Method for improvement of magnetic performance of sintered NdFeB lamellar magnet

Abstract

A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps. Firstly, material containing element R, H and X is to be covered on a surface of the sintered NdFeB magnet to form a finish coat. After that, proceed with a diffusion treatment and an aging treatment to the sintered NdFeB magnet with the finish coat in the environment of vacuum or inert gas. R is at least one of such elements as Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. H is hydrogen. X is at least one of such elements as C, O, N, S, B, Cl and Si.

Claims

1. A method for improvement of magnetic performance of a sintered NdFeB magnet, comprising: a material consisting of element R, H and X is firstly covered on a surface of the sintered NdFeB magnet to form a finish coat, and is proceeded with a diffusion treatment and an aging treatment to the sintered NdFeB magnet with the finish coat in the environment of vacuum or inert gas, wherein, R is at least one of such elements as Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, H is hydrogen, X is at least one of such elements as C, O, N, S, B and Si, wherein in the material consisting of element R, H and X, content of the element H in terms of mass percentage is 0.5%-2%, and content of the element X in terms of mass percentage is 0.5%-10%, wherein the sintered NdFeB magnet with the finish coat shall subject to a dehydrogenation treatment prior to the diffusion treatment, and the hydrogen content in the finish coat of the sintered NdFeB magnet in terms of mass percentage is 0.001%-0.2% after the dehydrogenation treatment.

2. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein the element R, H and X in the material exists as the product by chemical reaction of the mixture of the element R, H and X.

3. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein the element R, H and X in the material exists as the product by chemical reaction of the element X and R hydride.

4. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein the element R is at least one of such elements as Pr, Nd, Gd, Dy, Tb and Ho.

5. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein minimum size of the sintered NdFeB magnet in any direction is below 15 mm before forming the finish coat.

6. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein a dehydrogenation temperature is 200 C.-900 C. and the holding time is 0.1 h-30 h.

7. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 6, wherein the dehydrogenation temperature is 600 C.-800 C.

8. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein the diffusion treatment refers to heat preservation at the temperature of 700 C.-1000 C. for 1 h-30 h.

9. The method for improvement of magnetic performance of a sintered NdFeB magnet according to claim 1, wherein the aging treatment refers to heat preservation at the temperature of 400 C.-600 C. for 1 h-10 h.

Description

DESCRIPTION OF THE EMBODIMENTS

(1) The present invention is further described in detail as follows in combination with embodiments:

Embodiment 1

(2) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(3) {circle around (1)} Process the terbium metal in the hydrogen-oxygen mixed gas with oxygen content of 1% to obtain the coarse powder with hydrogen and oxygen content up to 9416 ppm and 3174 ppm respectively;

(4) {circle around (2)} Proceed with ball milling of coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.51 m;

(5) {circle around (3)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(6) {circle around (4)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 700 C.; dehydrogenation time is 0.5 h; diffusion treatment temperature is 900 C.; diffusion treatment time is 16 h; aging treatment temperature is 490 C.; aging treatment time is 4 h.

(7) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 107 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 2

(8) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(9) {circle around (1)} Process the dysprosium in the hydrogen gas to obtain the 1.sup.st coarse powder;

(10) {circle around (2)} Put the 1.sup.st coarse powder in the nitrogen-oxygen mixed gas with oxygen content up to 1.5% for deactivation for 24 h to obtain the 2.sup.nd coarse powder with hydrogen, oxygen and nitrogen content up to 9281 ppm, 3430 ppm and 2161 ppm respectively;

(11) {circle around (3)} Proceed with ball milling of the 2.sup.nd coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.45 m;

(12) {circle around (4)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(13) {circle around (5)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 680 C.; dehydrogenation time is 1 h; diffusion treatment temperature is 850 C.; diffusion treatment time is 12 h; aging treatment temperature is 500 C.; aging treatment time is 4 h.

(14) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 105 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 3

(15) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(16) {circle around (1)} Process the dysprosium in the hydrogen gas to obtain the 1.sup.st coarse powder;

(17) {circle around (2)} Put the 1.sup.st coarse powder in air for deactivation for 24 h to obtain the 2.sup.nd coarse powder with hydrogen, oxygen and nitrogen content up to 5154 ppm, 7208 ppm and 1140 ppm respectively;

(18) {circle around (3)} Proceed with ball milling of the 2.sup.nd coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.49 m;

(19) {circle around (4)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(20) {circle around (5)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 710 C.; dehydrogenation time is 2 h; diffusion treatment temperature is 900 C.; diffusion treatment time is 8 h; aging treatment temperature is 510 C.; aging treatment time is 4 h.

(21) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 107 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 4

(22) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(23) {circle around (1)} Process the DyFe alloy in the hydrogen-oxygen mixed gas with oxygen content up to 0.5% to obtain the coarse powder with hydrogen and oxygen content up to 9861 ppm and 2786 ppm respectively;

(24) {circle around (2)} Proceed with ball milling of the coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.58 m;

(25) {circle around (3)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(26) {circle around (4)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 650 C.; dehydrogenation time is 3 h; diffusion treatment temperature is 950 C.; diffusion treatment time is 20 h; aging treatment temperature is 480 C.; aging treatment time is 4 h.

(27) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 109 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 5

(28) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(29) {circle around (1)} Process the PrCu alloy in the hydrogen gas to obtain the 1.sup.st coarse powder;

(30) {circle around (2)} Put the 1.sup.st coarse powder in the nitrogen-oxygen mixed gas with oxygen content up to 1% for deactivation for 24 h to obtain the 2.sup.nd coarse powder with hydrogen, oxygen and nitrogen content up to 9538 ppm, 3269 ppm and 3290 ppm respectively;

(31) {circle around (3)} Proceed with ball milling of the 2.sup.nd coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.67 m;

(32) {circle around (4)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(33) {circle around (5)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 750 C.; dehydrogenation time is 0.3 h; diffusion treatment temperature is 800 C.; diffusion treatment time is 6 h; aging treatment temperature is 500 C.; aging treatment time is 4 h.

(34) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 103 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

(35) In the sintered NdFeB magnet as obtained with methods in Embodiment 1-5, select two magnets per embodiment; mark such sintered NdFeB magnets as test sample 1-1, 1-2, 2-1, 2-1, 3-1, 3-2, 4-1, 4-2, 5-1 and 5-2 respectively; mark sintered NdFeB magnet not coated as original sample. Select B-H instrument for measurement of permanent magnet material to carry out magnetic performance test for original sample and test samples in aforesaid embodiments; test data is as shown in Table 1.

(36) TABLE-US-00001 TABLE 1 Magnetic Performance of Original Samples and Test Samples in Embodiment 1-5 Maximum Magnetic Energy Remanence Coercivity Product Designation (kGs) (kOe) (MGsOe) Squareness Original 13.99 14.88 46.61 91.9 sample Test sample 13.75 24.12 45.86 95.5 1-1 Test sample 13.70 23.88 45.84 96.3 1-2 Test sample 13.69 20.10 45.88 95.2 2-1 Test sample 13.71 19.93 45.93 95.0 2-2 Test sample 13.70 18.51 44.72 94.3 3-1 Test sample 13.68 18.31 44.50 94.2 3-2 Test sample 13.70 19.22 45.71 95.5 4-1 Test sample 13.69 19.31 45.65 95.6 4-2 Test sample 13.67 17.10 44.71 95.4 5-1 Test sample 13.65 17.08 44.65 95.3 5-2

Embodiment 6

(37) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(38) {circle around (1)} Process the terbium metal in the hydrogen gas to obtained the coarse powder with hydrogen content up to 9590 ppm;

(39) {circle around (2)} Proceed with ball milling of the coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.54 m;

(40) {circle around (3)} Uniformly mix aforesaid fine powder and terbium oxide as per the mass ratio of 9:1 to obtain the fine powder material; uniformly mix the fine powder material with ethanol absolute, and spray it on the surface of sintered NdFeB magnet to form a finish coat with thickness up to 20 m; after that, proceed with drying treatment at the temperature of 80 C.;

(41) {circle around (4)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 700 C.; dehydrogenation time is 1 h; diffusion treatment temperature is 950 C.; diffusion treatment time is 10 h; aging treatment temperature is 510 C.; aging treatment time is 4 h.

(42) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 107 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 7

(43) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(44) {circle around (1)} Process the terbium metal in the hydrogen gas to obtained the 1.sup.st coarse powder;

(45) {circle around (2)} Put the 1.sup.st coarse powder in the nitrogen-oxygen mixed gas with oxygen content up to 1.5% for deactivation for 24 h to obtain the 2.sup.nd coarse powder with hydrogen, oxygen and nitrogen content up to 9378 ppm, 3525 ppm and 3417 ppm respectively;

(46) {circle around (3)} Proceed with ball milling of the 2.sup.nd coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.41 m;

(47) {circle around (4)} Uniformly mix aforesaid fine powder and terbium oxide as per the mass ratio of 9:1 to obtain the fine powder material; uniformly mix the fine powder material with ethanol absolute, and spray it on the surface of sintered NdFeB magnet to form a finish coat with thickness up to 20 m; after that, proceed with drying treatment at the temperature of 80 C.;

(48) {circle around (5)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 660 C.; dehydrogenation time is 2 h; diffusion treatment temperature is 890 C.; diffusion treatment time is 18 h; aging treatment temperature is 500 C.; aging treatment time is 4 h.

(49) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 107 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

Embodiment 8

(50) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(51) {circle around (1)} Process the terbium metal in the hydrogen-oxygen mixed gas with oxygen content of 1% to obtain the coarse powder with hydrogen and oxygen content up to 9891 ppm and 3157 ppm respectively;

(52) {circle around (2)} Proceed with ball milling of the coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.57 m;

(53) {circle around (3)} Uniformly mix aforesaid fine powder and silicon dioxide as per the mass ratio of 200:1 to obtain the fine powder material; uniformly mix the fine powder material with ethanol absolute, and spray it on the surface of sintered NdFeB magnet to form a finish coat with thickness up to 20 m; after that, proceed with drying treatment at the temperature of 80 C.;

(54) {circle around (4)} Proceed with dehydrogenation and diffusion treatment to the sintered NdFeB magnet as dried in proper sequence in the vacuum environment with pressure up to 6.010.sup.4 Pa prior to aging treatment; dehydrogenation temperature is 730 C.; dehydrogenation time is 0.5 h; diffusion treatment temperature is 980 C.; diffusion treatment time is 6 h; aging treatment temperature is 500 C.; aging treatment time is 4 h.

(55) In this embodiment, sintered NdFeB magnet is made from massive sintered NdFeB magnet through mechanical processing (cutting); its specification (diameterheight) is 107 mm; massive sintered NdFeB magnet is prepared based on such well-established processes as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB fabrication; sintered NdFeB magnet includes the following constituents: 29.5 wt. % Nd, 0.2 wt. % Dy, 1.0 wt. % B, residual Fe and other micro elements.

(56) In the sintered NdFeB magnet as obtained with methods in Embodiment 6-8, select two magnets per embodiment; mark such sintered NdFeB magnets as test sample 6-1, 6-2, 7-1, 7-2, 8-1 and 8-2 respectively; mark sintered NdFeB magnet not coated as original sample. Select B-H instrument for measurement of permanent magnet material to carry out magnetic performance test for original sample and test samples in aforesaid embodiments; test data is as shown in Table 2.

(57) TABLE-US-00002 TABLE 2 Magnetic Performance of Original Samples and Test Samples in Embodiment 6-8 Maximum Magnetic Energy Remanence Coercivity Product Designation (kGs) (kOe) (MGsOe) Squareness Original 13.99 14.88 46.61 91.9 sample Test sample 13.69 23.78 45.76 95.3 6-1 Test sample 13.71 23.93 45.93 96.0 6-2 Test sample 13.72 23.56 45.66 95.3 7-1 Test sample 13.69 23.62 45.70 95.2 7-2 Test sample 13.70 23.82 45.88 95.2 8-1 Test sample 13.71 23.90 45.93 95.1 8-2

(58) It can be seen from analysis of aforesaid embodiments that the sintered NdFeB magnet obtained with the method of the present invention is provided with high remanence, high coercivity, maximum magnetic energy product and excellent squareness.

Embodiment 9

(59) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(60) {circle around (1)} Process the terbium metal in the hydrogen-oxygen mixed gas with oxygen content up to 1% to obtain the coarse powder; check the hydrogen content in the coarse powder at this step;

(61) {circle around (2)} Proceed with ball milling of the coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.51 m;

(62) {circle around (3)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(63) {circle around (4)} Proceed with dehydrogenation to the sintered NdFeB magnet as dried in the vacuum environment with pressure up to 6.010.sup.4 Pa; dehydrogenation temperature is 700 C.; dehydrogenation time is 2 h; remove the magnet with finish coat under vacuum protection after dehydrogenation; check hydrogen content in the finish coat;

(64) {circle around (5)} Proceed with diffusion and aging treatment to the sintered NdFeB magnet after dehydrogenation.

Embodiment 10

(65) A method for improvement of magnetic performance of sintered NdFeB magnet includes the following steps:

(66) {circle around (1)} Process the dysprosium in the hydrogen gas to obtain the coarse powder; check hydrogen content in the coarse powder at this step;

(67) {circle around (2)} Deactivate the coarse powder in the nitrogen-oxygen mixed gas with oxygen content up to 1.5% for 24 h;

(68) {circle around (3)} Proceed with ball milling of the coarse powder for 8 h to obtain the powder material with average particle size per specific area up to 1.48 m;

(69) {circle around (4)} Uniformly mix aforesaid powder material with ethanol absolute, and evenly spray it on the surface of sintered NdFeB magnet to form a 20 m finish coat prior to drying at the temperature of 80 C.;

(70) {circle around (5)} Proceed with dehydrogenation to the sintered NdFeB magnet as dried in the vacuum environment with pressure up to 6.010.sup.4 Pa; dehydrogenation temperature is 730 C.; dehydrogenation time is 1 h; remove the magnet with finish coat under vacuum protection after dehydrogenation; check hydrogen content in the finish coat;

(71) {circle around (6)} Proceed with diffusion and aging treatment to the sintered NdFeB magnet after dehydrogenation.

(72) Mark the finish coat without hydrogenation in Embodiment 9 as test sample 9-1; mark the finish coat subjecting to dehydrogenation as test sample 9-2; mark the finish coat without hydrogenation in Embodiment 10 as test sample 10-1; mark the finish coat subjecting to dehydrogenation as test sample 10-2; use hydrogen content tester for measurement; measurement data is as shown in Table 3.

(73) TABLE-US-00003 TABLE 3 Hydrogen Content in Test Samples without Dehydrogenation and Test Samples Dehydrogenated Hydrogen Content Designation (ppm) Test sample 9-1 9851 Test sample 9-2 54 Test sample 10-1 9328 Test sample 10-2 41

(74) It can be seen from analysis of aforesaid Embodiment 9 and 10 that there exists high difference to hydrogen content in the finish coat before and after dehydrogenation; therefore, it is necessary to reduce the hydrogen content to a reasonable level through dehydrogenation so as to prevent adverse effect as imposed by extremely high hydrogen content on the magnetic performance of the magnet.