CN109065314B - Method for preparing high-coercivity magnet - Google Patents
Method for preparing high-coercivity magnet Download PDFInfo
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- CN109065314B CN109065314B CN201811044302.3A CN201811044302A CN109065314B CN 109065314 B CN109065314 B CN 109065314B CN 201811044302 A CN201811044302 A CN 201811044302A CN 109065314 B CN109065314 B CN 109065314B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- 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
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- 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
- H01F1/0575—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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- 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
- 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
- H01F41/0253—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 for manufacturing permanent magnets
- H01F41/0293—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 for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
Abstract
The invention discloses a preparation method of a high-coercivity magnet, which comprises the following steps: step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then spraying nano rare earth powder on the nano rare earth powderSequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the powder to obtain a layered mixture; and step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet. According to the preparation method of the high-coercivity magnet, the Nd-Fe-B powder and the nano rare earth powder are arranged in a layered mode to obtain the layered compound, and then the nano rare earth powder on each layer is uniformly diffused to Nd through heat treatment2Fe14B main phase grain boundary, uniformly coating Nd2Fe14The main phase B improves the anisotropy field of the magnet, and effectively inhibits the decline of remanence while improving the coercive force.
Description
Technical Field
The invention relates to the technical field of preparation methods of neodymium iron boron magnets, in particular to a preparation method of a high-coercivity magnet.
Background
The rare earth permanent magnetic material is a novel permanent magnetic material appearing in the end of the 60 s of the 20 th century. They have both high magnetic energy product and high coercive force, and are necessary functional materials in high and new technical fields. At present, the functional materials become indispensable functional materials in a plurality of fields such as aerospace, national defense and military industry, electronic communication, clean energy, transportation, mining machinery, medical care, household appliances and the like. Besides the inherent energy-saving advantages, the Sm-Co and Nd-Fe-B rare earth permanent magnet materials have the characteristics of high magnetic energy product and high coercivity, and can effectively promote the development of modern scientific technology and information industry towards integration, miniaturization and intellectualization. It is believed that with the rapid development of scientific technology, various devices or apparatuses composed of different types of permanent magnets (including rare earth permanent magnets) will increasingly enter people's daily life, thereby contributing to the progress and prosperity of modern society.
Permanent magnetic materials ideally retain their magnetic properties for a long time, and we also feel that in many cases there is no concern about the loss of magnetic properties, they appear to provide magnetic properties for a long time, unlike electrical power supplies which require at least battery replacement and are therefore "permanent". However, the magnetism of the permanent magnetic material is changed along with the use environment and time, and more exact description and systematic study on the stability of the permanent magnetic material are needed. The most intuitive description about the stability of the permanent magnet material is to compare the change degree of the permanent magnet performance of the magnet before and after the magnet is influenced by the surrounding environment in the application process. If the permanent magnetic property changes very little, the stability of the permanent magnetic material is good; if the permanent magnetic performance is greatly changed, the stability of the permanent magnetic material is poor.
Permanent magnetic materials are used as a magnetic field source, i.e. a constant or variable magnetic field without a current source is provided in a certain air gap, the former corresponding to static magnetic circuits and the latter corresponding to dynamic magnetic circuits. The magnetic field provided by the permanent magnet in the air gap is proportional to the square root of the magnetic energy product corresponding to the line of the working load in which the permanent magnet material is located, i.e. Hg∝(BH)1/2The working point with the highest material utilization rate should be selected to be the maximum magnetic energy product (BH)maxNearby. While the maximum energy product of a permanent magnetic material depends on the remanence B of the materialrMagnetically induced coercive force HcbIntrinsic coercive force HcjAnd demagnetization curve squareness. If these basic parameters change, the permanent magnetic properties of the magnet will certainly change, because these changes reflect the situation after the magnet is recharged. If the re-magnetization is not recoverable, it means that the magnet has a change in its macro-or microstructure, such as macroscopic magnet cracking, chipping, surface erosion, or microscopic grain size growth. Even if these several parameters are constant, the stability of the magnet is affected by variations in its operating point or permeability coefficient, which depends on the size and shape of the magnet, as well as the condition of the other materials with which it is made up for the device for magnetic applications.
The magnet has different use environments and different requirements on the stability of the permanent magnet material. For example, permanent magnets used in aerospace vehicles or military ballistic missiles vary greatly in ambient temperature and require a low temperature coefficient of the magnet to ensure proper operation of the device; the permanent magnet used in outer space is continuously irradiated by various high-energy rays except large change of environmental temperature difference, and the magnetic material must have radiation resistance; permanent magnets used in motors, gyroscopes and magnetic bearings that operate at high speeds require materials with high mechanical strength; the permanent magnet working in a high-frequency environment needs to have the lowest conductivity to reduce the eddy current loss and the heat productivity of the magnet; permanent magnets, which work in electro-vacuum devices such as magnetrons and traveling wave tubes, are desired to have high thermal conductivity in order to cool well, in addition to requiring a low temperature coefficient of the magnet; permanent magnets used in the field of ocean engineering, the surfaces of which are subject to erosion due to the action of humid air and salt, resulting in oxidation and corrosion of the surfaces of the magnets; in the permanent magnet used in the chemical engineering field, the corrosion of the magnet is also caused by the corrosion of various acids and alkalis on the surface of the magnet. In summary, permanent magnets can only operate stably for a long time if the permanent magnet material simultaneously satisfies permanent magnetic properties and some of the above-mentioned stability requirements in terms of certain physical or chemical properties.
The technology of the preparation process of the sintered magnet has been developed for half a century, and the technology comprises the technical means of Strip Casting (SC), hydrogen crushing (HD), Jet Milling (JM) and the like, so that the total rare earth content and the cost of the magnet are reduced, and the performance of the magnet is greatly improved. The new techniques developed in recent years are mainly represented by a grain boundary diffusion method (GBD) and a double alloy method (including a double main phase method) for optimizing grain boundaries, a grain refining method for obtaining a high coercive force, and the like. In addition, the wide adoption of the oxygen content control technology makes it possible for the magnet to obtain high magnetic performance (especially coercive force), and the oxygen control technology is also a key factor for maintaining the high stability and consistency of the sintered rare earth permanent magnet product. With the application of the sintered Nd-Fe-B magnet in the low-carbon economic fields of wind power generation, hybrid electric vehicles/pure electric vehicles, energy-saving household appliances/industrial motors and the like, the double high magnetic performance (high maximum magnetic energy product (BH)maxAnd high intrinsic coercivity Hcj) Sintered neodymium iron boron magnets have become a significant need.
In the process of manufacturing sintered neodymium-iron-boron permanent magnetic materials, heavy rare earth is generally added in the process of smelting alloy or is directly mixed in raw materials to improve the coercive force of a magnet, but the direct addition of the heavy rare earth can cause magnetic dilution to reduce residual magnetism and cause excessive consumption of the heavy rare earth to improve production cost, so that a preparation method capable of improving the coercive force of the magnet and ensuring high residual magnetism is needed.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
An object of the present invention is to provide a method for preparing a high coercive force magnet by layering Nd-Fe-B powder and nano rare earth powder to obtain a layered compound, and then uniformly diffusing the nano rare earth powder of each layer to Nd by heat treatment2Fe14B main phase grain boundary, uniformly coating Nd2Fe14The main phase B improves the anisotropy field of the magnet, and effectively inhibits the decline of remanence while improving the coercive force.
To achieve these objects and other advantages and in accordance with the purpose of the invention, a method for manufacturing a high coercive force magnet is provided, which includes the steps of:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture;
and step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
Preferably, in the preparation method of the high-coercivity magnet, the nano rare earth powder is one of rare earth dysprosium, rare earth terbium or rare earth dysprosium terbium alloy powder.
Preferably, in the preparation method of the high-coercivity magnet, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.5-99.7%, and the particle size of the Nd-Fe-B powder is 2.8-3.2 μm.
Preferably, in the method for preparing the high-coercivity magnet, the mass fraction of the nano rare earth powder in the layered mixture is not more than 0.5%.
Preferably, the heat treatment in step two of the preparation method of the high coercive force magnet is specifically: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100-205 ℃ and keeping for 0.5-2 h; heating to 400-560 ℃ and keeping for 0.5-3 h, heating to 750-810 ℃ and keeping for 1-3 h, continuing to heat to 850-920 ℃ and keeping for 4-15 h, continuing to heat to 1030-1070 ℃ and keeping for 3-10 h, then cooling to 480-560 ℃ and keeping for 2-6 h, and finally cooling to room temperature to obtain the high-coercivity magnetAnd (3) a body.
Preferably, in the preparation method of the high-coercivity magnet, after nano rare earth powder is sprayed on the upper surface of the Nd-Fe-B powder in the first step, a first suspension is sprayed on the nano rare earth powder, and then the Nd-Fe-B powder, the nano rare earth powder and the first suspension are alternately sprayed on the upper surface of the first suspension in sequence to obtain a layered mixture;
the preparation method of the first suspension comprises the following steps:
s1, mixing 2-4 parts by weight of nano aluminum nitride, 1-3 parts by weight of nano aluminum oxide, 3-5 parts by weight of nano titanium oxide, 2-3 parts by weight of nano zinc oxide, 2-5 parts by weight of nano magnesium oxide, 1-2 parts by weight of nano lanthanum oxide and 0.5-1 part by weight of nano bismuth oxide, adding 20-25 parts by weight of methanol and 50-60 parts by weight of water, uniformly stirring, adjusting the pH to 5-6 by using acetic acid, heating to 50-60 ℃ and keeping for 2-3 hours, adding 10-15 parts by weight of silane coupling agent, heating to 80-90 ℃ and keeping for 1-2 hours, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the step S1 in 20-25 parts by weight of acrylic acid, and stirring at a stirring speed of 800r/min for 10-15 min to obtain a first suspension;
wherein the mass fraction of the first suspension in the layered mixture is 0.1-0.2%.
Preferably, the method for producing a high coercive force magnet further comprises spraying a second suspension onto the surface of the obtained layered mixture, the method for producing the second suspension being: mixing 5-8 parts by weight of copper powder, 3-4 parts by weight of aluminum powder, 0.1-0.5 part by weight of gallium powder and 1-2 parts by weight of niobium powder, adding 5-10 parts by weight of gasoline and 8-12 parts by weight of boric acid ester, and uniformly mixing to obtain a second suspension, wherein the mass of the second suspension is 0.1% of that of the layered mixture.
Preferably, in the preparation method of the high-coercivity magnet, the particle sizes of the copper powder, the aluminum powder, the gallium powder and the niobium powder are 5-10 mu m.
The invention at least comprises the following beneficial effects:
1. according to the preparation method of the high-coercivity magnet, the Nd-Fe-B powder and the nano rare earth powder are arranged in a layered mode to obtain the layered compound, and then the nano rare earth powder on each layer is uniformly diffused to Nd through heat treatment2Fe14B main phase grain boundary, uniformly coating Nd2Fe14The main phase B improves the anisotropy field of the magnet, and improves the coercive force and the remanence at the same time.
2. The preparation method of the high-coercivity magnet also comprises the steps of spraying the first suspension, adding nano oxides such as nano aluminum nitride, nano aluminum oxide and nano titanium oxide into ethanol during the preparation of the first suspension, then carrying out surface modification treatment through a silane coupling agent, uniformly dispersing the nano mixtures in acrylic acid, then spraying the first suspension on the surface of nano rare earth powder, uniformly dispersing the nano oxides on the surface of the nano rare earth powder, and allowing the nano oxides to enter Nd through surface permeation and diffusion during the heat treatment process2Fe14In the B main phase, the nano-oxide of each layer can be dispersed in the main phase Nd2Fe14And B, a nano-particle pinning effect is formed at the grain boundary, so that the growth of crystal grains is hindered, the crystal grains are refined, and the microstructure is improved, thereby improving the coercive force of the magnet.
3. The preparation method of the high-coercivity magnet further comprises the step of spraying a second suspension, wherein gallium powder and niobium powder in the second suspension enter Nd through surface penetration diffusion in the heat treatment process2Fe14The grain boundary and the grain boundary intersection of the B main phase improve the Nd-rich phase relative to Nd2Fe14The wetting action of the crystal grains of the B main phase and the Nd-rich phase react to improve the microstructure of the magnet, so that the magnetic decoupling action between the crystal grains of the main phase is better played, the coercive force is improved, and meanwhile, the added metal powder can also refine Nd2Fe14The coercive force of the magnet can be further improved by carrying out thermal diffusion on the crystal grains of the B main phase and the metal powder in a penetration mode compared with the traditional mode.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
FIG. 1 is a schematic structural view of a layered mixture according to the present invention;
fig. 2 is a schematic structural view of the layered mixture after spraying the first suspension according to the present invention.
Detailed Description
The present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.
It is to be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified.
Example 1
A method of manufacturing a high coercivity magnet comprising the steps of:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture;
and step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet. The vacuum heating treatment process is a continuous grain boundary diffusion and grain boundary phase homogenization treatment process and a stepped temperature rise heating mode.
According to the preparation method of the high-coercivity magnet, a layered mixture can be obtained through a powder distribution device 1 of an existing full-automatic oxygen-free press, as shown in fig. 1, the powder distribution device 1 is placed in a magnetic field, firstly, a layer of Nd-Fe-B powder layer 1 is arranged in the powder distribution device 1, then, nano rare earth powder 3 is sprayed on the Nd-Fe-B powder layer 2, then, the Nd-Fe-B powder layer 2 and the nano rare earth powder layer are sequentially and alternately arranged, in practice, the number of specific layers such as 6 layers and 8 layers of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is not limited, and in the embodiment, the total number of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is 6 layers. And (3) applying pressure to the layered mixture after obtaining the layered mixture, pressing the layered mixture into a fixed shape, then placing the layered mixture in a briquetting machine to be pressed into a pressed compact, and then placing the pressed compact in a vacuum heat treatment furnace to be subjected to heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m. The invention manufactures high maximum energy product (BH) by a grain boundary diffusion methodmaxAnd high intrinsic coercivity HcjThe magnet of (1) controls the amount of rare earth entering the magnet grain boundary through grain boundary diffusion by controlling the addition amount of rare earth, generates a grain boundary neodymium-rich phase, avoids excessive amount, replaces Nd, and generates Dy2Fe14B or Tb2Fe14B causes the anisotropy field of the magnet to be enhanced, and the remanence is greatly reduced while the coercivity is improved.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100 ℃ and keeping for 0.5 h; and then heating to 400 ℃ and keeping for 0.5h, then heating to 750 ℃ and keeping for 1h, then heating to 850 ℃ and keeping for 4h, continuing heating to 1030 ℃ and keeping for 3h, then cooling to 480 ℃ and keeping for 2h, and finally cooling to room temperature to obtain the high-coercivity magnet. The magnet prepared by the method has the oxygen content of less than 600ppm and the carbon content of less than 800 ppm.
Example 2
A method of manufacturing a high coercivity magnet comprising the steps of:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture; in this example, the Nd-Fe-B powder layer and the nano rare earth powder layer were 6 layers in total.
And step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is terbium, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.6%, and the particle size of the Nd-Fe-B powder is 3 mu m.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 150 ℃ and keeping for 1.5 h; and then heating to 550 ℃ and keeping for 1.5h, then heating to 780 ℃ and keeping for 2h, continuing heating to 890 ℃ and keeping for 12h, then heating to 1050 ℃ and keeping for 6h, then cooling to 520 ℃ and keeping for 4h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The preparation method of the high-coercivity magnet keeps the oxygen content in the vacuum heat treatment furnace to be less than 600ppm and the carbon content to be less than 800ppm in the heat treatment process. This can be achieved by introducing an inert gas into the vacuum heat treatment furnace.
Example 3
Step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture; in this example, the Nd-Fe-B powder layer and the nano rare earth powder layer were 6 layers in total.
And step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is rare earth dysprosium terbium alloy powder, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.7%, and the particle size of the Nd-Fe-B powder is 3.2 mu m.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 205 ℃ and keeping for 2 h; and then heating to 560 ℃ and keeping for 2h, then heating to 810 ℃ and keeping for 3h, continuing to heat to 920 ℃ and keeping for 15h, continuing to heat to 1070 ℃ and keeping for 10h, then cooling to 560 ℃ and keeping for 6h, and finally cooling to room temperature to obtain the high-coercivity magnet.
Example 4
A method of manufacturing a high coercivity magnet comprising the steps of:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture; as shown in fig. 1, a powder distribution device 1 is placed in a magnetic field, a layer of Nd-Fe-B powder layer 1 is firstly arranged in the powder distribution device 1, then nano rare earth powder 3 is sprayed on the Nd-Fe-B powder layer 2, then the Nd-Fe-B powder layer 2 is sprayed, the two kinds of powder are alternately arranged in sequence, in practice, the number of specific layers of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 can be 6 layers and 8 layers in total, and in the embodiment, the number of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is 6 layers in total.
And step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100 ℃ and keeping for 0.5 h; and then heating to 400 ℃ and keeping for 0.5h, then heating to 750 ℃ and keeping for 1h, then heating to 850 ℃ and keeping for 4h, continuing heating to 1030 ℃ and keeping for 3h, then cooling to 480 ℃ and keeping for 2h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The preparation method of the high-coercivity magnet comprises the steps of spraying nano rare earth powder on the upper surface of Nd-Fe-B powder in the first step, then spraying a first suspension on the nano rare earth powder, and then sequentially and alternately spraying Nd-Fe-B powder, nano rare earth powder and the first suspension on the upper surface of the first suspension to obtain a layered mixture; that is, each layer is composed of Nd-Fe-B powder, nano rare earth powder and the first suspension liquid which are alternately arranged up and down, and fig. 2 shows a schematic structural diagram of an Nd-Fe-B powder layer 2, a nano rare earth powder layer 3 and a first suspension liquid layer 4.
The preparation method of the first suspension comprises the following steps:
s1, mixing 2 parts by weight of nano aluminum nitride, 1 part by weight of nano aluminum oxide, 3 parts by weight of nano titanium oxide, 2 parts by weight of nano zinc oxide, 2 parts by weight of nano magnesium oxide, 1 part by weight of nano lanthanum oxide and 0.5 part by weight of nano bismuth oxide, adding 20 parts by weight of methanol and 50 parts by weight of water, uniformly stirring, adjusting the pH to 5 by using acetic acid, heating to 50 ℃ and keeping for 2 hours, adding 10 parts by weight of silane coupling agent, heating to 80 ℃ and keeping for 1 hour, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the S1 in 20 parts by weight of acrylic acid, and stirring for 10min at the stirring speed of 800r/min to obtain a first suspension;
wherein the mass fraction of the first suspension in the layered mixture is 0.1%.
The preparation method of the high-coercivity magnet further comprises the step of spraying a second suspension on the surface of the obtained layered mixture, wherein the preparation method of the second suspension comprises the following steps: mixing 5 parts by weight of copper powder, 3 parts by weight of aluminum powder, 0.1 part by weight of gallium powder and 1 part by weight of niobium powder, adding 5 parts by weight of gasoline and 8 parts by weight of boric acid ester, and uniformly mixing to obtain a second suspension. The mass of the second suspension was 0.1% of the mass of the layered mixture.
According to the preparation method of the high-coercivity magnet, the particle size of copper powder, aluminum powder, gallium powder and niobium powder is 5 microns.
Example 5
Step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture; in this example, the Nd-Fe-B powder layer and the nano rare earth powder layer were 6 layers in total.
And step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is rare earth dysprosium terbium alloy powder, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.7%, and the particle size of the Nd-Fe-B powder is 3.2 mu m.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 205 ℃ and keeping for 2 h; and then heating to 560 ℃ and keeping for 2h, then heating to 810 ℃ and keeping for 3h, continuing to heat to 920 ℃ and keeping for 15h, continuing to heat to 1070 ℃ and keeping for 10h, then cooling to 560 ℃ and keeping for 6h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The preparation method of the high-coercivity magnet comprises the steps of spraying Nd-Fe-B powder on the upper surface of the Nd-Fe-B powder, spraying a first suspension on the nanometer rare earth powder, and then alternately spraying Nd-Fe-B powder, nanometer rare earth powder and the first suspension on the upper surface of the first suspension in sequence to obtain a layered mixture;
the preparation method of the first suspension comprises the following steps:
s1, mixing 4 parts by weight of nano aluminum nitride, 3 parts by weight of nano aluminum oxide, 5 parts by weight of nano titanium oxide, 3 parts by weight of nano zinc oxide, 5 parts by weight of nano magnesium oxide, 2 parts by weight of nano lanthanum oxide and 1 part by weight of nano bismuth oxide, adding 25 parts by weight of methanol and 60 parts by weight of water, uniformly stirring, adjusting the pH to 6 by using acetic acid, heating to 60 ℃ and keeping for 3 hours, adding 15 parts by weight of silane coupling agent, heating to 90 ℃ and keeping for 2 hours, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the S1 in 25 parts by weight of acrylic acid, and stirring for 15min at a stirring speed of 800r/min to obtain a first suspension;
wherein the mass fraction of the first suspension in the layered mixture is 0.2%.
The preparation method of the high-coercivity magnet further comprises the step of spraying a second suspension on the surface of the obtained layered mixture, wherein the preparation method of the second suspension comprises the following steps: mixing 8 parts by weight of copper powder, 4 parts by weight of aluminum powder, 0.5 part by weight of gallium powder and 2 parts by weight of niobium powder, adding 10 parts by weight of gasoline and 12 parts by weight of boric acid ester, and uniformly mixing to obtain a second suspension. The mass of the second suspension was 0.1% of the mass of the layered mixture.
According to the preparation method of the high-coercivity magnet, the particle size of copper powder, aluminum powder, gallium powder and niobium powder is 10 microns.
Comparative example 1
A method for preparing a magnet comprises the following steps:
mixing Nd-Fe-B powder and nano rare earth powder to obtain a mixture; pressing the mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the magnet.
According to the preparation method of the magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m.
The preparation method of the magnet comprises the following heat treatment processes: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10- 3Pa, heating to 1030 ℃ and keeping for 8h, then cooling to 480 ℃ and keeping for 4h, and then cooling to room temperature to obtain the magnet.
Comparative example 2
A method for preparing a magnet comprises the following steps:
mixing Nd-Fe-B powder and nano rare earth powder to obtain a mixture; pressing the mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the magnet.
According to the preparation method of the magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m.
The preparation method of the magnet comprises the following heat treatment processes:
vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100 ℃ and keeping for 0.5 h; and then heating to 400 ℃ and keeping for 0.5h, then heating to 750 ℃ and keeping for 1h, continuing heating to 850 ℃ and keeping for 10h, then heating to 1030 ℃ and keeping for 3h, then cooling to 480 ℃ and keeping for 2h, and finally cooling to room temperature to obtain the high-coercivity magnet.
Comparative example 3
A method for preparing a magnet comprises the following steps:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture; as shown in fig. 1, a powder distribution device 1 is placed in a magnetic field, a layer of Nd-Fe-B powder layer 1 is firstly arranged in the powder distribution device 1, then nano rare earth powder 3 is sprayed on the Nd-Fe-B powder layer 2, then the Nd-Fe-B powder layer 2 is sprayed, the two kinds of powder are alternately arranged in sequence, in practice, the number of specific layers of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 can be 6 layers and 8 layers in total, and in the embodiment, the number of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is 6 layers in total.
And step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the high-coercivity magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m.
The preparation method of the high-coercivity magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100 ℃ and keeping for 0.5 h; and then heating to 400 ℃ and keeping for 0.5h, then heating to 750 ℃ and keeping for 1h, continuing heating to 850 ℃ and keeping for 10h, then heating to 1030 ℃ and keeping for 3h, then cooling to 480 ℃ and keeping for 2h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The preparation method of the high-coercivity magnet comprises the steps of spraying nano rare earth powder on the upper surface of Nd-Fe-B powder in the first step, then spraying a first suspension on the nano rare earth powder, and then sequentially and alternately spraying Nd-Fe-B powder, nano rare earth powder and the first suspension on the upper surface of the first suspension to obtain a layered mixture; that is, each layer is composed of Nd-Fe-B powder, nano rare earth powder and the first suspension liquid, which are arranged at intervals up and down, and FIG. 2 shows a schematic structural diagram of an Nd-Fe-B powder layer 2, a nano rare earth powder layer 3 and a first suspension liquid layer 4.
The preparation method of the first suspension comprises the following steps:
s1, mixing 2 parts by weight of nano aluminum nitride, 1 part by weight of nano aluminum oxide, 3 parts by weight of nano titanium oxide, 2 parts by weight of nano zinc oxide, 2 parts by weight of nano magnesium oxide, 1 part by weight of nano lanthanum oxide and 0.5 part by weight of nano bismuth oxide, adding 20 parts by weight of methanol and 50 parts by weight of water, uniformly stirring, adjusting the pH to 5 by using acetic acid, heating to 50 ℃ and keeping for 2 hours, adding 10 parts by weight of silane coupling agent, heating to 80 ℃ and keeping for 1 hour, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the S1 in 20 parts by weight of acrylic acid, and stirring for 10min at the stirring speed of 800r/min to obtain a first suspension;
wherein the mass fraction of the first suspension in the layered mixture is 0.1%.
According to the preparation method of the magnet, the oxygen content in the vacuum heat treatment furnace is kept to be less than 600ppm and the carbon content is kept to be less than 800ppm in the heat treatment process. This can be achieved by introducing an inert gas into the vacuum heat treatment furnace.
Comparative example 4
The difference from comparative example 3 is that Nd-Fe-B powder, nano rare earth powder and the first suspension are directly mixed, pressed into a compact and heat treated.
Comparative example 5
A method for preparing a magnet comprises the following steps:
uniformly mixing Nd-Fe-B powder, nano rare earth powder, the first suspension and the second suspension to obtain a mixture; pressing the mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the magnet.
According to the preparation method of the magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the mixture is 99.5%, the particle size of the Nd-Fe-B powder is 2.8 mu m, the mass fraction of the first suspension is 0.1%, and the mass fraction of the second suspension is 0.1%.
The preparation method of the magnet comprises the following specific steps of: vacuumizing the vacuum heat treatment furnace to pressureLess than 7 x 10-3Pa, heating to 100 ℃ and keeping for 0.5 h; and then heating to 400 ℃ and keeping for 0.5h, then heating to 750 ℃ and keeping for 1h, continuing heating to 850 ℃ and keeping for 10h, then cooling to 480 ℃ and keeping for 2h, then heating to 1030 ℃ and keeping for 3h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The preparation method of the first suspension comprises the following steps:
s1, mixing 2 parts by weight of nano aluminum nitride, 1 part by weight of nano aluminum oxide, 3 parts by weight of nano titanium oxide, 2 parts by weight of nano zinc oxide, 2 parts by weight of nano magnesium oxide, 1 part by weight of nano lanthanum oxide and 0.5 part by weight of nano bismuth oxide, adding 20 parts by weight of methanol and 50 parts by weight of water, uniformly stirring, adjusting the pH to 5 by using acetic acid, heating to 50 ℃ and keeping for 2 hours, adding 10 parts by weight of silane coupling agent, heating to 80 ℃ and keeping for 1 hour, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the S1 in 20 parts by weight of acrylic acid, and stirring for 10min at the stirring speed of 800r/min to obtain a first suspension.
The preparation method of the magnet comprises the following steps: mixing 5 parts by weight of copper powder, 3 parts by weight of aluminum powder, 0.1 part by weight of gallium powder and 1 part by weight of niobium powder, adding 5 parts by weight of gasoline and 8 parts by weight of boric acid ester, and uniformly mixing to obtain a second suspension.
According to the preparation method of the high-coercivity magnet, the particle size of copper powder, aluminum powder, gallium powder and niobium powder is 5 microns.
Comparative column 6
A method for preparing a magnet comprises the following steps:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture;
and step two, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain the high-coercivity magnet. The vacuum heating treatment process is a continuous grain boundary diffusion and grain boundary phase homogenization treatment process and a stepped temperature rise heating mode.
According to the preparation method of the high-coercivity magnet, a layered mixture can be obtained through a powder distribution device 1 of an existing full-automatic oxygen-free press, as shown in fig. 1, the powder distribution device 1 is placed in a magnetic field, firstly, a layer of Nd-Fe-B powder layer 1 is arranged in the powder distribution device 1, then, nano rare earth powder 3 is sprayed on the Nd-Fe-B powder layer 2, then, the Nd-Fe-B powder layer 2 and the nano rare earth powder layer are sequentially and alternately arranged, in practice, the number of specific layers such as 6 layers and 8 layers of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is not limited, and in the embodiment, the total number of the Nd-Fe-B powder layer 1 and the nano rare earth powder layer 2 is 6 layers. And (3) applying pressure to the layered mixture after obtaining the layered mixture, pressing the layered mixture into a fixed shape, then placing the layered mixture in a briquetting machine to be pressed into a pressed compact, and then placing the pressed compact in a vacuum heat treatment furnace to be subjected to heat treatment to obtain the high-coercivity magnet.
According to the preparation method of the magnet, the nano rare earth powder is rare earth dysprosium, the mass fraction of the Nd-Fe-B powder in the layered mixture is 99.5%, and the particle size of the Nd-Fe-B powder is 2.8 mu m. The invention manufactures high maximum energy product (BH) by a grain boundary diffusion methodmaxAnd high intrinsic coercivity HcjThe magnet of (1) controls the amount of rare earth entering the magnet grain boundary through grain boundary diffusion by controlling the addition amount of rare earth, generates a grain boundary neodymium-rich phase, avoids excessive amount, replaces Nd, and generates Dy2Fe14B or Tb2Fe14B causes the anisotropy field of the magnet to be enhanced, and the remanence is greatly reduced while the coercivity is improved.
The preparation method of the magnet comprises the following specific heat treatment steps in the second step: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3And Pa, heating to 1030 ℃ and keeping for 8h, then cooling to 480 ℃ and keeping for 4h, and finally cooling to room temperature to obtain the high-coercivity magnet.
The results of testing the remanence (KGs) and the intrinsic coercivity (KOe) of the magnets prepared in examples 1 to 4 and comparative examples 1 to 6 are shown in Table 1.
TABLE 1-remanence and intrinsic coercivity of magnets prepared in different examples
| Examples | Remanence (KGs) | Coercive force (KOe) |
| Example 1 | 13.88 | 24.31 |
| Example 2 | 13.91 | 26.62 |
| Example 3 | 14.11 | 27.83 |
| Example 4 | 14.25 | 35.38 |
| Comparative example 1 | 13.83 | 18.83 |
| Comparative example 2 | 13.86 | 19.52 |
| Comparative example 3 | 13.92 | 32.43 |
| Comparative example 4 | 13.82 | 22.35 |
| Comparative example 5 | 13.94 | 23.73 |
| Comparative example 6 | 13.87 | 24.28 |
As can be seen from Table 1, the remanence (KGs) and the coercive force (KOe) of the magnets prepared in examples 1 to 3 are both greater than those of comparative examples 1 to 2, which shows that the coercive force can be effectively improved and the remanence can be improved by performing segmented heat treatment on a layered compound obtained by layering Nd-Fe-B powder and nano rare earth powder. The remanence (KGs) and the coercive force (KOe) of the magnet obtained in example 4 are both larger than those of the magnets obtained in examples 1-3, which shows that the performance of the magnet can be improved by adding the first suspension and the second suspension. Comparison between comparative example 3 and comparative example 4 shows that the remanence and the coercive force of the magnet can be further improved by the first suspension through spraying and penetrating compared with the direct mixing. As can be seen from comparative example 5 and example 4, the remanence and coercive force of the magnet can be further improved by directly mixing the first suspension and the second suspension in a spray penetration manner.
While embodiments of the invention have been disclosed above, it is not limited to the applications listed in the description and the embodiments, which are fully applicable in all kinds of fields of application of the invention, and further modifications may readily be effected by those skilled in the art, so that the invention is not limited to the specific details without departing from the general concept defined by the claims and the scope of equivalents.
Claims (5)
1. The preparation method of the high-coercivity magnet is characterized by comprising the following steps of:
step one, taking Nd-Fe-B powder, spraying nano rare earth powder on the upper surface of the Nd-Fe-B powder, and then sequentially and alternately spraying Nd-Fe-B powder and nano rare earth powder on the upper surface of the nano rare earth powder to obtain a layered mixture;
secondly, pressing the layered mixture into a pressed blank, and placing the pressed blank in a vacuum heat treatment furnace for heat treatment to obtain a high-coercivity magnet;
wherein the heat treatment in the second step is specifically as follows: vacuumizing the vacuum heat treatment furnace to a pressure of less than 7 x 10-3Pa, heating to 100-205 ℃ and keeping for 0.5-2 h; heating to 400-560 ℃ and keeping for 0.5-3 h, heating to 750-810 ℃ and keeping for 1-3 h, continuing to heat to 850-920 ℃ and keeping for 4-15 h, continuing to heat to 1030-1070 ℃ and keeping for 3-10 h, then cooling to 480-560 ℃ and keeping for 2-6 h, and finally cooling to room temperature to obtain the high-coercivity magnet;
the mass fraction of Nd-Fe-B powder in the layered mixture in the first step is 99.5% -99.7%, and the particle size of the Nd-Fe-B powder is 2.8-3.2 mu m;
the mass fraction of the nano rare earth powder in the layered mixture in the first step is not more than 0.5%.
2. The method of producing a high coercive force magnet as claimed in claim 1, wherein the nano rare earth powder is one of rare earth dysprosium, rare earth terbium or rare earth dysprosium terbium alloy powder.
3. The method for producing a high coercive force magnet as claimed in claim 1, wherein in the first step, after the nano rare earth powder is sprayed on the upper surface of the Nd-Fe-B powder, the first suspension is sprayed on the nano rare earth powder, and then the Nd-Fe-B powder, the nano rare earth powder, and the first suspension are alternately sprayed on the upper surface of the first suspension in this order to obtain a layered mixture;
the preparation method of the first suspension comprises the following steps:
s1, mixing 2-4 parts by weight of nano aluminum nitride, 1-3 parts by weight of nano aluminum oxide, 3-5 parts by weight of nano titanium oxide, 2-3 parts by weight of nano zinc oxide, 2-5 parts by weight of nano magnesium oxide, 1-2 parts by weight of nano lanthanum oxide and 0.5-1 part by weight of nano bismuth oxide, adding 20-25 parts by weight of methanol and 50-60 parts by weight of water, uniformly stirring, adjusting the pH to 5-6 by using acetic acid, heating to 50-60 ℃ and keeping for 2-3 hours, adding 10-15 parts by weight of silane coupling agent, heating to 80-90 ℃ and keeping for 1-2 hours, cooling, filtering, washing and drying to obtain a nano mixture;
s2, dissolving the nano mixture obtained in the step S1 in 20-25 parts by weight of acrylic acid, and stirring at a stirring speed of 800r/min for 10-15 min to obtain a first suspension;
wherein the mass fraction of the first suspension in the layered mixture is 0.1-0.2%.
4. The method for producing a high coercive force magnet as claimed in claim 3, further comprising spraying a second suspension to the surface of the resultant layered mixture, the second suspension being produced by: mixing 5-8 parts by weight of copper powder, 3-4 parts by weight of aluminum powder, 0.1-0.5 part by weight of gallium powder and 1-2 parts by weight of niobium powder, adding 5-10 parts by weight of gasoline and 8-12 parts by weight of boric acid ester, and uniformly mixing to obtain a second suspension, wherein the mass of the second suspension is 0.1% of that of the layered mixture.
5. The method for producing a high coercive force magnet according to claim 4, wherein the particle diameter of the copper powder, the aluminum powder, the gallium powder, and the niobium powder is 5 to 10 μm.
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| CN112017835B (en) * | 2020-08-20 | 2023-03-17 | 合肥工业大学 | Low-heavy rare earth high-coercivity sintered neodymium-iron-boron magnet and preparation method thereof |
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