CN110335733B - High-temperature-resistant neodymium-iron-boron magnet and preparation method thereof - Google Patents
High-temperature-resistant neodymium-iron-boron magnet and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a corrosion-resistant neodymium iron boron magnet and a preparation method thereof, relating to the technical field of magnetic materials, wherein the magnet comprises the following elements in percentage by weight: nd: 28.0% -30.2%, B: 2.0% -2.5%, Co: 5% -8%, Ti: 0.2% -0.5%, Ga: 0.09% -0.12%, Al: 2.0% -3.0%, heavy rare earth elements: 0% -0.2%, the balance being Fe and non-removable impurities. The neodymium iron boron magnet has good Curie temperature and coercive force, effectively improves the highest working temperature of the neodymium iron boron magnet, is prepared by the steps of primary smelting, secondary smelting, hydrogen breaking, jet milling, profiling and sintering, and has the characteristics of simple operation and convenience for mass production.
Description
Technical Field
The invention relates to the technical field of magnetic materials, in particular to a corrosion-resistant neodymium iron boron magnet and a preparation method thereof.
Background
The sintered neodymium-iron-boron magnet is a modern permanent magnet with the strongest magnetism, has excellent characteristics of high magnetic energy product, high cost performance and the like, is applied to the fields of aviation, aerospace, microwave communication technology, electronics, electroacoustic, electromechanics and the like, but the requirement of people for the sintered neodymium-iron-boron magnet is increased along with the continuous expansion of the application range of the permanent magnet, and the challenge is provided for the applicable temperature of the permanent magnet while the permanent magnet meets the equipment model.
In practical use, the maximum working temperature of a common magnet is taken as one of the measurement standards of the temperature characteristic of the magnet, and the improvement of the working temperature of the neodymium iron boron magnet is mainly focused on the following three aspects: increasing the Curie temperature T of the magnetcAnd improving the intrinsic coercive force H of the magnetcjAnd reducing the temperature coefficient of the magnet, the main method for reducing the temperature coefficient being to increase TcAnd Hcj。
To increase the curie temperature of neodymium-iron-boron magnets, one typically adds the element Co to the magnet. It has been found that T is in the range of 0 to 10 at% of CocIncreasing approximately along a straight line with increasing Co content, essentially every 1 at% Co, TcThe increase is 10.9 ℃. However, it was also found that the coercive force of the magnet was lowered by adding Co because Co is in the magnetSince a soft magnetic phase is formed in the grain boundary and the coercive force of the magnet is reduced by easily forming a nucleus in the demagnetized domain under a reverse magnetic field, alloy elements for enhancing the coercive force, such as Dy, Tb, Al, Nb, Ga, and the like, are added to the magnet at the same time. Therefore, the improvement of the working temperature of the neodymium iron boron magnet is largely attributed to the improvement of the coercive force of the neodymium iron boron magnet.
In the prior art, a double-alloy method is an effective way for improving the coercive force of a neodymium iron boron magnet, namely, a main phase alloy and a grain boundary phase alloy are respectively prepared, mixed according to a certain proportion, so that the grain boundary phase is uniformly dispersed around the main phase, and prepared by sintering, tempering and other processes. However, a chemical electromotive force difference exists between the main phase (-0.515V) and the neodymium-rich phase (-0.65V), so that intergranular corrosion exists between different phases to influence the corrosion resistance of the ndfeb magnet, and further, the improvement degree of the coercivity and the maximum operating temperature of the ndfeb magnet is limited.
Disclosure of Invention
In view of the defects in the prior art, a first object of the present invention is to provide a high temperature resistant ndfeb magnet, which has excellent corrosion resistance, high coercivity and high maximum operating temperature.
The second purpose of the invention is to provide a preparation method of the high-temperature-resistant neodymium-iron-boron magnet, which is simple to operate and convenient for mass production.
In order to achieve the first object, the invention provides the following technical scheme:
a high temperature resistant neodymium iron boron magnet, each element weight percent in the magnet as follows: nd: 28.0% -30.2%, B: 2.0% -2.5%, Co: 5% -8%, Ti: 0.2% -0.5%, Ga: 0.09% -0.12%, Al: 2.0% -3.0%, heavy rare earth elements: 0% -0.2%, the balance being Fe and non-removable impurities.
Further, the weight percentages of the elements in the magnet are as follows: nd: 29.5%, B: 2.3%, Co: 7.2%, Ti: 0.3%, Ga: 0.11%, Al: 2.5%, heavy rare earth elements: 0.1% and the balance Fe and non-removable impurities.
By adopting the technical scheme, the neodymium iron boron magnet is provided with elements such as Co, Ti, Ga, Al and the like, so that the Curie temperature and the coercive force of the neodymium iron boron magnet can be effectively improved, and the maximum working temperature of the neodymium iron boron magnet can be improved.
The titanium has excellent corrosion resistance, the melting point is 1668 +/-4 ℃, but the boiling point is as high as 3260 +/-20 ℃, and the titanium can be combined with Fe and Al elements to produce a high-strength light alloy and improve the coercive force of the neodymium iron boron magnet. The melting point of Ga is only 29.8 ℃, but the boiling point of Ga is as high as 2403 ℃; the melting point of Al is 660.37 ℃, and the boiling point is up to 2467.0 ℃. Therefore, when Ga and Al elements are added, the liquid phase temperature of the neodymium iron boron magnet can be reduced, and various performances such as spreading and mechanics of the neodymium iron boron magnet are optimized. Moreover, Ga can form peritectic binary state with Ti, improve the fluidity of Ti and facilitate the mixing of elements.
Heavy rare earth elements can enter the main phase as a substitute phase, and a connected region with high rare earth content is formed at the boundary of the main phase, so that the coercive force of the neodymium iron boron magnet is greatly improved, and the remanence almost has no influence. Meanwhile, after the grain boundary is permeated by the heavy rare earth, the grain boundary rare earth-rich phase is more continuous and clear, and the isolation exchange coupling effect is more effective.
Further, the weight ratio of the heavy rare earth elements is 2:1:1 Dy, Cr and V.
By adopting the technical scheme, Dy element is diffused into the surface layer region of the main phase crystal grains to partially replace Nd element therein to form an (Nd, Dy) FeB intermetallic compound, so that the magnetocrystalline anisotropy constant of the surface structure defect region of the crystal grains is improved, the main phase crystal grain epitaxial layer generates magnetic hardening, and the intrinsic coercive force of the magnet is obviously improved. Meanwhile, the addition of the Cr element can improve the wear resistance, oxidation resistance and corrosion resistance of the heavy rare earth layer, and the Cr element can also react with B to generate a CrB reinforcing phase, so that the structural strength of the rare earth layer is improved, and the bonding strength of the heavy rare earth layer and the magnetic material body is improved; v plays a role in refining and stopping grains, and improves the strength and toughness of the heavy rare earth.
On the basis of the above component ratio, when the heavy rare earth elements Dy, Cr and V are prepared according to the weight ratio of 2:1:1, the Curie temperature and the coercive force of the neodymium-iron-boron magnetic material can be effectively improved, so that the neodymium-iron-boron magnetic material can be well suitable for the working temperature up to 240 ℃.
In order to achieve the second object, the invention provides the following technical scheme:
a preparation method of a high-temperature-resistant neodymium-iron-boron magnet comprises the following steps:
firstly, primary smelting: b, Al and part of Fe are added into a vacuum atmosphere sintering furnace according to the specified weight percentage, nitrogen is introduced, the temperature is raised to 850-900 ℃, and then smelting is carried out for 1-2h, so as to obtain a premix;
secondly, remelting: discharging nitrogen in a vacuum atmosphere sintering furnace filled with the premix, adding Nd, Co, Ti, Ga, heavy rare earth elements and the rest Fe according to the specified weight percentage, continuously heating to 1550-1600 ℃, and carrying out mixed smelting to obtain a melt-spun sheet;
③ hydrogen breaking: crushing the melt-spun piece by hydrogen, and then preparing the melt-spun piece into micro powder in an air flow mill;
fourthly, profiling: mixing the micro powder under the protection of nitrogen, uniformly dispersing the micro powder, and then performing compression molding to obtain a neodymium iron boron blank;
fifthly, sintering: sintering the neodymium iron boron blank, keeping the sintering condition temperature at 1000-1040 ℃, keeping the temperature for 2-3h, cooling to 900 ℃, carrying out aging treatment, keeping the primary aging temperature at 900-950 ℃, keeping the temperature for 2-3h, cooling to below 150 ℃, keeping the secondary aging temperature at 540-580 ℃, keeping the temperature for 2-3h, cooling to below 80 ℃, and uniformly coating an antioxidant paint to obtain the neodymium iron boron magnet.
By adopting the technical scheme, part of Al in the neodymium iron boron magnetic material reacts with nitrogen at the temperature of 850-900 ℃ to generate AlN, and the raw material for preparing the neodymium iron boron magnetic material is heated uniformly in the smelting process due to the high thermal conductivity of AlN, so that the smelting efficiency of the neodymium iron boron magnetic material is accelerated.
And then, nitrogen is exhausted to the greatest extent, the continuous reaction between the nitrogen and Al can be reduced, so that the Al element has two forms in the neodymium iron boron magnetic material, the Al which does not participate in the reaction can play a role in refining grains, the coercive force and the Curie temperature of the neodymium iron boron magnet are improved, the liquid phase temperature of the neodymium iron boron magnet can be reduced to a certain extent, and the smelting of Ti element and other metal elements is accelerated.
Further, in the step (I), B is derived from hexagonal boron nitride and B-Fe intermediate alloy.
By adopting the technical scheme, the hexagonal Boron Nitride (BN) is converted into the cubic boron nitride under the catalytic action of the AlN, so that the strength of the neodymium iron boron magnet is effectively improved, the neodymium iron boron magnet has excellent coercive force, partial Fe can be introduced while the B-Fe intermediate alloy is introduced to complement the B element, the oxidation of the Fe element is reduced, and the corrosion resistance of the neodymium iron boron magnet is improved.
Further, in the step I, the weight ratio of the HBN to the B-Fe intermediate alloy is 1: 4.
by adopting the technical scheme, when the weight ratio of the HBN to the B-Fe intermediate alloy is 1:4, the improvement effect of the coercive force and the Curie temperature of the neodymium-iron-boron magnet reaches the best state, so that the weight ratio is preferably selected.
Further, in the step I, after nitrogen is introduced into the vacuum atmosphere sintering furnace and the temperature is raised to 850-900 ℃, the absolute pressure in the furnace is controlled to be 100 +/-0.5 Pa.
By adopting the technical scheme, in the sintering process, Al absorbs heat to be melted into liquid, B and Fe are still solid and are dispersed in Al liquid, and the introduced nitrogen reacts with Al on the surface under the control of the absolute pressure of 100Pa, so that part of Al is not reacted, and the content of Al in the two states reaches a stable state, so that the prepared neodymium iron boron magnet has good coercive force.
Further, in the third step, after the melt-spun sheet is crushed, polyethylene oxide fatty acid monoester and graphite are added, and the weight ratio of the polyethylene oxide fatty acid monoester to the graphite is 7: 3.
by adopting the technical scheme, the polyethylene oxide fatty acid monoester is liquid, and when the polyethylene oxide fatty acid monoester is compounded with graphite according to the weight ratio of 7:3, the polyethylene oxide fatty acid monoester can better carry the graphite to be uniformly coated on the surface of powder formed by the breakage of the melt-spun piece, so that the contact between air and the powder is isolated. In addition, the polyethylene oxide mono-fatty acid ester is an efficient antioxidant, and the graphite is a lubricant, so that the probability of oxidation of powder can be reduced, friction among the powder can be reduced, and the degree of orientation of the powder can be improved.
Meanwhile, the graphite can also be used as a reducing agent in the subsequent high-temperature sintering process, so that the powder is reduced, oxygen in the powder is removed, and the graphite is separated from the powder in the form of carbon dioxide, so that the influence on the magnetism of the final NdFeB magnet is avoided.
Furthermore, in the fifth step, the temperature of the neodymium iron boron blank is raised to 600 ℃ in the sintering process, and the heat preservation treatment is carried out for 25 min.
By adopting the technical scheme, when the neodymium iron boron blank is sintered, the temperature of the neodymium iron boron blank is raised to 650 ℃ and then is subjected to heat preservation treatment for 25min, so that water vapor, additives and the like on the surface of the powder can be separated from the powder.
And further, in the fifth step, before the sintered neodymium iron boron blank is coated with the antioxidant paint, under the protection of inert gas, the oxide layer and oil stains on the surface of the blank are cleaned by ultrasonic waves.
By adopting the technical scheme, the oxide layer, the oil stain and the oxide layer are cleaned by utilizing ultrasonic waves, when the sound wave pressure transmitted by ultrasonic vibration in the oil stain and the oxide layer reaches one atmospheric pressure, the sound wave pressure peak value of the ultrasonic waves can reach vacuum or negative pressure, but no negative pressure exists actually, so that great force is generated in the oil stain and the oxide layer, the oil stain and the oxide layer are pulled and cracked into cavities which are very close to vacuum, the cavities are cracked when the ultrasonic pressure is reversely maximized, the oil stain and the oxide layer are impacted by strong impact generated by cracking, the surface of the sheet is cleaned by the ultrasonic waves, the cleaning is more thorough, and after the sheet is cleaned by the ultrasonic waves, no residue is generated on the surface of the sheet due to the ultrasonic cleaning, and the cleaning effect is good.
In conclusion, the invention has the following beneficial effects:
1. the neodymium iron boron magnet is added with elements such as Co, Ti, Ga, Al and the like, so that the Curie temperature and the coercive force of the neodymium iron boron magnet can be effectively improved, and the highest working temperature of the neodymium iron boron magnet can be improved;
2. the invention sets the weight ratio of heavy rare earth elements as 2:1:1 Dy, Cr and V can effectively improve the Curie temperature and the coercive force of the neodymium iron boron magnetic material, so that the neodymium iron boron magnetic material can be well suitable for the working temperature up to 240 ℃;
3. the neodymium iron boron magnet is prepared by primary smelting, secondary smelting, hydrogen breaking, profiling and sintering, and has the characteristics of simple operation and convenience for mass production.
Drawings
Fig. 1 is a process flow diagram for preparing a neodymium iron boron magnet.
Detailed Description
The present invention is described in further detail below with reference to fig. 1.
Example 1
A method for preparing a high temperature resistant ndfeb magnet, as shown in fig. 1, comprising the following steps:
firstly, primary smelting: adding 1.85kg of BN, 7.42kg of B-Fe alloy and 2.0kg of Al powder into a vacuum atmosphere sintering furnace, introducing nitrogen into the vacuum atmosphere sintering furnace to control the absolute pressure in the furnace to be 100Pa, heating to 850 ℃, and smelting for 2 hours to obtain a premix;
secondly, remelting: discharging nitrogen in a vacuum atmosphere sintering furnace filled with the premix, sequentially adding 28.0kg of Nd powder, 5.0kg of Co powder, 0.2kg of Ti powder, 0.09kg of Ga powder and 55.44kg of Fe powder, continuously heating to 1550 ℃, and carrying out mixed smelting to obtain a melt-spun sheet;
③ hydrogen breaking: crushing the melt-spun sheet with hydrogen, preparing the crushed melt-spun sheet into micro powder in an air flow mill, and adding polyethylene oxide fatty acid monoester and graphite, wherein the weight ratio of the polyethylene oxide fatty acid monoester to the graphite is 7: 3;
fourthly, profiling: mixing the micro powder under the protection of nitrogen, uniformly dispersing the micro powder, and then performing compression molding to obtain a neodymium iron boron blank;
fifthly, sintering: sintering the neodymium iron boron blank, firstly heating to 600 ℃, carrying out heat preservation treatment for 25min, then continuously heating to 1000 ℃, carrying out heat preservation for 2h, then cooling to 900 ℃, carrying out aging treatment, wherein the first-stage aging temperature is 900 ℃, the second-stage aging temperature is 540 ℃, the second-stage aging temperature is 75 ℃ after carrying out heat preservation for 2h, cleaning an oxide layer and oil stains on the surface of the blank by using ultrasonic waves under the protection of inert gas, and then uniformly coating antioxidant paint to obtain the neodymium iron boron magnet.
Example 2 to example 4
Examples 2-4 adjustments were made to the components and component amounts based on the procedure of example 1, and are shown in table one below.
TABLE Components and component content tables of examples 1-4
Example 5-example 7
Examples 5-7 the parameters for making neodymium iron boron were adjusted based on the method of example 1, and see table two below.
TABLE two preparation parameters for example 1 and examples 5-7
Example 8
In this example, based on the method of example 1, polyethylene oxide mono fatty acid ester and graphite were not added after hydrogen breaking in step (c).
Example 9
In this example, the oxide layer and the oil stain on the surface of the green body were not cleaned by the ultrasonic wave in the fifth step based on the method of example 1.
Comparative example 1
This comparative example is based on the method of example 1, with no addition of Ti and Ga elements.
Comparative example 2
This comparative example is based on the method of example 1, without adding Ga and Al elements.
Performance detection
The coercivity and the Curie temperature of the NdFeB magnets prepared in the examples 1-9 and the comparative examples 1 and 2 are measured according to the detection standard GB/T13560-2017, and the detection results are shown in the following table III.
TABLE TRI EXAMPLES 1-9 AND COMPARATIVE EXAMPLES 1-2
Referring to table three, by comparing the detection results of the embodiments 1 to 4 with the detection results of the comparative examples 1 to 2, it can be obtained that the neodymium iron boron magnetic material of the present invention has high coercive force and curie temperature by adding elements such as Co, Ti, Ga, and Al, and can work and operate at a high working temperature.
Wherein, in the embodiment 2 and the embodiment 3, the weight ratio of the heavy rare earth elements is 2:1:1 Dy, Cr and V, so that the neodymium iron boron magnetic material can be better suitable for working temperature up to 240 ℃. The test result of example 3 is optimum among examples 1 to 4, and therefore example 3 is preferred.
Comparing the detection results of the embodiment 1 and the embodiment 5 to the detection results of the embodiment 7 respectively, it can be obtained that when the preparation parameters of the neodymium iron boron magnet are set according to the conditions that the primary smelting temperature is 850-900 ℃ for 1-2h, the absolute pressure is 100 +/-0.5 Pa, the weight ratio of HBN to B-Fe is 1:4, and the secondary smelting temperature is 1550-1600 ℃, the coercive force and the Curie temperature of the prepared neodymium iron boron magnet material can be improved to a certain extent.
Comparing the detection results of example 1 with those of example 8 and example 9, respectively, it can be seen that the structural stability of the ndfeb magnet can be improved by adding polyethylene oxide mono fatty acid ester and graphite and the operation of treating the surface of the blank with ultrasonic waves, thereby better increasing the maximum working temperature.
In conclusion, the neodymium iron boron magnetic material prepared by the invention has excellent Curie temperature and coercive force, can be well suitable for higher working temperature, has a simple preparation method and is convenient for mass production.
The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.
Claims (7)
1. The preparation method of the high-temperature-resistant neodymium-iron-boron magnet is characterized in that the weight percentages of all elements in the magnet are as follows: nd: 29.5%, B: 2.3%, Co: 7.2%, Ti: 0.3%, Ga: 0.11%, Al: 2.5%, other elements: 0.1%, and the balance of Fe and non-removable impurities, wherein the other elements are sequentially 2:1:1 Dy, Cr and V;
the method comprises the following steps:
firstly, primary smelting: b, Al and part of Fe are added into a vacuum atmosphere sintering furnace according to the specified weight percentage, nitrogen is introduced, the temperature is raised to 850-900 ℃, and then smelting is carried out for 1-2h, so as to obtain a premix;
secondly, remelting: discharging nitrogen in a vacuum atmosphere sintering furnace filled with the premix, adding Nd, Co, Ti, Ga, other elements and the rest Fe according to the specified weight percentage, continuously heating to 1550-1600 ℃, and carrying out mixed smelting to obtain a melt-spun sheet;
③ hydrogen breaking: crushing the melt-spun piece by hydrogen, and then preparing the melt-spun piece into micro powder in an air flow mill;
fourthly, profiling: mixing the micro powder under the protection of nitrogen, uniformly dispersing the micro powder, and then performing compression molding to obtain a neodymium iron boron blank;
fifthly, sintering: sintering the neodymium iron boron blank, keeping the sintering condition temperature at 1000-1040 ℃, keeping the temperature for 2-3h, cooling to 900 ℃, carrying out aging treatment, keeping the primary aging temperature at 900-950 ℃, keeping the temperature for 2-3h, cooling to below 150 ℃, keeping the secondary aging temperature at 540-580 ℃, keeping the temperature for 2-3h, cooling to below 80 ℃, and uniformly coating an antioxidant paint to obtain the neodymium iron boron magnet.
2. The method for preparing a high-temperature-resistant neodymium-iron-boron magnet according to claim 1, wherein in the step (r), B is derived from hexagonal boron nitride and a B-Fe intermediate alloy.
3. The method for preparing a high-temperature-resistant neodymium-iron-boron magnet according to claim 2, wherein in the step (r), the weight ratio of the HBN to the B-Fe intermediate alloy is 1: 4.
4. the method for preparing a high-temperature-resistant neodymium-iron-boron magnet according to claim 1, wherein in the step (r), after nitrogen is introduced into a vacuum atmosphere sintering furnace and the temperature is raised to 850-900 ℃, the absolute pressure in the furnace is controlled to be 100 +/-0.5 Pa.
5. The method for preparing a high-temperature-resistant neodymium-iron-boron magnet according to claim 1, wherein in the third step, after the melt-spun sheet is broken, polyethylene oxide fatty acid monoester and graphite are added, and the weight ratio of the polyethylene oxide fatty acid monoester to the graphite is 7: 3.
6. the method for preparing a high temperature resistant ndfeb magnet according to claim 1, wherein in the fifth step, the ndfeb blank is heated to 600 ℃ in the sintering process, and the heat preservation treatment is performed for 25 min.
7. The method for preparing a high temperature resistant ndfeb magnet according to claim 1, wherein in the fifth step, before coating the sintered ndfeb blank with the antioxidant paint, the oxide layer and the oil stain on the surface of the blank are cleaned by ultrasonic waves under the protection of inert gas.
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| CN111243848B (en) * | 2020-02-28 | 2022-01-04 | 安徽大地熊新材料股份有限公司 | Sintered neodymium-iron-boron magnet and preparation method thereof |
| CN111341513B (en) * | 2020-03-21 | 2021-08-31 | 余姚市宏伟磁材科技有限公司 | High-magnetic-performance neodymium iron boron magnet and preparation method thereof |
| CN112216462B (en) * | 2020-09-26 | 2024-05-28 | 宁波合力磁材技术有限公司 | Cerium-containing neodymium-iron-boron magnet with good corrosion resistance and preparation method thereof |
| CN113223802B (en) * | 2021-05-21 | 2022-02-22 | 慈溪市兴发磁业科技有限公司 | High-temperature-resistant neodymium-iron-boron magnet and preparation method thereof |
| CN114373593B (en) * | 2022-03-18 | 2022-07-05 | 宁波科宁达工业有限公司 | R-T-B magnet and preparation method thereof |
| CN115763051A (en) * | 2022-12-15 | 2023-03-07 | 浙江英洛华磁业有限公司 | High-performance low-gallium sintered permanent magnet and preparation method thereof |
| CN117990163B (en) * | 2024-04-03 | 2024-06-04 | 赣州华京稀土新材料有限公司 | Automatic performance detection system and method for NdFeB (neodymium iron boron) thin sheet |
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