METHOD FOR PREPARING RARE EARTH PERMANENT MAGNET MATERIAL

Abstract

A method for preparing rare earth permanent magnet material, comprising: firstly weighing powders of three raw materials, H, M and Q, according to the atomic percentage content in general formula H.sub.100-x-yM.sub.xQ.sub.y, and performing the mixing treatment and sieving treatment in a nitrogen gas or other oxygen-free environments to obtain a composite powder; then machining a sintered NdFeB magnet into a prescribed shape and size, and performing the surface cleaning and drying to obtain a NdFeB magnet to be treated; next, adhering the composite powder to the surface of the NdFeB magnet to be treated by static electricity in an oxygen-free environment; next performing a vacuum thermal treatment and tempering treatment sequentially thereby obtaining the rare earth permanent magnet material. For the above method, the efficiency is high and binding force between the heavy rare earth element attachments and the substrate magnet is strong, it is convenient for the residual powder materials to be recycled. The coercivity of the prepared NdFeB magnet can be increased by 4000-14000 Oe, the remanence is only reduced by 1-2%, and the magnet with equivalent performance can be saved 30% of the heavy rare earth usage amount.

Claims

1. A method for preparing rare earth permanent magnet material comprising: step 1, weighing powders of three raw materials, H, M and Q according to the atomic percentage content in a general formula H.sub.100-x-yM.sub.xQ.sub.y, and performing the mixing treatment and sieving treatment sequentially on the three raw materials in a nitrogen gas or other oxygen-free environments to obtain a composite powder; wherein: in the general formula, H is one or more in fluoride or oxide powders of Dy, Tb, DyTb, Ho and Gd, M is Nd or/and Pr metal powder(s), and Q is one or more in Cu, Al, Zn, Ga and Sn metal powders, x and y are respectively the atomic percentage contents of the raw material M and the raw material Q, x=0-20, y=0-40, and x and y are not zero at the same time; step 2, machining a sintered NdFeB magnet into a prescribed shape and size, and then performing the surface cleaning and drying to obtain a NdFeB magnet to be treated; step 3, adhering the composite powder to the surface of the NdFeB magnet to be treated by static electricity in an oxygen-free environment to obtain a NdFeB magnet, the surface of which is adhered with a composite powder film. step 4, performing vacuum thermal treatment on the NdFeB magnet, the surface of which is adhered with a composite powder film, and then furnace cooling to obtain a diffused NdFeB magnet. step 5, performing tempering treatment on the diffused NdFeB magnet to obtain the rare earth permanent magnet material.

2. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 1, x is 1-15, y is 4-25 in the general formula.

3. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 1, M is PrNd metal powder, and the mass ratio of Pr and Nd is 1:2-1:5.

4. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 1, the raw material powders have a particle size of 150 mesh, and the sieving treatment means sieving with a 150 mesh sieve.

5. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 2, the thickness of the NdFeB magnet to be treated in direction of orientation is 1-8 mm.

6. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 3, the thickness of the composite powder film is 10-40 m.

7. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 3, the composite powder is sprayed onto the surface of the NdFeB magnet to be treated by an electrostatic spray gun; in which, technological conditions are as follows: the voltage is 30-120 kv; the time is 5-40 s; the movement speed of the spray gun is 5-45 cm/s; the spray distance is 8-35 cm.

8. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 4, the conditions of the vacuum thermal treatment are as follows: the vacuum degree is higher than 10.sup.3 Pa, the holding temperature is 650-1050 C., and the holding time is 5-50 h.

9. The method for preparing rare earth permanent magnet material according to claim 8, wherein: the holding temperature is 830-870 C., and the holding time is 30-40 h; the furnace cooling is performed until the temperature is no more than 50 C.

10. The method for preparing rare earth permanent magnet material according to claim 1, wherein: in the step 5, the temperature of the tempering treatment is 420-640 C., the time thereof is 2-10 h.

11. The method for preparing rare earth permanent magnet material according to claim 10, wherein: the temperature of the tempering treatment is 420-480 C., the time is 4-6 h.

12. The method for preparing rare earth permanent magnet material according to claim 1, wherein: an aftertreatment step after the step 5 is further included, comprising: soaking the rare earth permanent magnet material in dilute nitric acid to remove residual attachments on the surface thereof, and then cleaning the rare earth permanent magnet material with a deionized water.

13. The method for preparing rare earth permanent magnet material according to claim 12, wherein: the dilute nitric acid is a solution of nitric acid in alcohol, the mass concentration is 2-10%, and the time of the soaking is 60-180 s.

14. The method for preparing rare earth permanent magnet material according to claim 13, wherein: the mass concentration of the solution of nitric acid in alcohol is 4-6%.

15. The method for preparing rare earth permanent magnet material according to claim 1, wherein: the procedure of the surface cleaning is as follows: firstly placing the sintered NdFeB magnet in a degreasing tank and soaking for 8-15 minutes to remove oil stain on the surface of the magnet; then performing the first water washing, acid pickling, the second water washing and ultrasonic treatment sequentially, finally, air drying the surface of the sintered NdFeB magnet; the acid pickling is performed with a dilute HNO.sub.3 and the time thereof is 20-45 s, and the time of the ultrasonic treatment is 20-45 s, the air drying is fast drying using strong wind.

16. The method for preparing rare earth permanent magnet material according to claim 6, wherein: the thickness of the composite powder film is 25-40 m.

17. The method for preparing rare earth permanent magnet material according to claim 7, wherein: the voltage is 50-90 kv in the step 3.

18. The method for preparing rare earth permanent magnet material according to claim 7, wherein: the time is 15-30 s in the step 3.

19. The method for preparing rare earth permanent magnet material according to claim 7, wherein: the movement speed of the spray gun is 10-30 cm/s in the step 3.

20. The method for preparing rare earth permanent magnet material according to claim 7, wherein: the spray distance is 15-25 cm in the step 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a technique flowchart of a preferred embodiment in the present invention.

[0033] FIG. 2 is a structural diagram of a rare earth permanent magnet material prepared in Example 1 of the present invention.

[0034] FIG. 3 is a variation diagram of magnetic performance of magnets before and after treatment in Example 1 of the present invention, of which the abscissa is Applied Field which is the external magnetic field intensity, and the ordinate is Magnetisation which is the magnetization intensity.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The present invention will be described further in detail below by examples in combination with the accompanying drawings in order to make the present invention more easily to understand clearly. The NdFeB magnet to be treated used in the following examples are all sintered NdFeB magnets. In each example, different brands and different batches of commercial sintered NdFeB magnet are used as the magnet to be treated, and the method in the present invention is applicable to various NdFeB magnets. The equipment used for electrostatic adhesion is electrostatic powder spray line. The manufacturer is Gu'anKeyuXinpeng Automation Control Equipment Co., Ltd., the electrostatic spray gun being the core part uses the spray gun of German Wagner.

[0036] FIG. 1 shows a process flow of one preferred embodiment of the method in the present invention, which specifically comprises the steps of: magnet cutting machining, magnet surface cleaning; powder preparing, powder mixing and sieving; preparing a magnet adhered with a powder film by electrostatic adhesion; grain boundary diffusion treatment and aging; magnet surface processing. Specific examples are given below.

EXAMPLE 1

[0037] (1) The composite powder was formulated in accordance with the powder ratio formula (TbF.sub.3).sub.95Nd.sub.2Al.sub.3. TbF.sub.3 powder with particle size of 150 mesh, metal Nd powder with particle size of 150 mesh and metal Al powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0038] (2) Firstly, sintered NdFeB magnet of commercial 50H brand was machined into a shape to be treated, of which the thickness in the direction of orientation is 1.96 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows: the magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 (concentration is 50 wt %) for 20 s. Then it was washed with water again and was treated by ultrasonic wave for 20 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0039] (3) In a nitrogen atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 70 kV, a time was 30 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with the composite powder film adhered to the surface thereof, and the thickness of the film was about 40 m.

[0040] (4) The NdFeB magnet with composite powder film adhered to the surface thereof obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 850 C. for 35 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 490 C. for 6 hours.

[0041] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 6 wt %) for 80 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0042] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 14240 Oe, the remanence is slightly reduced and is reduced by 190 Gs. The performance variation of the magnet before and after the treatment (that is, the NdFeB magnet to be treated obtained in the step (2) and the permanent magnet finally obtained after the treatment in the steps (3), (4) and (5) were performed the performance test, and so were the subsequent examples) are shown in Table 1. The microstructure of the rare earth permanent magnet material prepared in this embodiment is shown in FIG. 2. It can be seen from the figure that a uniform and continuous grain boundary phase is coated around the main phase particles, which will greatly improve the demagnetization coupling ability of the magnet in the external magnetic field and is beneficial to the improvement of the coercivity of the magnet. FIG. 3 is a variation diagram of magnetic performance before and after treatment in the example 1 of the present invention. It can be seen from the diagram that coercivity of sintered NdFeB is increased from 17740 Oe to 31980 Oe, that is, increased by 14240 Oe, and the remanence is slightly reduced and is reduced from 13960 Gs to 13770 Gs, that is, reduced by 190 Gs by the technical treatment of steps (3), (4) and (5) in this example.

EXAMPLE 2

[0043] (1) The composite powder was formulated in accordance with the powder ratio formula (DyF.sub.3).sub.95Nd.sub.1Al.sub.4. DyF.sub.3 powder with particle size of 150 mesh, metal Nd powder with particle size of 150 mesh and metal Al powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0044] (2) Firstly, sintered NdFeB magnet of commercial 48H brand was machined into a shape to be treated, of which the thickness in the direction of orientation was 3 mm Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was as shown as follows: the magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 20 s. Then it was washed with water again and was treated by ultrasonic wave for 20 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0045] (3) In a nitrogen atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 60 kV, a time was 25 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 30 m.

[0046] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 830 C. for 30 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 510 C. for 4 hours.

[0047] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 5.5 wt %) for 60 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0048] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 7500 Oe, the remanence is slightly reduced and is reduced by 175 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 3

[0049] (1) The composite powder was formulated in accordance with the powder ratio formula (TbF.sub.3).sub.95Cu.sub.5. TbF.sub.3 powder with particle size of 150 mesh and metal Cu powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0050] (2) Firstly, sintered NdFeB magnet of commercial 42M brand was machined into a shape to be treated, of which the thickness in the direction of orientation was 5 mm Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows: the magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed with water, and then it was acid pickled with dilute HNO.sub.3 for 35 s. Then it was washed with water again and was treated by ultrasonic wave for 35 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0051] (3) In a nitrogen atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 60 kV, a time was 25 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 30 m.

[0052] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 860 C. for 35 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 500 C. for 6 hours.

[0053] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 6.5 wt %) for 100 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0054] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 12000 Oe, the remanence is slightly reduced and is reduced by 180 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 4

[0055] (1) The composite powder was formulated in accordance with the powder ratio formula(HoF.sub.3).sub.97Pr.sub.1Cu.sub.2. HoF.sub.3 powder with particle size of 150 mesh, metal Pr powder with particle size of 150 mesh and metal Cu powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0056] (2) Firstly, sintered NdFeB magnet of commercial 42M brand was machined into a shape to be treated, in which the thickness in the direction of orientation was 3 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 25 s. Then it was washed with water again and was treated by ultrasonic wave for 25 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0057] (3) In a nitrogen atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 50 kV, a time was 15 s, a moving speed of the spray gun was 25 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 25 m.

[0058] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 850 C. for 35 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 480 C. for 4 hours.

[0059] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 5.5 wt %) for 60 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0060] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 4000 Oe, the remanence is slightly reduced and is reduced by 210 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 5

[0061] (1) The composite powder was formulated in accordance with the powder ratio formula ((DyTb)F.sub.3).sub.96Cu.sub.1Al.sub.3. (DyTb)F.sub.3 powder with particle size of 150 mesh, metal Cu powder with particle size of 150 mesh and metal Al powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0062] (2) Firstly, sintered NdFeB magnet of commercial 52SH brand was machined into a shape to be treated, in which the thickness in the direction of orientation is 6 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 45 s. Then it was washed with water again and was treated by ultrasonic wave for 45 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0063] (3) In a argon atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 65 kV, a time was 28 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 18 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 30 m.

[0064] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 870 C. for 40 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 520 C. for 6 hours.

[0065] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 6 wt %) for 90 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0066] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 11000 Oe, the remanence is slightly reduced and is reduced by 168 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

Example 6

[0067] (1) The composite powder was formulated in accordance with the powder ratio formula (GdF.sub.3).sub.98Cu.sub.2. GdF.sub.3 powder with particle size of 150 mesh and metal Cu powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0068] (2) Firstly, sintered NdFeB magnet of commercial 35M+ brand was machined into a shape to be treated, in which the thickness in the direction of orientation was 3 mm Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 25 s. Then it was washed with water again and was treated by ultrasonic wave for 25 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0069] (3) In a argon atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 65 kV, a time was 25 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 35 m.

[0070] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 840 C. for 35 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 490 C. for 4 hours.

[0071] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 5 wt %) for 60 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0072] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 4200 Oe, the remanence is slightly reduced and is reduced by 208 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 7

[0073] (1) The composite powder was formulated in accordance with the powder ratio formula (TbO.sub.3).sub.94Nd.sub.1Al.sub.5. TbO.sub.3 powder with particle size of 150 mesh, metal Nd powder with particle size of 150 mesh and metal Al powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were needed to perform under a nitrogen atmosphere.

[0074] (2) Firstly, sintered NdFeB magnet of commercial 48H+ brand was machined into a shape to be treated, in which the thickness in the direction of orientation was 8 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 45 s. Then it was washed with water again and was treated by ultrasonic wave for 45 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0075] (3) In a argon atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 75 kV, a time was 30 s, a moving speed of the spray gun was 20 cm/s and a spray distance was 20 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 40 m.

[0076] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 860 C. for 40 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 490 C. for 5 hours.

[0077] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 8 wt %) for 180 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0078] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 8000 Oe, the remanence is slightly reduced and is reduced by 185 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 8

[0079] (1) The composite powder was formulated in accordance with the powder ratio formula (DyO.sub.3).sub.97(PrNd).sub.2Al.sub.1. DyO.sub.3 powder with particle size of 150 mesh, metal PrNd powder (the mass ratio of Pr to Nd is 1:4) with particle size of 150 mesh and metal Al powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0080] (2) Firstly, sintered NdFeB magnet of commercial 42M brand was machined into a shape to be treated, in which the thickness in the direction of orientation was 6 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 45 s. Then it was washed with water again and was treated by ultrasonic wave for 45 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining a NdFeB magnet to be treated.

[0081] (3) In a argon atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 75 kV, a time was 30 s, a moving speed of the spray gun was 18 cm/s and a spray distance was 22 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface there, and the thickness of the film was about 40 m.

[0082] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 830 C. for 40 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 490 C. for 6 hours.

[0083] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 7 wt %) for 120 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0084] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 6500 Oe, the remanence is slightly reduced and is reduced by 190 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

EXAMPLE 9

[0085] (1) The composite powder was formulated in accordance with the powder ratio formula (TbF.sub.3).sub.46(DyO.sub.3).sub.48Nd.sub.2ZnSnCu.sub.2. TbF.sub.3 and DyO.sub.3 powder with particle size of 150 mesh, metal Nd powder with particle size of 150, metal Zn, Sn and Cu powder with particle size of 150 mesh were weighted. The above powders were mixed to be even, and were sieved through 150 mesh. The processes of powder mixing and sieving were performed under a nitrogen atmosphere.

[0086] (2) Firstly, sintered NdFeB magnet of commercial 46UH brand was machined into a shape to be treated, of which the thickness in the direction of orientation was 4.5 mm. Then the procedure of cleaning surface was entered, and the procedure of cleaning surface was shown as follows. The magnet was placed in the degreasing tank and was soaked for 10 min to remove the oil stain on the surface of the magnet. The surface was washed to clean with water, and then it was acid pickled with dilute HNO.sub.3 for 30 s. Then it was washed with water again and was treated by ultrasonic wave for 30 s, and the surface of the magnet was quickly dried by strong wind, thereby obtaining aNdFeB magnet to be treated.

[0087] (3) In a argon atmosphere, the composite powder prepared in step (1) was carried with positive electrons by a spray gun according to technological conditions that a voltage was 70 kV, a time was 25 s, a moving speed of the spray gun was 18 cm/s and a spray distance was 22 cm. It was accelerated and impacted onto the NdFeB magnet to be treated obtained in step (2) which was connected to the cathode, thereby obtaining a NdFeB magnet with composite powder film adhered to the surface thereof, and the thickness of the film was about 30 m.

[0088] (4) The NdFeB magnet with composite powder film adhered to the surface obtained in step (3) was placed in a vacuum thermal treatment furnace with a vacuum degree higher than 10.sup.3 Pa and was maintained at 845 C. for 30 hours. It was cooled inside the furnace to not higher than 50 C., and then tempering treatment was performed at 490 C. for 6 hours.

[0089] (5) The magnet obtained in step (4) was soaked in dilute nitric acid (the concentration was 5.0 wt %) for 80 s to remove residual attachments on the surface of the magnet. The magnet was cleaned with deionized water to obtain a magnet with improved performance.

[0090] The coercivity of the rare earth permanent magnet material prepared in this example is increased by 8500 Oe, the remanence is slightly reduced and is reduced by 170 Gs. The performance variation of the magnet before and after the treatment are shown in Table 1.

TABLE-US-00001 TABLE 1 Performance test results of the magnets before and after treatment in Eamples 1-9 Coercivity(kOe) Remanence (kGs) Size of before after before after Example permanent treat- treat- treat- treat- number magnet ment ment ment ment Example 1 20*15*1.96 mm 17.74 31.98 13.96 13.77 Example 2 25*15*3 mm 17.83 25.33 13.81 13.635 Example 3 25*15*5 mm 13.28 25.28 13.32 13.14 Example 4 25*15*3 mm 13.18 17.18 13.31 13.10 Example 5 30*15*6 mm 20.20 31.20 14.20 14.032 Example 6 25*15*3 mm 15.9 20.1 11.83 11.622 Example 7 35*15*8 mm 18.5 26.5 13.7 13.515 Example 8 35*15*6 mm 13.45 19.95 13.2 13.01 Example 9 35*15*4.5 mm 24.8 33.3 13.67 13.5

EXAMPLES 10-13

[0091] Except that the thicknesses of the composite powder films were different from that in Example 2, the other technological parameters in Examples 10-13 were the same as those in Example 2. Wherein, the thickness of the composite powder film in Example 10 was about 12 m, and the thickness of the composite powder film in Example 11 was about 20 m. The thickness of the composite powder film in Example 12 was about 5 m, and the thickness of the composite powder film in Example 13 was about 45 m. The performance variation of the magnets before and after treatment were shown in Table 2.

EXAMPLES 14-15

[0092] Except that the holding temperature and holding time in the vacuum thermal treatment were different from those in step (4) of Example 2, the other technological parameters in Examples 14-15 were the same as those in Example 2. Wherein, the conditions of vacuum thermal treatment were 1000 C. for 10 h, the conditions of the vacuum thermal treatment in Example 15 were 700 C. for 48 h. The performance variation of the magnets before and after treatment were shown in Table 2.

EXAMPLES 16-17

[0093] Except that the temperature and time of tempering treatment in step (4) were different from those in Example 2, the other technological parameters in Examples 16-17 were the same as those in Example 2. Wherein, the conditions of the tempering treatment in Example 16 were 430 C. for 8 h. The conditions of the tempering treatment in Example 17 were 640 C. for 2 h. The performance variation of the magnets before and after treatment were shown in Table 2.

TABLE-US-00002 TABLE 2 Performance test results of the magnets before and after treatment in Examples 10-17 Coercivity (kOe) Remanence (kGs) Size of before after before after Example permanent treat- treat- treat- treat- number magnet ment ment ment ment Example 10 25*15*3 mm 17.83 20.33 13.81 13.75 Example 11 25*15*3 mm 17.83 22.83 13.81 13.69 Example 12 25*15*3 mm 17.83 19.02 13.81 13.78 Example 13 25*15*3 mm 17.83 25.43 13.81 13.61 Example 14 25*15*3 mm 17.83 24.80 13.81 13.55 Example 15 25*15*3 mm 17.83 20.51 13.81 13.76 Example 16 25*15*3 mm 17.83 24.30 13.81 13.64 Example 17 25*15*3 mm 17.83 23.84 13.81 13.63

EXAMPLES 18-23

[0094] Except that the composition of the composite powder used were different from those in Example 2, the other technological parameters in Examples 18-23 were the same as those in Example 2; the specific composition of the composite powder and performance variation of the magnets before and after the treatment were shown in Table 3.

TABLE-US-00003 TABLE 3 Performance test results of the magnets before and after treatment in Examples 18-23 Size of Coercivity(kOe) Remanence (kGs) Example composition of the permanent before after before after number composite powder magnet treatment treatment treatment treatment Example 18 (DyF.sub.3).sub.50Nd.sub.10Al.sub.40 25*15*3 mm 17.83 22.09 13.81 13.71 Example 19 (DyF.sub.3).sub.55Nd.sub.20Al.sub.25 25*15*3 mm 17.83 22.92 13.81 13.69 Example 20 (DyF.sub.3).sub.85Nd.sub.5Al.sub.10 25*15*3 mm 17.83 24.96 13.81 13.66 Example 21 (DyF.sub.3).sub.70Nd.sub.10Al.sub.20 25*15*3 mm 17.83 23.61 13.81 13.68 Example 22 (DyF.sub.3).sub.83Nd.sub.10Al.sub.7 25*15*3 mm 17.83 24.80 13.81 13.66 Example 23 (DyF.sub.3).sub.75Nd.sub.18Al.sub.7 25*15*3 mm 17.83 24.32 13.81 13.67

[0095] Obviously, the above-mentioned examples are merely given for clearly illustration, and are not intended to limit the embodiments. For those skilled in the art, variations or changes of other different forms may be made on the basis of the above-mentioned illustration. There is no need and no way to exhaust all of the embodiments. Obvious variations or changes resulting therefrom are still within the protection scope of the present invention.