CN115274240A - Preparation method of high-performance low-cost sintered neodymium-iron-boron magnet - Google Patents
Preparation method of high-performance low-cost sintered neodymium-iron-boron magnet Download PDFInfo
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- CN115274240A CN115274240A CN202210437902.6A CN202210437902A CN115274240A CN 115274240 A CN115274240 A CN 115274240A CN 202210437902 A CN202210437902 A CN 202210437902A CN 115274240 A CN115274240 A CN 115274240A
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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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- B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
- B41M1/00—Inking and printing with a printer's forme
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
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- B41M1/00—Inking and printing with a printer's forme
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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
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Abstract
The invention discloses a high-performance low-cost sintered neodymium iron boron and a preparation method thereof, wherein the corners of a magnet are small in demagnetization factor and not easy to demagnetize, and the middle part is large in demagnetization factor and easy to demagnetize, so that the demagnetization resistance of different parts of the magnet is different, and by combining the demagnetization characteristic of the magnet, nano heavy rare earth powder or heavy rare earth compound powder with different thicknesses is printed by performing differential screen printing on the surface of the magnet, and then grain boundary diffusion is performed, so that the intrinsic coercive force of different parts of the magnet is improved differently, the requirements of customers on irreversible magnetic loss are met, and the usage amount of heavy rare earth elements is greatly reduced.
Description
Technical Field
The invention belongs to the technical field of sintered neodymium iron boron rare earth permanent magnet materials, and particularly relates to a low-cost high-performance sintered neodymium iron boron magnet which is prepared by printing nano rare earth powder or rare earth compound powder on the surface of the magnet by adopting a screen printing technology and then diffusing the nano rare earth powder or the rare earth compound powder through a crystal boundary.
Background
With the wider application field of the sintered Nd-Fe-B permanent magnet, the sintered Nd-Fe-B permanent magnet has a great application breakthrough in the fields of automobile motors, wind driven generators, servo motors, linear motors and the like in recent years. However, since rare earth is a strategic national resource, especially Tb, dy, etc., the reserves are not large and large, and the price is expensive, and in order to meet the higher working temperature of various motors, the existing sintered nd-fe-b manufacturers have to adopt a coating method to coat dysprosium or terbium compound powder on the surface of the magnet, and then perform grain boundary diffusion; although the material utilization rate can reach more than 90 percent by adopting the method, the differential coating of the surface of the magnet is difficult to realize, namely, the surface of the magnet can only be coated with the thickness without difference. However, as is known, the magnetic lines of force of the magnet always start from the N pole, pass through the external medium and enter the S pole. In the interior of the magnet, the magnetic force lines also point to the S pole from the N pole, which is equivalent to that a magnetic field Hd with the direction opposite to the magnetic induction B of the magnet is formed in the interior of the magnet, and in a simple way, the smaller the orientation direction of the magnet or the larger the diameter-height ratio is, the larger the demagnetization factor is; conversely, the longer the magnet orientation direction or the smaller the diameter-to-height ratio, the smaller the demagnetization factor. That is to say, the corner part has a smaller demagnetization factor and is not easy to demagnetize, and the middle part has a larger demagnetization factor and is easy to demagnetize, so that the intrinsic coercive force of the corner part of the magnet after crystal boundary diffusion is excessive due to non-differential coating, that is, the rare earth material used on the corner is too much, the waste of the rare earth material is caused, the bonding force is poor easily to occur in coating, and the bonding force of the powder coated on individual products is poor, so that unqualified products can be generated in batch products. At present, a sintered Nd-Fe-B manufacturer still adopts magnetron sputtering to carry out magnetron sputtering on pure dysprosium or pure terbium to the surface of a magnet, and then carries out grain boundary diffusion; the method has a good effect of improving the intrinsic coercive force of the magnet, but has the biggest problem of low material utilization rate, incapability of sputtering all dysprosium or terbium onto the surface of the magnet, generally about 30 percent of target material utilization rate, and expensive target material processing cost although residual targets can be processed into target materials.
Disclosure of Invention
Aiming at the problems in the existing grain boundary diffusion type sintered neodymium iron boron technology, the invention aims to design and provide a preparation method of high-performance low-cost sintered neodymium iron boron. The neodymium iron boron sheet which contains no heavy rare earth elements as much as possible and has the total rare earth content controlled below 30.5 percent by weight is subjected to screen printing of nano rare earth powder or rare earth compound powder and then subjected to grain boundary diffusion, so that the intrinsic coercive force of the magnet is effectively improved, and the use amount of the rare earth elements is greatly reduced.
The preparation method of the sintered neodymium-iron-boron magnet with high performance and low cost comprises the following steps:
1) Smelting: weighing and proportioning industrial pure metal raw materials according to NdFeB alloy components in percentage by mass, and quickly quenching a target raw material into an alloy cast sheet by adopting a vacuum quick-setting smelting furnace; the base alloy contains no heavy rare earth elements as much as possible, and the total amount of rare earth elements is controlled to 30.5% by weight or less, wherein the base alloy of the sintered NdFeB magnet contains Re in percentage by massaMbFe100-a-b-c-dBcCod(ii) a Re of the base alloy is two or more of Pr, nd, tb, dy, ho, gd, Y and Ce; m of the matrix alloy is two or more of Al, cu, ga, zr, nb and Ti; wherein a =28-32wt%, b =0-3wt%, c =0.85-1wt%, d =0.1-4wt%;
2) Hydrogen crushing: the method comprises the steps of performing hydrogen crushing on neodymium iron boron alloy sheets by using a hydrogen crushing furnace, performing hydrogen crushing for 2-4 hours, then performing dehydrogenation for 4-8 hours at the dehydrogenation temperature of 450-550 ℃, cooling the alloy cast sheets after dehydrogenation to 35 ℃, stopping cooling, standing for 60-120 minutes, introducing 20-100ppm pure oxygen into a hydrogen crushing reaction device after the cooling temperature is not increased, wherein the inside of the furnace has a certain temperature, the reaction kettle of the hydrogen crushing furnace does not rotate, and coarse powder is stirred ceaselessly during oxygen supplement, so that the coarse powder is uniformly and controllably absorbed oxygen. Stopping adding pure oxygen when the oxygen content in the neodymium iron boron alloy powder is below 10ppm, and continuously cooling to obtain neodymium iron boron alloy coarse powder after the oxygen content is stable and does not fluctuate;
3) Milling powder by airflow: adding a lubricant accounting for 0.1-0.5% of the mass of the coarse powder in the process of mixing the neodymium iron boron alloy coarse powder; after the coarse powder is stirred and mixed, further grinding the coarse powder by using a fluidized bed jet mill, wherein oxygen is not supplemented during the jet mill, and grinding the coarse powder into fine neodymium iron boron alloy powder; adding an antioxidant into the prepared neodymium iron boron alloy fine powder and uniformly mixing; the SMD of the alloy powder is 2.6-3.0 μm, the D90/D10 is less than 4.8, the D10 is more than 1.8, and the distribution value of 3-10 μm is more than 75%;
4) Stirring: adding a lubricant accounting for 0.1-0.5% of the mass of the coarse powder into the fine neodymium iron boron alloy powder, and mixing by adopting a three-dimensional stirrer;
5) Orientation forming: carrying out magnetic field orientation molding on the alloy powder under the protection of nitrogen to obtain a pressed compact;
6) Sintering and tempering: and (4) after vacuum sintering and tempering treatment, cooling the pressed compact to obtain the neodymium iron boron magnet. Sintering refers to sintering at 1000-1100 ℃ for 2-5h, and then tempering at 800-900 ℃ for 1-2 h and 450-550 ℃ for 2-5h; carrying out performance detection and oxygen content detection on the magnet; preferably, because the subsequent grain boundary diffusion is tempering, if the magnet is produced in continuous batch, the tempering can not be carried out after the base magnet is sintered on the premise that the processes of all the procedures are stable, and the density of the magnet is detected and monitored to be abnormal after the magnet is taken out of the furnace; the magnet which is not tempered has better effect of carrying out grain boundary diffusion;
7) Processing: processing the magnet into a thin magnetic sheet with the thickness of 1-10mm, wherein the magnetic sheet can be a square sheet, a tile or a round sheet;
8) Screen printing: carrying out silk-screen printing on nano rare earth powder or rare earth compound powder on a magnetic sheet, and putting the magnetic sheet with two surfaces subjected to silk-screen printing into a molybdenum sintering box in a nitrogen protection box;
9) Grain boundary diffusion: and (3) putting the magnetic sheets filled into the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 800-950 ℃, preserving heat for 8-20h for grain boundary diffusion, and tempering at 450-550 ℃ for 2-5h.
Further, the screen printing ink is a suspension of nano rare earth powder or rare earth compound powder, wherein the ratio of powder: the mass ratio of the organic solution is 30-50%:50 to 70 percent; the rare earth elements of the nano rare earth powder or the rare earth compound powder are praseodymium, neodymium, dysprosium, terbium, holmium and the like. Preferably, heavy rare earth elements dysprosium and terbium; the organic solution is selected from alcohols, and preferably, the organic solvent is absolute ethyl alcohol.
Further, the compound powder of rare earth includes, but is not limited to, common rare earth hydrides, rare earth fluorides or rare earth oxides. The purity of the nano rare earth powder or rare earth compound powder is more than 99.95 percent, and the particle size of the powder is 0.5-3um.
Further, the gas used in the screen printing is an inert gas such as nitrogen or argon.
Further, the screen printing is a printing of local printing or thickness differentiation according to setting, not a printing of no difference in overall thickness.
Furthermore, the oxygen content of the magnet to be printed is detected and monitored, the oxygen content of the magnet is less than or equal to 900ppm, and if the oxygen content of the magnet exceeds the value, the addition amount of the rare earth is properly compensated during screen printing. If the oxygen content of the magnet is 1000ppm, the oxygen content exceeds the standard 100ppm, namely 0.01 percent, then the rare earth addition amount needs to compensate 1 to 3 times of the overproof oxygen content, namely 0.01 to 0.03 percent of the rare earth addition amount.
According to the invention, the screen printing can be carried out on the surface of the magnet in a differentiated manner by setting, namely, the thicknesses of powder materials printed at different positions can be different, so that the waste of rare earth materials caused by the fact that the thicknesses of the whole surface coating and the magnetron sputtering are the same in the traditional coating method and the magnetron sputtering method can be avoided. Because the demagnetization factors of the corner parts of the magnet are small and not easy to demagnetize, and the demagnetization factors of the middle parts are large and easy to demagnetize, the demagnetization resistance of different parts of the magnet are different, and the screen printing quantity can be different by combining the demagnetization characteristic of the magnet, so that the use quantity of the nano rare earth powder or the compound powder of the rare earth can be greatly reduced, and the use quantity of the rare earth elements can be greatly reduced. For example, the tile-shaped magnetic sheet can be combined with the actual use condition of a client, for example, the inner arc is attached to the rotor, so that the inner arc part is not easy to demagnetize relatively, the printing quantity of the outer arc can be ensured, the printing quantity of the inner arc is reduced, and the use quantity of the nano rare earth powder or the rare earth compound powder can be effectively reduced.
Drawings
FIG. 1 is a schematic diagram of screen printing of nanometer heavy rare earth powder or heavy rare earth compound powder with different thicknesses on different parts of a magnet;
wherein, a-is a magnetic thin sheet, the printing thickness of the heavy rare earth or heavy rare earth compound of the region pointed by b is 6um, the printing thickness of the heavy rare earth or heavy rare earth compound of the region pointed by c is 10um, the printing thickness of the heavy rare earth or heavy rare earth compound of the region pointed by d is 14um, and the printing thickness of the region pointed by e is not printed.
Detailed Description
The present invention will be described in further detail with reference to specific examples to better understand the technical solution.
Example 1
S1, smelting
The mass percentage of the components of the matrix alloy is ReaMbFe100-a-b-c-dBcCod；
Re of the base alloy is Pr, nd, gd, the total amount of Re rare earth of the base alloy a =31wt%, wherein Gd is 3.5 wt%, the balance 25:75 of PrNd;
m of the base alloy is Al, cu, ga, zr, b =1.4wt%, wherein Al =0.9 wt%, cu =0.2 wt%, ga =0.1 wt%, zr =0.2 wt%;
b, c =0.92wt% of the base alloy;
co of the base alloy, d =0.8wt%;
fe of the base alloy, 65.88wt%.
The industrial pure metal raw materials are weighed and proportioned according to the alloy components in percentage by mass, and the target raw materials are quickly quenched into alloy cast sheets by a vacuum quick-setting smelting furnace.
S2, hydrogen crushing
The method comprises the following steps of performing hydrogen crushing on neodymium iron boron alloy sheets by using a hydrogen crushing furnace, performing hydrogen crushing for 4 hours, then performing dehydrogenation for 4 hours, wherein the dehydrogenation temperature is 550 ℃, cooling the alloy cast sheets after dehydrogenation to 35 ℃, stopping cooling and standing for 80 minutes, introducing 40ppm pure oxygen into a hydrogen crushing reaction device after the cooling temperature is not increased, wherein a certain temperature exists in the furnace, the reaction kettle of the hydrogen crushing furnace is not rotated, and coarse powder is continuously stirred during oxygen supplement, so that the coarse powder is uniform and can absorb oxygen controllably. And stopping adding pure oxygen when the oxygen content in the neodymium iron boron alloy coarse powder is below 10ppm, and continuously cooling to obtain the neodymium iron boron alloy coarse powder after the oxygen content is stable and does not fluctuate.
S3, airflow milling powder
Adding a lubricant accounting for 0.1 percent of the mass of the coarse powder in the process of mixing the neodymium iron boron alloy coarse powder; after stirring and mixing the coarse powder, further grinding the coarse powder by using a fluidized bed jet mill, wherein oxygen is not supplemented during the jet mill, and grinding the coarse powder into fine neodymium iron boron alloy powder; adding an antioxidant into the prepared neodymium iron boron alloy fine powder and uniformly mixing; the alloy powder SMD was 2.82 μm with D90/D10=4.65, D10=1.81,3-10 μm distribution =78.1%.
S4, stirring;
adding a lubricant accounting for 0.1 percent of the mass of the coarse powder into the fine neodymium iron boron alloy powder, and mixing for 2 hours by adopting a three-dimensional stirrer;
s5, orientation forming
Carrying out magnetic field orientation molding on the alloy powder under the protection of nitrogen to obtain a pressed compact;
s6, sintering and tempering
And (4) after vacuum sintering and tempering treatment, cooling the pressed compact to obtain the neodymium iron boron magnet. Sintering refers to sintering at 1090 ℃ for 4.5h, and then tempering at 900 ℃ for 2h and 500 ℃ for 4.5h; and (5) carrying out performance detection and oxygen content detection on the magnet.
S7, processing
Processing the magnet into thin magnetic sheets with the size specification of 50 × 40 × 3mm required by customers;
s8, screen printing
Screen-printing dysprosium oxide powder and absolute ethyl alcohol turbid liquid on the magnetic sheet, specifically printing the thicknesses of different areas as shown in figure 1, and putting the magnetic sheet with two surfaces subjected to screen printing into a molybdenum sintering box in a nitrogen protection box;
s9, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 12 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 1 was prepared.
Comparative example 1
A1 coating dysprosium oxide
Coating dysprosium oxide on the thin magnetic sheet with the size specification of 50 × 40 × 3mm prepared in the step S7 of the example 1, wherein the thickness of the double-side coating is 14um, and then filling the thin magnetic sheet into a molybdenum sintering box;
a2, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 12 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 2 was prepared.
Example 1 used screen printing of the present invention with dysprosium oxide powder differentially printed in the ranges and thicknesses shown in fig. 1, comparative example 1 directly used the base magnetic sheet prepared in example 1, and comparative example 1 double coated with dysprosium oxide powder of 14um each using a conventional coating method, the process parameters, magnetic properties and irreversible magnetic losses of both were plotted as in table 1:
TABLE 1
| Item | Sample No. 1 | Sample 2 |
| Magnet weight gain after diffusion (g) | 0.2039 | 0.4374 |
| Residual magnetism Br (KGs) at20 DEG C | 12.75 | 12.63 |
| Intrinsic coercive force Hcj (KOe) at20 DEG C | 20.70 | 22.90 |
| (BH)m(MGOe)at20℃ | 40.10 | 39.60 |
| Hk/Hcj at20℃ | 0.982 | 0.985 |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) max | 4.30％ | 4.70％ |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) min | 1.80％ | 1.90％ |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) avg | 3.10％ | 3.30％ |
From the above comparative data, it can be seen that example 1, the intrinsic coercive force of the final magnet is significantly lower than that of comparative example 1 because the film thickness of each region in screen printing is not the same, but from the results of 120 ℃ open circuit irreversible loss, both example 1 and comparative example 1 meet the customer requirements, the 120 ℃ open circuit 2 hours irreversible loss is 5% or less, while from the magnet weight gain, the magnet weight gain after diffusion of example 1 is significantly less than that of comparative example 1, the addition amount of dysprosium oxide of example 1 is only 0.45%, the addition amount of dysprosium oxide of comparative example 1 is 0.96%, the effect of final irreversible loss is the same, and the remanence and original magnetic flux values of example 1 are higher than those of comparative example 1, but the usage amount of dysprosium oxide is greatly reduced.
Example 2
S8, screen printing
Screen printing a suspension of nano pure dysprosium powder and absolute ethyl alcohol on the base magnetic sheet prepared in the step S7 of the embodiment 1, specifically printing the suspension in different areas with the thickness shown in figure 1, and putting the magnetic sheet with two surfaces subjected to screen printing into a molybdenum sintering box in a nitrogen protection box;
s9, grain boundary diffusion
Putting the magnetic sheets loaded into the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving heat for 12 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 3 was prepared.
Comparative example 2
A1, magnetron sputtering
Performing magnetron sputtering on a 50 × 40 × 3mm thin matrix magnetic sheet prepared in the step S7 of the example 1 to obtain pure dysprosium metal, wherein both surfaces are subjected to magnetron sputtering to obtain 14um, and then filling the obtained product into a molybdenum sintering box;
a2, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 12 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 4 was prepared.
Example 2 and comparative example 2, the base magnetic sheet prepared in example 1 was directly used, in example 2, 14um of nano-pure dysprosium powder was printed on each of both sides by using the screen printing of the present invention, in comparative example 2, 14um of pure dysprosium film was plated on each of both sides by using the conventional magnetron sputtering, and the process parameters, magnetic properties and irreversible magnetic loss of the two were compared as shown in table 2:
TABLE 2
| Item | Sample 3 | Sample No. 4 |
| Magnet weight gain after diffusion (g) | 0.2232 | 0.4788 |
| Residual magnetism Br (KGs) at20 DEG C | 12.65 | 12.55 |
| Intrinsic coercivity Hcj (KOe) at20 deg.C | 21.0 | 23.2 |
| (BH)m(MGOe)at20℃ | 39.9 | 39.3 |
| Hk/Hcj at20℃ | 0.986 | 0.982 |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) max | 3.90％ | 4.50％ |
| 120 ℃ 2h open circuit irreversible loss hirr (%) min | 1.50％ | 1.80％ |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) avg | 2.80％ | 3.00％ |
From the above comparative data, it can be seen that example 2, since the film thickness of each region in screen printing is different, the intrinsic coercive force of the final magnet is significantly lower than that of comparative example 2, but from the results of 120 ℃ open circuit irreversible loss, both example 2 and comparative example 2 satisfy the customer requirements that 120 ℃ open circuit 2 hours irreversible loss is 5% or less, whereas from the magnet weight gain, the magnet weight gain after diffusion of example 2 is significantly smaller than that of comparative example 2, the addition amount of dysprosium of example 2 is only 0.49%, while that of comparative example 2 is 1.05%, the effect of final irreversible loss is the same, and the values of residual magnetism and original magnetic flux of example 2 are higher than that of comparative example 2, but the amount of metal dysprosium is greatly reduced.
Example 3
S1, smelting
The mass percentage of the components of the matrix alloy is ReaMbFe100-a-b-c-dBcCod；
Re of the base alloy is Pr, nd, gd, the total amount of Re rare earth of the base alloy a =30.5wt%, wherein Gd is 1.5 wt%, the balance 25:75 of PrNd;
m of the base alloy is Al, cu, ga, zr, b =1.4wt%, wherein Al =0.7 wt%, cu =0.2 wt%, ga =0.1 wt%, zr =0.3 wt%.
B, c =0.96wt% of the base alloy;
co of the base alloy, d =0.8wt%;
fe of the base alloy, 65.34wt%.
The industrial pure metal raw materials are weighed and proportioned according to the alloy components in percentage by mass, and the target raw materials are quickly quenched into alloy cast sheets by adopting a vacuum quick-setting smelting furnace.
S2, hydrogen crushing
The method comprises the steps of performing hydrogen crushing on neodymium iron boron alloy sheets by using a hydrogen crushing furnace, performing hydrogen crushing for 4 hours, then performing dehydrogenation for 4 hours, wherein the dehydrogenation temperature is 550 ℃, cooling the alloy cast sheets after dehydrogenation to 35 ℃, stopping cooling and standing for 80 minutes, introducing 40ppm pure oxygen into a hydrogen crushing reaction device after the cooling temperature is not increased, wherein a certain temperature exists in the furnace, the reaction kettle of the hydrogen crushing furnace is not rotated, and coarse powder is continuously stirred during oxygen supplement, so that the coarse powder is uniform and can absorb oxygen controllably. And stopping adding pure oxygen when the oxygen content in the neodymium iron boron alloy coarse powder is below 10ppm, and continuously cooling to obtain the neodymium iron boron alloy coarse powder after the oxygen content is stable and does not fluctuate.
S3, airflow milling powder
Adding a lubricant accounting for 0.1 percent of the mass of the coarse powder in the process of mixing the neodymium iron boron alloy coarse powder; after stirring and mixing the coarse powder, further grinding the coarse powder by using a fluidized bed jet mill, wherein oxygen is not supplemented during the jet mill, and grinding the coarse powder into fine neodymium iron boron alloy powder; adding an antioxidant into the prepared neodymium iron boron alloy fine powder and uniformly mixing; the alloy powder SMD was 2.85 μm and D90/D10=4.75, D10=1.81,3-10 μm distribution =77.5%.
S4, stirring
Adding a lubricant accounting for 0.1 percent of the mass of the coarse powder into the fine neodymium iron boron alloy powder, and mixing for 2 hours by adopting a three-dimensional stirrer.
S5, orientation forming
And (3) carrying out magnetic field orientation molding on the alloy powder under the protection of nitrogen to obtain a pressed compact.
S6, sintering and tempering
And (4) after vacuum sintering and tempering treatment, cooling the pressed compact to obtain the neodymium iron boron magnet. Sintering refers to sintering at 1090 ℃ for 4.5h, and then tempering at 500 ℃ for 4.5h; and (5) carrying out performance detection and oxygen content detection on the magnet.
S7, processing
The magnet was machined into thin disks of 50 x 40 x 3mm gauge thickness as required by the customer.
S8, screen printing
Screen printing of suspension of terbium oxide powder and absolute ethyl alcohol is carried out on the magnetic sheet, specifically, different areas are printed with thicknesses shown in figure 1, the magnetic sheet with two surfaces subjected to screen printing is placed in a molybdenum sintering box in a nitrogen protection box.
S9, grain boundary diffusion
Putting the magnetic sheets loaded into the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving heat for 10 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 5 was prepared.
Comparative example 3
A1, coating Terbium oxide
Coating terbium oxide on a thin substrate magnetic sheet with the size specification of 50 × 40 × 3mm prepared in step S7 of example 3, with a double-sided coating thickness of 7um, and then loading the sheet into a molybdenum sintering box;
a2, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 10 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 6 was prepared.
Example 3, using the screen printing of the present invention, terbium oxide powder was differentially printed in the ranges and thicknesses shown in fig. 1, comparative example 3, using the base magnetic sheet prepared in example 3 directly, and comparative example 3 using a conventional coating method with 7um terbium oxide powder coated on both sides, the process parameters, magnetic properties and irreversible magnetic loss of which are shown in table 3.
TABLE 3
| Item | Sample No. 5 | Sample No. 6 |
| Magnet weight gain after diffusion (g) | 0.0953 | 0.2044 |
| Residual magnetism Br (KGs) at20 DEG C | 13.58 | 13.51 |
| Intrinsic coercivity Hcj (KOe) at20 deg.C | 20.6 | 22.8 |
| (BH)m(MGOe)at20℃ | 45.3 | 44.8 |
| Hk/Hcj at20℃ | 0.982 | 0.985 |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) max | 4.30％ | 4.10％ |
| 120 ℃ 2h open circuit irreversible loss hirr (%) min | 1.80％ | 0.70％ |
| 120 ℃ 2h open circuit irreversible loss hirr (%) avg | 3.00％ | 2.80％ |
From the above comparative data, it can be seen that example 3, since the film thickness of each region in screen printing is different, the intrinsic coercive force of the final magnet is significantly lower than that of comparative example 3, but from the results of 120 ℃ open circuit irreversible loss, both example 3 and comparative example 3 satisfy the requirements of the customers that 120 ℃ open circuit 2 hours irreversible loss is 5% or less, whereas from the magnet weight gain, the magnet weight gain after diffusion of example 3 is significantly smaller than that of comparative example 3, the addition amount of terbium oxide of example 3 is only 0.13%, and the addition amount of terbium oxide of comparative example 3 is 0.27%, the effect of final irreversible loss is the same, and the values of residual magnetism and original magnetic flux of example 3 are higher than that of comparative example 3, but the amount of terbium oxide is greatly reduced.
Example 4
S8, screen printing
Screen printing a suspension of nano pure terbium powder and absolute ethyl alcohol on the matrix magnetic sheet prepared in the step S7 of the embodiment 3, specifically printing the thicknesses in different areas as shown in figure 1, and putting the magnetic sheet with two surfaces subjected to screen printing into a molybdenum sintering box in a nitrogen protection box;
s9, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 10 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 7 was prepared.
Comparative example 4
A1, magnetron sputtering
Performing magnetron sputtering of pure terbium metal on the thin substrate magnetic sheet with the size specification of 50 × 40 × 3mm prepared in the step S7 of the example 3, wherein the magnetron sputtering is performed on both sides of the thin substrate magnetic sheet, and then putting the thin substrate magnetic sheet into a molybdenum sintering box;
a2, grain boundary diffusion
Putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 900 ℃, preserving the temperature for 10 hours to perform grain boundary diffusion, and tempering at 500 ℃ for 4.5 hours; sample 8 was prepared.
Example 4 and comparative example 4, the base magnetic sheet prepared in example 3 was directly used, 7um of nano-sized pure terbium powder was printed on each of both sides of example 4 using the screen printing of the present invention, and 7um of pure terbium thin film was plated on each of both sides of comparative example 4 using the conventional magnetron sputtering, and the process parameters, magnetic properties and irreversible magnetic loss of the two were compared in table 4.
TABLE 4
| Item | Example 4: sample 7 | Comparative example 4: sample 8 |
| Magnet weight gain after diffusion (g) | 0.1075 | 0.2304 |
| Residual magnetism Br (KGs) at20 DEG C | 13.57 | 13.5 |
| Intrinsic coercive force Hcj (KOe) at20 DEG C | 21.2 | 23.3 |
| (BH)m(MGOe)at20℃ | 45.15 | 44.6 |
| Hk/Hcj at20℃ | 0.985 | 0.984 |
| 120 ℃ 2h open-circuit irreversible loss hirr (%) max | 3.30％ | 3.60％ |
| 120 ℃ 2h open circuit irreversible loss hirr (%) min | 1.10％ | 0.50％ |
| 120 ℃ 2h open circuit irreversible loss hirr (%) avg | 2.00％ | 2.20％ |
From the above comparative data, it can be seen that example 4, since the film thickness of each region in screen printing is different, the intrinsic coercive force of the final magnet is significantly lower than that of comparative example 4, but from the results of the 120 ℃ open circuit irreversible loss, both example 4 and comparative example 4 satisfy the customer requirements that the 120 ℃ open circuit 2 hours irreversible loss is 5% or less, whereas from the magnet weight gain, the magnet weight gain after diffusion of example 4 is significantly smaller than that of comparative example 4, the addition amount of terbium of example 4 is only 0.14%, and the addition amount of terbium of comparative example 4 is 0.3%, the effect of the final irreversible loss is the same, and the values of residual magnetism and original magnetic flux of example 4 are higher than that of comparative example 4, but the amount of metal terbium is greatly reduced.
The invention relates to a preparation method of high-performance low-cost sintered neodymium iron boron. The neodymium iron boron sheet which contains no heavy rare earth elements as much as possible and has the total rare earth content controlled below 30.5 percent by weight is subjected to screen printing of nano rare earth powder or rare earth compound powder and then subjected to grain boundary diffusion, so that the intrinsic coercive force of the magnet is effectively improved, and the use amount of the rare earth elements is greatly reduced.
The method can be set to perform screen printing on the surface of the magnet in a differentiated mode, namely the thickness of materials printed on different parts can be different, so that the waste of rare earth materials caused by the fact that the thickness of the whole surface is the same as that of the magnetron sputtering in the traditional coating method and the magnetron sputtering method can be avoided. Because the demagnetization factors of the corner parts of the magnet are small and not easy to demagnetize, and the demagnetization factors of the middle parts are larger and easy to demagnetize, the demagnetization resistance of different parts of the magnet are different, and the screen printing amount can be different by combining the demagnetization characteristic of the magnet, so that the use amount of the nano rare earth powder or the compound powder of the rare earth can be greatly reduced, and the use amount of the rare earth element can be greatly reduced.
Claims (8)
1. The preparation method of the sintered NdFeB magnet with high performance and low cost is characterized by comprising the following steps:
1) Smelting: weighing and proportioning industrial pure metal raw materials according to NdFeB alloy components in percentage by mass, and quickly quenching a target raw material into a neodymium iron boron alloy cast sheet by adopting a vacuum quick-setting smelting furnace; the matrix alloy contains as little heavy rare earth elements as possible, and the total amount of rare earth elements is controlled to 30.5% by weight or less as possible;
2) Hydrogen crushing: placing the neodymium iron boron alloy cast sheet into a hydrogen crushing furnace for hydrogen crushing treatment, then carrying out dehydrogenation to obtain a dehydrogenated metal cast sheet, cooling to 35 ℃, stopping cooling, standing for 60-120 minutes, introducing 20-100ppm pure oxygen into a hydrogen crushing reaction device after the cooling temperature is not raised, stopping adding the pure oxygen when the hydrogen crushing reaction device displays that the oxygen in the hydrogen crushing reaction device is lower than 10ppm, and continuously cooling to obtain neodymium iron boron alloy coarse powder after the oxygen content is stable and does not fluctuate;
3) Milling powder by airflow: adding a lubricant accounting for 0.1-0.5% of the mass of the coarse powder in the process of mixing the neodymium iron boron alloy coarse powder; after the coarse powder is stirred and mixed, further grinding the coarse powder by using a fluidized bed jet mill, wherein oxygen is not supplemented during the jet mill, and grinding the coarse powder into fine neodymium iron boron alloy powder; adding an antioxidant into the prepared neodymium iron boron alloy fine powder and uniformly mixing; the SMD of the alloy powder is 2.6-3.0 μm, the D90/D10 is less than 4.8, the D10 is more than 1.8, and the distribution value of 3-10 μm is more than 75%;
4) Stirring: adding a lubricant accounting for 0.1-0.5% of the mass of the coarse powder into the fine neodymium iron boron alloy powder, and mixing by using a three-dimensional stirrer to obtain alloy powder;
5) Orientation forming: carrying out magnetic field orientation molding on the alloy powder under the protection of nitrogen to obtain a pressed blank;
6) Sintering and tempering: after vacuum sintering and tempering are carried out on the green compact, cooling to obtain a neodymium iron boron magnet, and carrying out performance detection and oxygen content detection on the magnet;
7) Processing: processing the magnet into thin magnetic sheets with thickness of 1-10mm, wherein the magnetic sheets can be square sheets, tiles or round sheets;
8) Silk-screen printing, namely, silk-screen printing is carried out on the magnetic sheet, and the magnetic sheet with two surfaces subjected to silk-screen printing is put into a molybdenum sintering box in a nitrogen protection box;
9) Grain boundary diffusion: and putting the magnetic sheets in the molybdenum sintering box into a sintering furnace, vacuumizing to high vacuum, heating to 800-950 ℃, preserving the heat for 8-20h for carrying out grain boundary diffusion, and tempering at 450-550 ℃ for 2-5h to obtain the sintered neodymium-iron-boron magnet with high performance and low cost.
2. The method for preparing a high-performance low-cost sintered ndfeb magnet as claimed in claim 1, wherein the hydrogen crushing time in step 2) is 2-4 hours, the dehydrogenation time is 4-8 hours, and the dehydrogenation temperature is 450-550 ℃.
3. The method for preparing sintered NdFeB magnet with high performance and low cost as claimed in claim 1, wherein the sintering in step 6) is sintering at 1000-1100 ℃ for 2-5h, and then tempering at 800-900 ℃ for 1-2 h and 450-550 ℃ for 2-5h.
4. The method for preparing sintered nd-fe-b magnet with high performance and low cost as claimed in claim 1, wherein the screen printing ink in step 8) is a suspension of nano rare earth powder or rare earth compound powder, wherein the powder: the mass ratio of the organic solution is 30-50:50-70 parts of; in the nano rare earth powder or rare earth compound powder, the rare earth element is praseodymium, neodymium, dysprosium, terbium or holmium, and the organic solution is alcohol.
5. The method for preparing sintered NdFeB magnet with high performance and low cost as claimed in claim 4, wherein the rare earth elements are heavy rare earth dysprosium and terbium, and the organic solvent is absolute ethyl alcohol.
6. The method of claim 4, wherein the nano-rare earth powder or compound powder of rare earth includes but is not limited to common hydrogenated rare earth powder or rare earth, fluorinated rare earth powder or rare earth, oxidized rare earth powder or rare earth; the purity of the nano rare earth powder or rare earth compound powder is more than 99.95 percent, and the particle size of the powder is 0.5-3um.
7. The method for preparing sintered nd-fe-b magnet with high performance and low cost according to claim 1, characterized in that the screen printing in step 8) is a local printing or a thickness differential printing according to the setting, rather than a full-area thickness non-differential printing.
8. The method for preparing sintered NdFeB magnet with high performance and low cost as claimed in claim 1, wherein the oxygen content of the magnet to be printed is detected and monitored, and the oxygen content of the magnet is less than or equal to 900ppm.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN118173373A (en) * | 2024-05-14 | 2024-06-11 | 中国科学院赣江创新研究院 | Grain boundary diffusion method for large-thickness NdFeB magnet |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN118173373A (en) * | 2024-05-14 | 2024-06-11 | 中国科学院赣江创新研究院 | Grain boundary diffusion method for large-thickness NdFeB magnet |
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