JP2013149862A - Method of manufacturing rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a rare earth magnet ensuring a high coersive force and excellent magnetization, by diffusing and infiltrating a modified alloy uniformly into the whole magnetic powder becoming a rare earth magnet material.SOLUTION: The method of manufacturing a rare earth magnet includes a first step for mixing a magnetic powder Q consisting of the main phase MP of an RE-Fe-B system (RE: at least one kind of Nd, Pr, Y), and a grain boundary phase BR around the main phase MP, and a modified alloy powder T consisting of an RE-M-RH alloy (M: transition metal element or typical metal element, RH: heavy rare-earth metal) or an RE-M alloy, melting the modified alloy powder by performing hot press, and producing a compact S while infiltrating the melt T' to the boundary surface of magnetic powder, and a second step for manufacturing a rare earth magnet C (orientation magnet) by performing hot plasticity processing of the compact S.

Description

  The present invention relates to a method for producing a rare earth magnet.

  Rare earth magnets using rare earth elements such as lanthanoids are also called permanent magnets, and their uses are used in motors for driving hard disks and MRI, as well as drive motors for hybrid vehicles and electric vehicles.

  Residual magnetization (residual magnetic flux density) and coercive force can be cited as indicators of the magnet performance of this rare earth magnet. However, in response to increased heat generation due to miniaturization of motors and higher current density, rare earth magnets used also The demand for heat resistance is further increasing, and how to maintain the coercive force of a magnet under high temperature use is one of the important research subjects in the technical field. Taking Nd-Fe-B magnets, one of the rare-earth magnets frequently used in vehicle drive motors, to refine crystal grains, use a composition alloy with a large amount of Nd, Attempts have been made to increase the coercivity by adding heavy rare earth elements such as high Dy and Tb.

  As rare earth magnets, in addition to general sintered magnets with a crystal grain (main phase) scale of 3 to 5 μm constituting the structure, nanocrystal magnets with crystal grains refined to a nanoscale of about 50 nm to 300 nm are available. Among them, nanocrystal magnets that can reduce the amount of expensive heavy rare earth elements added (free) while miniaturizing the crystal grains described above are currently attracting attention.

  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. In general, a method of producing a rare earth magnet (orientated magnet) by performing hot plastic working to impart the above-mentioned properties is applied.

  In Patent Document 1, a raw material obtained by mixing or coating a heavy rare earth modified alloy powder with an Nd—Fe—B alloy powder is first cold formed to produce a cold formed body, and this cold forming is performed. A manufacturing method of a rare earth magnet is disclosed in which a hot formed body is manufactured by hot forming the body, or a hot plastic processed body is manufactured by further hot plastic forming the hot formed body. According to this manufacturing method, heavy rare earth elements such as Dy concentrated in the grain boundary phase can be uniformly distributed, and the coercive force can be improved while suppressing a decrease in residual magnetic flux density.

  However, in the method of performing hot forming after cold forming, and further performing hot plastic working after hot forming, cold forming is performed in a state where the modified alloy is not melted. The Nd—Fe—B based alloy powder segregates or agglomerates particularly at the triple points, and the reformed alloy shifts to hot forming in a non-uniform distribution. For this reason, the modified alloy melted during hot forming or hot plastic working cannot be uniformly diffused and penetrated into all crystal grain boundaries, and the coercivity of the entire rare earth magnet cannot be sufficiently increased.

JP 2010-263172 A

  The present invention has been made in view of the above-described problems, and can provide a rare earth magnet having a high coercive force and good magnetization, which can uniformly diffuse and infiltrate the modified alloy throughout the magnetic powder as a rare earth magnet raw material. It aims at providing the manufacturing method which can be manufactured.

  In order to achieve the above object, a method for producing a rare earth magnet according to the present invention includes a RE-Fe-B main phase (at least one of RE: Nd, Pr, and Y) and a grain boundary around the main phase. Mixing magnetic powder consisting of RE-M-RH alloy (M: transition metal element or typical metal element, RH: heavy rare earth element) or RE-M alloy modified alloy powder, and hot pressing A first step of producing a molded body while melting the modified alloy powder and infiltrating the melt into the magnetic powder interface between the magnetic powders, and a second step of producing a rare earth magnet by hot plastic working the molded body. It consists of

  In the production method of the present invention, the reformed alloy powder is melted at the stage of producing the molded body (bulk body), and the melt of the modified alloy powder is sufficiently spread over the entire magnetic powder interface between the magnetic powders. By applying hot plastic working, the melt of the modified alloy powder is diffused and penetrated into the magnetic powder while giving magnetic anisotropy.

  Since the reformed alloy powder is melted in the process of manufacturing the formed body, the problem that the reformed alloy powder segregates, for example, at triple points between the magnetic powders cannot occur.

  In addition, since the melt of the modified alloy powder spreads to the magnetic powder interface between the magnetic powders, the magnetic separation between the magnetic powders is promoted at the stage of the compact, which also has a high coercive force and good magnetization. Rare earth magnets can be obtained.

  Here, as the “transition metal element or typical metal element”, any one of Cu, Mn, Co, Ni, Zn, Al, Ga, Sn and the like can be applied. As the “heavy rare earth element”, any one of Dy, Tb, Ho, and the like can be applied.

  In particular, when the modified alloy powder is made of RE-M-RH alloy, one of Nd-Cu-Dy alloy, Nd-Cu-Tb alloy, Nd-Al-Dy alloy, and Nd-Al-Tb alloy is used. In the case where the modified alloy powder is made of a RE-M alloy, it is preferable to use one of Nd-Cu alloy and Nd-Al alloy.

  For example, when using a modified alloy powder made of Nd-Cu-Dy alloy, although the melting point of the alloy differs depending on the component ratio (the melting point of 60Nd-30Cu-10Dy alloy is 533 ° C, 50Nd-30Cu-20Dy alloy The melting point of this modified alloy is generally less than 600 ° C.

  In addition, when the modified alloy is an Nd-Cu alloy, the melting point is as low as about 520 ° C, so the alloy can be melted in the range of 520 to 650 ° C, and the modified alloy is Nd-Al In the case of an alloy, the melting point is as low as 600 to 650 ° C.

  Because it can be melted at a low temperature by using a low melting point modified alloy powder in this way, a nanocrystalline magnet (crystal grain size) where coarsening of crystal grains becomes a problem when placed in a high temperature atmosphere of 800 ° C or higher Is about 50 nm to 300 nm), the production method of the present invention is suitable.

  As can be understood from the above description, according to the method for producing a rare earth magnet of the present invention, the reformed alloy powder is melted at the stage of producing the compact (bulk body), and the reformed alloy is applied to the entire magnetic powder interface between the magnetic powders. A rare earth magnet having a high coercive force and good magnetization can be produced by sufficiently spreading the melt of the powder and subjecting the compact to hot plastic working.

It is the schematic diagram explaining the 1st step of the manufacturing method of the rare earth magnet of this invention. FIG. 2 is a diagram illustrating a first step following FIG. 1. FIG. 3 is a diagram illustrating a first step following FIG. 2. It is the figure which expanded the structure | tissue of the molded object manufactured at the 1st step. FIG. 5 is an enlarged view of a portion V in FIG. 4 and shows a microstructure of a crystal structure. It is the schematic diagram explaining the 2nd step of the manufacturing method of the rare earth magnet of this invention. It is the figure which showed the microstructure of the crystal structure of the rare earth magnet manufactured at the 2nd step. It is the photograph figure which expanded the structure | tissue of the molded object of the comparative example. It is a figure which shows the EPMA (electron beam microanalysis) result of a comparative example. It is the photograph figure which expanded the structure | tissue of the molded object of an Example. It is a figure which shows the EPMA result of an Example. It is a figure which shows the experimental result which calculated | required the relationship between the addition amount of a modified alloy powder, and a coercive force regarding the molded object of an Example and each comparative example. It is a figure which shows the experimental result which calculated | required the relationship between a coercive force and magnetization regarding the rare earth magnet after the hot plastic working of an Example and each comparative example. (A) is an enlarged photograph figure of a test piece with an addition rate of 5% in the example, and (b) is an enlarged photograph figure of a test piece with an addition rate of 5% in a comparative example.

  Embodiments of a method for producing a rare earth magnet according to the present invention will be described below 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 (for example, having a particle size of about 1 μm).

(Rare earth magnet manufacturing method)
1, 2 and 3 are schematic views illustrating the first step of the method of manufacturing a rare earth magnet of the present invention in that order, and FIG. 4 is an enlarged view of the structure of the molded body manufactured in the first step. FIG. 5 is an enlarged view of a portion V in FIG. 4 and shows a microstructure of the crystal structure.

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

  Next, as shown in FIG. 2, a predetermined amount of magnetic powder Q and modified alloy powder T, which are obtained by roughly pulverizing the quenched ribbon B, are charged into a container and mixed to produce a green body raw material.

  As shown in FIG. 3, the produced molded body raw material R is filled in a cavity defined by a carbide die D and a carbide punch P that slides inside the hollow, and is pressed with the carbide punch P ( X direction) The main phase of RE-Fe-B system (RE: Nd, Pr, Y) of nanocrystal structure (currently 20nm to 200nm crystal grains) by applying current in the pressurizing direction and conducting heating. And a compact S composed of a grain boundary phase of an Nd—X alloy (X: metal element) around the main phase is manufactured by hot pressing (first step).

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

  On the other hand, the modified alloy powder is made of RE-M-RH alloy (M: transition metal element or typical metal element, RH: heavy rare earth element) or RE-M alloy. Here, as the transition metal element or the typical metal element, any one of Cu, Mn, Co, Ni, Zn, Al, Ga, Sn and the like can be applied, and as the heavy rare earth element, Dy, Any one of Tb, Ho, etc. can be applied.

  In particular, when the modified alloy powder is made of RE-M-RH alloy, one of Nd-Cu-Dy alloy, Nd-Cu-Tb alloy, Nd-Al-Dy alloy, and Nd-Al-Tb alloy is used. When the modified alloy powder is made of RE-M alloy, either Nd-Cu alloy or Nd-Al alloy is applied.

When using a modified alloy powder made of Nd-Cu-Dy alloy, although the melting point of the alloy differs depending on the component ratio (the melting point of 60Nd-30Cu-10Dy alloy is 533 ° C, the melting point of 50Nd-30Cu-20Dy alloy is 576 ° C.), the melting point of this modified alloy is generally less than 600 ° C. In addition, when the modified alloy is an Nd-Cu alloy, the melting point is as low as about 520 ° C, so the alloy can be melted in the range of 520 to 650 ° C, and the modified alloy is Nd-Al In the case of an alloy, the melting point is as low as 600 to 650 ° C.
The modified alloy powder having an average particle size of about 10 μm to 500 μm can be used.

  In the hot pressing shown in FIG. 4, the above-described modified alloy powder T having a low melting point is used, so that a relatively low temperature of about 500 ° C. to 700 ° C. (Nd alloy having a eutectic point at about 300 ° C. is used. If used, the modified alloy powder T can be melted by hot pressing (for example, holding at 50 to 500 MPa for 15 seconds or more to increase the density) by pressing at a temperature corresponding to the eutectic point. Therefore, the coarsening of the crystal grains constituting the nanocrystal magnet can be effectively suppressed.

  And since the melt T ′ of the reformed alloy powder obtained by melting the reformed alloy powder T spreads over the magnetic powder interface between the magnetic powders constituting the compact S, the periphery of the magnetic powder Q is 100% or 100%. It is possible to coat with a coverage close to. The microstructure of the structure of the magnetic powder Q of the compact S exhibits an isotropic crystal structure in which the crystal grain boundary phase BP is filled between the nanocrystal grains MP (main phase) as shown in FIG. .

  Once the molded body S is obtained in the first step, the molded body is then placed in the cavity defined by the cemented carbide die D and the cemented carbide punch P that slides in the hollow, as in the first step. By accommodating S and performing hot plastic working, the melt T ′ of the modified alloy powder diffuses into the grain boundary phase, and a rare earth magnet C having an increased coercive force is manufactured (second). Step).

  As shown in FIG. 7, the rare earth magnet C is a magnet whose magnetic anisotropy is imparted by hot plastic working and whose magnetization is increased.

  According to the rare earth magnet manufacturing method shown in the figure, the reformed alloy powder is melted at the stage where the compact S is manufactured, and the melt of the modified alloy powder is sufficiently spread over the entire magnetic powder interface between the magnetic powders. Next, magnetic powder is coated at a coverage of 100% or close to 100%, and then the compact is subjected to hot plastic working to diffuse the melt of the modified alloy powder into the grain boundary phase constituting the magnetic powder. As a result, the melt of the modified alloy powder can be uniformly diffused into the grain boundary with respect to all the magnetic powders, and a rare earth magnet having an extremely high coercive force can be manufactured.

[Experiment to determine the relationship between the amount of reformed alloy powder added to the compact and the coercive force, and the experiment to determine the relationship between the coercive force and magnetization of a rare earth magnet after hot plastic working and their results]
The present inventors conducted experiments for determining the relationship between the amount of the modified alloy powder added to the compact and the coercive force, and experiments for determining the relationship between the coercive force and magnetization of the rare earth magnet after hot plastic working. .

  In this experiment, Nd-Fe-B magnetic powder (commercially available Nd-Fe-B rapidly cooled powder) was used, and this powder had a composition of Nd30Co4B1Febal, an average crystal grain size of 50 nm to 300 nm, and an average powder grain size of about 200 μm. is there. The modified alloy powder is prepared by arc melting Nd, Cu ingot (weight ratio 80:20) to produce a reformed alloy ingot. Next, the produced ingot is pulverized by a cutter mill, and Nd-Cu Alloy powder (weight ratio 80:20, average particle size: 100 μm).

  The above-mentioned Nd-Fe-B magnetic powder and Nd-Cu modified alloy powder were mixed for 30 minutes with a V-type powder mixer, and the resulting mixed powder was manufactured into a 10 mm x 15 mm compact using a carbon die. . The experimental levels at this time are shown in Table 1 below. Next, the molded body was heated and held at 700 ° C. by high frequency, subjected to hot plastic working by compressing 75% at the sample height ratio at a strain rate of 1 / sec, and 2 × 2 at the center of the compressed sample A test piece was cut out by × 2 mm. In addition, the test piece of a comparative example reproduced the manufacturing method of patent document 1, and manufactured the rare earth magnet after a molded object and also hot plastic working.

  The obtained 2 mm square test piece was heat-treated at 650 ° C. for 60 minutes in an Ar gas atmosphere, and then evaluated for magnetic properties and observed for the structure. Here, the magnetic characteristics were evaluated by measuring the coercive force and magnetization at RT using a vibrating sample magnetometer.

  FIG. 8 shows an enlarged photograph of the structure of the molded body of the comparative example, FIG. 9 shows the EPMA (Electron Probe Micro Analyzer) result of the comparative example, and FIG. 10 shows the structure of the molded body of the example. The enlarged photograph is shown in FIG. 11, and the EPMA results of the examples are shown in FIG.

  Table 2 below shows the measurement results regarding the coercive force and magnetization of the compact and the measurement results regarding the coercivity and magnetization of the rare earth magnet after hot plastic working among the test pieces according to the comparative example and the example. . FIG. 12 shows the experimental results for determining the relationship between the amount of the modified alloy powder added and the coercive force for the compacts of the examples and comparative examples. In FIG. The experimental result which calculated | required the relationship between a coercive force and magnetization was shown about the rare earth magnet after plastic working. Further, FIG. 14a is an enlarged photograph of the test piece (No. 3) with an addition rate of 5% in the example, and FIG. 14b is an enlarged photograph of the test piece (No. 3) with an addition rate of 5% in the comparative example. is there.

  Regarding the experimental results and the observation results, from FIG. 8 to FIG. 11, the molded body of the comparative example can confirm the agglomerated portion of the modified alloy, whereas the molded body of the example is the magnetic powder between the magnetic powders in the molten modified alloy. It can be confirmed that it has spread to the interface and uniformly coated the magnetic powder surface.

  Further, from Table 2 and FIG. 12, it is demonstrated that the performance of the molded body of the example is improved in both the coercive force and the magnetization as compared with the comparative example. This is considered to be because the melt of the modified alloy powder coats the surface of each magnetic powder with a high coverage (about 100%).

  On the other hand, Table 2 and FIG. 13 demonstrate that the performance of both the coercive force and the magnetization of the rare earth magnet after hot plastic working of the example is improved as compared with the comparative example. This is because the reformed alloy powder melt covers the surface of each magnetic powder at a high coverage (about 100%), as described above for the compact that is the precursor. This is considered to be because the melt uniformly diffuses and penetrates into the grain boundary phase of each magnetic powder during hot plastic working.

  14A and 14B, no cracks occurred in the test pieces of the examples, but large cracks were confirmed in the test pieces of the comparative examples. This is considered to be caused by stress concentration in the test piece of the comparative example during hot plastic working, which causes cracking.

  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.

  W: Copper roll, B: Quenched ribbon (quenched ribbon), Q: Magnetic powder, T: Modified alloy powder, T ′: Molten liquid of modified alloy powder, R: Molded material raw material, D: Carbide die, P ... Carbide punch, S ... Molded body, C ... Rare earth magnet (orientation magnet), MP ... Main phase (nanocrystal grains, crystal grains), BP ... Grain boundary phase

Claims (2)

RE-Fe-B main phase (at least one of RE: Nd, Pr, Y), magnetic powder consisting of the grain boundary phase around the main phase, and RE-M-RH alloy (M: transition metal) Element or typical metal element, RH: heavy rare earth element) or RE-M alloy modified alloy powder is mixed, hot pressed to melt the modified alloy powder, and the melt is used as magnetic powder between magnetic powders. A first step of producing a molded body while penetrating the interface;
A method for producing a rare earth magnet comprising a second step of producing a rare earth magnet by hot plastic working the molded body.   Nd-Cu-Dy alloy, Nd-Cu-Tb alloy, Nd-Al-Dy alloy, Nd-Al-Tb alloy as RE-M-RH alloy, Nd-Cu alloy, Nd as RE-M alloy The method for producing a rare earth magnet according to claim 1, wherein any one of the Al alloys is used.

Images