JP2006097092A - Method for sintering rare-earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit a laid powder from exerting an adverse effect on a sintered compact (rare-earth magnet), and immediately separate sintered and fusion-bonded compacts from each other. <P>SOLUTION: The subject sintering method includes laying metallic particles 2 among green compacts 1, when stacking the green compacts 1 made of a raw powder for the magnet containing a rare-earth element, before sintering them. The metallic particle 2 to be used is, for instance, iron powder. Then, the sintered compacts are separated from each other by contacting them with an aqueous acid solution 5. The aqueous acid solution 5 is, for instance, an aqueous solution of nitric acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for sintering a rare earth magnet, and relates to a technique for preventing fusion and further easily separating a sintered body when a sintered body is laminated and sintered.

  Since rare earth magnets such as Nd—Fe—B based sintered magnets have advantages such as excellent magnetic properties, Nd as a main component is abundant in resources and relatively inexpensive, The demand tends to increase more and more. Under such circumstances, research and development for improving the magnetic properties of Nd—Fe—B based sintered magnets, improvement of manufacturing methods for manufacturing high-quality rare earth magnets, etc. are being promoted in various fields. .

  A rare earth magnet is basically formed by pressing an alloy powder (magnet raw material powder) obtained by pulverizing a raw material alloy in a magnetic field to form a compact, and then sintering the compact in a sintering furnace. It is manufactured by. In this case, if efficient sintering is performed, the compacts must be stacked and sintered. However, if the compacts are stacked and sintered, fusion between the products (sintered bodies) may occur. It becomes a problem.

Therefore, when the compacts are stacked and sintered, particles (powder) called a spread powder are placed between the compacts and sintered (for example, see Patent Document 1). ). For example, the spread powder is also spread between the sintering base plate and the molded body, and usually oxide powder is used (see, for example, Patent Document 2 and Patent Document 3).
JP 2001-335808 A JP 7-161560 A JP 2002-83730 A

  However, when an oxide powder is used as a spread between molded bodies, there are various disadvantages as described below, and an improvement is desired. First, the oxide powder adhering to the compact is reduced by the rare earth component contained in the compact during sintering, resulting in an increase in the amount of oxygen on the surface of the sintered compact (rare earth magnet). As a result, the magnetic characteristics are deteriorated. Second, the oxide powder adsorbs moisture in the air during storage in the air, which adversely affects (oxidizes) the magnetic properties of the magnet during sintering. Third, rare earth oxides are expensive. Fourthly, since oxide powders such as zirconium oxide (zirconia) are too small to be handled, it is effective to make them granular, for example, but this requires processing and increases costs. . Fifth, the oxide powder is non-magnetic, and the oxide powder falls if the spreading surface is not a horizontal surface. Therefore, depending on the product shape, the oxide powder cannot be sufficiently sprayed, and a sufficient effect can be obtained. I can't.

  Therefore, the present invention has been proposed in view of such a conventional situation, and can eliminate the inconvenience of using oxide powder as a spread powder, and has an adverse effect on a sintered body (rare earth magnet). An object of the present invention is to provide a rare earth magnet sintering method that can reduce costs, reduce the cost, and reliably obtain the effect of spreading powder.

  As a result of repeated investigations to achieve the above-mentioned object, the present inventors have concluded that it is effective to use metal particles as a spread powder, and can eliminate any inconvenience when using oxide powder. I came to get. In addition, when metal particles are used, it is inevitable that the sintered bodies are fused to some extent, but the sintered bodies fused through the metal particles can be easily separated by bringing them into contact with an acid aqueous solution. It came to obtain the knowledge of.

  The present invention has been completed based on these findings. That is, the method for sintering a rare earth magnet of the present invention is such that when a sintered compact of magnet raw material powder containing a rare earth element is laminated and sintered, at least after the metal particles are interposed between the compacts, the sintering is performed. The sintered body is separated by contacting with an acid aqueous solution.

  In the present invention, metal particles such as iron powder are used as the spread powder. Since the metal particles are not oxides, they do not oxidize the sintered body (rare earth magnet) and have little adverse effect on the rare earth magnet. Further, since the metal particles are dense, moisture adsorption during storage is less than that of the oxide powder, and in this respect, there is little adverse effect on the rare earth magnet.

  In addition, metal particles are cheaper than oxide powders, and those having an arbitrary particle size distribution are available, so there is no need to process them into granules like oxide powders, which is costly. This is far more advantageous than oxide powder. Furthermore, since metal particles such as iron powder are magnetic, they are attracted to the molded body by the residual magnetism of the remaining molded body, and can be spread on all surfaces of the molded body regardless of the shape of the molded body. Is done.

  However, when metal particles are used as the spread powder, the sintered bodies may be fused through the spread powder. In such a case, if a mechanical impact is applied to separate the sintered bodies, there is a possibility that chipping defects or the like may occur. Thus, in the present invention, the sintered compact (sintered body) is brought into contact with an acid aqueous solution, and the fused sintered body is separated. By contacting with the acid aqueous solution, the surface of the metal particles or the entire metal particles are dissolved, and the sintered body fused through the metal particles is quickly separated. At the time of separation, it is not necessary to apply a mechanical impact or the like, and chipping defects hardly occur. Although the surface of the sintered body (rare earth magnet) may be slightly dissolved by contact with the acid aqueous solution, even if the surface is dissolved, the characteristics are not deteriorated.

  For example, Patent Document 1 discloses that iron powder is used as a spread powder. However, in Patent Document 1, iron powder is only disclosed in the same row as oxide powder (cerium oxide), and spread powder is used. In terms of the function, the superiority of iron powder over oxide powder is not recognized at all. Further, in Patent Document 1, it is not recognized that fusion can occur when iron powder is used as a spread powder. Naturally, no consideration is given to the separation of the fused sintered body. It has not been.

  The present invention pays attention to the superiority as a spreading powder of metal particles such as iron powder and actively uses and selects it, and also realizes quick separation of the sintered body. The technology described is one that sets a line.

  According to the present invention, it is possible to eliminate inconveniences in the case where oxide powder is used for the spread powder. Specifically, adverse effects on the sintered body (rare earth magnet) can be suppressed, and the cost can be reduced. Moreover, it is possible to reliably obtain the effect of the spreader. Furthermore, according to the present invention, even when the sintered bodies are fused together, it is possible to separate them easily and quickly without causing defective chips.

  Hereinafter, the method for sintering a rare earth magnet according to the present invention will be described in detail.

  Rare earth magnets are basically formed by pressing a magnet raw material powder obtained by pulverizing a raw material alloy in a magnetic field to form a compact, and then sintering the compact in a sintering furnace, followed by an aging treatment. It is manufactured by doing.

The rare earth magnets to be manufactured are rare earth sintered magnets mainly composed of rare earth elements, such as neodymium iron boron magnets and samarium cobalt magnets. The neodymium iron boron-based magnet is, for example, R-T-B (where R is one or more of rare earth elements, where the rare earth element includes Y. T is a transition that requires Fe or Fe and Co as essential elements. 1 or 2 or more of metal elements, and B is boron.), Rare earth element R is 20 to 40% by weight, boron B is 0.5 to 4.5% by weight, and the balance is a transition metal The composition is such that it is element T. Here, R is one or more selected from rare earth elements, that is, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. Especially, since Nd is abundant in resources and relatively inexpensive, the main component is preferably Nd. Further, the inclusion of Dy is effective in improving the coercive force Hcj because it increases the anisotropic magnetic field.

  Alternatively, the additive element M can be added to form an R-T-B-M rare earth sintered magnet. In this case, examples of the additive element M include Al, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, Mo, Bi, and Ga. A seed | species or 2 or more types can be selected and added. The addition amount of these additional elements M is preferably 3% by weight or less in consideration of magnetic characteristics such as residual magnetic flux density. If the amount of additive element M added is too large, the magnetic properties may be deteriorated.

  Further, it can be applied not only to neodymium iron boron-based magnets but also to sintering of the samarium cobalt-based magnets (SmCo-based rare earth sintered magnets) and SmFeN-based magnets. Needless to say, it is applicable to all.

For the production of the rare earth magnet, for example, powder metallurgy is employed. Hereinafter, a method for producing a rare earth magnet, for example, a neodymium iron boron-based magnet by a powder metallurgy method will be described.

The production process of rare earth magnets by powder metallurgy is basically composed of alloying process, coarse pulverization process, fine pulverization process, forming process in magnetic field, sintering process, aging process, machining process, film forming process, etc. Is done. In order to prevent oxidation, most of the steps after sintering are performed in a vacuum or in an inert gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, etc.).

  In the alloying step, a raw material metal or alloy is blended in accordance with the magnet composition, melted in a vacuum or an inert gas, for example, Ar atmosphere, and cast into an alloy. As a casting method, a strip casting method (continuous casting method) in which a molten high-temperature liquid metal is supplied onto a rotating roll and an alloy thin plate is continuously cast is preferable from the viewpoint of productivity and the like. It is not something that can be done. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used.

  As the alloy, a single alloy having a final magnet composition may be used, or a plurality of types of alloys having different compositions may be mixed so as to have a final magnet composition. Mixing may be performed in any process of alloy, raw material coarse powder, and raw material fine powder, but mixing with an alloy is desirable from the viewpoint of mixing properties.

  In the coarse pulverization step, the previously cast raw alloy thin plate, ingot, or the like is pulverized until the particle size becomes approximately several tens of μm. As the pulverizing means, a stamp mill, a jaw crusher, a brown mill, or the like can be used. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen.

  The coarse pulverization step can be constituted by a plurality of steps in which a plurality of pulverization means are combined. For example, two steps of a hydrogen pulverization step and a mechanical coarse pulverization step can be performed. The hydrogen pulverization step is a step in which hydrogen is occluded in the cast raw material alloy and pulverized in a self-destructive manner utilizing the fact that the hydrogen occlusion amount varies depending on the phase. Thereby, it can grind | pulverize to the magnitude | size about particle size several mm. The mechanical coarse pulverization step is a step of pulverizing using a mechanical method such as a brown mill as described above. The raw alloy powder pulverized to a size of about several millimeters by the hydrogen pulverization step is used. Then, pulverize until the particle size is about several tens of μm. When performing the hydrogen pulverization step, the mechanical coarse pulverization step may be omitted.

  After the coarse pulverization step, a fine pulverization step is performed. This fine pulverization step is performed using, for example, a jet mill. The conditions for fine pulverization may be appropriately set according to the airflow pulverizer to be used, and the raw material alloy powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. A jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates powder particles by this high-speed gas flow, and collides powder particles with each other. Or, it is a method of crushing by generating a collision with a target or a container wall. Jet mills are generally classified into jet mills that use fluidized beds, jet mills that use vortex flow, jet mills that use impingement plates, and the like. In this pulverization step, for example, a fatty acid compound or the like may be added as a pulverization aid or a release agent before, after, or before and after pulverization, by about 0.03 to 0.4% by weight.

  After the pulverization step, the magnet raw material powder is formed in the magnetic field in the magnetic field forming step. Specifically, the magnet raw material powder obtained in the fine pulverization step is filled in a mold in which an electromagnet is arranged, and is molded in a magnetic field in a state where crystal axes are oriented by applying a magnetic field. Forming in the magnetic field may be either longitudinal magnetic field shaping or transverse magnetic field shaping. The forming in the magnetic field may be performed at a pressure of about 50 to 160 MPa in a magnetic field of 800 to 1500 kA / m, for example.

  The molded body is then sintered in a sintering step to form a rare earth magnet (neodymium iron boron-based magnet). In the present invention, for example, as shown in FIG. In addition, the compact 1 is stacked in a plurality of stages, here three stages, and sintered.

  At this time, the metal particles 2 are spread as a spread powder between the molded bodies 1, and the molded bodies 1 are overlapped via the metal particles 2. In addition, these molded bodies 1 are usually arranged and sintered on the sintering base plate 3, but the metal particles 2, which are the spread powder, are also scattered on the sintering base plate 3, and It is preferable that the metal particles 2 are interposed therebetween.

  Here, the metal particles 2 may be made of any metal material as long as it dissolves in an acid aqueous solution, such as iron powder, for example. It is preferable that there are metal particles such as atomized iron powder, reduced iron powder, alloy steel powder, etc., which are mainly composed of iron. The atomized iron powder is produced by a water atomization method or other methods, and can have an arbitrary particle size distribution depending on the production conditions and the like.

  The particle size distribution of the metal particles 2 is also important. If the particle size of the metal particles 2 is too small or too large, handling becomes difficult. Therefore, the optimum range of the particle diameter of the metal particles 2 is 80 μm to 250 μm.

  In the sintering step, the compact 1 is sintered in a vacuum or an inert gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, or the like). Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of a particle size and a particle size distribution, for example, what is necessary is just to sinter at 1000-1150 degreeC for about 2 hours.

  In the present invention, since the metal particles 2 are used as a spread powder, and the metal particles 2 are interposed between the molded bodies 1 to be overlaid, the molded bodies 1 are firmly bonded to each other by the sintering. There is nothing. Further, since the metal particles 2 are not oxides, the sintered product (sintered body = rare earth magnet) of the molded body 1 is not oxidized, and there is little adverse effect on the rare earth magnet. Furthermore, since the metal particles 2 are denser than the oxide powder, the adsorption of moisture during storage is less than that of the oxide powder, and in this respect as well, there are few adverse effects on the rare earth magnet.

The metal particles 2 are cheaper than oxide powders, and those having an arbitrary particle size distribution are available. Processing into granules like oxide powder is also unnecessary. Therefore, it is far more advantageous than oxide powder in terms of cost. Moreover, since the metal particles 2 such as iron powder are magnetic bodies, they are attracted to the molded body 1 by the residual magnetism of the molded body 1 that remains slightly. Therefore, spraying on all surfaces of the molded body 1 is realized regardless of the shape of the molded body 1.

  After the sintering, the obtained sintered body is preferably subjected to an aging treatment. This aging treatment is an important step in controlling the coercive force Hcj of the obtained rare earth magnet. For example, the aging treatment is performed in an inert gas atmosphere or in a vacuum. As the aging treatment, a two-stage aging treatment is preferable, and in the first aging treatment step, the temperature is maintained at a temperature of about 800 ° C. for 1 to 3 hours. In the second stage aging treatment step, the temperature is maintained at about 550 ° C. for 1 to 3 hours. Since the coercive force Hcj is greatly increased by heat treatment at around 600 ° C., when aging treatment is performed in a single stage, it is advisable to perform aging treatment at around 600 ° C.

  After the sintering process and the aging process, a machining process and a film forming process are performed, and the molded body 1 (sintered body) is fused with the metal particles 2 by the previous sintering process. It may be. Therefore, in order to eliminate this fused state, in the present invention, the molded body (sintered body) 1 fused through the metal particles 2 is brought into contact with the acid aqueous solution, and the surface of the metal particles 2 or the metal particles. Dissolve 2 whole.

  The method of bringing the fused molded body (sintered body) 1 into contact with the acid aqueous solution may be, for example, a method of spraying the molded aqueous body (sintered body) 1 fused with the acid aqueous solution, or the like. A method of immersing the fused formed body (sintered body) 1 in an acid aqueous solution may be used. FIG. 2 shows how the fusion is eliminated by dipping. The molded body (sintered body) 1 fused through the metal particles 2 is dipped in the acid aqueous solution 5 in the container 4 and left for a predetermined time. After that, the molded body (sintered body) 1 is taken out. Thereby, the surface of the metal particle 2 melt | dissolves, it falls from a molded object (sintered body 1), and is isolate | separated into each molded object (sintered body) 1. FIG. At the time of separation, it is not necessary to apply a mechanical impact or the like, and no chipping defect occurs. In the immersion of the acid aqueous solution, it is also effective to apply ultrasonic vibration to perform ultrasonic cleaning. If ultrasonic cleaning is performed in the acid aqueous solution 5, the dissolution of the metal particles 2 proceeds more rapidly, and separation in a short time becomes possible.

  As the acid aqueous solution 5, nitric acid, hydrochloric acid, sulfuric acid aqueous solution or the like can be used, and nitric acid aqueous solution is preferable. When using a nitric acid aqueous solution, the concentration is preferably about 1% to 10%. If the nitric acid concentration is too thin, it takes a long time for separation, which may adversely affect the characteristics of the rare earth magnet. On the other hand, if the nitric acid concentration is too high, dissolution proceeds excessively, and there is a possibility that the resulting rare earth magnet will be adversely affected.

  After separation of the molded body (sintered body) 1, a machining process and a film forming process are performed to complete a product. The machining step is a step of mechanically forming into a desired shape, and a predetermined machining is applied according to the product shape. The film forming step is a step performed for the purpose of suppressing oxidation of the obtained rare earth magnet, and for example, a plating film or a resin film is formed on the surface of the rare earth magnet.

  Hereinafter, specific examples to which the present invention is applied will be described based on experimental results. In addition, it cannot be overemphasized that this invention is not limited to description of a following example.

<Example 1>
In this example, a rectangular NdFeB magnet was manufactured as follows. That is, first, a magnet raw material powder having a composition of Nd 30.5% by weight, Dy 1.5% by weight, B 1.0% by weight, Co 0.5% by weight, and the balance Fe was prepared. A molded body was obtained by molding in a magnetic field to 0.0 mm and a height of 3.0 mm.

The produced compacts were stacked in five layers, and atomized iron powder was sprayed as a spread between the base plate for sintering and the compacts and between the compacts. The particle size of the atomized iron powder used was 80 μm to 250 μm. In this state, it was sintered in a sintering furnace and subjected to an aging treatment. The sintering was performed at a sintering temperature of 115 ° C. for 2 hours in a vacuum. Thereafter, an aging treatment was performed.

After completion of sintering and aging, the fused sintered body was immersed in an aqueous nitric acid solution having a concentration of 5% and separated into individual sintered bodies. When the magnetic properties of the rare earth magnet obtained as described above were measured, it was found that Br was 1350 (mT), Hcj was 1280 (kA / m), and (BH) max was 354 (kJ / m ³ ). Moreover, in the obtained rare earth magnet, almost no chipping defect was observed. When reduced iron powder was used instead of atomized iron powder, the same effect was obtained.

<Comparative Example 1>
A rectangular NdFeB magnet was manufactured in the same manner as in Example 1 except that oxide powder (yttria) was used as the bed powder. The magnetic properties of the obtained rare earth magnet were Br = 1343 (mT), Hcj = 1155 (kA / m), (BH) max = 348 (kJ / m ³ ), and were obtained in Example 1 above. Compared with rare earth magnets, a clear deterioration in characteristics was observed.

<Comparative example 2>
As in the previous Example 1, sintering was performed using atomized iron powder as the bed powder, and the fused sintered body was separated by applying mechanical force. The magnetic properties of the obtained rare earth magnet were Br = 1349 (mT), Hcj = 1282 (kA / m), (BH) max = 353 (kJ / m ³ ), and were obtained in Example 1 above. Magnetic properties equivalent to those of rare earth magnets were obtained. However, in the rare earth magnet as a product, 3 out of 10 chips were defective.

It is a schematic diagram which shows the mode of the superimposition of the molded object at the time of sintering. It is a schematic diagram which shows a mode that the fuse | melted molded object (sintered body) is immersed in acid aqueous solution and isolate | separated.

1 Molded body (sintered body), 2 metal particles, 3 base plate for sintering, 4 container, 5 acid aqueous solution

Claims (8)

  When the sintered compacts of magnet raw material powders containing rare earth elements are stacked and sintered, at least metal particles are interposed between the compacts and then sintered, and then contacted with an acid aqueous solution to separate the sintered compacts. A method for sintering a rare earth magnet.   2. The rare earth magnet sintering method according to claim 1, wherein the metal particles are particles mainly composed of iron.   3. The rare earth magnet sintering method according to claim 1, wherein the metal particles have a particle diameter of 80 to 250 [mu] m.   4. The rare earth magnet sintering method according to claim 1, wherein the acid aqueous solution is one or more selected from a nitric acid aqueous solution, a hydrochloric acid aqueous solution, and a sulfuric acid aqueous solution. 5.   5. The method for sintering a rare earth magnet according to claim 4, wherein the acid aqueous solution is a nitric acid aqueous solution.   6. The rare earth magnet sintering method according to claim 5, wherein the concentration of the nitric acid aqueous solution is 1% to 10%.   The method for sintering a rare earth magnet according to claim 1, wherein the contact with the acid aqueous solution is performed by dipping in the acid aqueous solution.   8. The rare earth magnet sintering method according to claim 7, wherein ultrasonic cleaning is performed at the time of the immersion.

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