JP6003446B2 - Method for manufacturing oriented magnet and rare earth magnet - Google Patents

Description

  The present invention relates to a method for producing an oriented magnet, which is a precursor of a rare earth magnet, and a method for producing a rare earth magnet using the oriented magnet produced by this method.

  An outline of an example of a method for producing a rare earth magnet is as follows. For example, a fine powder obtained by rapid solidification of a Nd-Fe-B metal melt is formed into a compact while being pressed, and the magnetic anisotropy is applied to the compact. Of rare earth magnet precursor (orientation magnet) by performing hot plastic working to impart a rare earth magnet, and a rare earth magnet is manufactured by diffusing and infiltrating a modified alloy that increases the coercive force of the rare earth magnet precursor. Is generally applied. Patent Document 1 discloses a technique in which a low-melting point Nd—Cu alloy is used as the modified alloy, and this is attached to the surface of the oriented magnet and diffused and permeated by heat treatment.

  In the general manufacturing method described above, an oxide film or a mold release agent used in the molding process often adheres to the surface of the oriented magnet as an impurity, If the modified alloy is placed on the oriented magnet from above and the modified alloy is melted to perform diffusion and penetration, the oxide film and impurities will inhibit the diffusion and penetration of the modified alloy and sufficiently increase the coercive force. The problem of being unable to do so can arise.

  To deal with this problem, Patent Document 2 discloses a method for manufacturing an anisotropic rare earth magnet in which a soft metal made of an alloy such as Ni or Cu is coated on the surface of a molded body in hot plastic working of a rare earth magnet. Has been. According to this method, surface oxidation of the molded body can be prevented even when heated in the atmosphere while preventing baking with the mold.

  However, even if a soft metal is coated on the surface of a molded body on which an oxide film is already formed, the adhesion is not always good, and the soft metal is easily peeled off. Furthermore, the soft metal is trying to secure lubricity with the mold, but since the soft metal is a solid lubricant, the coefficient of friction between the mold and the soft metal naturally increases, resulting in a large molding load during hot plastic working. Will be required.

JP 2011-061038 A JP-A-7-176443

  The present invention has been made in view of the problems described above, and can effectively remove the oxide film on the surface of the molded body before hot plastic working, and between the molded body and the mold in the subsequent hot plastic working. It is an object of the present invention to provide a method for producing an oriented magnet capable of ensuring good lubricity and a method for producing a rare earth magnet using the oriented magnet obtained by this method.

  In order to achieve the above-mentioned object, the method for producing an oriented magnet according to the present invention includes immersing a molded body obtained by pressure-molding a powder as a magnet material in molten glass, and in the molded body and the molten glass serving as an anode. A first step of energizing a circuit including a power source to which a disposed cathode member is connected and electrolytically polishing the surface of the molded body, a hot process comprising a molded body that has been electropolished and has molten glass attached to the surface This is a second step in which the plastic working precursor is housed in a mold and subjected to hot plastic working to produce an oriented magnet in which magnetic anisotropy is imparted to the hot plastic working precursor.

  The method for producing an oriented magnet according to the present invention is such that when a hot plastic working (also referred to as strong working) is performed to give magnetic anisotropy to the compact, the compact is immersed in molten glass and electropolished. The oxide film formed on the surface of the molded body can be effectively removed by electropolishing by subjecting the electrolytically polished molded body to hot plastic working with a molding die. Further, this improves the wettability of the molded body and the molten glass adhering to the surface of the molded body, and it is difficult for the lubricating film to break. Therefore, the mold and the molded body are subjected to hot plastic working in the mold. The friction coefficient between the two becomes small, and the molding load can be reduced.

  The oriented magnet to be produced by the production method of the present invention includes not only nanocrystalline magnets having a grain size of the main phase (crystal grains) constituting the structure of about 200 nm or less, but also those having a grain size of 300 nm or more, Includes a sintered magnet having a particle diameter of 1 μm or more, and is particularly suitable for a nanocrystalline magnet that requires hot plastic working.

  Here, “electrolytic polishing” is a method of obtaining a polishing effect by passing a direct current through an electrolytic solution with a metal workpiece as an anode and dissolving the workpiece surface. The workpiece surface is cut or worn, Unlike physical polishing that is smoothed by deformation or the like, it is an electrochemical polishing method in which no physical stress is applied to the workpiece, so that no residual stress is generated and a deteriorated layer is not generated during processing. In the production method of the present invention, molten glass having conductivity in the molten state is used as the electrolytic solution.

  Since not less than an oxide film is formed on the surface of the molded body, the wettability between the molten glass and the molded body can be achieved by removing this oxide film sufficiently by electrolytic polishing before the hot plastic working. Thus, it becomes possible to accommodate the molten glass on the surface of the molded body in a mold and perform hot plastic working. Since the molten glass adheres to the surface of the molded body, this plays the role of a lubricant, and the molding load during the hot plastic working of the molding die in the molding die can be reduced.

  Since the oxide film on the surface of the compact is sufficiently removed before the hot plastic working, the coercive force (magnetic properties) of the oriented magnet formed by hot plastic working and the rare earth magnet made of this oriented magnet can be reduced. Can be improved.

  In addition, in the case of hot plastic working, a molding load is applied after the molded body is heated. In the conventional manufacturing method, an oxide film is formed on the surface of the molded body even by heating the molded body. It was.

  Therefore, by immersing the molded body in the molten glass heated in the first step, heating of the molded body at the time of hot plastic working (here, the preceding stage) is performed with the high-temperature molten glass. Therefore, the molded body is heated in a state where it does not come into contact with air (oxygen), and it is possible to effectively suppress the formation of an oxide film when the molded body is heated.

  As an example of a manufacturing apparatus used in this manufacturing method, a storage tank that stores molten glass, a container that stores this tank and includes a heater such as infrared ray, electromagnetic wave, and high frequency, and the like are disposed in the storage tank. Examples include a cathode electrode member, an external circuit in which a power source is interposed by connecting the cathode electrode member and a molded body serving as an anode, and the like. Note that the molten glass can be generated by placing glass in a storage tank and heat-treating it with a heater or the like built in the apparatus to melt the glass.

  Moreover, the structure which immerses a molded object in molten glass in the attitude | position which connected the electrically conductive suspension jig to the terminal of this circuit, and hold | gripped the molded object with this suspension jig may be sufficient.

  As described above, the oxide film already generated on the surface of the molded body is removed, and further, the molded body in which no oxide film is generated during the heat treatment before the hot plastic working is hot plastic processed, An oriented magnet excellent in coercive force performance is manufactured.

  Further, the present invention extends to a method for producing a rare earth magnet, and this method diffuses and infiltrates a modified alloy that increases the coercive force into the oriented magnet produced in the second step of the production method. It manufactures rare earth magnets.

  Here, as described above, the modified alloy diffused and permeated into the oriented magnet is an alloy containing heavy rare earth elements such as Dy and Tb having high coercive force performance alone or containing heavy rare earth elements. -30Cu-10Dy alloy (eutectic point 503 ° C) or 50Nd-30Cu-20Dy (eutectic point 576 ° C), etc. may be used, but considering the material cost, etc., it does not contain heavy rare earth elements Nd-Cu alloy (eutectic point 520 ° C), Pr-Cu alloy (eutectic point 480 ° C), Nd-Pr-Cu alloy, Nd-Al alloy (eutectic point 640 ° C), Pr-Al Apply any one of alloy (650 ℃), Nd-Pr-Al alloy, Nd-Co alloy (eutectic point 566 ℃), Pr-Co alloy (eutectic point 540 ℃), Nd-Pr-Co alloy Is preferred.

  The rare earth magnet obtained by the production method of the present invention is obtained by further enhancing the coercive force performance of an oriented magnet having excellent magnetic properties.

  As can be understood from the above description, according to the method of manufacturing the oriented magnet and rare earth magnet of the present invention, the oxide film generated on the surface of the molded body by electrolytic polishing can be sufficiently removed. By removing the oxide film, molten glass having good wettability is attached to the molded body. When this molded body is hot plastic processed in the mold, the frictional load between the molded body and the mold can be reduced to reduce the molding load during hot plastic processing, and the coercive force An oriented magnet and a rare earth magnet excellent in magnetic properties represented by performance can be produced.

It is the schematic diagram explaining to manufacture of the molded object in the 1st step of the manufacturing method of the oriented magnet of this invention in order of (a) and (b). It is the figure explaining the microstructure of the molded object shown in FIG. 1b. FIG. 2 is a diagram for explaining a first step of the manufacturing method following FIG. 1. FIG. 4 is a diagram illustrating a second step following FIG. 3. It is a figure explaining the microstructure of the manufactured oriented magnet. It is the schematic diagram explaining the manufacturing method of the rare earth magnet using the oriented magnet manufactured with the manufacturing method of the oriented magnet demonstrated in FIGS. It is a figure explaining the microstructure of the manufactured rare earth magnet.

  Hereinafter, embodiments of a method for producing an oriented magnet and a rare earth magnet according to the present invention will be described with reference to the drawings. The illustrated example describes a method for producing a rare-earth magnet, which is a nanocrystalline magnet. However, the method for producing a rare-earth magnet of the present invention is not limited to the production of a nanocrystalline magnet, and relative crystal grains Of course, it can be applied to the production of large sintered magnets.

(Embodiment of manufacturing method of oriented magnet)
FIGS. 1a and 1b are schematic views illustrating, in that order, the production of the molded body in the first step of the method for producing an oriented magnet of the present invention, and FIG. 2 illustrates the microstructure of the molded body shown in FIG. 1b. FIG. 3 is a diagram for explaining the first step of the manufacturing method subsequent to FIG. 1, FIG. 4 is a diagram for explaining the second step following FIG. 3, and FIG. It is a figure explaining the microstructure of an orientation magnet.

  As shown in FIG. 1a, for example, an alloy ingot is melted at a high frequency by a melt spinning method using a single roll in a furnace not shown in an Ar gas atmosphere whose pressure is reduced to 50 kPa or less. To produce a quenched ribbon B (quenched ribbon), which is coarsely pulverized.

  As shown in FIG. 1B, the coarsely pulverized quenched ribbon B is filled into a cavity defined by a carbide die D and a carbide punch P sliding in the hollow, and is pressed with the carbide punch P. (X direction) Nd-Fe-B main phase (crystal grain size of about 50 nm to 200 nm) of nanocrystalline structure and Nd around the main phase by flowing current in the pressurizing direction and conducting heating. A compact S composed of a grain boundary phase of -X alloy (X: metal element) is produced.

  Here, the Nd—X alloy constituting the grain boundary phase is made of Nd and at least one alloy of Co, Fe, Ga, etc., for example, Nd—Co, Nd—Fe, Nd—Ga, One of Nd-Co-Fe and Nd-Co-Fe-Ga, or a mixture of two or more of these, is in an Nd-rich state.

  As shown in FIG. 2, the compact S exhibits an isotropic crystal structure in which the grain boundary phase BP is filled between the nanocrystal grains MP (main phase).

  An oxide film is formed on the surface of the molded body S which is molded, and if this oriented oxide film is formed by hot plastic processing with the oxide film remaining, the coercive force performance of the oriented magnet is lowered. End up. Therefore, a hot plastic working precursor is manufactured by removing the oxide film on the surface of the manufactured compact S.

  FIG. 3 is a diagram illustrating an oxide film removing apparatus and explaining an oxide film removing method. The illustrated oxide film removing apparatus E includes a storage tank Z that stores the molten glass L, a container Y that stores the storage tank Z and includes a heater Ya for infrared rays, electromagnetic waves, high frequencies, and the like. A cathode member G made of platinum or the like, a conductive suspension jig J that holds a molded body S to be an anode, and a circuit F in which the suspension jig J and the cathode member G are connected and a power source and a switch are interposed. It consists of and.

  First, solid glass (not shown) is accommodated in the storage tank Z, the heater Ya is operated, the glass is heated and melted, and a high-temperature molten glass L is generated in the storage tank Z. The molded body S immersed here is heat-treated to prepare for hot plastic working.

  Next, the circuit switch is turned on, and a current is passed between the molded body S, which is an anode, and the cathode member G through the conductive molten glass L, and the surface of the molded body S before being immersed in the molten glass L. The hot plastic working precursor is manufactured by removing the oxide film formed on the surface by electropolishing.

  By removing the oxide film by electropolishing, the wettability between the surface of the molded body S and the molten glass can be improved.

  Then, by performing the heat treatment of the molded body S in the previous stage of the hot plastic working in the molten glass L without oxygen, it is possible to suppress the formation of an oxide film on the surface of the molded body S during this heat treatment. it can.

  That is, by performing electropolishing and heat treatment in the high-temperature molten glass L, the oxide film already formed on the surface of the molded body S can be removed, and heat treatment can be performed as desired without forming an oxide film (above). , First step).

  Next, the molded body S, from which the oxide film has been removed and heat-treated, is taken out from the molten glass L, and the molded body S is made of a carbide die D as shown in FIG. The cemented carbide punch P is brought into contact with the end face in the longitudinal direction (the horizontal direction is the longitudinal direction in FIG. 1b), and hot plastic working is performed while pressing with the cemented carbide punch P (X direction). By this hot plastic working, as shown in FIG. 5, an oriented magnet C (rare earth magnet precursor) having a crystalline structure having anisotropic nanocrystal grains MP is manufactured (second step).

  In this hot plastic working, since molten glass having good wettability adheres to the surface of the molded body S, this molten glass becomes a lubricant between the molded body S and the carbide die D. It is possible to reduce the molding (forging) load during hot plastic working.

  When the degree of processing (compression rate) by hot plastic working is large, for example, the case where the compression rate is about 10% or more can be referred to as hot strong processing or simply strong processing.

  In the crystal structure of the oriented magnet C shown in FIG. 5, the nanocrystal grains MP have a flat shape, and the interface substantially parallel to the anisotropic axis is curved or bent.

  Next, as shown in FIG. 6, the manufactured oriented magnet C is accommodated in a high-temperature furnace H with a built-in heater, and a mass M of the reformed alloy is arranged above and below the rare earth magnet precursor C so that both are brought into contact with each other. The furnace has a high temperature atmosphere.

  Here, as the reforming alloy M, it is preferable to use an RE-Y alloy (RE: Nd, at least one of Pr, Y: transition metal element) that does not contain heavy rare earth elements. As the transition metal element Y, any one of Cu and Al is applied. Therefore, as the RE-Y alloy, any of Nd-Cu alloy, Nd-Al alloy, Pr-Cu alloy and Pr-Al alloy can be used. Or use a kind.

  When the above-exemplified alloy is used as the RE-Y alloy, the eutectic point of the Nd-Cu alloy is 520 ° C, the eutectic point of the Pr-Cu alloy is 480 ° C, the eutectic point of the Nd-Al alloy is 640 ° C, The eutectic point of the Pr—Al alloy is 650 ° C., both of which have a low melting point of 700 ° C. or less.

  When an Nd-Cu alloy is used as the reforming alloy M, the eutectic point is 520 ° C. Therefore, the temperature inside the high temperature furnace H is about 520 ° C or higher (eg, about 600 ° C). As a result, the Nd—Cu alloy, which is a modified alloy, melts.

  The molten Nd-Cu alloy melt diffuses and penetrates into the grain boundary phase BP, and Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe, Nd-Co-Fe-Ga and these A grain boundary phase in which a part or all of the mixed grain boundary phase is modified with the Nd—Cu alloy is formed.

  When Nd-Al alloy is used as the modified alloy M, the eutectic point is 640 ° C. Therefore, the Nd-Al alloy is melted by setting the temperature atmosphere at 640 to 650 ° C. The melt can be diffused and penetrated into the grain boundary phase, and Nd-Co, Nd-Fe, Nd-Ga, Nd-Co-Fe, Nd-Co-Fe-Ga and one of these Part or all of the grain boundary phase is modified with an Nd—Al alloy.

  Thus, by using a low melting point alloy alloy M having a low melting point of 700 ° C. or less and melting at a low temperature, for example, in the case of a nanocrystalline magnet, there is a problem when placed in a high temperature atmosphere of about 800 ° C. or more. The problem of coarsening of the crystal grains cannot occur.

  As shown in FIG. 7, by using any of the Nd-Cu alloy, Nd-Al alloy, Pr-Cu alloy, or Pr-Al alloy described above and performing heat treatment for a predetermined time at a temperature of 600 ° C. to 700 ° C. In addition, a rare earth magnet RM in which the grain boundary phase BP is modified to a composition rich in Nd or Pr is manufactured.

  As shown in the figure, an interface (specific surface) substantially parallel to the anisotropic axis is formed when the reforming by the reforming alloy M is sufficiently advanced. Thus, the rare earth magnet RM obtained by the manufacturing method described above has a low melting point of 700 ° C. or lower with respect to the oriented magnet C obtained by performing hot plastic working for imparting anisotropy to the compact S. By diffusing and infiltrating the melt of the reformed alloy into the grain boundary phase, residual strain generated by hot plastic working is removed by contacting the melt of the reformed alloy, and further refinement of crystal grains, The coercive force is improved by promoting the magnetic separation between crystal grains.

[Coercivity Performance Evaluation Experiment and Results]
The inventors of the present invention manufactured oriented magnets according to Examples and Comparative Examples by the following method, measured the coercive force of each oriented magnet, and formed molding loads during hot plastic working and of oriented magnets after processing. An experiment was conducted to measure the oxygen concentration and observe the presence or absence of baking of the mold.

(Example)
Using the apparatus shown in FIG. 3, glass (composition is P ₂ O ₅ : 55 mass%, Na ₂ O: 20 mass%, K ₂ O: 15.0 mass%, Al ₂ O ₃ : 9.5 mass%, conductivity) Is stored in a storage tank and heated until the whole reaches 790 ° C to melt the glass, and isotropic magnets (diameter 10mm, height 15mm) at room temperature in the molten glass Soaked. Next, a voltage was applied between the electrode and the isotropic magnet so that the current flowing to the magnet was 1 A / dm ^2, and this state was maintained for 5 minutes. Next, the isotropic magnet taken out from the molten glass was hot plastic processed at a strain rate of 1 / s until the height became 20% (3 mm) of the initial height by a forging press.

  When the surface after processing was observed, no baking was confirmed. The maximum load during hot plastic working is 18.4kN (average of 10 specimens), and the oxygen concentration of the magnet after machining is 1580ppm (average of 10 specimens, after removing the glass from the workpiece surface, the entire specimen is 150μm After crushing and stirring below, a measurement sample was collected.After the crushing operation, it was carried out in an Ar atmosphere.), The coercive force was 14.2 kN (average of 10 specimens, measured with a 1 mm square sample including the surface, The sampling position was the central part).

(Comparative example)
Using the apparatus shown in FIG. 3, glass (composition is P ₂ O ₅ : 55 mass%, Na ₂ O: 20 mass%, K ₂ O: 15.0 mass%, Al ₂ O ₃ : 9.5 mass%) in the storage tank The glass was melted by heating until the whole reached 790 ° C., and a normal temperature isotropic magnet (diameter 10 mm, height 15 mm) was immersed in the molten glass. Here, this state was maintained for 5 minutes without applying a voltage between the electrode and the isotropic magnet. Next, the isotropic magnet taken out from the molten glass was hot plastic processed at a strain rate of 1 / s until the height became 20% (3 mm) of the initial height by a forging press.

  When the surface after processing was observed, baking was confirmed on the surface in contact with the molded body in the mold. The maximum load during hot plastic working was 23.1 kN (average of 10 specimens), which was a higher value than in the examples. The oxygen concentration of the magnet after processing was 1880 ppm (average of 10 specimens, after removing the glass from the workpiece surface, the whole specimen was crushed to 150 μm or less, stirred, and a measurement sample was taken. The coercive force was 13.5kN (average of 10 specimens, measured with a 1mm square sample including the surface, sample collection position in the center). Was found to be decreasing.

  From this experiment, by performing hot plastic processing after removing the oxide film from the surface of the molded body by electropolishing, baking does not occur in the mold, and the forging load during hot plastic processing can be reduced. It has been demonstrated that oriented magnets (and rare earth magnets) with excellent coercivity performance can be produced.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  R: Copper roll, B: Quenched ribbon (quenched ribbon), D: Carbide die, P: Carbide punch, S ... Molded body, C ... Oriented magnet (rare earth magnet precursor), M ... Modified alloy (of Lump), MP ... main phase (nanocrystal grains, crystal grains), BP ... grain boundary phase, RM ... rare earth magnet, E ... oxide film removal device, Y ... container, Ya ... heater, Z ... storage tank, J ... hanging Jig, F ... Circuit, G ... Cathode member, L ... Molten glass, H ... High temperature furnace

Claims (5)

A molded body formed by pressure-molding a powder as a magnet material is immersed in molten glass, and a circuit including a power source in which the molded body serving as an anode is connected to a cathode member disposed in the molten glass is energized. A first step of electropolishing the surface of the molded body,
A hot plastic working precursor consisting of a molded body that has been electropolished and has molten glass attached to the surface is placed in a mold and subjected to hot plastic working, and the hot plastic working precursor is magnetically anisotropic. The manufacturing method of the oriented magnet which consists of a 2nd step which manufactures the oriented magnet to which was given.   The method for producing an oriented magnet according to claim 1, wherein in the first step, the molded body is immersed in the heated molten glass.   The method for producing an oriented magnet according to claim 2, wherein the molten glass is produced by heating solid glass.   In the first step, the molded body is immersed in molten glass in a state where the molded body is suspended by a conductive suspension jig, and the suspension jig forms a part of a circuit. The manufacturing method of the oriented magnet in any one of.   A method for producing a rare earth magnet, wherein a rare earth magnet is produced by diffusing and infiltrating a modified alloy for increasing the coercive force into the oriented magnet produced in the second step in the production method according to claim 1.

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