CN110767403B - Warm-pressing formed bonded magnet and preparation method thereof - Google Patents
Warm-pressing formed bonded magnet and preparation method thereof Download PDFInfo
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- CN110767403B CN110767403B CN201911076840.5A CN201911076840A CN110767403B CN 110767403 B CN110767403 B CN 110767403B CN 201911076840 A CN201911076840 A CN 201911076840A CN 110767403 B CN110767403 B CN 110767403B
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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
- H01F1/0578—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 bonded together
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- H—ELECTRICITY
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- 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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Abstract
A warm-pressing bonded magnet and a preparation method thereof are provided, the warm-pressing bonded magnet comprises anisotropic neodymium iron boron magnetic powder, adhesive and composite heat conducting agent. The preparation method comprises the steps of master alloy smelting, heat treatment, HDDR treatment, glue mixing, powder mixing, pre-pressing forming, orientation forming, curing and the like, wherein the heat conduction capability of a pre-pressed blank is enhanced by adding the composite heat conducting agent, so that the pre-pressed blank can reach the Tf conversion temperature of the added epoxy resin in a very short time, powder is in a uniform viscous state epoxy resin, powder particles are orderly arranged when in orientation, the orientation is more complete, the effect is more obvious, meanwhile, the density and the integral uniformity of a magnetic ring are improved during pressing, the situations of layering, incomplete gluing and the like during orientation pressing are avoided, and the uniformity degree of the orientation magnetic ring is higher; and the composite heat conducting agent can replace traditional lubricants such as zinc stearate, magnesium stearate and the like, so that the fluidity of the magnetic powder is improved.
Description
Technical Field
The invention relates to the technical field of bonded magnet materials, in particular to a warm-pressing formed bonded magnet and a preparation method thereof.
Background
The bonded neodymium iron boron permanent magnetic material has the advantages of strong magnetism, high shape freedom degree, good consistency and the like, and is widely applied to the fields of hard disks, optical disk drives, office automation, consumer electronics, household appliances, automobiles and the like. The magnetic powder for bonding the neodymium iron boron permanent magnet material at present mainly comprises two main categories of isotropy and anisotropy, the isotropy neodymium iron boron magnetic powder is prepared by a melt rapid quenching method, the maximum magnetic energy product is 12-18MGOe, the maximum magnetic energy product of the prepared isotropy neodymium iron boron bonded magnet is not more than 12MGOe, and the high-end requirement is difficult to meet. The anisotropic neodymium iron boron magnetic powder is usually prepared by an HDDR method, and due to the particularity of the microstructure, namely the parallel arrangement of fine grains (200 plus 500nm) in the direction of an easy magnetization axis, the maximum magnetic energy product of the anisotropic neodymium iron boron magnetic powder can reach 2-3 times of that of the isotropic magnetic powder, and a high-performance anisotropic bonded magnet can be prepared by a die pressing or injection molding process and accords with the development trend of miniaturization, light weight and precision of devices such as a rotating motor, and therefore, the market demand for the high-performance anisotropic bonded magnet is more and more urgent.
At present, anisotropic magnetic powder prepared by an HDDR method can be subjected to a series of surface treatments, cold pressing preforming and hot pressing orientation forming to obtain an anisotropic magnet meeting high performance requirements. However, the morphological structure of the anisotropic magnetic powder prepared by the HDDR method is not easy to control, and usually can not reach an ideal state (the circularity is 1); microcracks exist on the surface of the magnetic powder, and the magnetic powder can be further broken in the pressing process to influence the magnetic performance; the hot pressing process time is short, the heat conduction is slow, the orientation degree of the magnet is not high, and the surface magnetism is not large and uniform after magnetization; the lubricant is not easy to discharge, even reacts, and influences the magnetic performance.
Disclosure of Invention
In order to solve the problems, the invention provides a preparation method of a warm-pressing forming bonded magnet, which improves the fluidity of magnetic powder and the density of the magnet by improving the morphology structure of the magnetic powder, adds a composite heat conducting agent in the powder mixing process, has good powder coating capability, can better solve the problems of poor orientation degree and the like caused by slow heat transfer in the hot pressing process, and has a certain improvement effect on the fluidity of the powder.
In order to achieve the above purpose, the invention adopts the following scheme:
a first aspect of the present invention provides a warm-press formed bonded magnet, comprising: anisotropic neodymium iron boron magnetic powder, adhesive and composite heat conducting agent;
the anisotropic neodymium iron boron magnetic powder comprises the following components in percentage by mass: PrNd 20-30%, Fe 60-70%, B0.5-3.5%, Al 0.1-3.5%, Ga 0.1-3% and Nb 0.1-3%);
the adhesive comprises epoxy resin and a coupling agent, and the mass percentages of the epoxy resin and the coupling agent in the magnet are respectively as follows: 2.5 to 3 percent of epoxy resin and 0.1 to 1 percent of coupling agent;
the composite heat conducting agent accounts for 0.5-1% of the magnet by mass.
Further, the composite heat conducting agent comprises n-hexane, methyl decanoate and nano heat conducting composite powder, and the mass ratio of the n-hexane to the methyl decanoate to the nano heat conducting composite powder is 30-55: 1: 25-30.
Further, the specific particle diameter and the proportion of the anisotropic neodymium iron boron magnetic powder are as follows:
the diameter of the particles is less than or equal to 120mesh, and the mass percentage is 1-10%;
the particle diameter is 120-140 mesh, and the mass ratio is 3% -10%;
the particle diameter is 140-325 mesh, and the mass ratio is 50-90%;
the particle diameter is larger than 325mesh, and the mass ratio is 5-35%.
Further, the nano heat-conducting composite powder comprises at least one of nano silicon magnesium nitride, nano silicon carbide, nano aluminum nitride, nano boron nitride, high sphericity aluminum oxide and nano silicon nitride.
A second aspect of the present invention provides a method for producing a warm-press formed bonded magnet, for producing the warm-press formed bonded magnet as described above, comprising the steps of:
step one, smelting a master alloy: mixing all the raw materials according to the mass percentage of the anisotropic neodymium iron boron magnetic powder, carrying out medium-frequency induction heating on the mixed raw materials by a vacuum melting method to obtain molten metal, and then pouring the molten metal into a double-sided water-cooling fixed die to obtain an ingot;
step two, carrying out heat treatment on the ingot: putting the cast ingot into a vacuum heat treatment furnace, vacuumizing and heating to 1100-1200 ℃, filling argon to a certain pressure, keeping the temperature in the furnace constant for a period of time, then cooling in times and keeping for a period of time, and finally carrying out air cooling to room temperature to obtain the cast ingot;
step three, carrying out HDDR treatment on the ingot to obtain anisotropic neodymium iron boron magnetic powder;
step four, mixing the glue: screening anisotropic neodymium iron boron magnetic powder with different particle sizes, respectively adding 0.1-1% of coupling agent and 2.5-3% of epoxy resin in percentage by mass, dissolving in an organic solvent, and uniformly mixing by using a vacuum mixer to obtain intermediate powder with the surface uniformly coated with the epoxy resin;
step five, mixing powder: adding 0.5-1% of composite heat-conducting agent by mass percent, and uniformly mixing by using a mixer to obtain intermediate powder with the surface uniformly coated with the composite heat-conducting agent;
step six, prepressing and forming: the intermediate powder is filled into an automatic feeder, a mold used by a prepress is a circulating water-cooling mold, no heating step is needed in the pressing process, and the density of the pressed prepressed blank is 4.4-4.6 g/cm3；
Step seven, orientation forming: putting the pre-pressed blank into a die cavity of an orientation press, keeping the die temperature at 150-200 ℃ in the pressing process, magnetizing the pre-pressed blank for orientation pressing, and pressing to obtain the blank with the density of 6.0-6.5 g/cm3A green compact of (1);
step eight, curing: and putting the oriented pressed compact into a vacuum curing furnace, vacuumizing until the vacuum degree is below 0.3Pa, heating to 150-180 ℃ for curing, preserving the heat for 60-90 min, stopping heating, naturally cooling to room temperature, and discharging to obtain the warm-pressing molded bonded magnet.
Further, the cast ingot in the step one is a massive rapidly quenched neodymium iron boron alloy with a columnar crystal structure, and the thickness of the cast ingot is 15-30 mm.
Further, in the second step, the ingot is placed in a vacuum heat treatment furnace, the vacuum is pumped, the ingot is heated to 1100-1200 ℃, argon is filled to-0.08 MPa, the constant temperature in the furnace is kept for 20 hours, then the argon is filled to-0.04 MPa, the temperature is reduced, the temperature in the furnace is reduced to 900 ℃ within 15 minutes and is kept constant for 2 hours, the temperature in the furnace is reduced to 600 ℃ within 45 minutes and is kept constant for 2 hours, and the ingot is taken out after being cooled to room temperature by air.
Further, in the third step, the ingot is placed into an HDDR furnace, the airtightness of the device is checked, the ingot is vacuumized to be below 0.2Pa and heated to 170-200 ℃, and then hydrogen is filled to 95-100 kPa at the temperature for maintaining for 45-60 min;
vacuumizing to below 1Pa again, heating to 820-850 ℃, and filling hydrogen to 30-35 kPa at the temperature for 75-90 min;
raising the temperature to 880-900 ℃, filling hydrogen to 70-80 kPa, and maintaining the state for 25-35 min;
reducing the hydrogen pressure from 70-80 kPa to 5-6 kPa within 5min, reducing the hydrogen pressure to 4 kPa-4.5 kPa within 5-8 min, and keeping the hydrogen pressure at 3-4.5 kPa for 15 min-20 min;
cooling to 860-870 ℃, and meanwhile, forcibly discharging hydrogen to below 0.15 Pa;
and closing and heating, and cooling to below 30 ℃ to obtain the anisotropic neodymium iron boron magnetic powder.
Further, the method also comprises the step nine of surface treatment: and (3) carrying out electrophoretic coating or oil immersion treatment on the cured warm-pressing molded bonded magnet to prevent surface oxidation.
Further, the method also comprises the step ten of magnetizing: and carrying out multi-pole magnetization on the warm-pressing molded bonded magnet by using a proper magnetizing clamp according to requirements.
In summary, the invention provides a warm-pressing bonded magnet and a preparation method thereof, wherein the warm-pressing bonded magnet comprises anisotropic neodymium iron boron magnetic powder, a bonding agent and a composite heat conducting agent; the anisotropic neodymium iron boron magnetic powder comprises the following components in percentage by mass: 20 to 30 percent of PrNd, 60 to 70 percent of Fe, 0.5 to 3.5 percent of B, 0.1 to 3.5 percent of Al, 0.1 to 3 percent of Ga and 0.1 to 3 percent of Nb; the adhesive comprises epoxy resin and a coupling agent, and the mass percentages of the epoxy resin and the coupling agent in the magnet are respectively as follows: 2.5 to 3 percent of epoxy resin and 0.1 to 1 percent of coupling agent; the composite heat conducting agent accounts for 0.5-1% of the magnet by mass. The preparation method comprises the steps of master alloy smelting, heat treatment, HDDR treatment, glue mixing, powder mixing, pre-pressing forming, orientation forming, curing and the like, wherein the heat conduction capability of a pre-pressed blank is enhanced by adding the composite heat conducting agent, so that the pre-pressed blank can reach the Tf conversion temperature of the added epoxy resin in a very short time, powder is in a uniform viscous state epoxy resin, powder particles are orderly arranged when in orientation, the orientation is more complete, the effect is more obvious, meanwhile, the density and the integral uniformity of a magnetic ring are improved during pressing, the situations of layering, incomplete gluing and the like during orientation pressing are avoided, and the uniformity degree of the orientation magnetic ring is higher; and the composite heat conducting agent can replace traditional lubricants such as zinc stearate, magnesium stearate and the like, so that the fluidity of the magnetic powder is improved.
Drawings
Fig. 1 is a schematic flow chart of a method for manufacturing a warm-press formed bonded magnet according to an embodiment of the present invention;
FIG. 2(a) is a schematic view of the microstructure of anisotropic magnetic powder; FIG. 2(b) (c) is a schematic view of the microstructure of anisotropic magnetic powder (after mixing); FIG. 2(d) is a schematic view of the microstructure of an isotropic magnetic powder;
FIG. 3 is a schematic view of the surface of a powder coated with a coupling agent and an epoxy resin;
FIG. 4 is a schematic view of the surface of an epoxy-coated magnetic powder;
FIG. 5(a) is a schematic diagram of a powder structure with zinc stearate and magnesium stearate added; fig. 5(b) is a schematic diagram of a powder structure to which the composite heat conductive agent is added.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The invention provides a warm-pressing forming bonded magnet, which comprises anisotropic neodymium iron boron magnetic powder, a bonding agent and a composite heat conducting agent; the anisotropic neodymium iron boron magnetic powder comprises the following components in percentage by mass: 20 to 30 percent of PrNd, 60 to 70 percent of Fe, 0.5 to 3.5 percent of B, 0.1 to 3.5 percent of Al, 0.1 to 3 percent of Ga and 0.1 to 3 percent of Nb; the adhesive comprises epoxy resin and a coupling agent, and the mass percentages of the epoxy resin and the coupling agent in the magnet are respectively as follows: 2.5 to 3 percent of epoxy resin and 0.1 to 1 percent of coupling agent; the composite heat conducting agent accounts for 0.5-1% of the magnet by mass.
Further, the composite heat conducting agent comprises n-hexane, methyl decanoate and nano heat conducting composite powder, and the mass ratio of the n-hexane to the methyl decanoate to the nano heat conducting composite powder is 30-55: 1: 25-30. The composite heat conducting agent serves as a lubricant, and the fluidity of the magnetic powder is improved.
Further, the nano heat-conducting composite powder comprises at least one of nano silicon magnesium nitride, nano silicon carbide, nano aluminum nitride, nano boron nitride, high sphericity aluminum oxide and nano silicon nitride.
Further, the specific particle diameter and the proportion of the anisotropic neodymium iron boron magnetic powder are as follows: the diameter of the particles is less than or equal to 120mesh, and the mass percentage is 1-10%; the particle diameter is 120-140 mesh, and the mass ratio is 3% -10%; the particle diameter is 140-325 mesh, and the mass ratio is 50-90%; the particle diameter is larger than 325mesh, and the mass ratio is 5-35%. The density and the integral uniformity of the oriented magnetic ring can be improved by selecting the particle diameter and the mass ratio.
The warm-pressing formed bonded magnet prepared from the components and the proportion has the characteristics of high orientation degree, high density, high uniformity and the like.
A second aspect of the present invention provides a method for producing a warm-press formed bonded magnet, as shown in fig. 1, including the steps of:
step one, smelting a master alloy: all the raw materials are proportioned according to the mass percentage of the anisotropic neodymium iron boron magnetic powder, the proportioned raw materials are subjected to intermediate frequency induction heating by a vacuum melting method to form molten metal, and then the molten metal is poured into a double-sided water-cooling fixed die to obtain an ingot. Specifically, the cast ingot is a plate-shaped rapidly quenched neodymium iron boron alloy with a columnar crystal structure, and the thickness of the cast ingot is 15-30 mm.
Step two, heat treatment: and putting the cast ingot into a vacuum heat treatment furnace, vacuumizing and heating to 1100-1200 ℃, filling argon to a certain pressure, keeping the temperature in the furnace constant for a period of time, then cooling in times and keeping for a period of time, and finally carrying out air cooling to room temperature to obtain the finished product. Specifically, argon is filled to-0.08 MPa within the temperature range of 1100-1200 ℃, the furnace is kept at the constant temperature for 20h, then argon is filled to-0.04 MPa, the temperature is reduced, the temperature in the furnace is reduced to 900 ℃ within 15min and is kept constant for 2 h, the temperature in the furnace is reduced to 600 ℃ within 45min and is kept constant for 2 h, and then air cooling is carried out to reduce the temperature to room temperature, so that the material can be taken out of the furnace.
Step three, HDDR treatment: and (3) placing the cast ingot into an HDDR furnace for treatment to obtain anisotropic magnetic powder.
Specifically, the method comprises the following steps:
checking the air tightness of the equipment, vacuumizing to below 0.2Pa, heating to 170-200 ℃, and then filling hydrogen to 95-100 kPa at the temperature for 45-60 min;
vacuumizing to below 1Pa again, heating to 820-850 ℃, and filling hydrogen to 30-35 kPa at the temperature for 75-90 min;
raising the temperature to 880-900 ℃, filling hydrogen to 70-80 kPa, and maintaining the state for 25-35 min;
reducing the hydrogen pressure from 70-80 kPa to 5-6 kPa within 5min, reducing the hydrogen pressure to 4 kPa-4.5 kPa within 5-8 min, and keeping the hydrogen pressure at 3-4.5 kPa for 15 min-20 min;
cooling to 860-870 ℃, and meanwhile, forcibly discharging hydrogen to below 0.15 Pa;
and closing and heating, and cooling to below 30 ℃ to obtain the anisotropic neodymium iron boron magnetic powder.
Fig. 2(a) shows a schematic view of a microstructure of the anisotropic magnetic powder, where the anisotropic neodymium iron boron magnetic powder has an irregular bulk shape and a low circularity, but is significantly different from a sheet structure of the isotropic rapidly quenched magnetic powder, and fig. 2(b) (c) shows a schematic view of a microstructure of the anisotropic magnetic powder (after mixing); fig. 2(d) is a schematic view of the microstructure of the isotropic magnetic powder.
Step four, mixing the glue: the anisotropic magnetic powder is screened according to the proportion of different particle sizes, and the particle size distribution is as follows:
| ≤120mesh | 120～140mesh | 140～325mesh | ＞325mesh |
| 1％～10％ | 3％～10％ | 50％～90％ | 5％～35％ |
the reasonable proportion of the coarse particle size and the fine particle size can improve the flowability of the magnetic powder to the maximum extent, the small particles fill the gaps among the large particles, and the apparent density of the magnetic powder is effectively improved, so that the density of the magnet is improved.
Then respectively adding 0.1-1% of coupling agent and 2.5-3% of epoxy resin by mass percent, dissolving in an organic solvent, and uniformly mixing by using a vacuum stirrer to obtain intermediate powder with the surface uniformly coated with the epoxy resin, wherein the mixing process is shown in figure 3. Specifically, the coupling agent can be selected from silane or titanate; the organic solvent is acetone or absolute ethyl alcohol.
As shown in fig. 4, 1 is a magnetic powder particle, and epoxy resin 4 can play a role in filling and coating microcracks 2, edges and corners 3 and the like on the surface of the magnetic powder particle 1, improve the circularity of the powder particle, increase the flowability, play a certain role in buffering in the magnet pressing process, and prevent the powder particle from being broken and affecting the performance due to surface cracks and mutual extrusion of the edges and corners in the pressing process.
Step five, mixing powder: adding a composite heat-conducting agent, wherein the composite heat-conducting agent comprises n-hexane, methyl decanoate and nano heat-conducting composite powder (the nano heat-conducting composite powder comprises at least one of nano silicon magnesium nitride, nano silicon carbide, nano aluminum nitride, nano boron nitride, high sphericity alumina, nano silicon nitride and the like), the mass ratio of the nano silicon magnesium nitride to the nano silicon carbide to the nano aluminum nitride to the nano boron nitride to the high sphericity alumina to the nano silicon nitride is 30-55: 1: 25-30, and the mass ratio of the composite heat-conducting agent to the magnetic powder is 0.5-1%. In a specific embodiment, the adding proportion is 0.5%, and the mixture is uniformly mixed by using a mixer to obtain intermediate powder with the surface uniformly coated with the composite heat-conducting agent. Fig. 5(a) is a schematic diagram showing a powder structure to which zinc stearate and magnesium stearate (small particles in the drawing) are added, and fig. 5(b) is a schematic diagram showing a powder structure to which a composite thermal conductive agent (a part filled between powders) is added: compared with lubricants such as zinc stearate, magnesium stearate and the like, the composite heat conducting agent has a better coating effect on powder and has a larger improvement on the flowability.
Step six, prepressing and forming: the magnetic powder is filled into an automatic feeder, and the good fluidity ensures that the loose packed density of the magnetic powder can reach 3.1g/cm3And the left and right of the prepress is a circulating water-cooling mold, no heating step is needed in the pressing process, and the density of the pressed prepressed blank is about 4.4-4.6 g/cm3。
Step seven, orientation forming: putting the pre-pressed blank into a die cavity of an orientation press, wherein the orientation press has a heating function, the temperature of the die is kept at 150-200 ℃ in the pressing process, the heat preservation time is 10-30 s, magnetizing orientation pressing is carried out in a quadrupole (radiation) orientation press, and the pressing density is about 6.0-6.5 g/cm3The green compact of (4).
Step eight, curing: and (3) placing the oriented pressed compact into a vacuum curing furnace, vacuumizing until the vacuum degree is below 0.3Pa, heating to 150-180 ℃ for curing, keeping the temperature for 60-90 min, stopping heating, naturally cooling to room temperature, and discharging to obtain the warm-pressing bonded magnet.
Step nine, surface treatment: and performing electrophoretic coating or oil immersion treatment on the cured magnet to prevent surface oxidation.
Step ten, magnetizing: and carrying out multi-pole magnetization by using a proper magnetizing clamp according to requirements.
The present invention will be further described with reference to the following specific examples.
Example 1
(1) Preparing materials: 50kg of raw materials are prepared according to the formula, and the surface of the iron rod is subjected to rust removal and cleaning, and the rare earth materials are required to be free of moisture, oil stain and rust.
(2) Ingot casting: the prepared raw materials are subjected to medium-frequency induction heating to form molten metal through a vacuum melting method, and then the molten metal is poured into a double-sided water-cooling fixed die to finally obtain the plate-shaped rapidly-quenched neodymium-iron-boron alloy with a columnar crystal structure, wherein the columnar crystal proportion of the cast ingot is 70-90%, and the thickness of the cast ingot is 15-30 mm.
(3) And (3) heat treatment: putting the cast ingot into a vacuum heat treatment furnace, vacuumizing and heating to 1150 ℃, filling argon to-0.08 MPa, keeping the constant temperature in the furnace for 20h, then starting filling argon to-0.04 MPa, carrying out cooling operation, reducing the temperature in the furnace to 900 ℃ after 13min, keeping the temperature for 2 h, reducing the temperature in the furnace to 600 ℃ after 40min, keeping the temperature for 2 h, and then carrying out air cooling to room temperature and discharging.
(4) HDDR treatment: putting the ingot subjected to heat treatment into an HDDR furnace, checking the airtightness of equipment, vacuumizing to 0.18Pa, heating to 195 ℃, and then filling hydrogen to 97kPa at the temperature for maintaining for 60 min;
vacuumizing to 0.5Pa again, heating to 845 ℃, and filling hydrogen to 33kPa at the temperature for 85 min;
increasing the temperature to 895 ℃, filling hydrogen to 80kPa, and maintaining the state for 32 min;
reducing the hydrogen pressure from 80kPa to 5.5kPa for 3min, reducing the hydrogen pressure to 4.5kPa for 6min, and keeping the hydrogen pressure at 4.5kPa for 17 min;
cooling to 863 ℃, and meanwhile, forcibly discharging hydrogen to 0.1 Pa;
and closing and heating, and cooling to 25 ℃ to obtain the anisotropic magnetic powder.
(5) Mixing the glue: the anisotropic magnetic powder is screened according to the proportion of different particle sizes, and the particle size distribution is as follows:
| ≤120mesh | 120～140mesh | 140～325mesh | ＞325mesh |
| 2％ | 8％ | 70％ | 20％ |
respectively adding 0.15 percent of coupling agent and 2.55 percent of epoxy resin by mass percent, dissolving in acetone, and uniformly mixing by using a vacuum stirrer to obtain intermediate powder with the surface uniformly coated with the epoxy resin.
(6) Mixing powder: adding a composite heat-conducting agent (the mass ratio of n-hexane to methyl decanoate to the nano heat-conducting composite powder is 50:1:25), wherein the mass percentage of the addition is 0.5%, and uniformly mixing by using a mixer to obtain intermediate powder with the surface uniformly coated with the composite heat-conducting agent.
(7) Pre-pressing and forming: the mixed magnetic powder is filled into an automatic feeder of a preforming press, and the loose packing density of the magnetic powder reaches 3.15g/cm after testing3Adjusting parameters such as a loading position, a mold closing stroke and a pressing height of a press, pressing after the adjustment is finished, wherein the density of a pressed preform is 4.5-4.58 g/cm3。
(8) Orientation forming: superposing two pre-pressed blanks (one or more pre-pressed blanks can be placed according to product requirements) and placing the two pre-pressed blanks into a die cavity of an orientation press, keeping the die temperature at 170 ℃ in the pressing process, keeping the temperature for 30s, performing magnetizing orientation pressing in a quadrupole (radiation) orientation press, wherein the density of a pressed magnet is 6.0-6.15 g/cm3。
(9) And (3) curing: and putting the oriented magnet pressed compact into a vacuum curing furnace, vacuumizing until the vacuum degree is 0.3Pa, heating to 165 ℃ for curing, keeping the temperature for 90min, stopping heating, naturally cooling to room temperature, and discharging to obtain the warm-pressing bonded magnet.
(10) Surface treatment: and cleaning the surface of the solidified magnet, and then carrying out electrophoretic coating.
(11) And (3) magnetizing test: and applying the same magnetic field to magnetize the magnet through the magnetizing clamp, and testing the magnetic performance.
The properties of the magnet prepared in this example are compared with those of the magnet prepared in the prior art (i.e., normal process) in table 1.
Table 1 example one compares the properties of the magnet prepared in the first place with those of the magnet prepared in the prior art (i.e. normal process).
TABLE 1
As can be seen from table 1 above, the warm press formed bonded magnet obtained by the preparation method of the present invention has various properties higher than those of the magnet obtained by the normal process.
In summary, the invention provides a warm-pressing bonded magnet and a preparation method thereof, wherein the warm-pressing bonded magnet comprises anisotropic neodymium iron boron magnetic powder, a bonding agent and a composite heat conducting agent; the preparation method comprises the steps of master alloy smelting, heat treatment, HDDR treatment, glue mixing, powder mixing, pre-pressing forming, orientation forming, curing and the like, wherein the heat conduction capability of a pre-pressed blank is enhanced by adding the composite heat conducting agent, so that the pre-pressed blank can reach the Tf conversion temperature of the added epoxy resin in a very short time, powder is in a uniform viscous state epoxy resin, powder particles are orderly arranged when in orientation, the orientation is more complete, the effect is more obvious, meanwhile, the density and the integral uniformity of a magnetic ring are improved during pressing, the situations of layering, incomplete gluing and the like during orientation pressing are avoided, and the uniformity degree of the orientation magnetic ring is higher; secondly, a composite heat-conducting agent is adopted, the composite heat-conducting agent has strong coating capacity on the powder, and can quickly conduct heat in the orientation pressing process, so that the epoxy resin around the powder is converted into a viscous state from solid state acceleration, a better orientation environment is created for anisotropic magnetic powder, the degree of freedom of movement of the powder is large, and the orientation is more complete; when two or more pre-pressed blanks are subjected to orientation pressing simultaneously, the pre-pressed blanks are combined more tightly, the magnet added with the composite heat-conducting agent under the same quality and pressure can achieve higher density, the surface layering condition is not easy to occur, and the magnetic performance is more uniform and consistent.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
Claims (9)
1. A warm-press formed bonded magnet, comprising: anisotropic neodymium iron boron magnetic powder, adhesive and composite heat conducting agent;
the anisotropic neodymium iron boron magnetic powder comprises the following components in percentage by mass: 20 to 30 percent of PrNd, 60 to 70 percent of Fe, 0.5 to 3.5 percent of B, 0.1 to 3.5 percent of Al, 0.1 to 3 percent of Ga and 0.1 to 3 percent of Nb;
the adhesive comprises epoxy resin and a coupling agent, and the mass percentages of the epoxy resin and the coupling agent in the magnet are respectively as follows: 2.5 to 3 percent of epoxy resin and 0.1 to 1 percent of coupling agent;
the composite heat conducting agent accounts for 0.5-1% of the magnet by mass percent;
the composite heat conducting agent comprises n-hexane, methyl decanoate and nano heat conducting composite powder, and the mass ratio of the n-hexane to the methyl decanoate to the nano heat conducting composite powder is 30-55: 1: 25-30.
2. The warm-pressing formed bonded magnet according to claim 1, wherein the anisotropic neodymium iron boron magnetic powder has specific particle diameters and proportions of:
the diameter of the particles is less than or equal to 120mesh, and the mass percentage is 1-10%;
the particle diameter is 120-140 mesh, and the mass ratio is 3% -10%;
the particle diameter is 140-325 mesh, and the mass ratio is 50-90%;
the particle diameter is larger than 325mesh, and the mass ratio is 5-35%.
3. The warm-press formed bonded magnet according to claim 1, wherein the nano heat conductive composite powder comprises at least one of nano magnesium silicon nitride, nano silicon carbide, nano aluminum nitride, nano boron nitride, high sphericity alumina, and nano silicon nitride.
4. The method for producing a warm-press formed bonded magnet according to any one of claims 1 to 3, comprising the steps of:
step one, smelting a master alloy: mixing all the raw materials according to the mass percentage of the anisotropic neodymium iron boron magnetic powder, carrying out medium-frequency induction heating on the mixed raw materials by a vacuum melting method to obtain molten metal, and then pouring the molten metal into a double-sided water-cooling fixed die to obtain an ingot;
step two, carrying out heat treatment on the ingot: putting the cast ingot into a vacuum heat treatment furnace, vacuumizing and heating to 1100-1200 ℃, filling argon to a certain pressure, keeping the temperature in the furnace constant for a period of time, then cooling in times and keeping for a period of time, and finally carrying out air cooling to room temperature to obtain the cast ingot;
step three, carrying out HDDR treatment on the ingot to obtain anisotropic neodymium iron boron magnetic powder;
step four, mixing the glue: screening anisotropic neodymium iron boron magnetic powder with different particle sizes, respectively adding 0.1-1% of coupling agent and 2.5-3% of epoxy resin in percentage by mass, dissolving in an organic solvent, and uniformly mixing by using a vacuum mixer to obtain intermediate powder with the surface uniformly coated with the epoxy resin;
step five, mixing powder: adding 0.5-1% of composite heat-conducting agent by mass percent, and uniformly mixing by using a mixer to obtain intermediate powder with the surface uniformly coated with the composite heat-conducting agent;
step six, prepressing and forming: the intermediate powder is filled into an automatic feeder, a mold used by a prepress is a circulating water-cooling mold, no heating step is needed in the pressing process, and the density of the pressed prepressed blank is 4.4-4.6 g/cm3；
Step seven, orientation forming: putting the pre-pressed blank into a die cavity of an orientation press, keeping the die temperature at 150-200 ℃ in the pressing process, magnetizing the pre-pressed blank for orientation pressing, and pressing to obtain the blank with the density of 6.0-6.5 g/cm3A green compact of (1);
step eight, curing: and putting the oriented pressed compact into a vacuum curing furnace, vacuumizing until the vacuum degree is below 0.3Pa, heating to 150-180 ℃ for curing, preserving the heat for 60-90 min, stopping heating, naturally cooling to room temperature, and discharging to obtain the warm-pressing molded bonded magnet.
5. The method as claimed in claim 4, wherein the ingot in the first step is a block of rapidly quenched NdFeB alloy with a columnar crystal structure, and the thickness of the rapidly quenched NdFeB alloy is 15-30 mm.
6. The method as claimed in claim 4, wherein in the second step, the ingot is placed in a vacuum heat treatment furnace, the vacuum is pumped, the ingot is heated to 1100-1200 ℃, argon is filled to-0.08 MPa, the constant temperature in the furnace is maintained for 20 hours, then argon is filled to-0.04 MPa, the temperature is reduced, the temperature in the furnace is reduced to 900 ℃ within 15 minutes and is kept constant for 2 hours, the temperature in the furnace is reduced to 600 ℃ within 45 minutes and is kept constant for 2 hours, and the ingot is discharged after being cooled to room temperature by air cooling.
7. The method according to claim 4, wherein in the third step, the ingot is placed in an HDDR furnace, the airtightness of the device is checked, the ingot is vacuumized to be below 0.2Pa and heated to 170-200 ℃, and then hydrogen is filled to 95-100 kPa at the temperature for 45-60 min;
vacuumizing to below 1Pa again, heating to 820-850 ℃, and filling hydrogen to 30-35 kPa at the temperature for 75-90 min;
raising the temperature to 880-900 ℃, filling hydrogen to 70-80 kPa, and maintaining the state for 25-35 min;
reducing the hydrogen pressure from 70-80 kPa to 5-6 kPa within 5min, reducing the hydrogen pressure to 4 kPa-4.5 kPa within 5-8 min, and keeping the hydrogen pressure at 3-4.5 kPa for 15 min-20 min;
cooling to 860-870 ℃, and meanwhile, forcibly discharging hydrogen to below 0.15 Pa;
and closing and heating, and cooling to below 30 ℃ to obtain the anisotropic neodymium iron boron magnetic powder.
8. The method according to any one of claims 4 to 7, further comprising a step nine of surface treating: and (3) carrying out electrophoretic coating or oil immersion treatment on the cured warm-pressing molded bonded magnet to prevent surface oxidation.
9. The method of claim 8, further comprising the step of ten, magnetizing: and carrying out multi-pole magnetization on the warm-pressing molded bonded magnet by using a proper magnetizing clamp according to requirements.
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| CN113948303B (en) * | 2021-10-20 | 2023-05-05 | 合肥工业大学 | Sintered NdFeB radiation ring and preparation method thereof |
| CN116978657B (en) * | 2023-09-22 | 2024-03-08 | 江西金力永磁科技股份有限公司 | Multipolar radial oriented sintered NdFeB circular ring and preparation method thereof |
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Address after: 100088, 2, Xinjie street, Xicheng District, Beijing Patentee after: GRIREM ADVANCED MATERIALS Co.,Ltd. Patentee after: Youyan rare earth high technology Co., Ltd Address before: 100088, 2, Xinjie street, Xicheng District, Beijing Patentee before: GRIREM ADVANCED MATERIALS Co.,Ltd. Patentee before: Guoke rare earth new material Co., Ltd |