METHOD FOR PRODUCING A SINTERED R-IRON-BORON MAGNET

Abstract

A method for producing a sintered R-iron (Fe)-boron (B) magnet, the method including: (1) producing a sintered magnet R1-FeB-M; (2) washing the sintered magnet using an acid solution and deionized water, successively, and drying the sintered magnet to yield a treated magnet; (3) mixing a heavy rare earth element powder RX, an organic solid powder EP and an organic solvent ET to yield a slurry RXE, coating the slurry RXE on the surface of the treated magnet, and drying the treated magnet to yield a treatment unit; and (4) heating, quenching, and then aging the treatment unit.

Claims

1. A method for producing a sintered R-Iron-Boron (RFeB) magnet, the method comprising: (1) producing a sintered magnet R1-FeB-M, wherein R1 is neodymium (Nd), praseodymium (Pr), terbium (Tb), dysprosium (Dy), gadolinium (Gd), holmium (Ho), or a combination thereof, and accounts for 27-34 wt. % of the total weight of the sintered magnet R1-FeB-M; the boron (B) accounts for 0.8-1.3 wt. % of the total weight of the sintered magnet R1-FeB-M; M is titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), gallium (Ga), copper (Cu), silicon (Si), aluminum (Al), zirconium (Zr), niobium (Nb), tungsten (W), molybdenum (Mo), or a combination thereof, and accounts for 0-5 wt. % of the total weight of the sintered magnet R1-FeB-M; and the rest is Fe; (2) washing the sintered magnet using an acid solution and deionized water, successively, and drying the sintered magnet to yield a treated magnet; (3) mixing a heavy rare earth element powder RX, an organic solid powder EP and an organic solvent ET to yield a slurry RXE, coating the slurry RXE on a surface of the treated magnet, and drying the treated magnet to yield a treatment unit comprising a REX layer, wherein the heavy rare earth element powder RX is Dy powder, Tb powder, hydrogenated Dy powder, hydrogenated Tb powder, dysprosium fluoride powder, terbium fluoride powder, or a combination thereof, the organic solid powder EP is rosin-modified alkyd resin, thermoplastic phenolic resin, urea-formaldehyde resin, polyvinyl butyral, or a combination thereof, and the organic solvent ET is ethyl alcohol, ether, benzene, glycerol, ethanediol, or a combination thereof; and (4) heating the treatment unit in (3) at a temperature of between 850 C. and 970 C. for between 0.5 and 48 hrs, quenching the treatment unit, and then aging the treatment unit at a temperature of between 430 C. and 650 C. for between 2 and 10 hrs.

2. The method of claim 1, wherein a particle size of the heavy rare earth element powder RX is less than 100 m.

3. The method of claim 1, wherein in (3), the REX layer is between 3 and 500 m in thickness.

4. The method of claim 1, wherein in (3), a weight percent of the powder RX in the slurry RXE ranges from 30 wt. % to 90 wt. %.

5. The method of claim 1, wherein in (3), a thickness of the treated magnet in at least one direction is less than 10 mm.

6. The method of claim 2, wherein the particle size of the heavy rare earth element powder RX is less than 30 m

7. The method of claim 3, wherein the REX layer is between 10 and 200 m in thickness.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] For further illustrating the invention, experiments detailing a method for producing a sintered RFeB magnet are described hereinbelow combined with the drawings. It should be noted that the following examples are intended to describe and not to limit the invention.

Example 1

[0023] Raw materials were melted in a vacuum melting furnace under the protection of inert gas to form RFeB alloy scales with the thickness ranging from 0.1 mm to 0.5 mm. The metallographic grain boundaries of the scales were clear. After mechanical comminution and hydro-treatment, the alloy scales were ground by nitrogen gas flow until the surface mean diameter (SMD) was 3.2 m. The 15 KOe magnetic field orientation was adopted for compression molding to produce pressings. The density of the pressings was 3.95 g/cm.sup.3. The pressings were sintered in a vacuum in a sintering furnace. The pressings were sintered at the highest temperature of 1080 C. for 330 minutes to produce green pressings. After wire-electrode cutting, the green pressings become magnetic sheets. The size of the magnetic sheets was 40 mm*30 mm*2.1 mm and the size tolerance was 0.03 mm. The surface of the magnetic sheets was washed by acid solutions and deionized water. After drying treatment, a treated magnet M1 was produced. The composition of the treated magnet M1 is shown in Table 2 below.

[0024] Heavy rare earth element powder TbH, organic solid rosin-modified alkyd resin powder and ethanol were mixed to prepare a slurry RXE. The weight percents of the TbH, the rosin-modified alkyd resin powder and the ethanol were 60 wt. %, 5 wt. % and 35 wt. %, respectively. Stir the slurry RXE for about 60 minutes. Dip the treated magnet M1 in the slurry RXE for about 3 seconds and then take the treated magnet M1 out. Put the treated magnet M1 in a drying oven at a temperature of 70 C. for about 15 minutes to produce the treated magnet with an RXE layer on the surface.

[0025] Put the treated magnet with an RXE layer in a material box for heat treatment in heat treatment equipment. After the temperature rose to 920 C., keep the magnet at the temperature of 920 C. for 18 hours and then chill the magnet quickly. Then, the temperature rose to 500 C. for aging treatment (the aging treatment refers to the heat treatment process that the properties, shapes and sizes of alloy work pieces after solution treatment, cold plastic deformation or casting and forging change with time at a higher temperature or the room temperature). Keep the magnet at a temperature of 500 C. for 4 hours and then chill the magnet quickly to the room temperature to produce the magnet M2.

TABLE-US-00001 TABLE 1 Comparison of properties of magnet M2 and treated magnet M1 before diffusion treatment Density Br Hcj (BH) max Hk/Hcj Unit Items (g/cm.sup.3) kGs kOe MGOe M2 7.56 13.87 22.79 46.35 0.95 M1 7.56 14.06 13.46 47.09 0.97

TABLE-US-00002 TABLE 2 Comparison of main compositions of magnet M2 and treated magnet M1 before diffusion treatment Items B Al Co Dy Tb Pr Nd M2 measured value % 0.97 0.1 0.89 0.51 0.48 4.71 25.65 M1 measured value % 0.97 0.1 0.9 0.52 0 4.72 25.67

[0026] As shown in Tables 1 and 2, compared to the treated magnet M1, the residual magnetism Br of the magnet M2 is reduced by about 190 Gs, and the Hcj of the magnet M2 increases by about 9.33 KOe through this method. According to the composition tests, compared to the treated magnet M1, Tb of the magnet M2 increases by about 0.48 wt. %.

TABLE-US-00003 TABLE 3 Comparison of CSON element content between magnet M2 and treated magnet M1 before diffusion treatment Items C S % O % N % M2 measured value % 0.0742 0.0011 0.0999 0.0304 M1 measured value % 0.0721 0.0009 0.0980 0.0321

[0027] Table 3 shows the comparison of the CSON element content of the magnet before and after diffusion treatment. The content of C and the content of O both do not have an obvious increase. It means that most organic rosin-modified alkyd resin does not diffuse into the interior of the magnet during the diffusion process.

Example 2

[0028] Raw materials were melted in a vacuum melting furnace under the protection of inert gas to form RFeB alloy scales with the thickness ranging from 0.1 mm to 0.5 mm. The metallographic grain boundaries of the scales were clear. After mechanical comminution and hydro-treatment, the alloy scales were ground by nitrogen gas flow until the surface mean diameter (SMD) was 3.1 m. The 15 KOe magnetic field orientation was adopted for compression molding to produce pressings. The density of the pressings was 3.95 g/cm.sup.3. The pressings were sintered in a vacuum in a sintering furnace. The pressings were sintered at the highest temperature of 1085 C. for 330 minutes to produce green pressings. After wire-electrode cutting, the green pressings become magnetic sheets. The size of the magnetic sheets was 40 mm*30 mm*3 mm and the size tolerance was 0.03 mm. The surface of the magnetic sheets was washed by acid solutions and deionized water. After drying treatment, a treated magnet M3 was produced. The composition of the treated magnet M3 is shown in Table 5 below.

[0029] Heavy rare earth element powder TbF, polyvinyl butyral and ethanol were mixed to prepare a slurry RXE. The weight percents of the TbF, the polyvinyl butyral and the ethanol were 65 wt. %, 6 wt. % and 29 wt. %, respectively. Stir the slurry RXE for about 60 minutes. Dip the treated magnet M3 in the slurry RXE for about 3 seconds and then take the treated magnet M3 out. Put the treated magnet M3 in a drying oven at a temperature of 70 C. for about 15 minutes to produce the treated magnet with an RXE layer on the surface.

[0030] Put the treated magnet with an RXE layer in a material box for heat treatment in heat treatment equipment. After the temperature rose to 920 C., keep the magnet at the temperature of 930 C. for 20 hours and then chill the magnet quickly. Then, the temperature rose to 520 C. for aging treatment. Keep the magnet at a temperature of 520 C. for 4 hours and then chill the magnet quickly to the room temperature to produce the magnet M4.

TABLE-US-00004 TABLE 4 Comparison of properties of magnet M4 and treated magnet M3 before diffusion treatment Density Br Hcj (BH) max Hk/Hcj Unit Items (g/cm.sup.3) kGs kOe MGOe M2 7.56 14.19 24.32 48.25 0.95 M1 7.56 14.36 14.46 49.09 0.97

TABLE-US-00005 TABLE 5 Comparison of main compositions of magnet M4 and treated magnet M3 before diffusion treatment Items B Al Co Tb Pr Nd M2 measured value % 0.97 0.15 0.8 0.92 4.72 25.63 M1 measured value % 0.97 0.15 0.8 0.5 4.72 25.67

[0031] As shown in Tables 4 and 5, compared to the treated magnet M3, the residual magnetism Br of the magnet M4 is reduced by about 170 Gs, and the Hcj of the magnet M4 increases by about 9.86 KOe through this method. According to the composition tests, compared to the treated magnet M3, Tb of the magnet M4 increases by about 0.48 wt. %.

TABLE-US-00006 TABLE 6 Comparison of CSON element content between magnet M4 and treated magnet M3 before diffusion treatment Items C S % O % N % M2 measured value % 0.0721 0.0014 0.0673 0.0312 M1 measured value % 0.0678 0.0012 0.0636 0.0298

[0032] Table 6 shows the comparison of the CSON element content of the magnet before and after diffusion treatment. The content of C and the content of O both do not have an obvious increase. It means that most polyvinyl butyral does not diffuse into the interior of the magnet during the diffusion process.

Example 3

[0033] Raw materials were melted in a vacuum melting furnace under the protection of inert gas to form RFeB alloy scales with the thickness ranging from 0.1 mm to 0.5 mm. The metallographic grain boundaries of the scales were clear. The alloy scales were ground by jet milling to yield powders having the surface mean diameter (SMD) of 3.2 m. The 15 KOe magnetic field orientation was adopted for compression molding to produce pressings. The density of the pressings was 3.95 g/cm.sup.3. The pressings were sintered in a vacuum in a sintering furnace. The pressings were sintered at the highest temperature of 1085 C. for 300 minutes to produce green pressings. After wire-electrode cutting, the green pressings become magnetic sheets. The size of the magnetic sheets was 40 mm*25 mm*4.5 mm and the size tolerance was 0.03 mm. The surface of the magnetic sheets was washed by acid solutions and deionized water. After drying treatment, a treated magnet M5 was produced. The composition of the treated magnet M5 is shown in Table 8 below.

[0034] Heavy rare earth element powders TbF and Tb, organic solid urea resin and ethanol were mixed to prepare a slurry RXE, and the weight percents thereof were 60 wt. %, 6 wt. % and 34 wt. %, respectively. The maximum particle size of the mixed powders of TbF and Tb was less than 18 m. Stir the slurry RXE for about 60 minutes. The treated magnet M5 was coated with a layer of RXE slurry. Put the treated magnet M5 in a drying oven at a temperature of 90 C. for about 15 minutes to produce the treated magnet with an RXE layer on the surface. The weight of the treated magnet M5 was increased by 1.02 wt. %.

[0035] Put the treated magnet with an RXE layer in a material box for heat treatment in heat treatment equipment. After the temperature rose to 930 C., keep the magnet at the temperature of 930 C. for 25 hours and then chill the magnet quickly. Then, the temperature rose to 540 C. for aging treatment. Keep the magnet at a temperature of 540 C. for 4 hours and then chill the magnet quickly to the room temperature to produce the magnet M6.

TABLE-US-00007 TABLE 7 Comparison of properties of magnet M6 and treated magnet M5 before diffusion treatment Density Br Hcj (BH)max Hk/Hcj Unit Items (g/cm.sup.3) kGs kOe MGOe M2 7.58 14.16 25.22 47.87 0.94 M1 7.57 14.31 15.42 48.73 0.98

TABLE-US-00008 TABLE 8 Comparison of main compositions of magnet M6 and treated magnet M5 before diffusion treatment Items B Al Co Dy Tb Pr Nd M2 measured value % 0.98 0.1 0.6 0.68 0.91 5.87 22.37 M1 measured value % 0.99 0.1 0.6 0.70 0.5 5.88 22.40

[0036] As shown in Tables 7 and 8, compared to the treated magnet M5, the residual magnetism Br of the magnet M6 is reduced by about 150 Gs, and the Hcj of the magnet M6 increases by about 9.8 KOe through this method. According to the composition tests, compared to the treated magnet M5, Tb of the magnet M6 increases by about 0.41 wt. %. Since the magnet is relatively thick, the holding time for thermal treatment at 930 C. is significantly longer than that in examples 1 and 2.

TABLE-US-00009 TABLE 9 Comparison of CSON element content between magnet M6 and treated magnet M5 before diffusion treatment Items C S % O % N % M2 measured value % 0.0742 0.0011 0.0999 0.0304 M1 measured value % 0.0721 0.0009 0.0980 0.0321

[0037] Table 9 shows the comparison of the CSON element content of the magnet before and after diffusion treatment. The content of C and the content of 0 both do not have an obvious increase. It means that most urea resin does not diffuse into the interior of the magnet during the diffusion process.

[0038] Unless otherwise indicated, the numerical ranges involved in the invention include the end values. While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.