RARE EARTH PERMANENT MAGNET, PREPARATION METHOD AND USE THEREOF

Abstract

The permanent magnet comprises a main phase structure of R.sub.2T.sub.14B crystal grains, and R is a rare earth element; T comprises at least Mn, Fe, and optionally a transition metal comprising Co; B is boron; the permanent magnet further comprises Mn and heavy rare earth elements which are distributed in a grain boundary in a diffusion mode. The heavy rare earth element is selected from at least one selected from Dy, Ho and Tb. According to the rare earth permanent magnet prepared through the preparation method, more heavy rare earth elements can be diffused into the magnet core along the grain boundary, Hcj distribution of the permanent magnet is improved, and meanwhile the corrosion resistance and the mechanical property of the permanent magnet are improved.

Claims

1. A rare earth permanent magnet, comprising a main phase structure of R.sub.2T.sub.14B crystal grain, wherein: R is a rare earth element; T comprises at least Mn, Fe, and optionally a transition metal comprising Co; B is boron; the permanent magnet further comprises Mn and a heavy rare earth element diffused and distributed in a grain boundary; the heavy rare earth element is at least one selected from Dy, Ho, and Tb.

2. The rare earth permanent magnet according to claim 1, wherein R is selected from Nd, and optionally comprises or does not comprise at least one selected from Pr, Dy, Tb, Ho, Ce, and Gd; preferably, the permanent magnet further comprises M; preferably, M is at least one selected from aluminum (Al), titanium (Ti), copper (Cu), gallium (Ga), zirconium (Zr), and niobium (Nb).

3. The rare earth permanent magnet according to claim 1, wherein Mn has a content of x1 at a surface of the permanent magnet, the heavy rare earth has a content of y1 at the surface, Mn has a content of x2 at 500 m away from the surface, and the heavy rare earth has a content of y2 at 500 m away from the surface, wherein x1>x2 and y1>y2; preferably, the surface of the permanent magnet has a coercivity of z1, and a core of the permanent magnet has a coercivity of z2, wherein z1>z2; preferably, the permanent magnet has a thickness of m; preferably, the permanent magnet has a thickness of m15 mm; preferably, the permanent magnet satisfies the following formulas (1) and (2):
x1/x2y1/y2 (1)
[2*x1/x2(z1z2)/2/m]0 (2) preferably, the rare earth permanent magnet has an oxygen content below 2000 ppm.

4. The rare earth permanent magnet according to claim 1, wherein the permanent magnet is obtained by arranging a diffusion source on the surface of a matrix of a neodymium-iron-boron magnet and then performing diffusion heat treatment; preferably, the matrix of the neodymium-iron-boron magnet has an oxygen content below 2000 ppm; preferably, the diffusion source comprises at least Mn and a heavy rare earth, wherein Mn has a content of no more than 20% wt, preferably 0.1-20 wt %; preferably, the diffusion heat treatment comprises at least a two-stage heat treatment; preferably, the heat treatment comprises a first-stage heat treatment followed by a second-stage heat treatment; further, the first-stage heat treatment is performed under conditions including: a temperature of 800-1000 C. for at least 3 h; further, the second-stage heat treatment is performed under conditions including: a temperature of 400-650 C. for 1-15 h; preferably, the matrix of the neodymium-iron-boron magnet can be further subjected to blackening treatment before arranging the diffusion source; further, the blackening treatment conditions are as follows: in the atmosphere, the magnet is blackened at a temperature of 200-500 C. for 3-60 min.

5. A preparation method of the rare earth permanent magnet according to claim 1, comprising the following steps: (1) preparing a matrix of a neodymium-iron-boron magnet; (2) preparing a diffusion source comprising at least Mn and a substance comprising a heavy rare earth element; and (3) arranging the diffusion source in step (2) on a surface of the matrix, and performing diffusion heat treatment to obtain the rare earth permanent magnet; preferably, raw materials of the matrix comprise R, Fe, and B, and optionally comprise or do not comprise Co and/or M.

6. The preparation method according to claim 5, wherein the matrix has an oxygen content below 2000 ppm; preferably, in step (1), a method for preparing the matrix of the neodymium-iron-boron magnet comprises: smelting, milling, pressing, and sintering; preferably, in step (1), the matrix can be further subjected to blackening treatment; further, the conditions of the blackening treatment are as follows: in the atmosphere, the blackening treatment is performed at a temperature of 200-500 C. for 3-60 min.

7. The preparation method according to claim 5, wherein in step (2), Mn has a content of 0.01% to 20%, preferably 0.1% to 20%, such as 5%, 10%, or 15%, in the diffusion source; preferably, in step (2), the substance comprising the heavy rare earth element is selected from pure metals of heavy rare earths and/or compounds of heavy rare earth metals, preferably pure metals of heavy rare earths, in the diffusion source; preferably, the compound of the heavy rare earth metal is at least one selected from a fluoride of the heavy rare earth, an oxide of the heavy rare earth, a hydride of the heavy rare earth, and an oxyfluoride of the heavy rare earth.

8. The preparation method according to claim 5, wherein in step (3), the method for arranging comprises arranging the diffusion source to the surface of the matrix, such as at least one selected from thermal spraying, evaporation, coating, magnetron sputtering, burying, printing, and the like.

9. The preparation method according to claim 5, wherein in step (3), the diffusion heat treatment is performed under vacuum or an inert gas atmosphere; preferably, in step (3), the diffusion heat treatment comprises at least a two-stage heat treatment; preferably, the diffusion heat treatment comprises a first-stage heat treatment followed by a second-stage heat treatment; further, the first-stage heat treatment is performed under conditions comprising: a temperature of 800-1000 C. for at least 3 h; further, the second-stage heat treatment is performed under conditions comprising: a temperature of 400-650 C. for 1-10 h.

10. Use of the rare earth permanent magnet according to claim 1, preferably for a motor.

Description

DETAILED DESCRIPTION

[0064] The technical solutions of the present disclosure will be further illustrated in detail with reference to the following specific examples. It will be understood that the following examples are merely exemplary illustrations and explanations of the present disclosure, and should not be construed as limiting the protection scope of the present disclosure. All techniques implemented based on the content of the present disclosure described above are included within the protection scope of the present disclosure.

[0065] Unless otherwise stated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared using known methods.

[0066] In the following examples, the following tests were performed by taking magnets at different positions of the diffusion-treated magnet as samples to be tested. [0067] 1. Magnetic property test: 1 mm-1 mm-1 mm standard sample blocks were processed on the surface layer and the geometric center of the diffused magnet respectively, and the magnetic property test was performed on a pulsed magnetic field measuring instrument (PFM). [0068] 2. Composition test: the diffused magnet was divided into two parts in the diffusion direction, and the contents of Mn and the heavy rare earth at the surface and the center of the permanent magnet were measured, respectively, by using an X-ray fluorescence spectrometer (XRF), wherein the Mn content at the surface of the permanent magnet was denoted as x1, the heavy rare earth content at the surface was denoted as y1, the Mn content at 500 m from the surface of the permanent magnet to the interior of the magnet was denoted as x2, and the heavy rare earth content was denoted as y2. [0069] 3. Impact absorbing energy test: the diffused samples (about 55 mm-10 mm-6 mm in size) were tested for impact absorbing energy on an impact tester 5 times, and an average value was taken.

EXAMPLE 1

[0070] The preparation method of a rare earth permanent magnet was as follows.

(1) Preparation of Matrix of Sintered Neodymium-Iron-Boron Magnet:

[0071] Raw materials of sintered neodymium-iron-boron permanent magnets by weight percentage were comprised: 27% of PrNd, 4% of Dy, 2% of Co, 0.1% of Cu, 0.1% of Ga, 0.4% of Al, 0.1% of Zr, and 1% of B, with the balance being Fe. Alloy slices were prepared by using the raw materials described above through a rapid hardening and strip casting method.

[0072] The obtained rapid hardened slices described above were subjected to a hydrogen absorption treatment at a hydrogen absorption pressure of 0.2 MPa, followed by air flow milling to obtain a powder with an SMD of 2.8 m. An antioxidant fatty acid ester accounting for 0.05 wt % of the total amount of the raw materials was added and mixed homogeneously to obtain a fine alloy powder. The fine alloy powder described above was subjected to oriented-pressing in a magnetic field at a controlled intensity of the orientation field of 2 T, and then subjected to isostatic pressing at 170 MPa to obtain a compact.

[0073] The compact was subject to a vacuum heat treatment furnace for sintering at a controlled sintering temperature of 1065 C.

[0074] The sintered compact was machined into a matrix with a size of 55 mm10 mm6 mm, in which the dimension along the orientation direction was 6 mm, and the oxygen content of the matrix was below 2000 ppm.

(2) Preparation of Diffusion Source:

[0075] Tb powder and Mn powder were mixed in a ratio of 95% to 5% by weight percentage, and then 1% of 4-hexylresorcinol antioxidant and 5% of ethanol were added to be mixed into a slurry.

(3) Arrangement of Diffusion Source and Diffusion Heat Treatment:

[0076] The matrix in step (1) was blackened in air at a temperature of 300 C. for 40 min.

[0077] The slurry in step (2) was coated on the surface of the matrix and the diffusion heat treatment was performed. In the diffusion heat treatment process, the first-stage heat treatment was performed at a diffusion temperature of 940 C. for 30 h, followed by the second-stage heat treatment at 500 C. for h to obtain the rare earth permanent magnet in this example.

[0078] The magnetic properties and mechanical properties of the rare earth permanent magnet in this example were measured by the test methods described above.

EXAMPLE 2

[0079] The preparation method of a rare earth permanent magnet was as follows.

(1) Preparation of Matrix of Sintered Neodymium-Iron-Boron Magnet:

[0080] Raw materials of sintered neodymium-iron-boron permanent magnets by weight percentage comprise: 27% of PrNd, 4% of Dy, 2% of Co, 0.1% of Cu, 0.1% of Ga, 0.4% of Al, 0.1% of Zr, and 1% of B, with the balance being Fe. Alloy slices were prepared by using the raw materials described above through a rapid hardening and strip casting method.

[0081] The obtained rapid hardened slices described above were subjected to a hydrogen absorption treatment at a hydrogen absorption pressure of 0.2 MPa, followed by air flow milling to obtain a powder with an SMD of 2.8 An antioxidant fatty acid ester accounting for 0.05 wt % of the total amount of the raw materials was added and mixed homogeneously to obtain a fine alloy powder. The fine alloy powder described above was subjected to oriented-pressing in a magnetic field at a controlled intensity of the orientation field of 2 T, and then subjected to isostatic pressing at 170 MPa to obtain a compact. The compact described above was placed in a vacuum heat treatment furnace for sintering at a controlled sintering temperature of 1065 C.

[0082] The sintered compact was machined into a matrix with a size of 55 mm10 mm6 mm, in which the dimension along the orientation direction was 6 mm.

(2) Preparation of Diffusion Source:

[0083] Tb powder and Mn powder were mixed in a ratio of 85% to 15% by weight percentage, and then 1% of 4-hexylresorcinol antioxidant and 5% of ethanol were added to be mixed into a slurry.

(3) Arrangement of Diffusion Source and Diffusion Heat Treatment:

[0084] The matrix in step (1) was blackened in air at a temperature of 300 C. for 40 min in the atmosphere.

[0085] The slurry in step (2) was coated on the surface of the matrix and the diffusion heat treatment was performed. In the diffusion heat treatment process, the first-stage heat treatment was performed at a diffusion temperature of 940 C. for 30 h, followed by the second-stage heat treatment at 500 C. for 10 h to obtain the rare earth permanent magnet in this example.

[0086] The magnetic properties and mechanical properties of the permanent magnet in this example were measured by the test methods described above.

EXAMPLE 3

[0087] The preparation method of a rare earth permanent magnet was as follows.

(1) Preparation of Matrix of Sintered Neodymium-Iron-Boron Magnet:

[0088] Raw materials of sintered neodymium-iron-boron permanent magnets by weight percentage comprise: 27% of PrNd, 4% of Dy, 2% of Co, 0.1% of Cu, 0.1% of Ga, 0.4% of Al, 0.1% of Zr, and 1% of B, with the balance being Fe. Alloy slices were prepared by using the raw materials described above through a rapid hardening and strip casting method.

[0089] The obtained rapid hardened slices described above were subjected to a hydrogen absorption treatment at a hydrogen absorption pressure of 0.2 MPa, followed by air flow milling to obtain a powder with an SMD of 2.8 n antioxidant fatty acid ester accounting for 0.05 wt % of the total amount of the raw materials was added and mixed homogeneously to obtain a fine alloy powder. The fine alloy powder described above was subjected to oriented-pressing in a magnetic field at a controlled intensity of the orientation field of 2 T, and then subjected to isostatic pressing at 170 MPa to obtain a compact. The compact described above was subject to a vacuum heat treatment furnace for sintering at a controlled sintering temperature of 1065 C.

[0090] The sintered compact was machined into a matrix with a size of 55 mm10 mm6 mm, in which the dimension along the orientation direction was 6 mm.

(2) Preparation of Diffusion Source:

[0091] Tb and Mn were mixed in a ratio of 85% to 15% by weight percentage and then melted to prepare a diffusion source powder. 1% of 4-hexylresorcinol antioxidant and 5% of ethanol were added to be mixed into a slurry.

(3) Arrangement of Diffusion Source and Diffusion Heat Treatment:

[0092] The matrix in step (1) was blackened in air at a temperature of 300 C. for 40 min.

[0093] The slurry in step (2) was coated on the surface of the matrix and the diffusion heat treatment was performed. In the diffusion heat treatment process, the first-stage heat treatment was performed at a diffusion temperature of 940 C. for 30 h, followed by the second-stage heat treatment at 500 C. for 10 h to obtain the rare earth permanent magnet in this example.

[0094] The magnetic properties and mechanical properties of the permanent magnet in this example were measured by the test methods described above.

EXAMPLE 4

[0095] The preparation method of a rare earth permanent magnet was as follows.

(1) Preparation of Matrix of Sintered Neodymium-Iron-Boron Magnet:

[0096] Raw materials of sintered neodymium-iron-boron permanent magnets by weight percentage comprise: 27% of PrNd, 4% of Dy, 2% of Co, 0.1% of Cu, 0.1% of Ga, 0.4% of Al, 0.1% of Zr, and 1% of B, with the balance being Fe. Alloy slices were prepared by using the raw materials described above through a rapid hardening and strip casting method.

[0097] The obtained rapid hardened slices described above were subjected to a hydrogen absorption treatment at a hydrogen absorption pressure of 0.2 MPa, followed by air flow milling to obtain a powder with an SMD of 2.8 m. antioxidant fatty acid ester accounting for 0.05 wt % of the total amount of the raw materials was added and mixed homogeneously to obtain a fine alloy powder. The fine alloy powder described above was subjected to oriented-pressing in a magnetic field at a controlled intensity of the orientation field of 2 T, and then subjected to isostatic pressing at 170 MPa to obtain a compact.

[0098] The compact described above was subject to a vacuum heat treatment furnace for sintering at a controlled sintering temperature of 1065 C.

[0099] The sintered compact was machined into a matrix with a size of 55 mm10 mm6 mm, in which the dimension along the orientation direction was 6 mm.

(2) Preparation of Diffusion Source:

[0100] Terbium fluoride and Mn were mixed in a ratio of 95% to 5% by weight percentage and then melted to prepare a diffusion source powder. 1% of 4-hexylresorcinol antioxidant and 5% of ethanol were added to be mixed into a slurry.

(3) Arrangement of Diffusion Source and Diffusion Heat Treatment:

[0101] The matrix in step (1) was blackened in air at a temperature of 300 C. for 40 min.

[0102] The slurry in step (2) was coated on the surface of the matrix and the diffusion heat treatment was performed. In the diffusion heat treatment process, the first-stage heat treatment was performed at a diffusion temperature of 940 C. for 30 h, followed by the second-stage heat treatment at 500 C. for 10 h to obtain the rare earth permanent magnet in this example.

[0103] The magnetic properties and mechanical properties of the magnet in this example were measured by the test methods described above.

EXAMPLE 5

[0104] The preparation method in this example was substantially the same as that in Example 1, except that the acid cleaning treatment was used instead of the blackening treatment before the arrangement of the diffusion source.

Comparative Example 1

[0105] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source was 100% Tb.

Comparative Example 2

[0106] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source comprises 95% Tb and 5% Al.

Comparative Example 3

[0107] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source comprises 95% Tb and 5% Ti.

Comparative Example 4

[0108] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source comprises 75% Tb and 25% Mn.

Comparative Example 5

[0109] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source comprises 95% terbium fluoride and 5% Al.

Comparative Example 6

[0110] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (2), the diffusion source comprises 90% terbium fluoride, 5% Mn, and 5% Al.

Comparative Example 7

[0111] The preparation method in this comparative example was substantially the same as that in Example 1, except that, in step (1), the raw materials of sintered neodymium-iron-boron permanent magnets comprise: 27% of PrNd, 4% of Dy, 2% of Co, 0.1% of Cu, 0.1% of Ga, 0.4% of Al, 0.1% of Zr, 1% of B, and 0.2% of Mn, with the balance being Fe.

[0112] Table 1 is a summary of Mn and Tb element distributions at different positions of the permanent magnets in the examples and the comparative examples described above, comprising Mn and Tb contents at the surface and at 500 m away from the surface, and whether formula (1) is satisfied or not.

TABLE-US-00001 TABLE 1 Summary of Mn and Tb element distributions at different positions of permanent magnet Whether Diffusion x1 x2 y1 y2 formula 1 source Pretreatment (wt %) (wt %) (wt %) (wt %) x1/x2 y1/y2 is satisfied Example 1 95% Tb + 5% Mn Blackening 0.09 0.02 1.35 0.38 4.5 3.55 Yes Example 2 85% Tb + 15% Mn Blackening 0.12 0.03 1.44 0.39 4.0 2.85 Yes Example 3 85% Tb + 15% Mn Blackening 0.13 0.02 1.65 0.46 6.5 2.50 Yes Example 4 95% TbF + 5% Mn Blackening 0.12 0.02 1.71 0.33 6.0 5.18 Yes Example 5 95% Tb + 5% Mn Acid 0.13 0.02 1.96 0.37 6.5 5.30 Yes cleaning Comparative 100% Tb Blackening 0.01 0.01 2.14 0.31 1 10.13 No Example 1 Comparative 95% Tb + 5% Al.sup. Blackening 0.01 0.01 3.05 0.28 1 14.46 No Example 2 Comparative 95% Tb + 5% Ti Blackening 0.02 0.01 2.53 0.33 2.0 16.76 No Example 3 Comparative 75% Tb + 25% Mn Blackening 0.15 0.03 3.62 0.31 5.0 11.68 No Example 4 Comparative 95% TbF + 5% Al.sup. Blackening 0.01 0.01 3.96 0.44 1.0 9.00 No Example 5 Comparative 90% TbF + 5%.sup. Blackening 0.1 0.02 1.99 0.36 5.0 5.53 No Example 6 Mn + 5% Al Comparative 100% Tb Blackening 0.22 0.21 3.44 0.41 1.0 8.39 No Example 7

[0113] Table 2 is a summary of the coercivity of the surface, the coercivity of the core, and the magnetic properties of the surface and the core of the permanent magnets in the examples and comparative examples described above, comprising the coercivity difference, the impact absorbing energy of the magnet, and the like.

TABLE-US-00002 TABLE 2 Summary of magnetic properties Impact Whether z1 z2 z1-z2 absorbing formula 2 (kA/m) (kA/m) (kA/m) energy (J) is satisfied Example 1 2701 2610 91 2.49 Yes Example 2 2723 2627 96 2.44 Yes Example 3 2715 2610 105 2.41 Yes Example 4 2711 2593 118 2.40 Yes Example 5 2733 2590 143 2.35 Yes Comparative 2723 2547 176 2.15 No Example 1 Comparative 2712 2567 145 2.21 No Example 2 Comparative 2736 2517 219 2.09 No Example 3 Comparative 2711 2538 173 2.15 No Example 4 Comparative 2678 2511 167 2.11 No Example 5 Comparative 2690 2533 157 2.11 No Example 6 Comparative 2703 2503 200 2.13 No Example 7

[0114] In summary, from Tables 1 and 2, it can be seen that in Examples 1-5, by introducing an appropriate amount of Mn into the diffusion source, the heavy rare earth concentration difference y1/y2 in the rare earth permanent magnet prepared by the present disclosure was smaller, the uniformity of the magnetic properties of the magnet was improved, the coercivity difference z1z2 between the surface and the core of the magnet was smaller, and the impact toughness (impact absorbing energy) of the magnet was also improved.

[0115] It can be seen from Comparative Examples 1 and 5 that since the blackening treatment was not performed before the arrangement of the diffusion source, the reaction of the crystal grains and the grain boundary on the surface of the matrix with the diffusion source was faster, so that the diffusion source entering the interior of the matrix was relatively reduced, thereby slightly reducing the uniformity of the permanent magnet compared with Example 1.

[0116] It can be seen from Comparative Examples 1 and 4 that the uniformity of the permanent magnet was slightly reduced by using terbium fluoride as a diffusion source.

[0117] It can be seen from Comparative Examples 1 and 4 that when Mn was not contained in the diffusion source or the Mn content was more than 20%, the coercivity difference between the surface layer and the core of the permanent magnet was increased, and the uniformity of the permanent magnet was deteriorated.

[0118] It can be seen from Comparative Examples 2, 5, and 6 that since the diffusion source comprised Al element with a lower melting point, the crystal grains on the surface layer of the magnet were excessively reacted with the diffusion source to form a reverse core-shell structure, thereby reducing the coercivity on the surface of the magnet.

[0119] It can be seen from Comparative Example 3 that when the diffusion source comprised Ti element with a high melting point, the heavy rare earth was difficult to diffuse into the interior of the magnet effectively, so that the coercivity of the core of the magnet was reduced and the difference between the inside and outside was increased.

[0120] In Comparative Example 7, Mn was added to the diffusion matrix material, Mn was uniformly distributed in the permanent magnet, and there was no concentration gradient of Mn in the interior of the permanent magnet, so that the diffusion effect was inferior to that in Example 1 although the diffusion treatment was performed.

[0121] The exemplary embodiments of the present disclosure have been described above. However, the protection scope of the present application is not limited to the above embodiments. Any modification, equivalent, improvement and the like made by those skilled in the art without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.