Manufacturing method of green compacts of rare earth alloy magnetic powder and a manufacturing method of rare earth magnet

Abstract

The present invention discloses a manufacturing method of green compacts of rare earth alloy magnetic powder and a manufacturing method of rare earth magnet, it is a manufacturing method that pressing the rare earth alloy magnetic powder added with organic additive in a closed space filled with inert gases to manufacture the green compacts, wherein the rare earth alloy magnetic powder is compacted under magnetic field in a temperature atmosphere of 25 C.-50 C. and a relative humidity atmosphere of 10%-40%. This method is to set the temperature of the inert atmosphere in a fully closed space, inhibiting bad forming phenomenon of the magnet with low oxygen content (broken, corner-breakage, crack) after sintering, and increasing the degree of orientation, Br and (BH)max.

Claims

1. A method of manufacturing a green compact composed of rare earth alloy magnetic powder, the method comprising: (a) preparing a rare earth alloy magnetic powder in a closed space by: (i) providing a melt comprised of a rare earth alloy; (ii) rapidly cooling the melt at a cooling rate ranging between 100 C/s and 10000 C/s to solidify the rare earth alloy; (iii) performing hydrogen decrepitation on the solidified rare earth alloy to provide a decrepitated alloy; and (iv) crushing the decrepitated alloy using a fine crusher provided in a pulverizing room having a controlled atmosphere to obtain said rare earth alloy magnetic powder, the controlled atmosphere having a concentration of less than 100 ppm of an oxide gas comprised of at least one of oxygen and water; and (b) preparing said green compact by: (i) pressing the rare earth alloy magnetic powder with at least one organic additive under a magnetic field in a closed space having an atmosphere comprised of at least one inert gas, having a temperature ranging from 40 C.-45 C. and a relative humidity ranging from 20%-35%, to provide said green compact.

2. The method according to claim 1, wherein the rare earth alloy magnetic powder is a NdFeB series rare earth alloy magnetic powder.

3. The method according to claim 2, wherein the atmosphere during pressing has a an oxygen concentration below 1000 ppm.

4. The method according to claim 3, wherein the organic additive is at least one of a mineral oil, a synthetic oil, an animal oil, a vegetable oil, at least one organic ester, a paraffin, a polyethylene wax, a modified wax, and wherein a weight ratio of the organic additive and the rare earth alloy magnetic powder ranges from 0.011.5:100.

5. The method according to claim 4, wherein the at least one organic ester is a methyl caprylate.

6. A method of manufacturing a rare earth magnet from a green compact composed of a rare earth alloy magnetic powder, the method comprising: (a) preparing said rare earth alloy magnetic powder in a closed space by: (i) providing a melt comprised of a rare earth alloy; (ii) rapidly cooling the melt at a cooling rate ranging between 100 C/s and 10000 C/s to solidify the rare earth alloy; (iii) performing hydrogen decrepitation on the solidified rare earth alloy to provide a decrepitated alloy; and (iv) crushing the decrepitated alloy using a fine crusher provided in a pulverizing room having a controlled atmosphere to obtain a rare earth alloy magnetic powder, the controlled atmosphere having a concentration of less than 100 ppm of an oxide gas comprised of at least one of oxygen and water; and (b) preparing said green compact by pressing the rare earth alloy magnetic powder with at least one organic additive under a magnetic field in a closed space having an atmosphere comprised of at least one inert gas, having a temperature ranging from 40 C.-45 C. and a relative humidity ranging from 20%-35% provide said green compact; and (c) sintering the green compact to provide said rare earth magnet.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The present invention will be further described with the embodiments.

(2) First Embodiment

(3) The present invention takes NdFeB rare earth alloy magnetic powder for example to describe the pressing process under the magnetic field.

(4) The method includes following manufacturing flow: raw material preparing.fwdarw.smelting.fwdarw.casting.fwdarw.hydrogen crushing.fwdarw.micro grinding.fwdarw.pressing under magnetic field.fwdarw.sintering.fwdarw.heat treatment.fwdarw.magnetic property evaluation.fwdarw.oxygen content evaluation of the sintered magnet.

(5) In the raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, the weight ratio of the components is shown in TABLE 1.

(6) TABLE-US-00001 TABLE 1 The weight ratio of the components Nd Fe B Co 30.5 68 1 0.5

(7) Based on above weight ratio, 500 Kg raw material is prepared.

(8) In melting process: the prepared raw materials are put into a crucible made of aluminum oxide, using a high frequency vacuum induction melting furnace to vacuum smelt the raw materials to 1500 C. in a 10.sup.2 Pa vacuum.

(9) In casting process: Ar gas is filled to the melting furnace to 10.sup.2 Mpa after vacuum melting, then centrifugal casting method is used to cast in order to get rapid solidified alloy in a cooling rate of 1000 C./s3000 C./s.

(10) In hydrogen decrepitation process: the crushing room with rapid solidified alloy is pumped at room temperature, then filling with hydrogen with 99.5% purity to 0.1 Mpa, leave for 2 hours, after that, heating the crushing room and pumping at the same time, then keeping vacuum in 500 C. for 2 hours, then cooling it, getting the crushed specimen out.

(11) In micro grinding process: at an atmosphere with oxidizing gas below 100 ppm, the pressure of the crushing room is 0.4 Mpa, the crushed specimen is then grinded by air-flow mill, the average particle size of the grinded powder is 3.4 m. The oxidizing gas is oxygen and/or hydrogen.

(12) Adding methyl caprylate to the grinded powder, the additive amount is 0.2% of the weight of the rare earth alloy magnetic powder, the mixture is well blended by V-type mixer.

(13) In pressing under magnetic field process: dividing the powder into 10 equal parts, using a right orientation type magnetic filed molding, each part is then formed to a cube with edge 25 mm in an 1.8 T of orientation filed and 0.6 ton/cm.sup.2 of forming pressure, then the cubes get demagnetization in 0.2 T magnetic filed.

(14) It is formed in argon atmosphere, the oxygen content stays below 1000 ppm, the forming machine is configured with humidifier and cooling device, it is formed in a temperature vibration range of 10 C.55 C. and a relative humidity vibration range of 545%. The pure inert gas is filled to the fully closed space, bits of leakage may happen that leading to temperature and humidity different (for example, cooling water is provided in the magnetic filed generator of the magnetic field molding, the water from the seam of the cooling water and the condensation water will influence the humidity. Besides, the window of the magnetic filed pressing machine is applied with resin plate, the glove is made of rubber, outside air is easily permeated in, that also influence the humidity controlling), therefore, humidifier and cooling device are applied to control the humidity.

(15) In the examination of corner-breakage of green compacts: permanent magnet material is unqualified if there is even a little bit corner-breakage, by visual inspection, if broken, corner breakage or crack having more than 3 mm length is found, it is unqualified. In the sintering progress: the formed bodies are moved to the sintering furnace to sinter, in a vacuum of 10.sup.2 Pa for 2 hours in 200 C. and for 2 hours in 900 C., then sintering for 2 hours in 1050 C., after that filling in Ar gas to 0.1 MPa, cooling to room temperature.

(16) In the heating progress, the sintered magnet is heated for 1 hour in 580 C. in high purity Ar gas, then cooling it to room temperature and get it out.

(17) In magnetic property evaluation progress: the sintered magnet is tested by NIM-10000H nondestructive testing of large rare earth permanent magnet of China metrology institute, the testing temperature is 20 C.

(18) In the oxygen content of sintered magnet evaluation progress: the oxygen content of the sintered magnet is tested by EMGA-620W oxygen and nitrogen analyzer of Japan HORIBA company.

(19) In corner-breakage and crash of sintered magnet examination progress: a permanent magnet is unqualified if there is even a little bit of corner-breakage or crash, by visual inspection, any corner-breakage or crash of the green compacts longer than 3 mm is determined to be unqualified, calculating the failure rate consolidating with the unqualified products during forming.

(20) TABLE 2 shows magnetic property comparison between the first embodiment and a comparing sample (formed in different temperatures).

(21) TABLE-US-00002 TABLE 2 magnetic property comparison Oxygen Temperature Content of inside the Relative the HAST Sintered Serial Humidity machine Failure Br Hcj SQ (BH)max weightlessness magnet No (%) ( C.) Rate (%) (kGs) (kOe) (%) (MGOe) (mg) (ppm) 1 5 10 32 13.9 13.2 87.5 42.3 42.8 285 2 6 15 22 13.9 13.3 87.6 42.1 20.7 280 3 8 20 3 14 13.4 88 43.1 10.5 287 4 10 25 0 14.3 14.9 97.7 50.0 3 300 5 15 30 0 14.4 14.9 97.8 50.7 2.9 332 6 20 31 0 14.6 15.2 98.1 52.3 2.8 459 7 30 40 0 14.6 15.2 97.8 52.0 2.6 589 8 35 45 0 14.6 15.1 97.6 51.8 2.5 674 9 40 50 0 14.5 15.1 98.3 51.6 2.3 920 10 45 55 19 13.9 11.4 78.5 38.0 102.5 2820

(22) Second Embodiment

(23) The second embodiment has following differences from the first embodiment:

(24) 1) the organic additive added to the grinded powder is methyl caprylate, the amount is 0.2% of the weight of the rare earth alloy magnetic powder, the mixture is well blended by V-type mixer.

(25) 2) In pressing under magnetic field process: dividing the powder into 10 equal parts, using a right orientation type magnetic filed molding, each part is then compacted to a cube with edge 25 mm in an 1.8 T of orientation filed and 0.8 ton/cm.sup.2 of forming pressure, then the cubes get demagnetization in 0.2 T magnetic filed.

(26) It is formed in argon atmosphere, the oxygen content stays below 1000 ppm, the forming machine is configured with humidifier and cooling device, it is formed in a temperature vibration range of 10 C.55 C. and a relative humidity vibration range of 545%.

(27) TABLE 3 shows magnetic property comparison between the second embodiment and a comparing sample (formed in different temperatures).

(28) TABLE-US-00003 TABLE 3 magnetic property comparison Oxygen Temperature Content of inside the Relative the HAST Sintered Serial Humidity machine Failure Br Hcj SQ (BH)max weightlessness magnet No (%) ( C.) Rate (%) (kGs) (kOe) (%) (MGOe) (mg) (ppm) 1 5 10 25 12.8 12.8 85.2 35.2 50.6 347 2 6 15 12 12.9 12.9 85.2 35.4 32.5 326 3 8 20 1 13.1 13.0 88 41.4 8.9 338 4 10 25 1 14.0 14.7 96.5 47.3 3.5 550 5 15 30 1 14.0 14.8 96.6 47.3 3.3 582 6 20 31 0 14.5 14.8 97.1 51.0 3.3 603 7 30 40 0 14.4 15.0 97.2 50.4 3.2 687 8 35 45 0 14.4 15.1 96.8 50.5 3.1 824 9 40 50 0 14.0 14.9 97.3 47.7 3.0 1046 10 45 55 35 13.5 10.3 70.6 32.2 142.0 3221

(29) Third Embodiment

(30) The third embodiment has following differences from the first embodiment:

(31) 1) the organic additive added to the grinded powder is methyl caprylate, the amount is 1.5% of the weight of the rare earth alloy magnetic powder, the mixture is well blended by V-type mixer.

(32) 2) In pressing under magnetic field process: dividing the powder into 10 equal parts, using a right orientation type magnetic filed molding, each part is then compacted to a cube with edge 25 mm in an 1.8 T of orientation filed and 0.3 ton/cm.sup.2 of forming pressure, then the cubes get demagnetization in 0.2 T magnetic filed.

(33) It is formed in argon atmosphere, the oxygen content stays below 1000 ppm, the forming machine is configured with humidifier and cooling device, it is formed in a temperature vibration range of 10 C.55 C. and a relative humidity vibration range of 545%.

(34) TABLE 4 shows magnetic property comparison between the third embodiment and a comparing sample (formed in different temperatures).

(35) TABLE-US-00004 TABLE 4 magnetic property comparison Oxygen Temperature Content of inside the Relative the HAST Sintered Serial Humidity machine Failure Br Hcj SQ (BH)max weightlessness magnet No (%) ( C.) Rate (%) (kGs) (kOe) (%) (MGOe) (mg) (ppm) 1 5 10 19 13.5 13.0 87.4 40.2 39.8 265 2 6 15 11 13.8 13.2 87.5 41.7 25.6 252 3 8 20 8 14.1 13.3 89.0 44.2 18.5 280 4 10 25 1 14.2 14.8 97.5 49.1 3.5 295 5 15 30 1 14.5 14.9 97.6 51.3 3.0 312 6 20 31 0 14.5 15.1 98.0 52.4 3.0 423 7 30 40 0 14.6 15.2 97.9 52.2 3.6 550 8 35 45 0 14.5 15.2 97.8 52.2 2.8 626 9 40 50 1 14.6 15.0 98.1 52.3 2.9 720 10 45 55 21 13.6 11.2 78.2 36.2 89.5 2016

(36) As can be seen from the third embodiment, even the added weight is up to 1.5% of the rare earth alloy magnetic powder, a little amount of C, 0 is left in the sintered magnet, so that it can well perform its lubricant property, it not only increases the degree of orientation and forming property, but also ensures the Br, Hcj and (BH)max not to be influenced.

(37) It is important to note that SQ=Hk/Hcj in TABLE 2, TABLE 3, TABLE 4.

CONCLUSION

(38) As can be seen from TABLE 1, TABLE 2, TABLE 3, TABLE 4, the Br, (BH)max, Hcj of the obtained sintered magnet are increased, reasons are that:

(39) On one hand, when the atmosphere temperature exceeds 20 C., the organic addictive is softened to exercise its lubrication effect, as a result, the Br, (BH)max, Hcj of the obtained sintered magnet are significantly increased. In particular, when the atmosphere temperature exceeds 31 C., the lubrication effect is further developing, the Br, (BH)max, Hcj of the obtained sintered magnet are further increased as well.

(40) On the other hand, the sintered magnet is formed in the magnetic field at a controlled relative humidity of 10%-40% in inert atmosphere, the proper water is served as lubricant, thus enhancing the degree of orientation and increasing the Br, (BH)max, it can also eliminate electrostatic and solve the problems of broken, corner breakage or crack of the sintering rare earth magnet.

(41) On still another, the present invention is applied with powder of low oxygen content and low water content.

(42) Combining above three aspects, the obtained magnet has high-performance, medium-low oxygen content and is well compacted in inert atmosphere with oxygen content below 1000 ppm, the degree of orientation, Br, (BH)max of the obtained sintered magnet are increased as well.

(43) The reason of higher coercivity can not be explained based on existing known theory, maybe one reason is the medium-low oxygen content below 1000 ppm of the sintered magnet. As in the first embodiment, the second embodiment and the third embodiment, the magnet is compacted in medium-low oxygen content atmosphere, it can presume that the microelement C, O of the organic additive is reacted with Nd rich, and thus forming the eutectic low melting point product.

(44) If the atmosphere temperature exceeds 50 C., the temperature is too high, during from compacting to sintering, the organic additive and the magnetic components largely react and thus forming Nd rich phase and carbide, with the increasing of the oxygen content, it forms a number of rare earth type carbide, rare earth type oxide, rare earth oxycarbide, the coercivity of the Nd rich phase is offset to stop increasing, so that the coercivity and the squareness are decreased, the HAST experimental result fails, and the Br, (BH)max are decreased.

(45) Although the present invention has been described with reference to the preferred embodiments thereof for carrying out the patent for invention, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the patent for invention which is intended to be defined by the appended claims.

INDUSTRIAL APPLICABILITY

(46) The present invention is to obtain green compacts of rare earth alloy powder with low-medium oxygen content that the green compacts is pressed and compacted in inert atmosphere with low oxygen content and low-medium relative humidity, and finally obtained is high-performance sintered magnet with oxygen content below 2500 ppm.