CN108122655B - Sintered NdFeB magnet and preparation method thereof - Google Patents
Sintered NdFeB magnet and preparation method thereof Download PDFInfo
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
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- H01F1/053—Alloys characterised by their composition containing rare earth metals
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- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
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- H01F41/02—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 for manufacturing cores, coils, or magnets
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Abstract
A sintered NdFeB magnet comprising an Nd: 18.2 wt%, Pr: 6.0 wt%, Tb: 1.4 wt%, Al: 0.25 wt%, Cu: 0.10wt%, Co: 1.00 wt%, Ga: 0.09wt%, B: 0.96 wt%, Ag: 0.05 to 0.11wt%, Si: 0.09wt%, La: 0.07wt%, Eu:0.06wt%, In: 0.08wt%, Zn:1.3 wt%, Sn:0.9wt%, the balance being Fe and non-removable impurities. The sintered NdFeB magnet has high magnetic energy and coercive force. And the preparation method can effectively eliminate factors influencing the magnetic energy and the coercive force of the sintered NdFeB magnet, thereby having a positive promoting effect on the quality of the sintered NdFeB magnet.
Description
Technical Field
The invention relates to the field of magnet manufacturing, in particular to a sintered NdFeB magnet and a preparation method thereof.
Background
Permanent magnet materials have been developed as key materials for supporting electronic devices, and the development is moving towards high magnetic energy product and high coercivity. At present, the rare earth magnet is widely applied to many fields, such as a recent walking robot with a mechanical head, a special motor of an integrated technology supported by the rare earth NdFeB magnet, an automobile automatic system and the like, which become new application fields.
Due to the characteristics of the NdFeB material, in the prior art, if the coercive force Hcj of the magnet is to be increased, the remanence Br of the magnet is affected; if the remanence Br of the magnet is increased, the coercive force Hcj of the magnet is influenced, so that the magnet has higher Hcj but cannot simultaneously have higher magnetic energy product (BH) max, and the use range of the magnet is influenced to a certain extent.
Nd2Fe14The theoretical maximum magnetic energy product of the intermetallic compound B is 64MGOe, which isTo achieve higher magnetic energy product, the alloy composition should be controlled to be as close to Nd as possible2Fe14B, and high density and high coercive force are achieved by liquid phase sintering.
Disclosure of Invention
The invention aims to provide a sintered NdFeB magnet and a preparation method thereof, which are close to the component ratio of the NdFeB magnet of 2: 14: 1 as much as possible, and the production process of the magnet is refined, so that the performance of the manufactured magnet is obviously improved, the coercivity is improved, and simultaneously, a higher remanence level is kept, and the magnetic energy product (BH) max is more than 52MGOe, and the coercivity Hcj is more than 19 kOe.
The above object of the present invention is achieved by the following technical solutions: a sintered NdFeB magnet characterized by: the Nd: 15.3-21.1 wt%, Pr: 4.4-7.8 wt%, Tb: 1.0-1.8 wt%, Al: 0.1 to 0.4 wt%, Cu: 0.09-0.12 wt%, Co: 0.1 to 2wt%, Ga: 0.04-0.14 wt%, B: 0.94-0.98 wt%, Ag: 0.05 to 0.17wt%, Si: 0.04-0.14 wt%, La: 0.05 to 0.10wt%, Eu: 0.03-0.09 wt%, In: 0.06-0.10 wt%, Zn:1.2 to 1.4 wt%, Sn:0.6 to 1.2wt%, the balance being Fe and non-removable impurities.
Preferably, a sintered NdFeB magnet includes Nd: 18.2 wt%, Pr: 6.0 wt%, Tb: 1.4 wt%, Al: 0.25 wt%, Cu: 0.10wt%, Co: 1.00 wt%, Ga: 0.09wt%, B: 0.96 wt%, Ag: 0.05 to 0.11wt%, Si: 0.09wt%, La: 0.07wt%, Eu:0.06wt%, In: 0.08wt%, Zn:1.3 wt%, Sn:0.9wt%, the balance being Fe and non-removable impurities.
By adopting the technical scheme, the sintered NdFeB magnet contains elements such as Zn, Cu and Ag, so that the strength of the sintered NdFeB magnet can be effectively improved, and the probability of breakage of the NdFeB magnet in the collision process can be reduced.
Meanwhile, Ga is silvery white metal, the melting point is only 29.8 ℃, the Ga can be melted in the palm of a human hand, but the boiling point of the Ga is very high and reaches 2403 ℃, so that the integral liquidus temperature of the NdFeB magnet material can be reduced when the Ga content is increased, and various properties such as spreading and mechanics of the NdFeB magnet material are optimized. Moreover, Ga can be combined with various components In the NdFeB magnet material, Ga and In form eutectic, the eutectic temperature is 15.7 ℃, Ga can be dissolved In 10% to form beta solid solution with excellent performance, Ga-Cu forms peritectic binary state, Ga can be dissolved In Cu In 17.5%, single-phase alpha solid solution is formed, the plasticity and the processability are good, Ag-Ga also forms peritectic binary state, and Ag-14Ga still has excellent plasticity and variable processing.
In has a melting point lower than that of metal Sn, and the addition of In can reduce the solid-liquid phase line range of the NdFeB magnet material more remarkably, and In, which is similar to Sn, can reduce the melting interval of the NdFeB magnet material and improve the overall fluidity of the NdFeB magnet material, thereby being beneficial to the mixing of elements.
La originally has a strong magnetic property, and contributes to improvement of the magnetic energy product of the NdFeB magnet.
A method for preparing a sintered NdFeB magnet comprises the following steps:
s1, adding Nd, Pr, Tb, Co, B, Ag, Cu, Si, Zn, Sn and Fe into a vacuum induction rapid hardening furnace according to specified mass fractions for smelting;
s2, after all substances In S1 are melted, adding La, Eu, Al, In and Ga into a vacuum induction rapid hardening furnace according to specified mass fractions, and mixing and smelting the substances together with the substances to obtain a melt-spun alloy sheet;
s3, crushing the melt-spun alloy sheet in a hydrogenation furnace, and then preparing the melt-spun alloy sheet into micro powder in an air flow mill;
s4, mixing the micro powder under the protection of nitrogen to uniformly disperse the particle size;
s5, compacting the micro powder in the S4 under the protection of nitrogen;
s6, placing the pressed blank into a vacuum sintering furnace for sintering under the protection of nitrogen, wherein the sintering temperature is 1045-1080 ℃, the heat preservation time is 3-5 hours, then Ar gas is filled for cooling to 900 ℃, then the aging treatment is carried out in the vacuum furnace, the first-stage aging temperature is 900-950 ℃, the heat preservation time is 3-5 hours, then Ar gas is filled for cooling to below 100 ℃, the second-stage aging temperature is 600-610 ℃, the heat preservation time is 3-5 hours, then Ar gas is filled, the blank is cooled to below 80 ℃, taken out of the furnace, and the antioxidant paint is uniformly coated.
By adopting the technical scheme, the elements are firstly added into the vacuum induction rapid hardening furnace in two batches according to the melting point, so that all the elements can be fully melted and mixed.
Secondly, the processes of powder mixing and compression molding are carried out under the protection of nitrogen, so that the probability of oxidation of the NdFeB magnet material can be reduced. Furthermore, after sintering, the temperature is directly reduced to 900 ℃, and the first stage of aging treatment is started, so that the efficiency of the aging treatment can be ensured, and on the other hand, the influence of the cooling rate on the magnetic performance of the magnet is not great at the temperature, thereby providing convenience for the continuity of production.
Finally, a layer of antioxidant paint is further coated on the surface of the prepared NdFeB magnet, so that the antioxidant performance of the NdFeB magnet in the daily use process can be effectively improved, and the service life of the NdFeB magnet is prolonged.
Preferably, the Cu and Si are derived from a Cu-Si master alloy.
By adopting the technical scheme, the Cu-Si intermediate alloy is added, and Si is introduced to inhibit the volatilization of Zn while Cu is introduced, so that the occurrence of pores in the NdFeB magnet in the sintering process is avoided. And the addition of Zn in the NdFeB magnet can effectively improve the oxidation resistance of the NdFeB magnet.
Secondly, the dendritic segregation of Sn energy and Cu-Si intermediate alloy is aggravated, so that the hot rolling structure of the alloy during melting is refined, the mechanical property of the strip-casting alloy sheet is obviously changed, and the strip-casting alloy sheet is more easily broken in the processes of hydrogen explosion and jet milling
Moreover, the addition of Cu and Si can further improve the impact resistance of the finished NdFeB magnet, and reduce the probability of the NdFeB magnet being broken in the using process.
Preferably, after the melt-spun alloy sheet is crushed in S3, a mixture of methyl acetate, polyethylene oxide mono-fatty acid ester and graphite is added, wherein the mass ratio of the methyl acetate to the polyethylene oxide mono-fatty acid ester to the graphite is 5: 1.
By adopting the technical scheme, because the polyethylene oxide mono-fatty acid ester and the methyl acetate are both in liquid state, the polyethylene oxide mono-fatty acid ester and the methyl acetate can carry graphite to uniformly coat the surface of the powder, thereby isolating the contact between air and the powder. And polyethylene oxide mono fatty acid ester is a high-efficiency antioxidant, and methyl acetate and graphite are lubricants, so that the probability of oxidation of powder can be reduced, friction among the powder can be reduced, and the orientation degree of the powder is improved. In addition, the graphite can also be used as a reducing agent in the subsequent high-temperature sintering process, so that the graphite can play a role in reducing the powder, removes oxygen elements in the powder, and simultaneously releases the powder in the form of carbon dioxide, thereby avoiding influencing the magnetism of the final NdFeB magnet.
Preferably, in the sintering process of the blank in S6, when the temperature of the vacuum sintering furnace is raised to 650 ℃, the heat preservation treatment is carried out for 30min, and when the temperature is raised to 750 ℃, the heat preservation treatment is carried out for 15 min.
By adopting the technical scheme, when the temperature of the vacuum sintering furnace is raised to 650 ℃, the heat preservation treatment is carried out for 30min, so that the water vapor, the additives and the like on the surface of the powder can be separated from the powder. When the temperature reaches 750 ℃, the degree of freedom of the gas atomic layer of N atoms adsorbed by the powder and bonded to the powder before that time is increased, and at that time, it is released from the NdN state, so that the influence on the performance of the NdFeB magnet can be reduced.
Preferably, when the temperature of the vacuum sintering furnace is increased to 650 ℃, the absolute pressure in the vacuum sintering furnace is controlled to be 100 Pa.
By adopting the technical scheme, lanthanum hydride is easily generated with La element in the hydrogen explosion process, the magnetism of the lanthanum hydride is lower than that of the La element, part of the lanthanum hydride even has diamagnetism, H is easily separated from the lanthanum hydride under the conditions of 650 ℃ and 100Pa, the remanence of a magnet sample is almost unchanged, and the magnetic energy and the coercive force are increased along with the increase of dehydrogenation gas pressure.
Preferably, after the first aging is finished in S6, the temperature of the blank is cooled to below 100 ℃ in 1min, and then the temperature is raised to 600 ℃ within 10min, and then the second aging treatment is performed.
By adopting the technical scheme, the NdFeB magnet can be rapidly cooled and then rapidly heated, so that the H of the NdFeB magnet can be ensuredERemain at a correspondingly higher level.
Preferably, the antioxidant paint comprises, by mass, 56 parts of acrylic acid, 3 parts of sodium dodecyl benzene sulfonate, 2 parts of carbamide, 1 part of graphene, 603 parts of an anti-flash rust agent RAYBO, 4 parts of aluminum tripolyphosphate, 20 parts of distilled water, 2 parts of barium sulfate and 1 part of bentonite.
By adopting the technical scheme, the antioxidant paint has a strong antioxidant function, and sodium dodecyl benzene sulfonate and carbamide in the antioxidant paint can act synergistically to effectively inhibit damage of insect pests to the NdFeB magnet, so that the service life of the NdFeB magnet is further prolonged.
In conclusion, the invention has the following beneficial effects:
1. the NdFeB magnet is added with elements such as La, In and Ga, so that the melting point of the NdFeB magnet material can be reduced, and the flowability of the NdFeB magnet material In a molten state can be improved, thereby being beneficial to improving the processing efficiency;
2. since La has good magnetism, the magnetic energy product of the NdFeB magnet can be effectively improved after the La is added into the NdFeB magnet;
3. during sintering, the temperature of the vacuum sintering furnace is increased in a stepwise manner, so that water vapor, organic matters and N, H elements which are bonded with other elements of the NdFeB magnet material can be effectively removed, thereby reducing the influence on the magnetic energy and coercive force of the NdFeB magnet.
Drawings
Fig. 1 is a flow chart of a process for producing a sintered NdFeB magnet.
Detailed Description
The present invention is described in further detail below with reference to fig. 1.
The first embodiment,
A method for preparing a sintered NdFeB magnet comprises the following steps:
step one, adding 15.3 wt% of Nd, 4.4 wt% of Pr, 1.0 wt% of Tb, 0.1 wt% of Co, 0.94 wt% of B, 0.05 wt% of Ag, 0.09wt% of Cu, 0.04 wt% of Si, 1.2wt% of Zn, 0.6 wt% of Sn, 76.0 wt% of Fe and non-removable impurities into a vacuum induction rapid hardening furnace for smelting, wherein the smelting temperature is controlled at 2800 ℃, and Cu and Si are added into the vacuum induction rapid hardening furnace in a Cu-Si intermediate alloy mode;
step two, after all the substances In the S1 are melted, adding 0.05 wt% of La, 0.03 wt% of Eu, 0.1 wt% of Al, 0.06wt% of In and 0.04 wt% of Ga into a vacuum induction rapid hardening furnace to be mixed and smelted together with the previous substances, and obtaining a melt-spun alloy sheet;
thirdly, crushing the melt-spun alloy sheet in a hydrogenation furnace, adding a mixture of methyl acetate, polyethylene oxide fatty acid monoester and graphite, and then preparing the mixture into micro powder in an air flow mill, wherein the differential average particle size is controlled to be 2.5 mu m;
mixing the micro powder under the protection of nitrogen to uniformly disperse the particle size, wherein the nitrogen can be selected according to actual conditions;
step five, compacting the micro powder in the S4 under the protection of nitrogen;
sixthly, putting the pressed blank into a vacuum sintering furnace for sintering under the protection of nitrogen, wherein the sintering temperature is firstly increased to 650 ℃ from the normal temperature, the absolute pressure in the vacuum sintering furnace is ensured to be 100Pa, the heat preservation lasts for 30min, then the temperature is continuously increased to 750 ℃, the heat preservation lasts for 15min, finally the temperature is increased to 1045-1080 ℃, and the heat preservation time is 3-5 hours
And step seven, after the step six is finished, filling Ar gas to cool to 900 ℃, then carrying out aging treatment in a vacuum sintering furnace, keeping the temperature at 900-950 ℃ for 3-5 hours, filling Ar gas, cooling to below 100 ℃ in 1min, raising the temperature to 600 ℃ within 10min, carrying out second-stage aging temperature at 600-610 ℃, keeping the temperature for 3-5 hours, filling Ar gas, cooling to below 80 ℃, discharging, cutting the blank into a required shape by using a cutting machine, and uniformly coating antioxidant paint after magnetizing.
Here, the mass ratio of methyl acetate, polyethylene oxide monofatty acid ester and graphite was 5: 1. The antioxidant paint is prepared by uniformly mixing 56Kg of acrylic acid, 3Kg of sodium dodecyl benzene sulfonate, 2Kg of carbamide, 1Kg of graphene, 603Kg of flash rust inhibitor RAYBO, 4Kg of aluminum tripolyphosphate, 20Kg of distilled water, 2Kg of barium sulfate and 1Kg of bentonite at the temperature of 60 ℃.
Based on the preparation method of the example I, the following table shows examples II to fifth:
the magnetic energy and coercive force of the first embodiment to the fifth embodiment are detected according to the detection standard GB/T13012-2006, and the following table results are obtained:
| test items | Example one | Example two | EXAMPLE III | Example four | EXAMPLE five |
| Magnetic energy product (BH) max/MGOe | 52.4 | 54.4 | 53.8 | 53.7 | 53.9 |
| Coercive force Hcj/kOe | 19.4 | 21.6 | 20.8 | 21.2 | 20.9 |
As is clear from the results in the table, the sintered NdFeB magnet of the present invention has a magnetic energy product (BH) max > 52MGOe and a coercive force Hcj > 19kOe, and is thus suitable for application in more various high-end fields.
In addition, the sintered NdFeB magnets obtained in examples one to five were examined according to standard GBT 12796-:
as is apparent from the above table, the sintered NdFeB magnet of the present invention has strong mechanical properties, and the probability of breakage of the sintered NdFeB magnet when impacted is reduced, thereby further widening the application range of the sintered NdFeB magnet of the present invention.
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 (4)
1. A sintered NdFeB magnet characterized by: the Nd: 15.3-21.1 wt%, Pr: 4.4-7.8 wt%, Tb: 1.0-1.8 wt%, Al: 0.1 to 0.4 wt%, Cu: 0.09-0.12 wt%, Co: 0.1 to 2wt%, Ga: 0.04-0.14 wt%, B: 0.94-0.98 wt%, Ag: 0.05 to 0.17wt%, Si: 0.04-0.14 wt%, La: 0.05 to 0.10wt%, Eu 0.03 to 0.09wt%, In: 0.06-0.10 wt%, Zn 1.2-1.4 wt%, Sn 0.6-1.2 wt%, and Fe and irremovable impurities in balance;
the preparation method comprises the following steps:
s1, adding Nd, Pr, Tb, Co, B, Ag, Cu, Si, Zn, Sn and Fe into a vacuum induction rapid hardening furnace according to specified mass fractions for smelting;
s2, after all substances In S1 are melted, adding La, Eu, Al, In and Ga into a vacuum induction rapid hardening furnace according to specified mass fractions, and mixing and smelting the substances together with the substances to obtain a melt-spun alloy sheet;
s3, crushing the melt-spun alloy sheet in a hydrogenation furnace, and then preparing the melt-spun alloy sheet into micro powder in an air flow mill;
s4, mixing the micro powder under the protection of nitrogen to uniformly disperse the particle size;
s5, compacting the micro powder in the S4 under the protection of nitrogen;
s6, placing the pressed blank into a vacuum sintering furnace for sintering under the protection of nitrogen, wherein the sintering temperature is 1045-1080 ℃, the heat preservation time is 3-5 hours, then Ar gas is filled for cooling to 900 ℃, then the aging treatment is carried out in the vacuum furnace, the first-stage aging temperature is 900-950 ℃, the heat preservation time is 3-5 hours, then Ar gas is filled, the temperature is cooled to below 100 ℃ in 1min, then the temperature is raised to 600-610 ℃ in 10min, Ar gas is filled after the heat preservation time is 3-5 hours, the blank is cooled to below 80 ℃, and the blank is taken out of the furnace and is evenly coated with antioxidant paint;
in S3, after the melt-spun alloy sheet is crushed, adding a mixture of methyl acetate, polyethylene oxide fatty acid monoester and graphite, wherein the mass ratio of the methyl acetate to the polyethylene oxide fatty acid monoester to the graphite is 5: 5: 1;
in the sintering process of the blank in the S6, when the temperature of the vacuum sintering furnace is raised to 650 ℃, carrying out heat preservation treatment for 30min, and then when the temperature is raised to 750 ℃, carrying out heat preservation treatment for 15 min;
when the temperature of the vacuum sintering furnace is increased to 650 ℃, the absolute pressure in the vacuum sintering furnace is controlled at 100 Pa.
2. A sintered NdFeB magnet according to claim 1, characterized in that: the Nd: 18.2 wt%, Pr: 6.0 wt%, Tb: 1.4 wt%, Al: 0.25 wt%, Cu: 0.10wt%, Co: 1.00 wt%, Ga: 0.09wt%, B: 0.96 wt%, Ag: 0.05 to 0.11wt%, Si: 0.09wt%, La: 0.07wt%, Eu:0.06wt%, In: 0.08wt%, Zn 1.3 wt%, Sn 0.9wt%, and the balance Fe and non-removable impurities.
3. A sintered NdFeB magnet according to claim 1, characterized in that: the Cu and Si are derived from a Cu-Si master alloy.
4. A sintered NdFeB magnet according to claim 1, characterized in that: the anti-oxidation paint comprises, by mass, 56 parts of acrylic acid, 3 parts of sodium dodecyl benzene sulfonate, 2 parts of carbamide, 1 part of graphene, 603 parts of an anti-flash rust agent RAYBO, 4 parts of aluminum tripolyphosphate, 20 parts of distilled water, 2 parts of barium sulfate and 1 part of bentonite.
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| CN109161941B (en) * | 2018-08-09 | 2020-09-11 | 浙江工业大学 | Method for priming sintered neodymium-iron-boron magnet copper composite graphene coating to improve corrosion resistance and product |
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