MANUFACTURING METHOD OF SINTERED ND-FE-B PERMANENT MAGNET

Abstract

The present disclosure refers to a preparation method for improving the coercive force of a sintered Nd—Fe—B magnet and comprises: preparing Nd—Fe—B alloy flakes by a strip casting process, followed by hydrogen decrepitation of the Nd—Fe—B alloy flakes and jet milling to obtain an Nd—Fe—B powder; mixing Nd—Fe—B powder and an amount of 0.1 to 5 wt. % of a nanoparticulate powder in a powder mixing machine to obtain a powder mixture; modification of the powder mixture obtained in step B) under inert conditions in a mechanical mixing equipment such that the particles of the Nd—Fe—B powder are rounded and the nanoparticulate powder adheres to the particle surface of the Nd—Fe—B powder; mixing in a lubricant to the modified Nd—Fe—B powder in a powder mixing machine; and align pressing the modified Nd—Fe—B powder into a green body, sintering the green body, and aging of the obtained sintered Nd—Fe—B magnet.

Claims

1. A preparation method for improving the coercive force of a sintered Nd—Fe—B magnet, the method comprising in the order the steps of: A) preparing Nd—Fe—B alloy flakes by a strip casting process, followed by hydrogen decrepitation of the Nd—Fe—B alloy flakes and jet milling to obtain an Nd—Fe—B powder; B) mixing Nd—Fe—B powder and an amount of 0.1 to 5 wt. % of a nanoparticulate powder in a powder mixing machine to obtain a powder mixture; C) modification of the powder mixture obtained in step B) by applying mechanical energy under inert conditions in a mechanical mixing equipment such that the particles of the Nd—Fe—B powder are rounded and the nanoparticulate powder adheres to the particle surface of the Nd—Fe—B powder; D) mixing in a lubricant to the modified Nd—Fe—B powder in a powder mixing machine; and E) align pressing the modified Nd—Fe—B powder into a green body, sintering the green body, and aging of the obtained sintered Nd—Fe—B magnet.

2. The method of claim 1, wherein the Nd—Fe—B alloy flakes comprise: Nd and, optionally, one or more additional rare earth metals, wherein a total amount of the rare earth metals RE is in the range of 28 wt. %≤RE≤32 wt. %; B being present in an amount of 0.8 wt. %≤B≤1.2 wt %; M being one or more metal selected from the group consisting of Al, Cu, Mg, Zn, Co, Ti, Zr, Nb, and Mo, wherein a total amount of M is in the range of 0 wt. %≤M≤5 wt. %; and the balance element is Fe.

3. The method of one of claim 1, wherein the Nd—Fe—B powder obtained by step A) has an average particle size of D50=2.5 μm to 5 μm.

4. The method of one of claim 1, wherein the nanoparticulate powder has an average particle size of D50=20 nm to 100 nm.

5. The method of claim 1, wherein the nanoparticulate powder comprises a metal or an oxide selected from the group consisting of Dy, Tb, Nd, Pr, Al, Cu Mg, Zn, Ti, Zr, Nb, and Mo, or a combination thereof.

6. The method of claim 1, wherein an amount of the added lubricant in step D) is in the range of 0.05 to 0.2 wt. %.

7. The method of claim 1, wherein in step E) while compressing the modified Nd—Fe—B powder during the align pressing an orienting magnetic field of 1.8 T to 2.5 T is applied.

8. The method of claim 1, wherein in step E) the green body is sintered in a vacuum furnace at a temperature in the range of 950° C. to 1100° C. for 6 to 12 hours.

9. The method of claim 1, wherein in step E) the sintered Nd—Fe—B achieved by sintering are subjected to an aging including a first heat treatment at 850° C. to 900° C. for 3 to 5 hours and a second heat treatment at 460° C. to 700° C. for 3 to 6 hours.

10. The method of claim 2, wherein the Nd—Fe—B powder obtained by step A) has an average particle size of D50=2.5 μm to 5 μm.

11. The method of claim 3, wherein the nanoparticulate powder has an average particle size of D50=20 nm to 100 nm.

12. The method of claim 11, wherein the nanoparticulate powder comprises a metal or an oxide selected from the group consisting of Dy, Tb, Nd, Pr, Al, Cu Mg, Zn, Ti, Zr, Nb, and Mo, or a combination thereof.

13. The method of claim 12, wherein an amount of the added lubricant in step D) is in the range of 0.05 to 0.2 wt. %.

14. The method of claim 13, wherein in step E) while compressing the modified Nd—Fe—B powder during the align pressing an orienting magnetic field of 1.8 T to 2.5 T is applied.

15. The method of claim 14, wherein in step E) the green body is sintered in a vacuum furnace at a temperature in the range of 950° C. to 1100° C. for 6 to 12 hours.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0032] FIG. 1 is a scanning electron microscope (SEM) image of the Nd—Fe—B magnet according to Example 1 of the present disclosure.

[0033] FIG. 2 is a scanning electron microscope (SEM) image of the Nd—Fe—B magnet according to Comparative Example 1.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0034] In the following, further detailed descriptions of the present disclosure are given. It shall be noted that the embodiments are used only to interpret the present disclosure and do not have any limiting effect on it.

EXAMPLE 1

[0035] The exemplary preparation method for preparing a sintered Nd—Fe—B magnet comprises the following steps:

[0036] Alloy sheets having the composition of (PrNd).sub.32Co.sub.1Al.sub.0.35Ti.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0037] The alloy sheets are subjected to hydrogen decrepitation process to break the sheets into smaller pieces.

[0038] After the decrepitation process, the alloy pieces are pulverized in a jet milling process under nitrogen to prepare an alloy powder having an average particle size of about D50=2.5 μm.

[0039] An amount of 0.1 wt. % nanoparticulate copper powder is added into the Nd—Fe—B powder and then mixed in a powder mixing machine (3D mixer) for 2 hours. The nanoparticulate copper powder has an average particle size of about D50=20 nm.

[0040] Next, the powder mixture obtained in previous step is added to a mechanical mixing equipment (Mechanical fusing machine, Wuxi Xinguang Powder Technology Co., LTD). Modification of the powder mixture is performed under inert gas conditions, at a running speed of 2000 rpm for 60 min, and at a temperature of 25° C.

[0041] The modification conditions are such that the powder particles are subjected to extrusion, friction and shearing action in the mechanical mixing process, wherein the sharp edges and corners of the powder particles are eroded to improve powder roundness. Meanwhile, due to the high surface activation energy, the surface of Nd—Fe—B powder particle interacts with the nanoparticulate powder, which makes the nanoparticulate powder evenly distributed on the surface of Nd—Fe—B powder, and then forms a kind of coating layer.

[0042] After the mechanical mixing process, an amount of 0.1 wt. % lubricant is added into the modified Nd—Fe—B powder and mixed for 3 h in a 3D mixer, wherein the addition of lubricant is to prevent oxidation and is conducive to subsequent compression.

[0043] The modified Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0044] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1020° C. for 12 hours, then argon is pumped for rapid cooling.

[0045] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 660° C. for 6 hours.

COMPARATIVE EXAMPLE 1

[0046] The production was carried out in the same manner as Example 1 except that no nanoparticulate copper powder is added and no modification by a mechanical mixing process is applied:

[0047] The alloy sheets have the composition (PrNd).sub.32Co.sub.1Al.sub.0.35Cu.sub.0.1Ti.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) and are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0048] The alloy sheets are subjected to hydrogen decrepitation process to break the sheets into smaller pieces.

[0049] After the decrepitation process, the alloy pieces are pulverized in a jet milling process under nitrogen to prepare an alloy powder having an average particle size of D50=2.5 μm.

[0050] An amount of 0.1 wt. % lubricant is added into the Nd—Fe—B powder and mixed for 3 h in a 3D mixer, wherein the addition of lubricant is to prevent oxidation and is conducive to subsequent compression.

[0051] The Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0052] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1020° C. for 12 hours, then argon is pumped in for rapid cooling.

[0053] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 660° C. for 6 hours.

[0054] The magnetic properties of the magnets obtained in Embodiment 1 and Comparative Example 1 are shown in Table 1.

TABLE-US-00001 TABLE 1 Br(T) Hcj(kA/m) (BH)m(kJ/m.sup.3) Hk/Hcj Example 1 1.365 1637 354 0.98 Comparative 1.367 1441 355 0.98 Example 1

[0055] Compared with Comparative Example 1, the coercive force of the magnet in Example 1 increases from 18.1 KOe to 20.57 KOe. The magnet prepared by the method described in the present disclosure has a higher coercive force, which is due to the fact that the nanoparticulate copper reacts with the rare earth rich phase to form the copper rich phase with low melting point during the heat treatment. The distribution of grain boundary phase is improved, which makes the main phase grains separated, thus improving the coercivity of the magnet. The modifications caused by the inventive process are also illustrated by the SEM images of FIG. 1 (magnet of Example 1) and FIG. 2 (magnet of Comparative Example 1).

EXAMPLE 2

[0056] The exemplary preparation method for preparing a sintered Nd—Fe—B magnet comprises the following steps:

[0057] The alloy sheets having the composition of (PrNd).sub.29.5Co.sub.1Ga.sub.0.2B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0058] The alloy sheets are subjected to hydrogen decrepitation process to break the sheets into smaller pieces.

[0059] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0060] The nanoparticulate powders of Dy.sub.70Cu.sub.30 (D50=50 nm) and TiO.sub.2 (D50=20 nm) are added into the Nd—Fe—B powder and then mixed in a 3D mixer for 2 hours, wherein the addition amount converted into Dy and Ti is 0.5% and 0.1% of the weight of Nd—Fe—B, respectively.

[0061] Next, the mixing powder obtained in previous step is added to a mechanical mixing equipment and injected with inert gas at a running speed of 5000 rpm for 30 min under a temperature of 25° C.

[0062] After the mechanical mixing process, an amount of 0.1 wt. % lubricant is added into the modified Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0063] The modified Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0064] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1060° C. for 12 hours, then argon is pumped for rapid cooling.

[0065] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 480° C. for 3 hours.

COMPARATIVE EXAMPLE 2

[0066] Compared with Example 2, the mechanical mixing process of adding nanoparticulate powder is not performed in this Comparative Example, and the Nd—Fe—B magnet is prepared as follows:

[0067] The alloy sheets having the composition of (PrNd).sub.29.5Dy.sub.0.5Co.sub.1Cu.sub.0.1Ga.sub.0.2Ti.sub.0.1B.sub.1.0Fe.sub.bal (wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0068] The alloy sheets are subjected to hydrogen desorption process to break the sheets into more smaller pieces.

[0069] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0070] An amount of 0.1 wt. % lubricant is added into the Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0071] The Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0072] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1060° C. for 12 hours, then argon is pumped for rapid cooling.

[0073] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 480° C. for 3 hours.

[0074] The magnetic properties of the magnets obtained in Example 2 and Comparative Example 2 are shown in Table 2.

TABLE-US-00002 TABLE 2 Br(T) Hcj(kA/m) (BH)m(kJ/m.sup.3) Hk/Hcj Example 2 1.450 1418 412 0.98 Comparative 1.455 1235 408 0.98 Example 2

[0075] Compared with Comparative Example 2, the remanence and coercivity of magnets in Example 2 are higher. Dy.sub.70Cu.sub.30 powder is coated on the surface of Nd—Fe—B powder by mechanical mixing, and (Pr,Nd,Dy).sub.2Fe.sub.14B epitaxial layer is formed on the powder surface during heat treatment, which increases the magnetic crystal anisotropy field of the magnet, thus improving the coercivity of magnets. In addition, TiO.sub.2 with high melting point oxide plays a pinning role in grain boundary and inhibits grain growth, which is also helpful to improve the coercivity of magnets.

EXAMPLE 3

[0076] The exemplary preparation method for preparing a sintered Nd—Fe—B magnet comprises the following steps:

[0077] The alloy sheets having the composition of Nd.sub.29Co.sub.1Al.sub.0.1Cu.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0078] The alloy sheets are subjected to hydrogen desorption process to break the sheets into more smaller pieces.

[0079] After the decrepitation process, the alloy pieces are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0080] Amount of 0.5 wt. % nanoparticulate Dy powder (D50=50 nm) and amount of 0.1 wt. % nanoparticulate Nb powder (D50=20 nm) are added into the Nd—Fe—B powder and then mixed in a 3D mixer for 2 hours.

[0081] Next, the mixing powder obtained in previous step is added to a mechanical mixing equipment and injected with inert gas at a running speed of 8000 rpm for 5 min under a temperature of 25° C.

[0082] After the mechanical mixing process, an amount of 0.1 wt. % lubricant is added into the nano-coated Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0083] The nano-coated Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0084] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1070° C. for 6 hours, then argon is pumped for rapid cooling.

[0085] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 500° C. for 3 hours.

COMPARATIVE EXAMPLE 3

[0086] Compared with Example 3, the mechanical mixing process of adding nanoparticulate powder is not performed in this comparative example, and the Nd—Fe—B magnet is prepared as follows:

[0087] The alloy sheets having the composition of Nd.sub.29Dy.sub.0.5Co.sub.1Al.sub.0.1Cu.sub.0.1Nb.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0088] The alloy sheets are subjected to hydrogen desorption process to break into more smaller pieces.

[0089] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0090] An amount of 0.1 wt. % lubricant is added into the Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0091] The Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0092] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1070° C. for 6 hours, then argon is pumped for rapid cooling.

[0093] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 500° C. for 3 hours.

[0094] The magnetic properties of the magnets obtained in embodiment 3 and Comparative Example 3 are shown in Table 3.

TABLE-US-00003 TABLE 3 Br(T) Hcj(kA/m) (BH)m(kJ/m.sup.3) Hk/Hcj Example 3 1.462 1314 416 0.98 Comparative 1.461 1137 415 0.98 Example 3

[0095] As shown in Table 3, the magnet prepared by the disclosure has higher coercivity, which indicates that the coating of Nd—Fe—B powder by mechanical mixing has a good effect.

EXAMPLE 4

[0096] The exemplary preparation method for preparing a sintered Nd—Fe—B magnet comprises the following steps:

[0097] The alloy sheets having the composition of (PrNd).sub.29.8Co.sub.1.5Cu.sub.0.15Ga.sub.0.2Ti.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1480° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0098] The alloy sheets are subjected to hydrogen desorption process to break the sheets into more smaller pieces.

[0099] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0100] An amount of 0.2 wt. % nanoparticulate Tb powder (D50=20 nm) is added into the Nd—Fe—B powder and then mixed in a 3D mixer for 2 hours.

[0101] Next, the mixing powder obtained in previous step is added to a mechanical mixing equipment and injected with inert gas at a running speed of 350 rpm for 180 min under a temperature of 500° C.

[0102] After the mechanical mixing process, an amount of 0.2 wt. % lubricant is added into the nano-coated Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0103] The nano-coated Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0104] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1050° C. for 12 hours, then argon is pumped for rapid cooling.

[0105] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 500° C. for 3 hours.

COMPARATIVE EXAMPLE 4

[0106] Compared with Example 4, the mechanical mixing process of adding nanoparticulate terbium powder is not performed in this control group, and the Nd—Fe—B magnet is prepared as follows:

[0107] The alloy sheets having the composition of (PrNd).sub.29.8Tb.sub.0.2Co.sub.1Cu.sub.0.15Ga.sub.0.2Ti.sub.0.2B.sub.1.0Fe.sub.bal(wt. %)

[0108] are prepared by a strip casting process at the melting temperature of 1480° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0109] The alloy sheets are subjected to hydrogen desorption process to break the sheets into more smaller pieces.

[0110] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=4.0 μm.

[0111] An amount of 0.2 wt. % lubricant is added into the Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0112] The Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0113] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 1050° C. for 12 hours, then argon is pumped for rapid cooling.

[0114] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 500° C. for 3 hours.

[0115] The magnetic properties of the magnets obtained in Embodiment 4and Comparative Example 4 are shown in Table 4.

TABLE-US-00004 TABLE 4 Br(T) Hcj(kA/m) (BH)m(kJ/m.sup.3) Hk/Hcj Example 4 1.456 1441 409 0.98 Comparative 1.445 1262 399 0.98 Example 4

[0116] As can be seen from Table 4, the magnets prepared by mechanically mixing modified Nd—Fe—B powder have higher magnetic properties. The terbium added by this method mostly exists in the surface layer of powder particles, so as to avoid the sharp decline of magnet Js resulting in the decrease of remanence. In addition, the rounding of Nd—Fe—B powder is also conducive to the improvement of magnetic remanence, which improves the magnetic remanence and coercivity.

EXAMPLE 5

[0117] The exemplary preparation method for preparing a sintered Nd—Fe—B magnet comprises the following steps:

[0118] The alloy sheets having the composition of (PrNd).sub.29.5Co.sub.1Al.sub.0.1Cu.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0119] The alloy sheets are subjected to hydrogen desorption process to break the sheets into more smaller pieces.

[0120] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=5.0 μm.

[0121] An amount of 5 wt. % nanoparticulate Pr.sub.68Cu.sub.32 powder (D50=50 nm) is added into the Nd—Fe—B powder and then mixed in a 3D mixer for 2 hours.

[0122] Next, the mixing powder obtained in previous step is added to a mechanical mixing equipment and injected with inert gas at a running speed of 500 rpm for 180 min under a temperature of 300° C.

[0123] After the mechanical mixing process, an amount of 0.1 wt. % lubricant is added into the nano-coated Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0124] The nano-coated Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0125] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 950° C. for 12 hours, then argon is pumped for rapid cooling.

[0126] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 460° C. for 3 hours.

COMPARATIVE EXAMPLE 5

[0127] Compared with Example 5, the mechanical mixing process of adding nanoparticulate Pr.sub.68Cu.sub.32 powder is not performed in this control group, and the Nd—Fe—B magnet is prepared as follows:

[0128] The alloy sheets having the composition of (PrNd).sub.29.5Co.sub.1Al.sub.0.1Cu.sub.0.1B.sub.1.0Fe.sub.bal(wt. %) are prepared by a strip casting process at the melting temperature of 1450° C., wherein the thickness of the alloy sheet is between 0.25 mm to 0.35 mm.

[0129] The alloy sheets are subjected to hydrogen desorption process to break into more smaller pieces.

[0130] After the decrepitation process, the alloy powders are pulverized in a jet milling step under nitrogen to prepare an alloy powder having an average particle size of D50=5.0 μm.

[0131] An amount of 0.1 wt. % lubricant is added into the Nd—Fe—B powder and mixed for 3 h in a 3D mixer.

[0132] The Nd—Fe—B powder is compressed into compacts under the protection of nitrogen while applying an orienting magnetic field of 1.8 T.

[0133] The compacts are subjected to a sintering step in a vacuum furnace at a temperature of 950° C. for 12 hours, then argon is pumped for rapid cooling.

[0134] Then, the sintered compacts are treated by a first heat treatment step at 850° C. for 3 hours, and a second heat treatment step at 460° C. for 3 hours.

[0135] The magnetic properties of the magnets obtained in embodiment 5 and Comparative Example 5 are shown in Table 5.

TABLE-US-00005 TABLE 5 Br(T) Hcj(kA/m) (BH)m(kJ/m.sup.3) Hk/Hcj Example 5 1.392 1486 378 0.97 Comparative 1.451 1078 404 0.97 Example 5

[0136] As can be seen from Table 5, the coercivity of the magnet prepared by the present disclosure is significantly improved, but the remanence is reduced more. This is because the proportion of addition is large, which increases the total amount of rare earth in the magnet, so the remanence decreases obviously.

EXAMPLE 6

[0137] The differences with Example 1 are as follows: the rotating speed is 350 r/min, the time is 180 min, and the temperature is 500° C. in the mechanical mixing process. The test results are shown in Table 6.

A) EXAMPLE 7

[0138] The differences with Example 1 are as follows: the rotating speed is 1000 r/min, the time is 150 min, and the temperature is 400° C. in the mechanical mixing process. The test results are shown in Table 6.

EXAMPLE 8

[0139] The differences with Example 1 are as follows: the rotating speed is 4000 r/min, the time is 120 min, and the temperature is 300° C. in the mechanical mixing process. The test results are shown in Table 6.

EXAMPLE 9

[0140] The differences with Example 1 are as follows: the rotating speed is 6000 r/min, the time is 80 min, and the temperature is 200° C. in the mechanical mixing process. The test results are shown in Table 6.

COMPARATIVE EXAMPLE 6

[0141] The differences with Example 1 are as follows: the rotating speed is 200 r/min, the time is 80 min, and the temperature is 15° C. in the mechanical mixing process. The test results are shown in Table 6.

TABLE-US-00006 TABLE 6 Br(T) Hcj(kA/m) Hk/Hcj Example 6 1.366 1504 0.98 Example 7 1.398 1665 0.98 Example 8 1.392 1654 0.98 Example 9 1.385 1652 0.98 Comparative 1.353 1449 0.98 Example 6

EXAMPLE 10

[0142] The difference from Example 1 is that the nanoparticulate powder is aluminum powder (the average particle size is 20 nm, and the weight ratio to Nd—Fe—B powder is 0.1%). The test results are shown in Table 7.

EXAMPLE 11

[0143] The difference from Example 1 is that the nanoparticulate powder is Dy powder (the average particle size is 50 nm, and the weight ratio to Nd—Fe—B powder is 0.1%) and Nb powder (the average particle size is 20 nm, the weight ratio to Nd—Fe—B powder is 0.1%). The test results are shown in Table 7.

EXAMPLE 12

[0144] The difference from Example 1 is that the nanoparticulate powder is Pr.sub.68Cu.sub.32 powder (the average particle size is 50 nm, and the weight ratio to Nd—Fe—B powder is 0.1%). The test results are shown in Table 7.

EXAMPLE 13

[0145] The difference from Example 1 is that the nanoparticulate powder is Dy.sub.70Cu.sub.30 powder (the average particle size is 50 nm, and the weight ratio to Nd—Fe—B powder is 0.1%) and TiO.sub.2 powder (the average particle size is 20 nm, the weight ratio to Nd—Fe—B powder is 0.1%). The test results are shown in Table 7.

TABLE-US-00007 TABLE 7 Br(T) Hcj(kA/m) Hk/Hcj Example 10 1.345 1540 0.98 Example 11 1.372 1676 0.98 Example 12 1.360 1648 0.98 Example 13 1.375 1660 0.98