NEODYMIUM-IRON-BORON MAGNET, PREPARATION METHOD AND USE THEREOF

Abstract

A neodymium-iron-boron (NdFeB) magnet is represented by a chemical formula R1-R2-Fe-M-B, and has a composite structure of a high-coercivity region and a high-remanence region. In the formula R1 is a rare earth element comprising at least Nd, R2 is a heavy rare earth element comprising at least Dy and/or Tb, and M is a transition metal element comprising at least Co. The neodymium-iron-boron magnet can greatly improve resistance to high-temperature demagnetization and inhibit reduction of magnetic flux of a magnet by adopting a small amount of Dy/Tb. The magnet can be used in an embedded high-speed motor. The preparing method for the magnet improves the material utilization and the production efficiency, and is feasible for a large-scale production.

Claims

1. A neodymium-iron-boron magnet, wherein the neodymium-iron-boron magnet is represented by a chemical formula R1-R2-Fe-M-B and having a composite structure of a high-coercivity region and a high-remanence region; wherein, R1 is a rare earth element comprising at least Nd, R2 is a heavy rare earth element comprising at least Dy and/or Tb, and M is a transition metal element comprising at least Co.

2. The neodymium-iron-boron magnet according to claim 1, wherein R2 in the neodymium-iron-boron magnet has a content of ≤1.0 wt %, such as ≤0.8 wt %, preferably ≤0.5 wt %.

3. The neodymium-iron-boron magnet according to claim 1, wherein the neodymium-iron-boron magnet has a high-coercivity region with a high R2 content and a high-remanence region with a low R2 content; preferably, the distribution of the high-coercivity region and the high-remanence region is substantially as shown in FIG. 1; preferably, the concentration difference Δ1 of R2 between a surface layer of the high-remanence region and a position at 1 mm inside the magnet is less than or equal to 0.1%; preferably, the concentration difference Δ2 of R2 between a surface layer of the high-coercivity region and a position at 1 mm inside the neodymium-iron-boron magnet is greater than or equal to 0.15%; preferably, Δ2/Δ1≥1.5, preferably Δ2/Δ1≥2; preferably, the high-coercivity region has a width of 1-5 mm, preferably 1.5-4 mm, and the central region has a high-remanence region; wherein, the high-coercivity region herein is defined as a region extending from a surface layer of the magnet to a certain position inside of the magnet, where the concentration difference of R2, comparing to surface layer of the magnet, is 1%, and the width of the high-coercivity region is defined as the distance between the surface layer and the position inside of the magnet mentioned above.

4. The neodymium-iron-boron magnet according to claim 1, wherein R1 further comprises at least one selected from lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), europium (Eu) and scandium (Sc) in addition to Nd; preferably, R1 in the neodymium-iron-boron magnet has a content of 28-32 wt %.

5. The neodymium-iron-boron magnet according to claim 1, wherein R2 further comprises at least one selected from gadolinium (Gd), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and yttrium (Y) in addition to Dy and/or Tb; preferably, M further comprises at least one selected from Cu, Ga, Zr, Ti, Al, Mn, Zn and W in addition to Co; preferably, the Co in the neodymium-iron-boron magnet has a content of 1-3 wt %; preferably, based on the neodymium-iron-boron magnet, the remaining transition metal elements other than Co in M have a content of ≤2 wt %; preferably, B in the neodymium-iron-boron magnet has a content of 0.5-1.3 wt %; preferably, the neodymium-iron-boron magnet further comprises an inevitable impurity.

6. A preparing method for the neodymium-iron-boron magnet according to claim 1, comprising the following steps: manufacturing or preparing a base magnet with an R1-Fe-M-B-based structure, forming films on two opposite surfaces of the base magnet respectively with the heavy rare earth element R2 at least comprising Dy and/or Tb, and then performing diffusion treatment, wherein R2 diffuses from the surface of the magnet to the inside along a grain boundary of the base magnet and then is enriched at the grain boundary, so as to obtain the neodymium-iron-boron magnet.

7. The preparing method for the neodymium-iron-boron magnet according to claim 6, wherein the base magnet is a regular hexahedron; preferably, the two opposite surfaces are two opposite surfaces that are neither perpendicular to a magnetizing direction of the magnet, nor perpendicular to a pressing direction in which the magnet is formed; preferably, R2 is formed to the films on the surfaces of the magnet by a method including, but not limited to, vacuum evaporation, magnetron sputtering or coating; preferably, equal amounts of R2 are vacuum-evaporated, magnetron-sputtered or coated on the two opposite surfaces of the magnet; preferably, the diffusion treatment is performed under a vacuum degree of <10.sup.−2 Pa; preferably, the diffusion treatment is accomplished by performing by a first heating, a first incubation, quenching cooling, and then a second heating and a second incubation successively.

8. Use of the neodymium-iron-boron magnet according to claim 1 in an embedded motor.

9. A magnetic steel, comprising the neodymium-iron-boron magnet according to claim 1.

10. An embedded motor, comprising the neodymium-iron-boron magnet according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 is a schematic diagram of a high-remanence region and a high-coercivity region of the neodymium-iron-boron magnet according to the present disclosure.

[0055] FIG. 2 is a schematic diagram of a diffusion surface of the neodymium-iron-boron magnet according to the present disclosure.

[0056] FIG. 3 is a schematic structural diagram of the embedded motor (a) and the magnetic steel (b).

[0057] FIG. 4 is a relationship diagram of coercivity and diffusion depth.

DETAILED DESCRIPTION

[0058] The technical scheme of the present disclosure will be further illustrated in detail with reference to the following specific examples. It should be understood that the following examples are merely exemplary illustration and explanation 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 encompassed within the protection scope of the present disclosure.

[0059] Unless otherwise stated, the starting materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

[0060] The method for measuring concentration difference of heavy rare earth elements in the examples comprises the following steps:

[0061] the high-remanence region: from the surface layer of the center position of the surface of the magnet perpendicular to the magnetizing direction to the inside of the magnet, small test pieces with a size of 1×1×1 mm were processed respectively, soaked in an acid until completely dissolved, and then measuring the content of R2 and the content difference Δ1 of R2 by a spectrum method;

[0062] the high-coercivity region: defining one side of the high-coercivity region far away from the high-remanence region as a surface layer, from the surface layer to the inside of the magnet, small test pieces with a size of 1×1×1 mm were processed respectively, soaked in an acid until completely dissolved, and then measuring the content of R2 and the content difference Δ2 of R2 by a spectrum method.

[0063] The squareness referred herein is measured by a magnetometer with the final magnet as a sample standard size. The gradient distribution of coercivity referred herein is measured by processing a test piece with a size of 1×1×1 mm on a magnet and using a strong pulse PFM06 device.

Example 1

[0064] A R1-Fe-M-B-based magnet was prepared in this example. The raw material alloy was prepared according to the following composition proportions: R1 is Nd with a content of 30.5 wt %; Co has a content of 1.5 wt %; M is Al, Cu and Ga with contents of 0.1 wt %, 0.1 wt % and 0.15 wt %, respectively; B has a content of 0.95 wt %, the balance is Fe and inevitable impurities, such as C, N, etc. The specific preparing process of the neodymium-iron-boron-based magnet comprises:

[0065] a) smelting: putting the above prepared raw materials into a crucible by adopting a vacuum induction smelting furnace, heating to 1480° C., melting the raw materials into molten steel, pouring the molten steel fully dissolved onto a quenching roller, quenching-cooling, nucleating and crystallizing on the roller surface, and gradually growing to form alloy flakes;

[0066] b) pulverizing: performing HD crushing and then jet milling on the obtained alloy flakes to obtain jet-milled powders having an average particle size with SMD of 3.0 μm;

[0067] c) pressing: adding 0.3 wt % of a lubricant into the jet-milled powders, mixing for 120 min by using a mixer, pouring the mixture into a film cavity of a press, and pressing and forming under the action of an external magnetic field of 2.5 T;

[0068] d) sintering: putting the pressed compact body into a sintering furnace, incubating at 1075° C. for 300 min, and then quenching-cooling the compact body to room temperature at a cooling speed of 20° C./min to manufacture the sintered neodymium-iron-boron-based magnet.

[0069] The base magnet was processed into a small piece with a size of 10-10-10 mm, and Dy metal sputtering coating on the surface of the base magnet according to Table 1 was performed by adopting a magnetron sputtering method.

TABLE-US-00001 TABLE 1 Different coating positions of metal Dy on the surface of a magnet Test No. Application position of metal Dy 1 None 2 two opposite surfaces perpendicular to the orientation direction, each surface being sputtered with 0.4 wt % of Dy based on the weight of the magnet 3 two opposite surfaces perpendicular to the pressing direction, each surface being sputtered with 0.4 wt % of Dy based on the weight of the magnet 4 two opposite surfaces which are neither perpendicular to the orientation direction, nor perpendicular to the pressing direction, each surface being sputtered with 0.4 wt % of Dy based on the weight of the magnet

[0070] Then the magnets treated according to Table 1 were put into a diffusion furnace for diffusion treatment, wherein the furnace had a vacuum degree of <10.sup.−2 Pa, then the magnets in the furnace were heated to 900° C., incubated for 600 min, quenching-cooled at a speed of 15° C./min to room temperature, and then further heated to 550° C. and incubated for 240 min to obtain the finished magnets. The magnetic properties and the compositions of the finished magnets were measured, and the results are shown in Table 2.

TABLE-US-00002 TABLE 2 Summary of properties and compositions of finished magnets Concentration High- difference coercivity Magnetic of heavy region moment Test rare earth (%) Width Coercivity (mWb .Math. No. Δ1 Δ2 Δ2/Δ1 (mm) (kA/m) Hk/Hcj cm) 1 — — — 0 1055 0.98 0.1406 2 — — — — 1513 0.97 0.1392 3 0.05 0.37 7.4 1.2 1346 0.85 0.1402 4 0.04 0.22 5.5 2.4 1476 0.93 0.1398

[0071] The coercivity, squareness and magnetic moment in the above tests 1, 2, 3 and 4 were comprehensively compared. Among them, test 4 had the highest comprehensive performance, the width of the high-coercivity region is 2.4 mm, and thus the demagnetization-susceptible region when the motor runs at a high speed can be covered. Further, the test piece was processed in the diffusion direction, and the relationship between the coercivity and the diffusion depth was measured, as shown in FIG. 4. It can be seen that, in test 2 in which the diffusion is along the magnetizing direction, the average value of coercivity was highest and the fluctuation change was smallest along the diffusion depth; in test 3 in which the diffusion is along the pressing direction, the coercivity formed a sharp peak value on the diffusion surface and occurred a sharp decline when the diffusion entered a position at 1 mm inside the magnet, and the coercivity at the center position was almost equivalent to that of the magnet without diffusion treatment; in test 4, the coercivity of the magnet was reduced in gradient at a position of 0-3 mm on the surface layer of the magnet, the coercivity of the outermost layer was diffused due to the magnetizing direction of test 2, namely the demagnetization resistance of the outermost layer was superior to that of test 2, and gradually became gentle at a position of more than 3 mm on the surface layer, the coercivity was about 250 kA/m higher than that of the magnet without diffusion treatment, and the demagnetization resistance of the magnet was also improved to a certain extent.

Example 2

[0072] A R1-Fe-M-B-based magnet prepared in this example. The raw material alloy was prepared according to the following composition proportions: R1 is Nd with a content of 31 wt %; Dy has a content of 0.5 wt % and Co has a content of 2.0 wt %; M is Al, Cu and Ga with contents of 0.15 wt %, 0.15 wt % and 0.1 wt %, respectively; B has a content of 0.98 wt %, the balance is Fe and inevitable impurities, such as C, N, etc. The specific preparing process of the neodymium-iron-boron-based magnet are as follows:

[0073] a) smelting: putting the above prepared raw materials into a crucible by adopting a vacuum induction smelting furnace, heating to 1460° C., melting the raw materials into molten steel, pouring the molten steel fully dissolved onto a quenching roller, quenching-cooling, nucleating and crystallizing on the roller surface, and gradually growing to form alloy flakes;

[0074] b) pulverizing: performing HD crushing and then jet milling on the obtained alloy flakes to obtain jet-milled powders having an average particle size with SMD of 2.8 μm;

[0075] c) pressing: adding 0.2 wt % of a lubricant into the jet-milled powders, mixing for 180 min by using a mixer, pouring the mixture into a film cavity of a press, and pressing and forming under the action of an external magnetic field of 2.5 T;

[0076] d) sintering: putting the pressed compact body into a sintering furnace, incubating at 1070° C. for 270 min, and then quenching-cooling the compact body to room temperature at a cooling speed of 10° C./min to manufacture the sintered neodymium-iron-boron-based magnet.

[0077] The base magnet was processed into 40-8-20 and 40-8-2.5 square pieces (20 and 2.5 were the thickness in the magnetizing direction respectively), and metal Tb was coated on the surface of the base magnet according to the coating method as shown in Table 3.

TABLE-US-00003 TABLE 3 Different position treatment of metal Tb on the surface of a magnet Test No. Magnet size Application position of metal Tb 5 40-8-2.5 None 6 40-8-20 two opposite surfaces with a size of 40 × 20, each surface being coated uniformly with 0.2 wt % of Tb based on the weight of the magnet 7 40-8-2.5 two opposite surfaces with a size of 40 × 8, each surface being coated uniformly with 0.2 wt % of Tb based on the weight of the magnet

[0078] Then the magnets treated according to Table 3 were put into a diffusion furnace for diffusion treatment, wherein the furnace had a vacuum degree of <10.sup.−2 Pa, then the magnets in the furnace were heated to 900° C., incubated for 600 min, quenching-cooled at a speed of 15° C./min to room temperature, and then heated to 550° C. and incubated for 240 min to obtain the finished magnets. The square piece of 40-8-20 after the diffusion treatment in test 6 was processed into a test piece of 40-8-2.5, and the magnetic properties and compositions were measured together with the test pieces in test 5 and test 7. The test results are shown in Table 4.

TABLE-US-00004 TABLE 4 Summary of properties and compositions of finished magnets High- Mag- coer- netic Tb civity mo- content (%) region Hcj (kA/m) ment Test Δ2/ Width Surface 3-mm Hk/ (mWb .Math. No. Δ1 Δ2 Δ1 (mm) layer position Hcj cm) 5 — — — 0 1256 1248 0.99 0.1071 6 0.03 0.19 6.33 2.0 2224 1984 0.95 0.1056 7 — — — 2068 2013 0.97 0.1049

[0079] Compared with test 7, magnet in test 6 had lower coercivity at the position of 3 mm, but the coercivity of the outermost layer was 156 kA/m higher than that of test 7, so that the demagnetization of an external magnetic field on the magnet can be effectively resisted; meanwhile, the magnetic moment was higher by about 0.6%, the reduction of the magnetic moment was effectively avoided, and the high-efficiency output of the magnetic field of the magnet was ensured.

[0080] The above examples according to the present disclosure have been described above. However, the present disclosure is not limited thereto. Any modification, equivalent, improvement and the like made without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.