CN112908664B - Method for preparing rare earth sintered magnet - Google Patents
Method for preparing rare earth sintered magnet Download PDFInfo
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- CN112908664B CN112908664B CN201911222495.1A CN201911222495A CN112908664B CN 112908664 B CN112908664 B CN 112908664B CN 201911222495 A CN201911222495 A CN 201911222495A CN 112908664 B CN112908664 B CN 112908664B
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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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/02—Compacting only
- B22F3/03—Press-moulding apparatus therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/02—Compacting only
- B22F3/04—Compacting only by applying fluid pressure, e.g. by cold isostatic pressing [CIP]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
- B22F2003/248—Thermal after-treatment
Abstract
The invention provides a method for preparing a rare earth sintered magnet with a non-single easy magnetization direction, which comprises the following steps: splicing the N pressed compacts to form a combined pressed compact, enabling orientation directions between adjacent pressed compacts to form an included angle theta, pressing the combined pressed compact in an isostatic pressing mode to form an isostatic pressed compact, and performing high-temperature sintering and tempering on the isostatic pressed compact; wherein N is more than or equal to 2,0 degree is more than theta and less than 90 degrees. After the sintered magnet prepared by the process is saturated and magnetized, the surface magnetic field of the sintered magnet is far higher than that of the sintered magnet with a single easy magnetization direction under the same condition. In addition, the process flow is simple, resin is not required to be introduced to modify the magnetic powder, the carbon and oxygen contents of the magnet are not increased, and a pre-sintering decarburization process is not required to be added in the high-temperature sintering process.
Description
Technical Field
The invention belongs to the technical field of rare earth sintered magnet preparation, and particularly relates to a method for preparing a rare earth sintered magnet with a non-single easy magnetization direction.
Background
Rare earth sintered magnets have high remanence and high coercive force, and are widely used in the fields of automobile motors and the like. The higher the magnetic field strength at the magnet surface, the higher the driving force that can be achieved by the motor. For example, automotive motors, whose development requires motors to provide greater and greater driving forces, mean that the surface magnetic field strength of the magnets needs to be further increased. The sintered magnet is prepared by a conventional process, an orientation magnetic field is required to be applied to orient the pressed compact in the pressing process, the orientation direction of the pressed compact is consistent with the orientation direction of the orientation magnetic field, and the direction of easy magnetization in the sintered magnet is the same as the orientation direction of the pressed compact. If it is desired to increase the magnetic field strength at the surface of the magnet, the remanence of the magnet is only increased continuously. Along with the development of the preparation process, the lifting space of the remanence of the magnet is smaller and smaller, and along with the higher and higher requirement of the surface magnetic field intensity of the magnet, the requirement cannot be met gradually by simply depending on the mode of improving the remanence of the magnet.
A different magnet design concept can solve this problem: on the basis of keeping the magnetic property of the magnet material unchanged, if different areas in the magnet have different easy magnetization directions, after an external magnetic field with ultrahigh magnetic field strength is applied to magnetize the magnet, the magnet with different easy magnetization directions can generate a plurality of magnetic fields which are not parallel to each other on the surface of the magnet. The superposition of the magnetic fields causes the maximum value of the surface magnetic field intensity of the magnet to be far higher than the maximum surface magnetic field intensity of the magnet with only one easy magnetization direction. When the area generating the maximum surface magnetic field is used as the working area of the magnet in the motor, the design requirement of the motor of the future automobile can be met.
If the two sintered and tempered magnets are bonded by using the adhesive, the orientation directions of the two sintered and tempered magnets form an angle, so that the bonded magnets have two easy magnetization directions, and the required magnet is obtained. However, when the bonded magnet is applied to a motor rotor, the bonded magnet may crack due to the rotor moving at a high speed, and the temperature of the working environment is high, so that the magnet is cracked due to the failure of the adhesive, and the normal work of the motor is influenced.
In order to solve the above problems, chinese patent application CN107430935 discloses a method for preparing a sintered magnet, in which each partitioned portion of the sintered magnet has different directions of easy magnetization, and the directions of easy magnetization are not parallel. The preparation process comprises mixing magnetic powder particles with hot-melt resin to obtain a first molded body, and applying a parallel magnetic field to orient the parts of the first molded body in the same orientation direction. The first shaped body is then subjected to a deformation process to obtain a second shaped body, the deformation process causing portions of the second shaped body to have different orientations. And finally, pre-burning and decarbonizing the second formed body, and then sintering at high temperature to form the magnet. However, because the process adopts the first forming body prepared by mixing the resin containing 1wt% -40 wt% and the magnetic powder, the pre-burning decarburization treatment is carried out in the hydrogen atmosphere at a certain temperature to reduce the carbon content and the oxygen content of the magnet. The pre-burning decarburization treatment in mass production often requires a long time, and it is not easy to completely remove carbon and other impurity elements brought in by the resin. The residual carbon content in the magnet is high, which is not beneficial to improving the magnetic performance of the magnet. In addition, the resin discharge is environmentally hazardous due to the relatively large amount of resin used in the process. In addition, the process adopts the method of pre-burning and decarbonizing the pressed blank in the hydrogen atmosphere under the high-temperature condition, the management and control of the hydrogen are difficult in the production process, and once the hydrogen overflows, the pressed blank is exposed to the explosion risk. Therefore, the technical scheme has poor application prospect in actual production.
Disclosure of Invention
In view of the deficiencies of the prior art, the present invention provides a method for preparing a rare earth sintered magnet having a non-single easy magnetization direction. After the sintered magnet prepared by the process is saturated and magnetized, the surface magnetic field of the sintered magnet is far higher than that of the sintered magnet with a single easy magnetization direction under the same condition. In addition, the process flow is simple, resin is not required to be introduced to modify the magnetic powder, the carbon and oxygen contents of the magnet are not increased, and a pre-sintering decarburization process is not required to be added in the high-temperature sintering process.
The technical scheme includes that N pressed compacts are spliced to form a combined pressed compact, an included angle theta is formed between orientation directions of adjacent pressed compacts, the combined pressed compact is pressed to form an isostatic pressed compact in an isostatic pressing mode, and the isostatic pressed compact is subjected to high-temperature sintering and tempering treatment; wherein N is more than or equal to 2, theta is more than 0 degree and less than 90 degrees.
In some embodiments of the present invention, the adjacent compacts comprise a first compact having a joggled face at an angle θ 1 to the orientation direction and a second compact having a joggled face at an angle θ 2 to the orientation direction, wherein θ 1 is 0 ° ≦ θ 1 < 90 °, θ 2 is 0 ° ≦ θ 2 < 90 °, and θ 1+ θ 2= θ.
In some embodiments of the present invention, the joining surface of the first compact is parallel to the orientation direction, and the joining surface of the second compact has an angle θ 2= θ with the orientation direction.
In some embodiments of the present invention, the first compact and the second compact are the same shape.
In some embodiments of the present invention, the green compact is prepared using a magnetic field forming press comprising a die and a bilaterally symmetric electromagnet, the die comprising a first upper die, a first lower die, a second upper die having an angle, a second lower die having an angle, and a bilaterally symmetric female die, the female die being connected to the first upper die, the first lower die, the second upper die, the second lower die, and the electromagnet, respectively, the first upper die being further connected to the second upper die, the first lower die being further connected to the second lower die, a space being formed by the second upper die and the second lower die for preparing the green compact, a first inner surface of the second lower die having an angle with an orientation direction equal to θ 1 or θ 2.
In some embodiments of the invention, when N is greater than or equal to 3, the included angle theta between adjacent pressed compacts is not equal.
In some embodiments of the invention, the compacts are orientation-compacted with a fine powder having a particle size D50= 2.0-6 μm, an orientation magnetic field of 1.6-2.5T, and a density of 3.5-4.5 g/cm 3 。
In some embodiments of the invention, the fine powder is prepared from coarse powder, the coarse powder is prepared by crushing an alloy thin strip with the average thickness of 0.2-0.5 mm through a hydrogen explosion process, the hydrogen explosion process is used for dehydrogenation for 1-8 hours at 400-600 ℃, and the hydrogen content of the coarse powder is 1000-1500 ppm.
In some embodiments of the invention, the isostatic compact is formed using cold isostatic pressing at a pressure of 100 to 300MPa.
In some embodiments of the invention, the sintering temperature of the high-temperature sintering is 1000-1100 ℃, and the sintering time is 1-6 h; the tempering treatment comprises high-low temperature secondary tempering, wherein the high-temperature tempering is carried out for 0.5-5 h at the temperature of 800-950 ℃, and the low-temperature tempering is carried out for 0.5-6 h at the temperature of 450-520 ℃.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
Fig. 1 is a schematic diagram of a green compact structure of a rare earth sintered magnet having a non-single easy magnetization direction according to an embodiment of the present invention.
Fig. 2 is a flow chart of a process for preparing a rare earth sintered magnet having a non-single easy magnetization direction according to an embodiment of the present invention.
Fig. 3 is a partial structural schematic view of a conventional magnetic field molding press.
FIG. 4 is a schematic structural view of a rare earth sintered magnet having a non-single direction of easy magnetization prepared by the process shown in FIG. 2.
Fig. 5 is a schematic view of a partial structure of a magnetic field forming press according to an embodiment of the present invention.
Fig. 6 is a schematic diagram of a process of preparing a rare earth sintered magnet and cutting the rare earth sintered magnet to form a working magnet according to still another embodiment of the present invention, (a) is a schematic diagram of cutting a first green compact and a second green compact, (b) is a schematic diagram of splicing the first green compact and the second green compact to form a combined green compact, (c) is a schematic diagram of a cutting direction of the rare earth sintered magnet obtained after isostatic pressing and sintering tempering of the combined green compact, and (d) is a schematic diagram of the working magnet formed after cutting.
Fig. 7 (a) is a plan view of a working magnet prepared according to still another embodiment of the present invention, and fig. 7 (b) is a front view.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The terms "first", "second", etc. in this application are used to distinguish between different objects and not to describe a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus. Furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly and include, for example, fixed or removable connections or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in this application will be understood to be a specific case for those of ordinary skill in the art.
Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the specification. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein may be combined with other embodiments.
The method for preparing the rare earth sintered magnet with the non-single easy magnetization direction comprises the following steps: splicing the N pressed compacts to form a combined pressed compact, enabling the orientation directions of the adjacent pressed compacts to form an included angle theta, pressing the combined pressed compact in an isostatic pressing mode to form an isostatic pressed compact, and performing high-temperature sintering and tempering on the isostatic pressed compact to obtain the composite material; wherein N is more than or equal to 2, theta is more than 0 degree and less than 90 degrees.
The easy magnetization direction of the sintered magnet is the orientation direction of the pressed compact, compared with the magnet prepared by the conventional magnet preparation method, the magnet prepared by the method has only one easy magnetization direction, the magnet prepared by the method has a plurality of easy magnetization directions, and the included angle between the adjacent easy magnetization directions is equal to the included angle theta between the orientation directions of the adjacent pressed compacts when the combined pressed compact is formed.
The method has simple process flow, does not need to introduce resin to reform the magnetic powder, does not increase the carbon and oxygen content of the magnet, and does not need to increase the pre-sintering decarburization process in the high-temperature sintering process.
Fig. 1 is a view showing a structure of a green compact of a rare earth sintered magnet having a non-single easy magnetization direction according to an embodiment of the present invention. The two adjacent pressed blanks are respectively a first pressed blank and a second pressed blank, the included angle between the orientation direction of the first pressed blank and the orientation direction of the second pressed blank is theta, and theta is larger than 0 degree and smaller than 90 degrees. The double-arrow line in the figure indicates the orientation direction. The included angle between the splicing surface of the first pressed compact and the second pressed compact in contact with the orientation direction is theta 1, the included angle between the splicing surface of the second pressed compact and the first pressed compact in contact with the orientation direction is theta 2, wherein theta 1 is more than or equal to 0 degrees and less than 90 degrees, theta 2 is more than or equal to 0 degrees and less than 90 degrees, and theta 1+ theta 2= theta.
Preferably, the first green compact and the second green compact have the same shape.
According to the invention, the first green compact and the second green compact are prepared into the required shapes before the green compacts are combined and spliced, and then the green compacts are spliced. Of course, there are other ways to prepare a combined compact or an isostatic compact. The present invention is also intended to cover a case where N green compacts are joined together to form a combined green compact, and the combined green compact is press-formed by isostatic pressing, and the orientation directions of the adjacent first and second green compacts are not perpendicular or parallel to each other.
The pressed compact is prepared into a required shape firstly, and then the pressed compact is spliced, and the pressed compact before splicing can be prepared by cutting the pressed compact in a conventional mode, or is directly prepared from fine powder by adopting a magnetic field forming press.
Fig. 2 shows a process flow of preparing a rare earth sintered magnet with a non-single easy magnetization direction by cutting a compact according to an embodiment of the present invention, which includes:
s21: the pressed compacts are pressed by the conventional forming press in fig. 3, N pressed compacts are selected, and the N pressed compacts are processed into required shapes by wire cutting or other cutting tools, wherein the required shapes include x first pressed compacts with the included angles between the splicing surfaces and the orientation direction being theta 1 and y second pressed compacts with the included angles between the splicing surfaces and the orientation direction being theta 2. Wherein, when N is an odd number, x = [ N/2] +1, y = [ N/2], [ N/2] represents the integer part of the real number N/2 (e.g., [3/2] is equal to 1, and [7/2] is equal to 3). When N is an even number, x = y = N/2. Theta 1 is more than or equal to 0 degree and less than 90 degrees, theta 2 is more than or equal to 0 degree and less than 90 degrees, and theta 1+ theta 2= theta.
The magnetic field forming press shown in fig. 3 includes a die and electromagnets YA1, YA2 which are bilaterally symmetric. The die comprises an upper punch A, a lower punch B and female dies C1 and C2 which are symmetrical left and right. The female dies C1 and C2 are respectively connected with the upper die A, the lower die B and the electromagnets YA1 and YA2. The space formed by the upper die A, the lower die B and the female dies C1 and C2 is used for preparing a pressed blank.
S22: and mutually attaching the splicing surfaces of the x first pressed blanks and the splicing surfaces of the y second pressed blanks to form a combined pressed blank. The first green compact and the second green compact in the combined green compact are arranged at an interval, and the orientation directions of the adjacent first green compact and second green compact in the combined green compact form an included angle theta.
It should be noted that the included angle between the green compact formed by cutting and the orientation direction may also be θ 3, θ 4 \8230; \8230andθ N, and the angle of each included angle may be different as long as it is satisfied that θ, which is an included angle formed by the orientation directions of the adjacent first green compact and the second green compact, is greater than 0 ° and smaller than 90 °.
S23: and pressing the combined compact by an isostatic pressing mode to form an isostatic pressed compact.
S24: and (3) carrying out high-temperature sintering and tempering on the isostatic pressing compact to obtain the finished product.
FIG. 4 is a rare earth sintered magnet with a non-single direction of easy magnetization prepared by the process flow shown in FIG. 2. Where N =5,x =3,y =2, θ 1=0 °, θ 2= θ. The double-arrow line in the figure indicates the orientation direction.
Fig. 5 is a schematic view showing a part of a magnetic field forming press for directly preparing a green compact from magnetic powder according to an embodiment of the present invention. The magnetic field forming press comprises a die and electromagnets YA1 and YA2 which are bilaterally symmetrical. The die comprises a first upper punch A1, a first lower punch B1, a second upper punch A2 with an angle, a second lower punch B2 with an angle and two bilaterally symmetrical female dies C1 and C2. The female dies C1 and C2 are respectively connected with the first upper die A1, the first lower die B1, the second upper die A2, the second lower die B2 and the electromagnets YA1 and YA2, the first upper die A1 is also connected with the second upper die A2, and the first lower die B1 is also connected with the second lower die B2. The space formed by the second upper die A2 and the second lower die B2 is used for preparing a compact. The inner surface of the first upper die A2 or the second lower die B2 has an angle equal to θ 1 or θ 2 with the orientation direction.
The pressed compact prepared by the die can replace a pressed compact obtained by processing in the embodiment of fig. 2 by wire cutting or other cutting methods, and the side surface of the pressed compact contacting with the inner surface of the second upper punch or the inner surface of the second lower punch is used as a splicing surface for splicing. Because need not the cutting can splice, then carry out processes such as isostatic pressing and high-temperature sintering, tempering, the flow is simpler, and required manpower and materials are also less, and the cost reduction is a lot.
FIG. 6 is a schematic view showing a process of preparing a rare earth sintered magnet having a non-single easy magnetization direction and cutting it to form a working magnet according to another embodiment of the present invention, including:
s61: pressing the pressed blanks by the magnetic field forming press in fig. 3, as shown in fig. 6 (a), selecting one pressed blank as a first pressed blank, and using one side surface parallel to the orientation direction as a splicing surface for performing combined splicing with a second pressed blank. And cutting the other cuboid pressed blank by using a metal wire to prepare a second pressed blank, so that the included angle theta between the cut processing surface (namely the splicing surface combined with the first pressed blank) and the orientation direction is formed. As shown in fig. 6 (b), the joining surface of the first green compact and the joining surface of the second green compact are joined together, and then the combined green compact formed after joining is subjected to isostatic pressing to form an isostatic pressed compact.
S62: the combined compact is compacted by isostatic pressing to form an isostatic pressed compact.
S63: and (3) carrying out high-temperature sintering and tempering treatment on the isostatic pressing compact.
S64: as shown in fig. 6 (c), the rare earth sintered magnet after the high-temperature sintering and tempering treatment is cut to form a desired working magnet as shown in fig. 6 (d).
The invention preferably applies an oriented compaction of the green compacts with fine powder having a particle size D50= 2.5-6 μm. Among them, more preferably, the orientation magnetic field is 1.6 to 2.5T. More preferably, the green compact has a density of 3.5 to 4.5g/cm 3 。
Preferably, the fine powder is prepared from coarse powder, and the coarse powder is formed by crushing an alloy thin strip with the average thickness of 0.2-0.5 mm through a hydrogen explosion process. Wherein, more preferably, the hydrogen explosion process is dehydrogenation for 1 to 8 hours at 400 to 600 ℃, and the hydrogen content of the coarse powder is 1000 to 1500ppm. More preferably, the alloy thin strip is formed by a rapid solidification process, and the thickness of the alloy thin strip is 0.2-0.5 mm.
In the present invention, cold isostatic pressing is preferably used to form an isostatic compact. Wherein the cold isostatic pressure is preferably 100 to 300MPa.
In the present invention, the sintering temperature for high-temperature sintering is preferably 1000 to 1100 ℃ and the sintering time is preferably 1 to 6 hours.
In the present invention, preferably, the tempering treatment includes high and low temperature secondary tempering. More preferably, the high temperature tempering is carried out at 800-950 ℃ for 0.5-5 h, and the low temperature tempering is carried out at 450-520 ℃ for 0.5-6 h.
The present invention will be described below with reference to specific examples. The values of the process conditions taken in the following examples are exemplary and ranges of values are provided as indicated in the foregoing summary, and reference may be made to conventional techniques for process parameters not specifically noted. The detection methods used in the following examples are all conventional in the industry.
Examples
The magnet formula of the N35SH grade sintered neodymium iron boron magnet is selected for proportioning, and an alloy thin strip is prepared through a rapid hardening process, wherein the thickness of the thin strip is 0.2-0.4 mm. Dehydrogenation was carried out at 540 ℃ for 6 hours by a hydrogen crushing step to obtain coarse powder having a hydrogen content of 1200ppm, and the coarse powder was put into a jet mill to carry out fine powder milling to obtain fine powder having a D50=4.0 μm. Pressing multiple cuboid pressed compacts in magnetic field with magnetic field intensity of 1.8T and blank density of 4.2g/cm 3 。
By adopting the magnet preparation method shown in fig. 6, part of the rectangular green compacts is selected as the first green compact, and one side surface of the first green compact parallel to the orientation direction is used as a splicing surface for performing combined splicing with the second green compact. A part of the rectangular parallelepiped green compacts is cut by using a metal wire to prepare second green compacts, so that included angles θ between the cut surfaces (which are spliced surfaces combined with the first green compacts in this embodiment) and the orientation direction are 0 °, 30 °, 45 °, 60 °, and 90 ° (that is, θ 1=0 °, θ 2=0 °, 30 °, 45 °, 60 °, or 90 ° in this embodiment), respectively. And (3) bonding the splicing surface of the first pressed compact and the splicing surface of the second pressed compact together, and then performing isostatic pressing on the combined pressed compact formed after bonding to form an isostatic pressed compact, wherein the isostatic pressure is 200MPa. And (3) putting the isostatic pressing compact into a vacuum sintering furnace for sintering and tempering, wherein the sintering temperature is 1050 ℃, the heat preservation time is 6 hours, the tempering adopts a high-low temperature secondary tempering process, the high-temperature tempering process is 920 ℃ for 2 hours, and the low-temperature tempering process is 480 ℃ for 4 hours. The density of the sintered magnet is 7.55-7.56 g/cm 3 . And carrying out linear cutting processing on the rare earth sintered magnet obtained after sintering and tempering to obtain the required working magnet.
The working magnet produced in this example had dimensions of 12mm × 11mm × 4mm, with the 11mm × 4mm plane (fig. 7 (b)) being parallel to both easy magnetization directions. Fig. 7 (a) is a top view (size 12mm × 11 mm) of the working magnet produced in this example, fig. 7 (b) (size 11mm × 4 mm) is a front view, in which the double-arrow line indicates two directions of easy magnetization, and the black portion and the gray portion have the same size, and are respectively a portion obtained by sintering and tempering the first green compact and a portion obtained by sintering and tempering the second green compact, which account for 50% of each, and points c1 to c15 are surface magnetic field strength test points.
No cracks were observed in the sintered magnets at the remaining θ angles, except that cracks were observed in the sintered magnet at θ =90 °.
Since the θ =90 ° sintered body was cracked, the magnetic properties were measured for the working magnets of the remaining θ angles, regardless of the measurement of the magnetic properties. And (3) magnetizing under a saturated pulse magnetic field (the magnetic field intensity is 6T), wherein the direction of the magnetizing field is parallel to the orientation direction of the first green compact. The magnetic performance test of the working magnet, including room temperature demagnetization curve test and surface magnetic field strength test, is performed, and the data is shown in table 1. In the magnetic field intensity test of the surface of the magnet, 15 points (points c 1-c 15 in the figure 7 (a)) are respectively selected on the surface of each working magnet by adopting a gauss meter to serve as test points, and the maximum value and the minimum value are recorded. When in measurement, the normal direction of the coil plane of the Hall probe of the gaussmeter is parallel to the plane of the 12mm multiplied by 11mm surface of the magnet and is tightly attached to the surface. Among them, the θ =0 ° magnet corresponds to a conventional magnet, and has only one easy magnetization direction.
TABLE 1 magnetic Properties of working magnets at different theta angles
B max The maximum value of the surface magnetic field intensity of the measuring points c1 to c15, B min The minimum value of the surface magnetic field intensity of the measuring points c 1-c 15 is obtained.
B max boost (％)＝(B max -B' max )/B' max *100, wherein, B' max The maximum magnetic field strength of the surface of the prepared working magnet is theta =0 deg.
As can be seen from Table 1, the working magnets prepared at θ of 30 °, 45 ° and 60 °, respectively, have a large improvement in the maximum surface magnetic field strength, although the remanence is lower than that of a magnet having a single orientation direction, B max boost (%) can reach more than 30%.
In conclusion, the method of the present invention can prepare the rare earth sintered magnet with non-single easy magnetization direction, and the maximum surface magnetic field intensity of the rare earth sintered magnet is far higher than that of the rare earth sintered magnet with single easy magnetization direction. The method of the invention does not need to mix the magnetic powder particles with the resin, does not need the pre-sintering decarburization process, has simple process and no harm to the environment, and does not increase the carbon content and the oxygen content of the sintered magnet.
It should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (9)
1. A method of producing a rare earth sintered magnet, characterized by comprising: splicing the N pressed compacts to form a combined pressed compact, enabling the orientation directions of the adjacent pressed compacts to form an included angle theta, pressing the combined pressed compact in an isostatic pressing mode to form an isostatic pressed compact, and performing high-temperature sintering and tempering treatment on the isostatic pressed compact; wherein N is more than or equal to 2, theta is more than 0 degree and less than 90 degrees;
the adjacent pressed blanks comprise a first pressed blank and a second pressed blank, an included angle between the splicing surface of the first pressed blank and the orientation direction is theta 1, an included angle between the splicing surface of the second pressed blank and the orientation direction is theta 2, wherein theta 1 is larger than or equal to 0 degrees and smaller than 90 degrees, theta 2 is larger than or equal to 0 degrees and smaller than 90 degrees, and theta 1+ theta 2= theta.
2. A method as claimed in claim 1, characterized in that the splicing face of the first compact is parallel to the orientation direction and the second splicing face of the second compact is at an angle θ 2= θ to the orientation direction.
3. The method of claim 1, wherein the first compact and the second compact are the same shape.
4. The method of claim 1, wherein the green compact is prepared using a magnetic field forming press comprising a die and a bilaterally symmetric electromagnet, the die comprising a first upper die, a first lower die, a second upper die with an angle, a second lower die with an angle, and a bilaterally symmetric female die, the female die being connected to the first upper die, the first lower die, the second upper die, the second lower die, and the electromagnet, respectively, the first upper die being further connected to the second upper die, the first lower die being further connected to the second lower die, the space formed by the second upper die and the second lower die being used to prepare the green compact, the second lower die having an inner surface with an angle equal to θ 1 or θ 2 with the orientation direction.
5. The method of claim 1, wherein when N ≧ 3, the included angle θ between adjacent compacts is unequal.
6. The method according to claim 1, characterized in that the compacts are orientation-compacted with a fine powder having a particle size D50= 2.5-6 μm, an orientation magnetic field of 1.6-2.5T and a density of 3.5-4.5 g/cm 3 。
7. The method as claimed in claim 6, wherein the fine powder is prepared from coarse powder, the coarse powder is obtained by crushing an alloy thin strip with an average thickness of 0.2-0.5 mm through a hydrogen explosion process, the hydrogen explosion process is performed at 400-600 ℃ for dehydrogenation for 1-8 h, and the hydrogen content of the coarse powder is 1000-1500 ppm.
8. The method of claim 1, wherein the isostatic compact is formed using cold isostatic pressing at a pressure of 100 to 300MPa.
9. The method according to claim 1, wherein the sintering temperature of the high-temperature sintering is 1000-1100 ℃, and the sintering time is 1-6 h; the tempering treatment comprises high-low temperature secondary tempering, wherein the high-temperature tempering is carried out at the temperature of 800-950 ℃ for 0.5-5 h, and the low-temperature tempering is carried out at the temperature of 450-520 ℃ for 0.5-6 h.
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