CN114743784A - Method for improving coercive force of sintered neodymium-iron-boron magnet by utilizing grain boundary diffusion technology - Google Patents
Method for improving coercive force of sintered neodymium-iron-boron magnet by utilizing grain boundary diffusion technology Download PDFInfo
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- 229910001172 neodymium magnet Inorganic materials 0.000 title claims abstract description 50
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000005324 grain boundary diffusion Methods 0.000 title claims abstract description 12
- 238000005516 engineering process Methods 0.000 title claims abstract description 7
- 238000005245 sintering Methods 0.000 claims description 34
- 239000011248 coating agent Substances 0.000 claims description 29
- 238000000576 coating method Methods 0.000 claims description 29
- 230000005291 magnetic effect Effects 0.000 claims description 27
- 239000000843 powder Substances 0.000 claims description 27
- QJVKUMXDEUEQLH-UHFFFAOYSA-N [B].[Fe].[Nd] Chemical compound [B].[Fe].[Nd] QJVKUMXDEUEQLH-UHFFFAOYSA-N 0.000 claims description 25
- 238000004321 preservation Methods 0.000 claims description 20
- 238000005496 tempering Methods 0.000 claims description 20
- 238000009792 diffusion process Methods 0.000 claims description 19
- 239000007788 liquid Substances 0.000 claims description 19
- 229910001279 Dy alloy Inorganic materials 0.000 claims description 15
- 229910052692 Dysprosium Inorganic materials 0.000 claims description 13
- 229910045601 alloy Inorganic materials 0.000 claims description 13
- 239000000956 alloy Substances 0.000 claims description 13
- 239000002270 dispersing agent Substances 0.000 claims description 11
- 238000009736 wetting Methods 0.000 claims description 11
- 239000002202 Polyethylene glycol Substances 0.000 claims description 10
- KBQHZAAAGSGFKK-UHFFFAOYSA-N dysprosium atom Chemical compound [Dy] KBQHZAAAGSGFKK-UHFFFAOYSA-N 0.000 claims description 10
- 229920001223 polyethylene glycol Polymers 0.000 claims description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 8
- 238000000280 densification Methods 0.000 claims description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 5
- 230000006835 compression Effects 0.000 claims description 5
- 238000007906 compression Methods 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 5
- 239000003960 organic solvent Substances 0.000 claims description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 4
- 238000001291 vacuum drying Methods 0.000 claims description 4
- 229910000531 Co alloy Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 239000003502 gasoline Substances 0.000 claims description 2
- 238000010902 jet-milling Methods 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 2
- 229920001577 copolymer Polymers 0.000 description 15
- 125000003903 2-propenyl group Chemical group [H]C([*])([H])C([H])=C([H])[H] 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 10
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 description 10
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- OMIGHNLMNHATMP-UHFFFAOYSA-N 2-hydroxyethyl prop-2-enoate Chemical compound OCCOC(=O)C=C OMIGHNLMNHATMP-UHFFFAOYSA-N 0.000 description 5
- 239000008367 deionised water Substances 0.000 description 5
- 229910021641 deionized water Inorganic materials 0.000 description 5
- 238000010992 reflux Methods 0.000 description 5
- 238000003756 stirring Methods 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 230000005389 magnetism Effects 0.000 description 3
- 229910052761 rare earth metal Inorganic materials 0.000 description 3
- BAPJBEWLBFYGME-UHFFFAOYSA-N Methyl acrylate Chemical compound COC(=O)C=C BAPJBEWLBFYGME-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
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- 230000005294 ferromagnetic effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000006247 magnetic powder Substances 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
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Classifications
-
- 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
-
- 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
- H01F41/0266—Moulding; Pressing
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Hard Magnetic Materials (AREA)
- Powder Metallurgy (AREA)
Abstract
The invention discloses a method for improving the coercive force of a sintered neodymium-iron-boron magnet by utilizing a grain boundary diffusion technology, which relates to the technical field of magnet materials.
Description
The technical field is as follows:
the invention relates to the technical field of magnet materials, in particular to a method for improving the coercive force of a sintered neodymium iron boron magnet by utilizing a grain boundary diffusion technology.
Background art:
the sintered Nd-Fe-B magnet has higher remanence and magnetic energy product, good dynamic recovery characteristic and high cost performance than other permanent magnets, and is widely applied to the fields of electronics, automobiles, computers, energy sources, medical appliances and the like. However, the sintered nd-fe-b magnet has a low coercive force and cannot meet the requirements of some high-end application fields.
The method for preparing the high-coercivity neodymium iron boron magnet commonly used in the field is to add heavy rare earth element Dy into the neodymium iron boron magnet, and the following three methods are mainly adopted at present: the first mode is that Dy-containing metal or alloy is directly added in the smelting process, Dy distribution in the magnet obtained by the method is uniform, but residual magnetism and magnetic energy product are obviously reduced while the coercive force of the magnet is improved due to non-ferromagnetic coupling of Dy and Fe; the second mode is to add metal or alloy powder containing Dy into the magnetic powder before the orientation pressing by a double-alloy mode, which has the advantages that the shape and the size of the magnet are not limited, but the Dy element is unevenly distributed, enriched in Nd-rich phase and less in Dy element content in grain boundary phase; the third mode is to diffuse and add Dy into the magnet through grain boundary rich Nd after the magnet is sintered by a grain boundary diffusion method, and the consumption of Dy elements is small, but the problem of uneven distribution of the Dy elements also exists, so that the comprehensive magnetic performance of the magnet is influenced.
The invention content is as follows:
the invention aims to solve the technical problem of providing a method for improving the coercive force of a sintered neodymium-iron-boron magnet by utilizing a grain boundary diffusion technology, which can obviously improve the coercive force of the sintered neodymium-iron-boron magnet under the condition of not reducing the residual magnetism of the sintered neodymium-iron-boron magnet, thereby optimizing the comprehensive magnetic property of the sintered neodymium-iron-boron magnet.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
the method for improving the coercive force of the sintered neodymium iron boron magnet by utilizing the grain boundary diffusion technology comprises the following steps:
(1) preparing neodymium-iron-boron-based quick-setting sheets by adopting a quick-setting sheet process;
(2) crushing neodymium-iron-boron-based quick-setting sheets by hydrogen and carrying out jet milling to prepare neodymium-iron-boron-based powder;
(3) carrying out magnetic field orientation compression on the neodymium iron boron-based powder, and carrying out vacuum semi-dense sintering in a vacuum sintering furnace to obtain a blank;
(4) uniformly mixing dysprosium alloy powder, an organic solvent and a wetting dispersant to obtain a diffusion liquid;
(5) coating the diffusion liquid on the surface of the blank, and performing vacuum drying to obtain a blank of the dysprosium-containing alloy coating;
(6) and carrying out vacuum densification sintering and tempering on the blank containing the dysprosium alloy coating in a vacuum sintering furnace to obtain the sintered neodymium iron boron magnet.
The average thickness of the neodymium iron boron-based quick-setting flake is 0.3-0.35 mm.
The average grain diameter of the neodymium iron boron-based powder is 3-5 mu m.
The magnetic field adopts a direct current pulse magnetic field, and the pressure of the magnetic field is 1.8-2.0T.
The sintering temperature in the vacuum semi-dense sintering is 900-950 ℃, the heat preservation time is 1-3h, and the density is 90-95%.
The dysprosium alloy powder is one or more of Dy-Cu, Dy-Al, Dy-Ni and Dy-Co alloy powder, the average grain diameter is 3-5 mu m, and the mass fraction of Dy is 70-80%.
The mass fraction of the dysprosium alloy powder in the diffusion liquid is 2-5%.
The organic solvent is one or more of ethanol, acetone and gasoline.
The wetting dispersant is polyethylene glycol, and the mass fraction of the wetting dispersant in the diffusion liquid is 2-5%.
Dysprosium alloy powder and an organic solvent are mixed to form a suspension, the uniformity and stability of metal particles in the suspension are poor, the uniform coating of a diffusion liquid on the surface of a magnet cannot be ensured, the thickness consistency of a formed coating and the distribution uniformity of metal elements in the coating are directly influenced, and the subsequent grain boundary diffusion effect is further influenced. Therefore, the wetting dispersant is added into the diffusion liquid, so that the uniformity and the stability of the diffusion liquid can be improved, the wettability of the diffusion liquid on the surface of the magnet can be improved, the thickness of the coating and the consistency of the thickness of the coating are ensured, the distribution uniformity of metal elements in the coating is improved, and the comprehensive magnetic performance of the magnet is improved through grain boundary diffusion subsequently.
The drying temperature in the vacuum drying is 50-100 ℃, and the heat preservation time is 1-3 h.
The thickness of the dysprosium alloy coating is 50-100 μm.
The sintering temperature during the vacuum densification sintering is 1050-.
The tempering is divided into two stages, the first-stage tempering temperature is 900-950 ℃, and the heat preservation time is 1-3 h; the secondary tempering temperature is 500-550 ℃, and the heat preservation time is 2-4 h.
Polyethylene glycol is a wetting dispersant commonly used in the coating field, but the dispersion effect of polyethylene glycol on dysprosium alloy powder is not good when the polyethylene glycol is applied to the invention, so that the invention also adopts an allyl thiourethane-hydroxyethyl acrylate copolymer as the wetting dispersant, namely the wetting dispersant is the allyl thiourethane-hydroxyethyl acrylate copolymer, and the mass fraction of the wetting dispersant in the diffusion liquid is 2-5%.
The weight average molecular weight of the allyl thiourethane-hydroxyethyl acrylate copolymer is 2000-3000, and the structural formula is as follows:
m and n are polymerization degrees, and m: n is more than or equal to 2.
The preparation method of the allyl thiourethane-hydroxyethyl acrylate copolymer comprises the following steps: adding 1/3-1/2 potassium persulfate into deionized water, heating to 60-70 ℃, stirring for dissolving, adding allyl thiourethane, hydroxyethyl acrylate and the rest potassium persulfate, heating to a reflux state, reacting at constant temperature, and distilling under reduced pressure to remove water to obtain the allyl thiourethane-hydroxyethyl acrylate copolymer.
The beneficial effects of the invention are: according to the invention, the heavy rare earth element Dy is introduced into the grain boundary phase and the main phase crystal grain surface layer by using a grain boundary diffusion mode, the distribution uniformity of the heavy rare earth element Dy in the sintered NdFeB magnet is improved, and the coercive force of the sintered NdFeB magnet can be obviously improved under the condition of not reducing the residual magnetism of the sintered NdFeB magnet, so that the comprehensive magnetic property of the sintered NdFeB magnet is optimized, and the application range of the sintered NdFeB magnet is widened.
The specific implementation mode is as follows:
in order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.
The components and mass percentages of the neodymium iron boron based powder in the following examples and comparative examples are Nd 13.5%, Co 0.2%, B5.0%, Cu 0.1%, and the balance of Fe.
Example 1
(1) A quick-setting flake process is adopted to prepare neodymium-iron-boron-based quick-setting flakes with the average thickness of 0.32 mm.
(2) The neodymium-iron-boron-based quick-setting sheet is crushed by hydrogen and milled by airflow to obtain neodymium-iron-boron-based powder with the average grain diameter of 3.5 mu m.
(3) Carrying out orientation compression on the neodymium iron boron-based powder through a magnetic field, wherein the magnetic field adopts a direct current pulse magnetic field, the magnetic field pressure is 2.0T, and carrying out vacuum semi-compact sintering in a vacuum sintering furnace, the sintering temperature is 950 ℃, the heat preservation time is 2h, and the density is 95%, so as to obtain a blank.
(4) Uniformly mixing Dy-Co alloy powder (75 mass percent of Dy) with the mass percent of 3% and the average grain diameter of 3-5 mu m, absolute ethyl alcohol and 3% by mass of polyethylene glycol to obtain the diffusion liquid.
(5) And coating the diffusion liquid on the surface of the blank, and drying in vacuum at the drying temperature of 80 ℃ for 3h to obtain the blank of the dysprosium-containing alloy coating, wherein the thickness of the dysprosium alloy coating is 80 mu m.
(6) Carrying out vacuum densification sintering and tempering on the blank of the dysprosium-containing alloy coating in a vacuum sintering furnace, wherein the sintering temperature is 1050 ℃, and the heat preservation time is 3 h; tempering is divided into two stages, wherein the temperature of the first stage tempering is 900 ℃, and the heat preservation time is 3 h; the secondary tempering temperature is 550 ℃, and the heat preservation time is 3 hours, so that the sintered neodymium iron boron magnet is obtained.
Example 2
(1) The neodymium iron boron-based quick-setting flake with the average thickness of 0.32mm is prepared by adopting a quick-setting flake process.
(2) The neodymium-iron-boron-based quick-setting sheet is crushed by hydrogen and milled by airflow to obtain neodymium-iron-boron-based powder with the average grain diameter of 3.5 mu m.
(3) Carrying out orientation compression on the neodymium iron boron-based powder through a magnetic field, wherein the magnetic field adopts a direct current pulse magnetic field, the magnetic field pressure is 2.0T, and carrying out vacuum semi-compact sintering in a vacuum sintering furnace, the sintering temperature is 900 ℃, the heat preservation time is 3h, and the density is 92%, so as to obtain a blank.
(4) Uniformly mixing 5 mass percent of Dy-Ni alloy powder (the mass percent of Dy is 70%) with the average grain diameter of 3-5 mu m, absolute ethyl alcohol and 5 mass percent of polyethylene glycol to obtain the diffusion liquid.
(5) And coating the diffusion liquid on the surface of the blank, and drying in vacuum at the drying temperature of 100 ℃ for 2h to obtain the blank of the dysprosium-containing alloy coating, wherein the thickness of the dysprosium alloy coating is 60 mu m.
(6) Carrying out vacuum densification sintering and tempering on the blank of the dysprosium-containing alloy coating in a vacuum sintering furnace, wherein the sintering temperature is 1050 ℃, and the heat preservation time is 3 h; tempering is divided into two stages, the first-stage tempering temperature is 950 ℃, and the heat preservation time is 2 hours; and the secondary tempering temperature is 500 ℃, and the heat preservation time is 4 hours, so that the sintered neodymium-iron-boron magnet is obtained.
Example 3
(1) The neodymium iron boron-based quick-setting flake with the average thickness of 0.32mm is prepared by adopting a quick-setting flake process.
(2) The neodymium-iron-boron-based quick-setting sheet is crushed by hydrogen and milled by airflow to obtain neodymium-iron-boron-based powder with the average grain diameter of 3.5 mu m.
(3) Carrying out orientation compression on the neodymium iron boron-based powder through a magnetic field, wherein the magnetic field adopts a direct current pulse magnetic field, the magnetic field pressure is 1.8T, and carrying out vacuum semi-compact sintering in a vacuum sintering furnace, the sintering temperature is 900 ℃, the heat preservation time is 3h, and the density is 90%, so as to obtain a blank.
(4) Uniformly mixing Dy-Cu alloy powder (the mass fraction of Dy is 80%) with the mass fraction of 2% and the average grain diameter of 3-5 μm, absolute ethyl alcohol and polyethylene glycol with the mass fraction of 3% to obtain the diffusion liquid.
(5) And coating the diffusion liquid on the surface of the blank, and drying in vacuum at the drying temperature of 80 ℃ for 3h to obtain the blank of the dysprosium-containing alloy coating, wherein the thickness of the dysprosium alloy coating is 100 mu m.
(6) Carrying out vacuum densification sintering and tempering on the blank of the dysprosium-containing alloy coating in a vacuum sintering furnace, wherein the sintering temperature is 1100 ℃, and the heat preservation time is 3 h; tempering is divided into two stages, the first-stage tempering temperature is 900 ℃, and the heat preservation time is 2 hours; and (4) performing secondary tempering at 500 ℃ for 3h to obtain the sintered neodymium-iron-boron magnet.
Example 4
Example 4 was obtained by replacing the polyethylene glycol of example 2 with the allylthiourethane-hydroxyethyl acrylate copolymer prepared as follows.
Adding 1.5mmol of potassium persulfate into deionized water, heating to 60-70 ℃, stirring for dissolving, adding 0.1mol of allyl thiourethane, 0.05mol of hydroxyethyl acrylate and 1.5mmol of potassium persulfate, heating to a reflux state, reacting at constant temperature, and distilling under reduced pressure to remove water to obtain the allyl thiourethane-hydroxyethyl acrylate copolymer.
Example 5
Example 5 was obtained by replacing the polyethylene glycol of example 2 with the allylthiourethane-hydroxyethyl acrylate copolymer prepared as follows.
Adding 1.5mmol of potassium persulfate into deionized water, heating to 60-70 ℃, stirring for dissolving, adding 0.15mol of allyl thiourethane, 0.05mol of hydroxyethyl acrylate and 1.5mmol of potassium persulfate, heating to a reflux state, reacting at constant temperature, and distilling under reduced pressure to remove water to obtain the allyl thiourethane-hydroxyethyl acrylate copolymer.
Comparative example 1
Comparative example 1 was obtained by replacing the allyl thiourethane-hydroxyethyl acrylate copolymer in example 1 with a methyl acrylate-hydroxyethyl acrylate copolymer prepared as follows.
Adding 1.5mmol of potassium persulfate into deionized water, heating to 60-70 ℃, stirring for dissolving, adding 0.15mol of methyl acrylate, 0.05mol of hydroxyethyl acrylate and 1.5mmol of potassium persulfate, heating to a reflux state, reacting at constant temperature, and distilling under reduced pressure to remove water to obtain the methyl acrylate-hydroxyethyl acrylate copolymer.
Comparative example 2
Comparative example 2 was obtained by replacing the allyl thiourethane-hydroxyethyl acrylate copolymer in example 1 with an acrylamide-hydroxyethyl acrylate copolymer prepared as follows.
Adding 1.5mmol of potassium persulfate into deionized water, heating to 60-70 ℃, stirring for dissolving, adding 0.15mol of acrylamide, 0.05mol of hydroxyethyl acrylate and 1.5mmol of potassium persulfate, heating to a reflux state, reacting at a constant temperature, and distilling under reduced pressure to remove water to obtain the acrylamide-hydroxyethyl acrylate copolymer.
Comparative example 3
Comparative example 3 was obtained by eliminating steps (4) and (5) in example 1, i.e., without preparing a dysprosium-containing alloy coating.
The magnetic properties of the magnet were measured using an HS-40 type B-H loop tester and the results are shown in Table 1. The test was performed in triplicate and the average was taken.
TABLE 1
| Remanence (kGs) | Coercive force (kOe) | |
| Example 1 | 12.47 | 17.95 |
| Example 2 | 12.50 | 20.64 |
| Example 3 | 12.48 | 18.73 |
| Example 4 | 12.51 | 21.47 |
| Example 5 | 12.52 | 21.89 |
| Comparative example 1 | 10.86 | 16.58 |
| Comparative example 2 | 10.73 | 16.24 |
| Comparative example 3 | 12.50 | 13.72 |
As can be seen from Table 1, the coercive force of the sintered NdFeB magnet can be obviously improved through the preparation of the dysprosium-containing alloy coating and the grain boundary diffusion, and the remanence of the sintered NdFeB magnet cannot be obviously reduced.
The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (10)
1. The method for improving the coercive force of the sintered neodymium iron boron magnet by utilizing the grain boundary diffusion technology is characterized by comprising the following steps of: the method comprises the following steps:
(1) preparing neodymium-iron-boron-based quick-setting sheets by adopting a quick-setting sheet process;
(2) crushing neodymium-iron-boron-based quick-setting sheets by hydrogen and preparing neodymium-iron-boron-based powder by jet milling;
(3) carrying out magnetic field orientation compression on the neodymium iron boron-based powder, and carrying out vacuum semi-dense sintering in a vacuum sintering furnace to obtain a blank;
(4) mixing dysprosium alloy powder, an organic solvent and a wetting dispersant uniformly to obtain a diffusion liquid;
(5) coating the diffusion liquid on the surface of the blank, and performing vacuum drying to obtain a blank of the dysprosium-containing alloy coating;
(6) and carrying out vacuum densification sintering and tempering on the blank containing the dysprosium alloy coating in a vacuum sintering furnace to obtain the sintered neodymium iron boron magnet.
2. The method of claim 1, wherein: the average thickness of the neodymium iron boron-based quick-setting flake is 0.3-0.35 mm; the average grain diameter of the neodymium iron boron based powder is 3-5 mu m.
3. The method of claim 1, wherein: the magnetic field adopts a direct current pulse magnetic field, and the pressure of the magnetic field is 1.8-2.0T.
4. The method of claim 1, wherein: the dysprosium alloy powder is one or more of Dy-Cu, Dy-Al, Dy-Ni and Dy-Co alloy powder, the average grain diameter is 3-5 mu m, and the mass fraction of Dy is 70-80%; the mass fraction of the dysprosium alloy powder in the diffusion liquid is 2-5%.
5. The method of claim 1, wherein: the organic solvent is one or more of ethanol, acetone and gasoline.
6. The method of claim 1, wherein: the wetting dispersant is polyethylene glycol, and the mass fraction of the wetting dispersant in the diffusion liquid is 2-5%.
7. The method of claim 1, wherein: the drying temperature in the vacuum drying is 50-100 ℃, and the heat preservation time is 1-3 h.
8. The method of claim 1, wherein: the thickness of the dysprosium alloy coating is 50-100 μm.
9. The method of claim 1, wherein: the sintering temperature during the vacuum semi-dense sintering is 900-950 ℃, the heat preservation time is 1-3h, and the density is 90-95%; the sintering temperature during the vacuum densification sintering is 1050-1100 ℃, and the heat preservation time is 2-4 h.
10. The method of claim 1, wherein: the tempering is divided into two stages, the first-stage tempering temperature is 900-950 ℃, and the heat preservation time is 1-3 h; the secondary tempering temperature is 500-550 ℃, and the heat preservation time is 2-4 h.
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