R-T-B-BASED SINTERED MAGNET AND PREPARATION METHOD THEREFOR

Abstract

An R-T-B-based sintered magnet and a preparation method therefor. The R-T-B-based sintered magnet comprises: R, B, Ti, Ga, Al, Cu, and T. The contents thereof are as follows: R is 29.0-33%; the content of B is 0.86-0.93%; the content of Ti is 0.05-0.25%; the content of Ga is 0.3-0.5%, but not 0.5%; the content of Al is 0.6-1%, but not 0.6%; the content of Cu is 0.36-0.55%. The percentage is the mass percentage. Under the condition that no heavy rare earth is added or a small amount of heavy rare earth is added, by using a low B technology, not only the remanence performance of the R-T-B-based sintered magnet is improved, but also the coercivity and the squareness of the magnet are ensured.

Claims

1. An R-T-B-based sintered magnet, wherein the R-T-B-based sintered magnet comprises R, B, Ti, Ga, Al, Cu and T by the following percentage: 29.0-33% of R; 0.86-0.93% of B; 0.05-0.25% of Ti; 0.3-0.5% of Ga, exclusive of 0.5%; 0.6-1% of Al, exclusive of 0.6%; 0.36-0.55% of Cu; wherein, R is rare earth element comprising at least Nd, B is boron, Ti is titanium, Ga is gallium, Al is aluminum, Cu is copper, T comprises Fe and Co; the percentage is mass percentage.

2. The R-T-B-based sintered magnet of claim 1, wherein R is 30.2-33%; or, RH in R is 0 or not more than 1%, such as 0% or 0.5%; or, B is 0.915-0.93%, such as 0.915%, 0.92% or 0.93%; or, Ti is 0.15-0.25%, such as 0.15%, 0.2% or 0.25%; or, Ga is 0.3-0.455%, such as 0.3%, 0.4% or 0.455%; or, Al is 0.65-1%, exclusive of 1%, such as 0.65%, 0.7%, 0.8% or 0.9%; or, Cu is 0.45-0.55%, such as 0.45%, 0.5% or 0.55%; or, Fe and Co are a balance of 100% mass percentage; or, C, N and O of the R-T-B-based sintered magnet in total are 1000 ppm-3500 ppm; the percentage is mass percentage.

3. The R-T-B-based sintered magnet of claim 1, wherein the R-T-B-based sintered magnet comprises a main phase and a grain boundary phase; wherein the main phase comprises R.sub.2T.sub.14B, the grain boundary phase comprises R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y and rare earth oxide phase; wherein, x/y=1.5-3; a/b=2-5; (a+b)/c=30-70; the main phase is 94-98%; the R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y is 1-3.5%; the rare earth oxide phase is 1-2.5%, the percentage is volume percentage.

4. The RTB-based sintered magnet of claim 1, wherein the R-T-B-based sintered magnet comprises 31.5% of Nd, 0.92% of B, 0.5% of Co; 0.9% of Al, 0.45% of Cu, 0.455% of Ga, 0.2% of Ti, and Fe as a balance; the percentage is mass percentage; or, the R-T-B-based sintered magnet comprises 31.5% of Nd, 0.92% of B, 0.5% of Co; 1.0% of Al, 0.5% of Cu, 0.455% of Ga, 0.2% of Ti, and Fe as a balance; the percentage is mass percentage; or, the R-T-B-based sintered magnet comprises 31.5% of Nd, 0.5% of Dy; 0.915% of B, 0.5% of Co; 0.7% of Al, 0.55% of Cu, 0.455% of Ga, 0.25% of Ti, and Fe as a balance; the percentage is mass percentage; or, the R-T-B-based sintered magnet comprises 30.2% of Nd, 0.93% of B, 1.5% of Co; 0.65% of Al, 0.4% of Cu, 0.3% of Ga, 0.15% of Ti, and Fe as a balance; the percentage is mass percentage; or, the R-T-B-based sintered magnet comprises 33% of Nd, 0.86% of B, 3.0% of Co; 0.8% of Al, 0.36% of Cu, 0.4% of Ga, 0.05% of Ti, and Fe as a balance; the percentage is mass percentage.

5. An R-T-B-based sintered magnet, wherein the R-T-B-based sintered magnet comprises a main phase and a grain boundary phase; the main phase comprises R.sub.2T.sub.14B, the grain boundary phase comprises R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y and rare earth oxide phase; wherein, x/y=1.5-3; a/b=2-5; (a+b)/c=30-70; the main phase content is 94-98%; the R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y is 1-3.5%; the rare earth oxide phase is 1-2.5%, the percentage is volume percentage.

6. The R-T-B-based sintered magnet of claim 5, in the grain boundary R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y, x/y=1.5-3, a:b:c=(10-40):(6-19):1.

7. A method for preparing the R-T-B-based sintered magnet of claim 1, wherein the method involves smelting, casting, hydrogen decrepitating, jet milling, forming, sintering and aging a raw material of the R-T-B-based sintered magnet successively.

8. The method of claim 7, wherein the smelting is carried out in a high frequency induction vacuum melting furnace; or, the smelting has a temperature of 1450-1550° C.; or, the casting is carried out under an Ar gas conditions; or, the casting is carried out at a gas pressure of 20-70 kPa; or, the casting has a copper roller wheel speed of 0.4-2 m/s, such as 1 m/s; or, the casting produces an R-T-B alloy sheet having a thickness of 0.15-0.5 mm; or, the hydrogen decrepitation has a hydrogen absorption temperature of 20-300° C.; or, the hydrogen decrepitation has a hydrogen absorption pressure of 0.12-0.19 MPa; or, the hydrogen decrepitation has a hydrogen desorption time of 0.5-5 h, such as 2 h; or, the hydrogen decrepitation has a hydrogen desorption temperature of 450-600° C.; or, the jet milling is to add the R-T-B alloy powder into jet milling machine for successively pulverizing by jet milling to obtain a fine powder; or, the forming is carried out under a magnetic field strength above 1.8 T, and protection of nitrogen gas atmosphere; or, the sintering comprises four steps: (1) a heat treatment at a temperature of 150-300° C. for 1-4 h; (2) a heat treatment at a temperature of 400-600° C. for 1-4 h; (3) a heat treatment at a temperature of 800-900° C. for 1-4 h; (4) a heat treatment at a temperature of 1000-1090° C. for more than 3 h; the aging comprises a primary aging and a secondary aging.

9. An R-T-B-based sintered magnet, which is prepared by the method of claim 7.

10. A use of the R-T-B-based sintered magnet of claim 1, as a magnetic steel of motor rotor.

11. The R-T-B-based sintered magnet of claim 2, wherein Co is 0.5-3%; or Fe is 60-68%.

12. The R-T-B-based sintered magnet of claim 3, in the grain boundary, R.sub.x—(Cu.sub.a—Ga.sub.b—Al.sub.c).sub.y, x/y=1.5-3, a:b:c=(10-40):(6-19):1.

13. The method of claim 8, wherein the melting furnace has a vacuum degree of less than 0.1 Pa; or, the smelting temperature of 1500-1550° C.; or, the casting is carried out at a gas pressure of 30-50 kPa; or, the R-T-B alloy sheet has a thickness of 0.2-0.35 mm; or, the fine powder has a medium value particle size D.sub.50 of 3-5.5 μm; or, the jet milling has a pulverization pressure of 0.3-0.5 MPa; or, the primary aging has a temperature of 850° C.-950° C.; or, the secondary aging has a temperature of 440° C.-540° C.

14. The method of claim 13, wherein the melting furnace has a vacuum degree of less than 0.02 Pa.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0073] FIG. 1 is a graph illustrating an observation result of the R-T-B-based sintered magnet of Example 1 by means of EPMA.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0074] The present invention will be further illustrated by Examples described below, which, however, are not intended to limit the scope of the present invention. For the experimental methods in which no specific conditions are specified in the following Examples, selections are made according to conventional methods and conditions or according to the product instructions.

[0075] Element mass percent and magnetic properties of the R-T-B-based sintered magnets in Examples 1-5 and Comparative Examples 6-12 are shown in Table 1 below. In Table 2, “Br” referred to remanence, “Hcj” referred to intrinsic coercivity, and Hk/Hcj referred to squareness (squareness ratio), ‘/’ referred to being free of the element.

TABLE-US-00001 TABLE 1 Element mass percentage and magnetic properties of the R-T-B-based sintered magnets Hk/ NOs: Nd Pr Dy Fe B Co Al Cu Ga Ti Br Hcj Hcj 1 31.5 / / bal. 0.92 0.5 0.9 0.45 0.455 0.2 13.23 22.33 0.98 2 31.5 / / bal. 0.92 0.5 1.0 0.5 0.455 0.2 12.95 22.8 0.98 3 31.5 / 0.5 bal. 0.915 0.5 0.7 0.55 0.455 0.25 13 23.2 0.99 4 30.2 / / bal. 0.93 1.5 0.65 0.4 0.3 0.15 13.5 20.52 0.97 5 33 / / bal. 0.86 3.0 0.8 0.36 0.4 0.05 12.5 20.6 0.95 6 31.5 0 0 bal. 0.92 0.5 0.7 0.4 0.455 0 13.3 19.8 0.97 7 31.5 0 0 bal. 0.92 0.5 0.55 0.4 0.455 0.2 13.09 20.6 0.96 8 31.5 0 1.5 bal. 0.92 0.5 0.7 0.4 0.455 0.2 12.5 22.03 0.98 9 31.5 0 2.5 bal. 0.92 0.5 0.7 0.4 0.455 0.2 12.13 24.3 0.99 10 24.45 7.91 0 bal. 0.95 0.53 0.37 0.13 0.53 0.36 12.77 22.42 0.95 11 31.5 0 0 bal. 0.83 0.5 0.7 0.4 0.455 0.2 13.03 21.6 0.85 12 31.5 0 0 bal. 0.92 0.5 0.7 0.2 0.2 0.5 12.63 17.9 0.95

Example 1

[0076] The preparation method for the R-T-B-based sintered magnet was as follows:

(1) Smelting: According to the element mass percentage of all Examples and Comparative examples shown in Table 1, the raw materials that satisfy the element mass percentage were prepared.
The raw materials were smelted in a high frequency induction vacuum melting furnace, wherein the melting furnace had a vacuum degree of less than 0.02 Pa, the smelting had a temperature of 1500-1550° C.
(2) Casting: The casting was carried out under an Ar gas conditions, to obtain an R-T-B alloy sheet.
The casting was carried out at a gas pressure of 30-50 kPa. The casting had a copper roller wheel speed of 1 m/s.
The casting produced an R-T-B alloy sheet having a thickness of 0.25 mm.
(3) Hydrogen decrepitation: The hydrogen decrepitation had a hydrogen absorption temperature of 25° C. The hydrogen decrepitation had a hydrogen absorption pressure of 0.19 MPa. The hydrogen decrepitation had a hydrogen desorption time of 2 h. The hydrogen decrepitation had a hydrogen desorption temperature of 550° C. The R-T-B alloy casting strip was hydrogen decrepitated under conditions above to obtain an R-T-B alloy powder.
(4) Jet milling: The R-T-B alloy powder was added into jet milling machine for successively pulverizing by jet milling to obtain a fine powder. The jet milling had a pulverization pressure of 0.3-0.5 MPa, such as 0.4 MPa.
The fine powder had a medium value particle size D.sub.50 of 4 μm.
(5) Forming: The fine powder was oriented and formed under a certain magnetic field strength to obtain a compact.
The forming was carried out under a magnetic field strength above 1.8 T and the protection of nitrogen gas atmosphere.
(6) Sintering, which was divided into four steps (this batch was 10 kg):
a heat treatment at a temperature of 150-300° C. for 2 h;
a heat treatment at a temperature of 400-600° C. for 2 h;
a heat treatment at a temperature of 800-900° C. for 4 h;
a heat treatment at a temperature of 1000-1090° C. for 5 h.

(7) Aging

[0077] The temperature of the primary grade was 900° C.; the temperature of the secondary aging was 480° C.

[0078] The parameters in the preparation method are the same as those in the preparation method of Example 1 except that the selected raw materials are different in the preparation methods of Examples 2-5 and Comparative Examples 6-12.

Effect Example

[0079] FIG. 1 is a result of micro analysis of Example 1 by a field-emission electron probe micro analyzer (EPMA).

[0080] The results of micro analysis of R-T-B-based sintered magnets in Examples 1-5 and Comparative Example 8 are shown in Table 2

TABLE-US-00002 TABLE 2 Results of micro analysis of R-T-B-based sintered magnets NOs: Main phase Content Grain boundary phase Content 1 Nd.sub.12.8-14Fe.sub.76-78Co.sub.0.5-0.6Al.sub.0.9-1.45 95%-97% Nd.sub.1.5-2.1 − (Cu.sub.10-28 − Ga.sub.8-12 − Al.sub.1).sub.1 1.5-2.5% B.sub.5.55-5.65 2 Nd.sub.12.8-13.9Fe.sub.76-78Co.sub.0.5-0.6Al.sub.1.4-2.4 94%-96% Nd.sub.1.5-1.9 − (Cu.sub.15-40 − Ga.sub.6-19 − Al.sub.1).sub.1   2-2.5% B.sub.5.4-5.6 3 Nd.sub.12.8-14.1Dy.sub.0.1-0.2Fe.sub.76-78Co.sub.0.5-0.6 95%-97% Nd.sub.1.5-2.5Dy.sub.0-0.5 − (Cu.sub.10-28 − Ga.sub.8-12 − Al.sub.1).sub.1   2-2.5% Al.sub.1.4-2.4B.sub.5.4-5.7 4 Nd.sub.12.5-13.6Fe.sub.76-78Co.sub.0.5-0.6Al.sub.1.2-1.7 96%-98% Nd.sub.1.5-1.9 − (Cu.sub.10-26 − Ga.sub.6-8 − Al.sub.1).sub.1 1-2% B.sub.5.5-5.6 5 Nd.sub.13.6-15.2Fe.sub.75-77Co.sub.0.5-0.6Al.sub.1.4-2 94%-96% Nd.sub.2.1-3 − (Cu.sub.16-36 − Ga.sub.12-16 − Al.sub.1).sub.1 2.5-3.5% B.sub.5.1-5.4 8 Nd.sub.13.1-14.2Fe.sub.76-77.5Co.sub.0.5-0.6 93%-96% Nd.sub.70-80Fe.sub.5-15Cu.sub.2-5Al.sub.3-8Ga.sub.2-5 3%-6.5% Al.sub.0.3-0.75B.sub.5.3-5.6