CN112614685A - Sintered neodymium-iron-boron permanent magnet oxygen control preparation method and prepared neodymium-iron-boron permanent magnet - Google Patents
Sintered neodymium-iron-boron permanent magnet oxygen control preparation method and prepared neodymium-iron-boron permanent magnet Download PDFInfo
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
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- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0573—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes obtained by reduction or by hydrogen decrepitation or embrittlement
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- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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Abstract
The invention belongs to the technical field of rare earth permanent magnet materials, and particularly relates to an oxygen control preparation method of a sintered neodymium iron boron permanent magnet and the prepared neodymium iron boron permanent magnet. The method comprises the steps of preparing raw materials, smelting, carrying out hydrogen crushing to obtain coarse powder, adding an antioxidant into the coarse powder, carrying out airflow milling to prepare powder under the condition of no oxygen supplementation, adding a lubricant into the obtained fine powder, sampling to test the oxygen content in the fine powder, adding water into the fine powder, uniformly stirring to obtain powder, and carrying out forming, isostatic pressing, sintering and tempering to obtain the neodymium-iron-boron permanent magnet. The addition amount of water is calculated according to the test result of the oxygen content of the fine powder and the target oxygen content, the oxygen replenishment amount is accurately controlled, and after the water and the fine powder are uniformly mixed, oxygen generated by decomposition in the sintering process is uniformly combined with the neodymium iron boron, so that the oxygen content in the magnet is uniformly and stably distributed, and the coercive force and the overall performance of the magnet are improved.
Description
Technical Field
The invention belongs to the technical field of rare earth permanent magnet materials, and particularly relates to an oxygen control preparation method of a sintered neodymium iron boron permanent magnet and the prepared neodymium iron boron permanent magnet.
Background
Neodymium iron boron (NdFeB) is currentlyThe rare earth permanent magnetic material with the strongest magnetism has good coercive force (Hcj), high magnetic energy product (8MGOe-64MGOe) and high temperature resistance, and related products are widely applied to the fields of electric automobiles, wind power generation, variable frequency air conditioners, nuclear magnetic resonance, optical disk drivers, instruments, mineral separation, toys and the like. In the process of manufacturing the sintered Nd-Fe-B permanent magnet material, oxygen inevitably enters the sintered Nd-Fe-B magnet from the atmosphere, although the ultra-pure raw material is used, the pure ternary sintered Nd-Fe-B-O permanent magnet cannot be manufactured, actually the quaternary Nd-Fe-B-O system permanent magnet is a permanent magnet, and the oxygen brought in the preparation process has the performance on the sintered Nd-Fe-B permanent magnet material, especially HcjThere is a significant impact. At present, the preparation of the high-performance sintered Nd-Fe-B permanent magnet usually adopts a low-oxygen process route, but for the sintered Nd-Fe-B magnet with high rare earth total (more than 33 percent), the oxygen content of the magnet is HcjIs not so low as oxygen is better, but magnet HcjWill increase with increasing oxygen content and decrease after increasing to a certain level. It has been shown that an appropriate oxygen content can improve the magnetic properties and stability of the magnet. Therefore, the control of the oxygen content is of great significance to the manufacture of high-performance sintered Nd-Fe-B permanent magnets and is also a great technical problem which troubles the production of sintered Nd-Fe-B permanent magnet materials.
At present, certain oxygen is mainly added in the air flow milling process in China, and the purpose of oxygen control is realized by isolating and controlling the oxygen (reducing the oxygen content in the subsequent production process as much as possible) in the subsequent production, for example, pure oxygen is absorbed into the air flow milling machine in the air flow milling and crushing process in the invention application with the publication number of CN108133818A, so that the direct adsorption and oxidation of air and water vapor are avoided, and the magnetic performance of the sintered neodymium iron boron magnet is improved. However, the oxygen content of the sintered nd-fe-b permanent magnet is not only influenced by the temperature and humidity of the working environment, but also related to the specific surface area of the powder particles, and the finer the particles, the larger the specific surface area, the easier the particles are oxidized. Because of the influence of the microstructure of the smelting cast piece and the hydrogen crushing process, the particle size of coarse powder is difficult to control during the air flow milling, and the retention time of the coarse powder in a milling chamber during the air flow milling also influences the oxygen absorption content of magnetic powder. In the process of milling powder by the jet mill, the particle size of the powder is reduced after the powder collides with each other, the specific surface area is increased, a large amount of heat can be released to increase the temperature of the magnetic powder, and the higher the temperature is, the more violent the oxygen absorption of the magnetic powder is. Therefore, the uniformity of the oxygen content of the neodymium iron boron magnetic powder is difficult to realize by adding oxygen through the jet mill, and the consistency of the oxygen content on the microscopic level is difficult to realize even if the later-stage powder is stirred. To obtain a high-performance sintered ndfeb permanent magnet, not only the oxygen content of the magnet needs to be controlled within a stable range, but also the oxygen distribution in the magnetic powder needs to be uniform to ensure the consistency of the magnet performance in molding, pressing and sintering.
Disclosure of Invention
Aiming at the technical problems, the invention aims to provide an oxygen control preparation method of a sintered neodymium iron boron permanent magnet, which realizes uniform, stable and controllable oxygen content in the sintered neodymium iron boron magnet.
The above object of the present invention is achieved by the following technical solutions:
an oxygen-controlling preparation method of a sintered neodymium-iron-boron permanent magnet comprises the steps of preparing materials, smelting, and carrying out hydrogen crushing to obtain coarse powder, adding an antioxidant into the coarse powder, carrying out airflow milling to prepare powder under the condition of no oxygen supplementation to obtain fine powder, then adding a lubricant, sampling to test the oxygen content in the fine powder, adding water into the fine powder, uniformly stirring to obtain powder, and carrying out forming, isostatic pressing, sintering and tempering to obtain the neodymium-iron-boron permanent magnet.
The particle size of the powder obtained by the airflow milling is small, the specific surface area is large, the powder is easy to oxidize, and at present, certain oxygen is supplemented in the powder making process to ensure that the powder is slightly passivated so as to prevent the oxygen content from being too high due to severe oxidation in the subsequent forming process. However, in the process of jet milling, the powder collides with each other to release heat, oxygen absorption is aggravated, the uniformity of the oxygen content in the magnetic powder is difficult to ensure by adding oxygen through the jet mill, and the oxygen supplement amount is difficult to control.
In the above preparation method, the amount of water added is calculated as follows: m × (w)0-w1) X 18/16; wherein M is the weight of the fine powder, w0To a target oxygen content, w1Is the oxygen content in the fine powder, and w1≤w0。
When testing the oxygen content, firstly sampling, preparing a magnet sample by molding, isostatic pressing, sintering and tempering under the control of an oxygen-free process, and taking the central part of the magnet sample to test the oxygen content (w)1). According to the oxygen content test result and the target oxygen content (w) of the product2) And calculating the weight of the oxygen needing to be increased, and further obtaining the addition amount of the water. According to the invention, water with corresponding weight is accurately added according to the actual oxygen content after the powder is milled by the airflow mill, so that the oxygen content in the neodymium iron boron magnet tends to be stable and is controlled within a certain constant range.
In the preparation method, the smelting comprises the following specific steps: putting raw materials into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the dried materials to be 80-120 KW, setting the time to be 10-30 minutes, filling argon to be-0.07-0.055 MPa when the vacuum degree is lower than 3Pa, then increasing the power to 480-550 KW, and starting to smelt; after the raw materials are melted, continuously melting for 8-10 minutes, adjusting the power to 350-400 KW, and refining for 2-5 minutes; the surface of the alloy liquid turns silvery white, and casting is carried out to obtain a cast sheet.
In the preparation method, the hydrogen crushing comprises the following specific steps: and (3) putting the cast piece into a hydrogen crushing furnace, absorbing hydrogen until the cast piece is saturated, and then heating to 500-600 ℃ for dehydrogenation until the pressure is lower than 20Pa to obtain coarse powder.
In the preparation method, before the powder is prepared by the jet mill, the jet mill is required to be subjected to oxygen discharge until the oxygen concentration is not more than 5 ppm.
In the preparation method, the average particle diameter SMD of the fine powder is 2.5-3.0 μm, and the particle size distribution ratio is not more than (X90/X10) 5.0.
In the preparation method, in the process of preparing the powder by the jet mill, the addition amount of the antioxidant is 0.05-0.2% of the weight of the coarse powder, and the addition amount of the lubricant is 0.05-0.2% of the weight of the fine powder.
In the above preparation method, the molding specifically comprises: under the nitrogen atmosphere, the powder is placed in a magnetic field of a press with the temperature of more than 1.5T and is subjected to orientation forming to obtain the powder with the density of 3.6-4.2 g/cm3The green compact of (1).
In the forming process, the oxygen content of the nitrogen atmosphere is controlled to be less than 0.05 percent.
In the above preparation method, the isostatic pressing is specifically: wrapping the green body with a plastic film, vacuum packaging, placing into an isostatic pressing machine, and performing isostatic pressing treatment under the oil pressure of 150-300MPa to further increase the density of the blank to 4.4-4.8g/cm3。
In the above preparation method, the sintering specifically is: removing vacuum bag and film under nitrogen protection, placing in a graphite box, placing in a furnace, and vacuumizing to 5.0 × 10-1Heating to 800-900 ℃ below Pa, preserving heat for 3-6 hours, and reducing the vacuum degree to 10-1And (4) continuously heating to 1000-1100 ℃ below Pa, and sintering for 2-10 hours.
In the above preparation method, the tempering specifically is: and cooling the sintered product to be below 100 ℃ by filling argon gas, heating the sintered product to 860 to 950 ℃, preserving the heat for 1 to 4 hours, performing primary tempering, cooling the sintered product to be below 80 ℃ by filling argon gas after heat preservation, heating the sintered product to be 440 to 520 ℃, preserving the heat for 3 to 6 hours, performing secondary tempering, cooling the sintered product to be below 60 ℃ by filling argon gas after heat preservation, and discharging the sintered product.
The invention also aims to provide the sintered neodymium-iron-boron permanent magnet prepared by the preparation method.
The sintered Nd-Fe-B permanent magnet comprises the following chemical components in percentage by mass: PrNd: 28-33 wt%, Ho: 1-5 wt%, B: 0.92-1.1 wt%, Al: 0-0.8 wt%, Cu: 0.05-0.3 wt%, Co: 0.1 to 2 wt%, Ga: 0 to 0.5 wt%, Zr: 0 to 0.5 wt%, and the balance Fe.
In a preferred embodiment of the present invention, the sintered nd-fe-b permanent magnet comprises the following chemical components by mass percent: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, and the balance Fe.
Compared with the prior art, the invention has the following advantages:
1. in the invention, no oxygen is added in the powder preparation process of the airflow mill, water is added to supplement oxygen after the fine powder is prepared, and oxygen generated by decomposition in the sintering process is uniformly combined with the neodymium iron boron after the water and the fine powder are uniformly mixed, so that uniform oxygen control of the neodymium iron boron magnet can be realized.
2. The water addition amount is calculated according to the test result of the oxygen content of the fine powder and the target oxygen content, so that accurate oxygen supplement is realized, the supplemented oxygen is obtained through water decomposition instead of direct oxygen charging, the stability of the oxygen content in the neodymium iron boron permanent magnet can be controlled, and the consistency of the oxygen on microscopic distribution can be ensured.
3. The neodymium iron boron permanent magnet prepared by the invention carries out reasonable oxygen control through process optimization, so that the oxygen content in the magnet is uniform and stable, and the coercive force and the overall performance of the magnet are favorably improved.
Detailed Description
The technical solution of the present invention is further described and illustrated by the following specific examples. The raw materials used in the examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art, unless otherwise specified. It should be understood that the specific embodiments described herein are merely to aid in the understanding of the invention and are not intended to limit the invention specifically.
Example 1
The embodiment provides a preparation method of a sintered neodymium-iron-boron permanent magnet, which comprises the following steps:
(1) preparing materials: weighing the following raw materials in percentage by weight: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, the balance being Fe;
(2) smelting: sequentially loading finely crushed materials such as iron bars, ferroboron and the like and praseodymium-neodymium into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the drying to be 100KW, setting the time to be 10 minutes, filling argon to-0.065 MPa when the vacuum degree is lower than 3Pa, increasing the power to 500KW, and starting to smelt; continuing to smelt for 10 minutes after the iron rod is completely smelted, adjusting the power to 360KW, and refining for 5 minutes; when the alloy liquid level is changed into silvery white, casting to obtain a cast sheet;
(3) hydrogen crushing: putting the cast sheet into a hydrogen crushing furnace, absorbing hydrogen until the cast sheet is saturated, and then heating the cast sheet to 550 ℃ for dehydrogenation until the temperature is lower than 20Pa to obtain coarse powder;
(4) milling: adding 0.105kg of antioxidant into 105kg of coarse powder, firstly carrying out oxygen discharge on an air flow mill until the oxygen concentration is less than or equal to 5ppm, then grinding the coarse powder into fine powder under the condition of no oxygen supplement, and then adding 0.105kg of lubricant into the fine powder; the volume average particle diameter SMD of the fine powder is 2.6 mu m and the particle size distribution ratio (X90/X10) is less than or equal to 5.0 measured by a Newpatakg laser particle size tester;
(5) and (3) testing the oxygen content: weighing 5kg of sample from the powder obtained in the step (4), forming, isostatic pressing, sintering and tempering to obtain a neodymium-iron-boron magnet sample, measuring the oxygen content (w) in the sample by adopting an IRO-II type oxygen measuring instrument at the central part of the sample1) The result was 0.038%; wherein, the molding, isostatic pressing, sintering and tempering processes are the same as the steps (7) to (9);
(6) adding water and stirring: according to M x (w)0-w1) X 18/16 calculating Water addition amount, wherein, target oxygen content (w)0) 0.2 percent, and the weight (M) of the sampled fine powder is 100kg, 0.182kg of water is added into the fine powder, and the fine powder and the water are stirred for 8 hours on a three-dimensional American-like stirrer to be fully and uniformly mixed;
(7) molding: ensuring that the oxygen content of the seal box is less than 0.05 percent under the protection of nitrogen, and molding the powder in a mold with a magnetic field of a press machine more than 1.5T to obtain the molding density of 3.8g/cm3The green compact of (a);
(8) isostatic pressing: wrapping the green body with plastic film, vacuum packaging, placing into isostatic pressing machine, performing isostatic pressing under 200MPa oil pressure to further increase the density of the green body to 4.7g/cm3；
(9) Sintering and tempering: removing vacuum bag and film under nitrogen protection, placing in a graphite box, placing in a furnace, and vacuumizing to 5.0 × 10-1Pa or lessHeating to 850 deg.C, holding for 4 hr, and reducing vacuum degree to 10-1Continuously heating to 1000 ℃ below Pa, and sintering for 8 hours; and cooling the mixture to below 100 ℃ by filling argon after sintering, heating the mixture to 920 ℃, preserving heat for 3 hours, carrying out primary tempering, cooling the mixture to below 80 ℃ by filling argon after heat preservation, heating the mixture to 460 ℃, preserving heat for 5 hours, carrying out secondary tempering, cooling the mixture to below 60 ℃ by filling argon after heat preservation, and discharging the mixture.
Example 2
The embodiment provides a preparation method of a sintered neodymium-iron-boron permanent magnet, which comprises the following steps:
(1) preparing materials: weighing the following raw materials in percentage by weight: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, the balance being Fe;
(2) smelting: sequentially loading finely crushed materials such as iron bars, ferroboron and the like and praseodymium-neodymium into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the drying to be 100KW, setting the time to be 10 minutes, filling argon to-0.065 MPa when the vacuum degree is lower than 3Pa, increasing the power to 500KW, and starting to smelt; continuing to smelt for 10 minutes after the iron rod is completely smelted, adjusting the power to 360KW, and refining for 5 minutes; when the alloy liquid level is changed into silvery white, casting to obtain a cast sheet;
(3) hydrogen crushing: putting the cast sheet into a hydrogen crushing furnace, absorbing hydrogen until the cast sheet is saturated, and then heating the cast sheet to 550 ℃ for dehydrogenation until the temperature is lower than 20Pa to obtain coarse powder;
(4) milling: adding 0.105kg of antioxidant into 105kg of coarse powder, firstly carrying out oxygen discharge on an air flow mill until the oxygen concentration is less than or equal to 5ppm, then grinding the coarse powder into fine powder under the condition of no oxygen supplement, and then adding 0.105kg of lubricant into the fine powder; the volume average particle diameter SMD of the fine powder is 2.6 mu m and the particle size distribution ratio (X90/X10) is less than or equal to 5.0 measured by a Newpatakg laser particle size tester;
(5) and (3) testing the oxygen content: weighing 5kg of sample from the powder obtained in the step (4), forming, isostatic pressing, sintering and tempering to obtain a neodymium-iron-boron magnet sample, measuring the oxygen content (w) in the sample by adopting an IRO-II type oxygen measuring instrument at the central part of the sample1)，The result was 0.041%; wherein, the molding, isostatic pressing, sintering and tempering processes are the same as the steps (7) to (9);
(6) adding water and stirring: according to M x (w)0-w1) X 18/16 calculating Water addition amount, wherein, target oxygen content (w)0) 0.3 percent, and the weight (M) of the sampled fine powder is 100kg, 0.291kg of water is added into the fine powder, and the fine powder and the water are stirred for 8 hours on a three-dimensional American-like stirrer to be fully and uniformly mixed;
(7) molding: ensuring that the oxygen content of the seal box is less than 0.05 percent under the protection of nitrogen, and molding the powder in a mold with a magnetic field of a press machine more than 1.5T to obtain the molding density of 3.8g/cm3The green compact of (a);
(8) isostatic pressing: wrapping the green body with plastic film, vacuum packaging, placing into isostatic pressing machine, performing isostatic pressing under 200MPa oil pressure to further increase the density of the green body to 4.7g/cm3；
(9) Sintering and tempering: removing vacuum bag and film under nitrogen protection, placing in a graphite box, placing in a furnace, and vacuumizing to 5.0 × 10-1Heating to 800 deg.C below Pa, maintaining for 5 hr, and reducing vacuum degree to 10-1Continuously heating to 1100 ℃ below Pa, and sintering for 6 hours; and cooling the mixture to below 100 ℃ by filling argon after sintering, heating the mixture to 920 ℃, preserving heat for 3 hours, carrying out primary tempering, cooling the mixture to below 80 ℃ by filling argon after heat preservation, heating the mixture to 460 ℃, preserving heat for 5 hours, carrying out secondary tempering, cooling the mixture to below 60 ℃ by filling argon after heat preservation, and discharging the mixture.
Example 3
The embodiment provides a preparation method of a sintered neodymium-iron-boron permanent magnet, which comprises the following steps:
(1) preparing materials: weighing the following raw materials in percentage by weight: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, the balance being Fe;
(2) smelting: sequentially loading finely crushed materials such as iron bars, ferroboron and the like and praseodymium-neodymium into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the drying to be 100KW, setting the time to be 10 minutes, filling argon to-0.065 MPa when the vacuum degree is lower than 3Pa, increasing the power to 500KW, and starting to smelt; continuing to smelt for 10 minutes after the iron rod is completely smelted, adjusting the power to 360KW, and refining for 5 minutes; when the alloy liquid level is changed into silvery white, casting to obtain a cast sheet;
(3) hydrogen crushing: putting the cast sheet into a hydrogen crushing furnace, absorbing hydrogen until the cast sheet is saturated, and then heating the cast sheet to 550 ℃ for dehydrogenation until the temperature is lower than 20Pa to obtain coarse powder;
(4) milling: adding 0.105kg of antioxidant into 105kg of coarse powder, firstly carrying out oxygen discharge on an air flow mill until the oxygen concentration is less than or equal to 5ppm, then grinding the coarse powder into fine powder under the condition of no oxygen supplement, and then adding 0.105kg of lubricant into the fine powder; the volume average particle diameter SMD of the fine powder is 2.8 mu m and the particle size distribution ratio (X90/X10) is less than or equal to 5.0 measured by a Newpatakg laser particle size tester;
(5) and (3) testing the oxygen content: weighing 5kg of sample from the powder obtained in the step (4), forming, isostatic pressing, sintering and tempering to obtain a neodymium-iron-boron magnet sample, measuring the oxygen content (w) in the sample by adopting an IRO-II type oxygen measuring instrument at the central part of the sample1) The result was 0.043%; wherein, the molding, isostatic pressing, sintering and tempering processes are the same as the steps (7) to (9);
(6) adding water and stirring: according to M x (w)0-w1) X 18/16 calculating Water addition amount, wherein, target oxygen content (w)0) 0.4 percent, and the weight (M) of the sampled fine powder is 100kg, then 0.402kg of water is added into the fine powder, and the fine powder and the water are stirred for 8 hours on a three-dimensional American-like stirrer to be fully and uniformly mixed;
(7) molding: ensuring that the oxygen content of the seal box is less than 0.05 percent under the protection of nitrogen, and molding the powder in a mold with a magnetic field of a press machine more than 1.5T to obtain the molding density of 3.8g/cm3The green compact of (a);
(8) isostatic pressing: wrapping the green body with plastic film, vacuum packaging, placing into isostatic pressing machine, performing isostatic pressing under 200MPa oil pressure to further increase the density of the green body to 4.7g/cm3；
(9) Sintering and tempering: removing vacuum bag and film under nitrogen protection, placing in a graphite box, charging into a furnace, and vacuumizingTo 5.0X 10-1Heating to 850 deg.C below Pa, maintaining for 4 hr, and reducing vacuum degree to 10-1Continuously heating to 1000 ℃ below Pa, and sintering for 8 hours; and cooling the gas filled with argon to below 100 ℃ after sintering, heating the gas filled with argon to 950 ℃, preserving the heat for 2 hours, carrying out primary tempering, cooling the gas filled with argon to below 80 ℃ after heat preservation, heating the gas filled with argon to 500 ℃, preserving the heat for 4 hours, carrying out secondary tempering, cooling the gas filled with argon to below 60 ℃ after heat preservation, and discharging the gas from the furnace.
Comparative example 1
The comparative example provides a method for preparing a sintered neodymium-iron-boron permanent magnet, comprising the following steps:
(1) preparing materials: weighing the following raw materials in percentage by weight: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, the balance being Fe;
(2) smelting: sequentially loading finely crushed materials such as iron bars, ferroboron and the like and praseodymium-neodymium into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the drying to be 100KW, setting the time to be 10 minutes, filling argon to-0.065 MPa when the vacuum degree is lower than 3Pa, increasing the power to 500KW, and starting to smelt; continuing to smelt for 10 minutes after the iron rod is completely smelted, adjusting the power to 360KW, and refining for 5 minutes; when the alloy liquid level is changed into silvery white, casting to obtain a cast sheet;
(3) hydrogen crushing: putting the cast sheet into a hydrogen crushing furnace, absorbing hydrogen until the cast sheet is saturated, and then heating the cast sheet to 550 ℃ for dehydrogenation until the temperature is lower than 20Pa to obtain coarse powder;
(4) milling: adding 0.105kg of antioxidant into 105kg of coarse powder, firstly carrying out oxygen discharge on an air flow mill until the oxygen concentration is less than or equal to 5ppm, then grinding the coarse powder into fine powder under the condition of no oxygen supplement, and then adding 0.105kg of lubricant into the fine powder; the volume average particle diameter SMD of the fine powder is 2.5 mu m and the particle size distribution ratio (X90/X10) is less than or equal to 5.0 measured by a Newpatakg laser particle size tester;
(5) molding: ensuring that the oxygen content of the seal box is less than 0.05 percent under the protection of nitrogen, and molding the powder in a mold with a magnetic field of a press machine more than 1.5T to obtain the molding density of 3.9g/cm3The green compact of (a);
(6) Isostatic pressing: wrapping the green body with plastic film, vacuum packaging, placing into isostatic pressing machine, performing isostatic pressing under 200MPa oil pressure to further increase the density of the green body to 4.6g/cm3；
(7) Sintering and tempering: removing vacuum bag and film under nitrogen protection, placing in a graphite box, placing in a furnace, and vacuumizing to 5.0 × 10-1Heating to 850 deg.C below Pa, maintaining for 4 hr, and reducing vacuum degree to 10-1Continuously heating to 1000 ℃ below Pa, and sintering for 8 hours; and cooling the mixture to below 100 ℃ by filling argon after sintering, heating the mixture to 920 ℃, preserving heat for 3 hours, carrying out primary tempering, cooling the mixture to below 80 ℃ by filling argon after heat preservation, heating the mixture to 460 ℃, preserving heat for 5 hours, carrying out secondary tempering, cooling the mixture to below 60 ℃ by filling argon after heat preservation, and discharging the mixture.
Comparative example 2
The comparative example provides a method for preparing a sintered neodymium-iron-boron permanent magnet, comprising the following steps:
(1) preparing materials: weighing the following raw materials in percentage by weight: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, the balance being Fe;
(2) smelting: sequentially loading finely crushed materials such as iron bars, ferroboron and the like and praseodymium-neodymium into a crucible of a rapid hardening furnace, vacuumizing the rapid hardening furnace to below 1Pa, starting to dry the materials, setting the power of the drying to be 100KW, setting the time to be 10 minutes, filling argon to-0.065 MPa when the vacuum degree is lower than 3Pa, increasing the power to 500KW, and starting to smelt; continuing to smelt for 10 minutes after the iron rod is completely smelted, adjusting the power to 360KW, and refining for 5 minutes; the alloy liquid surface is changed into silvery white, and casting is carried out to obtain a casting sheet;
(3) hydrogen crushing: putting the cast sheet into a hydrogen crushing furnace, absorbing hydrogen until the cast sheet is saturated, and then heating the cast sheet to 550 ℃ for dehydrogenation until the temperature is lower than 20Pa to obtain coarse powder;
(4) milling: adding 0.105kg of antioxidant into 105kg of coarse powder, performing jet milling to prepare powder, injecting pure oxygen into the jet mill in the process, wherein the supplement amount of the pure oxygen is 1.0-3.0L/h, and adding 0.105kg of lubricant into the prepared fine powder; the volume average particle diameter SMD of the fine powder is 2.7 mu m and the particle size distribution ratio (X90/X10) is less than or equal to 5.0 measured by a Newpatakg laser particle size tester;
(5) molding: ensuring that the oxygen content of the seal box is less than 0.05 percent under the protection of nitrogen, and molding the powder in a mold with a magnetic field of a press machine more than 1.5T to obtain the molding density of 3.8g/cm3The green compact of (a);
(6) isostatic pressing: wrapping the green body with plastic film, vacuum packaging, placing into isostatic pressing machine, performing isostatic pressing under 200MPa oil pressure to further increase the density of the green body to 4.5g/cm3；
(7) Sintering and tempering: removing vacuum bag and film under nitrogen protection, placing in a graphite box, placing in a furnace, and vacuumizing to 5.0 × 10-1Heating to 850 deg.C below Pa, maintaining for 4 hr, and reducing vacuum degree to 10-1Continuously heating to 1000 ℃ below Pa, and sintering for 8 hours; and cooling the mixture to below 100 ℃ by filling argon after sintering, heating the mixture to 920 ℃, preserving heat for 3 hours, carrying out primary tempering, cooling the mixture to below 80 ℃ by filling argon after heat preservation, heating the mixture to 460 ℃, preserving heat for 5 hours, carrying out secondary tempering, cooling the mixture to below 60 ℃ by filling argon after heat preservation, and discharging the mixture.
Measurement of remanence B of sintered NdFeB magnets of examples 1 to 3 and comparative examples 1 to 2 with QT-800 fully automatic permanent magnet characteristic Rapid testerr(kGs) coercive force Hcj(kOe), maximum magnetic energy product (BH)max(MGOe) and the square degree of the extrapolation curve Hk/Hcj, and the test results are shown in Table 1.
TABLE 1 magnetic Properties of the Neodymium iron boron magnets of examples 1-3 and comparative examples 1-2
From the above results, it can be seen that the coercive force of the sintered nd-fe-b permanent magnet prepared in the example of the present invention is significantly higher than that of the permanent magnets in comparative examples 1-2, and H isk/HcjAnd higher. Therefore, the method ensures that the oxygen content in the prepared neodymium iron boron magnet is stable and uniformly distributed through an effective oxygen control technology, so that the consistency of the magnet is better, and the overall performance of the neodymium iron boron permanent magnet is obviously improved.
The above embodiments are not exhaustive of the range of parameters of the claimed technical solutions of the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope of the claimed technical solutions of the present invention, and if no specific description is given for all the parameters involved in the technical solutions of the present invention, there is no unique combination of the parameters with each other that is not replaceable.
The specific embodiments described herein are merely illustrative of the spirit of the invention and do not limit the scope of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (10)
1. An oxygen control preparation method of a sintered neodymium iron boron permanent magnet is characterized by comprising the steps of preparing materials, smelting and carrying out hydrogen crushing to obtain coarse powder, adding an antioxidant into the coarse powder, carrying out airflow milling to obtain fine powder under the condition of no oxygen supplementation, then adding a lubricant, sampling to test the oxygen content in the fine powder, adding water into the fine powder, uniformly stirring to obtain powder, and carrying out forming, isostatic pressing, sintering and tempering to obtain the neodymium iron boron permanent magnet.
2. The method for preparing the sintered NdFeB permanent magnet according to claim 1, wherein the addition amount of water is calculated according to the following formula: m × (w)0-w1) X 18/16; wherein M is the weight of the fine powder, w0To a target oxygen content, w1Is the oxygen content in the fine powder, and w1≤w0。
3. The method for preparing the sintered NdFeB permanent magnet according to claim 1, wherein the jet mill is subjected to oxygen discharge until the oxygen concentration is not more than 5ppm before the powder is milled by the jet mill.
4. The method for preparing the sintered NdFeB permanent magnet according to claim 1, wherein the average particle diameter (SMD) of the fine powder is 2.5-3.0 μm, and the particle size distribution ratio is not more than (X90/X10) 5.0.
5. The method for preparing the sintered NdFeB permanent magnet according to claim 1, wherein in the process of milling the powder by the jet mill, the addition amount of the antioxidant is 0.05-0.2% of the weight of the coarse powder, and the addition amount of the lubricant is 0.05-0.2% of the weight of the fine powder.
6. The method for preparing the sintered NdFeB permanent magnet according to claim 1, wherein the molding specifically comprises: and under the nitrogen atmosphere, placing the powder in a magnetic field of a press with the temperature of more than 1.5T, and performing orientation forming to obtain a green body.
7. The method for preparing the sintered NdFeB permanent magnet according to claim 6, wherein the oxygen content of the nitrogen atmosphere is controlled to be less than 0.05% during the forming process.
8. A sintered ndfeb permanent magnet characterized in that it is produced by the method of claim 1.
9. The sintered NdFeB permanent magnet of claim 8, comprising the following chemical components in mass percent: PrNd: 28-33 wt%, Ho: 1-5 wt%, B: 0.92-1.1 wt%, Al: 0-0.8 wt%, Cu: 0.05-0.3 wt%, Co: 0.1 to 2 wt%, Ga: 0 to 0.5 wt%, Zr: 0 to 0.5 wt%, and the balance Fe.
10. The sintered ndfeb permanent magnet according to claim 9, characterized by comprising the following chemical components in mass percent: PrNd: 29 wt%, Ho: 4 wt%, B: 0.94 wt%, Al: 0.9 wt%, Cu: 0.2 wt%, Co: 0.2 wt%, Ga: 0.1 wt%, Zr: 0.1 wt%, and the balance Fe.
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