B is 0.88-1.0wt%, and the content of M is 0.65-2wt%, the balance is Fe, R is composed of a first rare earth element and a second rare earth element, and the first rare earth element is selected from one or more of Ce, Pr, Nd, Gd, Ho and Y, The second rare earth element is selected from one or both of Dy and Tb, and the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from Cu, Al, Zr, Nb, Ti and Ga one or more of B) melting the raw materials after the batching to obtain a quick-setting sheet alloy; the thickness of the quick-setting sheet alloy is 1.5-4 mm; C) crushing the quick-setting sheet alloy with hydrogen and jet milling to obtain alloy fine powder; the average particle size of the jet milled powder is 1.8-3 μm; D) forming, sintering and machining the alloy fine powder in sequence to obtain NdFeB semi-finished products; E) coating the slurry containing the second rare earth element and M on the surface of the NdFeB semi-finished product, and obtaining a sintered NdFeB permanent magnet after heat treatment; The heat treatment includes high-temperature treatment and low-temperature treatment in sequence, the temperature of the high-temperature treatment is 700-900°C, the holding time is 6-10h, the temperature of the low-temperature treatment is 480-580°C, and the holding time is 4-10h . 2. The preparation method according to claim 1, characterized in that, in step B), the raw material for smelting includes the second rare earth element and M, or the raw material does not include the second rare earth element but includes M , or the raw materials do not include rare earth elements and M. 3 . The preparation method according to claim 1 , characterized in that, the average particle size of the hydrogen-crushed powder is 10-30 μm, and the average particle size of the jet-milled powder is 1.8-3 μm. 4 . 4. The preparation method according to claim 1, characterized in that the grain size of the NdFeB semi-finished product is 3-8 μm. 5. preparation method according to claim 1, is characterized in that, also comprises solvent in described slurry, the mass ratio of the powder that described second rare earth element forms and described solvent is 1:1, and described solvent is selected from One or more of alcohol solvents and lipid solvents. 6. preparation method according to claim 1, is characterized in that, the process of described sintering is specifically: The formed green body is sintered at 1000-1090°C for 6-16 hours under vacuum condition, then tempered to 850-950°C for 1.5-3 hours, then kept at 400-600°C for 1.5-5 hours and then cooled. 7. The preparation method according to claim 1, characterized in that, during the smelting process, the thickness of the quick-setting sheet alloy is 1.5-4mm, and the pouring temperature is 1350-1450°C. 8. The sintered NdFeB permanent magnet prepared by the preparation method according to any one of claims 1 to 7, comprising: The balance is Fe; R is composed of a second rare earth element and a first rare earth element, the first rare earth element is selected from one or more of Ce, Pr, Nd, Gd, Ho and Y, and the second rare earth element is selected from Dy and One or two of Tb, the content of the second rare earth element is greater than 0 and less than or equal to 2wt%; M is selected from one or more of Cu, Al, Zr, Nb, Ti and Ga. 9. The sintered NdFeB permanent magnet according to claim 8, characterized in that the content of the second rare earth element is 0.8-2wt%.