Rare earth magnet and method for manufacturing the same

Abstract

Provided are a rare earth magnet capable of suppressing deterioration of magnetic properties and a method for manufacturing the same. The rare earth magnet of the present invention comprises a magnet body containing a rare earth element R1, a transition metal element T, and boron B and comprising a main phase, wherein a region of a constituent surface constituting the surface of the magnet body near a corner of the magnet body is a machined surface obtained by removal processing, and a region of the constituent surface closer to the center than the region near the corner is a non-machined surface that has not been subjected to removal processing.

Description

Technical Field

[0001] The present invention relates to a rare earth magnet and a method for producing the same, and relates to a rare earth magnet having a magnet body containing a rare earth element, a transition metal element, and boron, and a method for producing the same. Background Art

[0002] Rare earth magnets, such as Nd-Fe-B rare earth magnets, are known as high-performance magnets with excellent magnetic properties. They are used in motors such as internal magnet motors (IPM motors) installed in electric vehicles such as electric vehicles (EVs) and hybrid vehicles (HVs). The magnet body contains rare earth elements, transition metal elements, and boron, and consists of a main phase and a secondary phase surrounding the main phase and containing more rare earth elements than the main phase. In these rare earth magnets, while the main phase exhibits strong magnetism, the secondary phase magnetically separates the main phases (magnetically separating them), generating coercive force (coercive force), thereby achieving high magnetic properties.

[0003] When such rare earth magnets are used in actual motors, etc., raw material powders containing rare earth elements, transition metal elements, and boron are compressed and molded into the shape of the magnet body for making the rare earth magnet to obtain a pressed powder compact. After the pressed powder compact is sintered to obtain a sintered body, the sintered body is formed into the shape and size of the final product by cutting, cutting, and other removal processes, thereby producing the magnet body. As a result, the surface portion of the rare earth magnet magnet body is processed, and secondary phases are removed, or damage such as cracks or stress caused by processing strain is generated. As a result, since the coercive force is reduced in the surface portion, there is a situation where gradual demagnetization occurs, even when the demagnetizing magnetic field is small, and the demagnetization becomes larger as the demagnetizing magnetic field becomes larger. As a result, the magnetic properties of the surface portion are reduced compared to the interior, and the magnetic properties of the rare earth magnet may deteriorate. In particular, in electric vehicle motors, the possibility of deterioration of the magnetic properties due to demagnetization of the rare earth magnet is high.

[0004] To address this problem, the following technology has been applied: by subjecting a material containing rare earth elements to heat treatment on the surface of a machined surface of a magnet body serving as a rare earth magnet, the rare earth elements are diffused into the magnet body, thereby modifying the surface portion of the magnet body and restoring the magnetic properties of the rare earth magnet. As a rare earth magnet to which this technology is applied, for example, Patent Document 1 describes a rare earth magnet formed by machining a magnet block raw material. By allowing rare earth metals to diffuse and penetrate from the magnet surface into the magnet interior to a depth equivalent to or greater than the radius of the crystal grains exposed on the outermost surface of the magnet, the deteriorated and damaged areas caused by machining are modified to provide the desired magnetic properties. Furthermore, Patent Document 2 describes a rare earth sintered magnet, wherein the magnet body of the rare earth sintered magnet is formed by sintering a molded body formed from a raw alloy fine powder containing rare earth elements, transition metal elements, and boron. The magnet body is coated with a chemical vapor growth film primarily composed of rare earth elements, and the surface is restored.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-304038

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-285859 Summary of the Invention

[0009] Conventional methods for manufacturing rare earth magnets of this type involve sintering the powder compact to obtain a sintered body as described above. The sintered body is then formed into the desired shape and size for the product through subtractive processing. This involves subtractive processing of the entire surface of the sintered body when producing the magnet base. As a result, the entire surface of the magnet base becomes a processed surface. Consequently, secondary phases are removed, damage is generated, or stress is applied to the surface of the entire surface of the magnet base. This degrades the magnetic properties of the surface compared to the interior of the magnet base, potentially significantly degrading the magnetic properties of the rare earth magnet.

[0010] On the other hand, when rare earth elements are diffused throughout the entire surface of the constituent surfaces of the magnet body in order to suppress such significant deterioration in magnetic properties, the amount of expensive rare earth elements used increases, potentially leading to an increase in manufacturing costs.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a rare earth magnet capable of suppressing deterioration of magnetic properties and a method for producing the same.

[0012] In order to solve the above-mentioned problems, the rare earth magnet of the present invention is characterized in that it has a magnet body containing a rare earth element R1, a transition metal element T and boron B and including a main phase, and the area of ​​the constituent surface of the surface of the above-mentioned magnet body near the corner of the above-mentioned magnet body is a processed surface obtained by removal processing, and the area of ​​the above-mentioned constituent surface closer to the center than the area near the above-mentioned corner is a non-processed surface that has not been removed.

[0013] According to the rare earth magnet of the present invention, deterioration of magnetic properties can be suppressed.

[0014] The rare earth magnet may further include a rare earth rich layer provided on the processed surface of the magnet body.

[0015] In addition, in order to solve the above-mentioned problems, the manufacturing method of the rare earth magnet of the present invention is a method for manufacturing the above-mentioned rare earth magnet, which is characterized by comprising: a molding step, in which a raw material powder containing a rare earth element R1, a transition metal element T and boron B is compression-molded into the shape of the above-mentioned magnet original body for making the above-mentioned rare earth magnet to obtain a molded body; a sintering step, in which the above-mentioned molded body is sintered to obtain a sintered body; and a processing step, in which the corners of the above-mentioned sintered body and excess parts near the corners are removed and processed to make the above-mentioned magnet original body.

[0016] According to the method for producing a rare earth magnet of the present invention, it is possible to suppress deterioration of the magnetic properties of the rare earth magnet.

[0017] The method for producing the rare earth magnet may further include a heat treatment step in which a heat treatment is performed while a diffusion material containing the rare earth element R2 is present on the processed surface of the magnet body.

[0018] In addition, in order to solve the above-mentioned problems, the manufacturing method of the rare earth magnet of the present invention is characterized in that it comprises: a recovery step of recovering the above-mentioned rare earth magnet from the motor; and a heat treatment step of performing heat treatment in a state in which a diffusion material containing the rare earth element R2 is present on the above-mentioned processed surface of the above-mentioned magnet body of the above-mentioned rare earth magnet.

[0019] According to the method for producing a rare earth magnet of the present invention, a rare earth magnet with deteriorated magnetic properties can be regenerated to a rare earth magnet with restored magnetic properties.

[0020] According to the present invention, it is possible to suppress deterioration of the magnetic properties of the rare earth magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 (a) is a schematic perspective view showing the rare earth magnet according to the first embodiment, and (b) is a schematic cross-sectional view taken along line AA of the rare earth magnet shown in (a).

[0022] Figure 2 (a) is a schematic perspective view showing a rare earth magnet according to the conventional art, and (b) is a schematic cross-sectional view taken along line AA of the rare earth magnet shown in (a).

[0023] Figure 3 (a) is a schematic perspective view showing a rare earth magnet according to a second embodiment, and (b) is a schematic cross-sectional view taken along line AA of the rare earth magnet shown in (a).

[0024] Figure 4 (a) is a schematic perspective view showing a rare earth magnet according to the conventional art, and (b) is a schematic cross-sectional view taken along line AA of the rare earth magnet shown in (a).

[0025] Figure 5 It is a diagram schematically showing the flow of a method for producing a rare earth magnet according to the second embodiment.

[0026] Figure 6 (a) and (b) are schematic cross-sectional views of the main parts of the method for producing a rare earth magnet according to the second embodiment.

[0027] Figure 7 (a) to (c) are schematic cross-sectional views of the main parts of the method for producing a rare earth magnet according to the second embodiment.

[0028] Figure 8 (a) to (d) are schematic cross-sectional views of the main parts of the method for producing a rare earth magnet according to the third embodiment.

[0029] Figure 9 These are diagrams showing a SEM image of a cross section of the boundary portion between the magnet body and the processed layer of the vapor-deposited film in the rare earth magnet of Reference Example 2, and an EPMA image of the Nd amount.

[0030] Figure 10 (a) is a schematic cross-sectional view showing a BH curve tracer according to JIS C 2501 as a measuring device used for measuring a JH curve, and (b) is a diagram showing the procedure of applying a magnetic field when measuring a JH curve.

[0031] Figure 11 This is a diagram showing JH curves measured for the rare earth magnets of Reference Examples 1 and 2.

[0032] Description of Reference Numerals

[0033] 1 Rare earth magnet

[0034] 10 Magnet Prototype

[0035] 10a Main phase particles (main phase)

[0036] 10b Vice-President

[0037] 10s watch face

[0038] 12 component surfaces

[0039] 12A Area near the corner

[0040] 12a Processing surface (grinding surface)

[0041] 12a' Processing surface (cut surface)

[0042] 12B Central Area

[0043] 12b Non-machined surface

[0044] 14 corners

[0045] 16 Crack

[0046] 20 Rare earth-rich layer

[0047] 40 Diffusion layer

[0048] 5. Raw material powder

[0049] 50 Molded body

[0050] 60 sintered body

[0051] 60c Excess parts at and near corners

[0052] 30 diffusion materials DETAILED DESCRIPTION

[0053] Hereinafter, embodiments of the rare earth magnet and the method for producing the same according to the present invention will be described.

[0054] First, an overview of the rare earth magnet according to the embodiment will be described by taking the rare earth magnet according to the first embodiment as an example. Figure 1 (a) is a schematic perspective view showing a rare earth magnet according to the first embodiment. Figure 1 (b) is along Figure 1 (a) is a schematic cross-sectional view of the rare earth magnet taken along line AA. Figure 2 (a) is a schematic perspective view showing a rare earth magnet according to the prior art. Figure 2 (b) is along Figure 2 (a) is a schematic cross-sectional view of the rare earth magnet taken along line AA.

[0055] like Figure 1 (a) and Figure 1As shown in FIG. 2( b ), the rare earth magnet 1 according to the first embodiment comprises a rectangular parallelepiped magnet body 10 containing a rare earth element R1, a transition metal element T, and boron B, and including main phase particles (main phase) 10a and subphases 10b surrounding the main phase particles 10a. The main phase particles 10a are R2Fe 14 The secondary phase 10b is a phase with a B-type crystal structure, containing a higher amount of the rare earth element R1 than the primary phase particles 10a. Of all the constituent surfaces 12 constituting the surface 10s of the magnet body 10, regions 12A near the corners 14 of the magnet body 10 are ground (removed) as processed surfaces (ground surfaces) 12a. Of all the constituent surfaces 12, regions 12B located closer to the center than the regions 12A near the corners 14 are unground as unprocessed surfaces 12b. Although not shown, the rare earth magnet 1 also includes a Ni plating layer or coating film formed on the surface 10s of the magnet body 10 through surface treatment.

[0056] On the other hand, Figure 2 (a) and Figure 2 As shown in FIG. 1( b ), a conventional rare earth magnet 100 includes, similarly to the first embodiment, a rectangular parallelepiped magnet body 10 containing a rare earth element R1, a transition metal element T, and boron B, and comprising main phase grains (main phase) 10a and secondary phases 10b surrounding the main phase grains 10a. However, unlike the first embodiment, the entire surface 10s of the magnet body 10, that is, all of the constituent surfaces 12, are ground surfaces (ground surfaces) 12a. Consequently, the secondary phases 10b are removed from the entire surface portion of all of the constituent surfaces 12 of the magnet body 10, generating cracks 16 that reach the interior of the magnet body 10 and stresses caused by machining strain. As a result, the coercivity of the surface portion of the constituent surfaces 12 of the magnet body 10 decreases significantly, significantly degrading the magnetic properties of the rare earth magnet 100.

[0057] In contrast, in the rare earth magnet 1 according to the first embodiment, of all the constituent surfaces 12 of the magnet body 10, only the region 12A near the corners 14 serves as the processed surface 12a, while the region 12B located closer to the center of the region 12A serves as the unprocessed surface 12b. Furthermore, while the secondary phase 10b is removed from the surface portion of the processed surface 12a, causing cracks 16 reaching the interior of the magnet body 10 or stress due to processing strain, the secondary phase 10b is not removed from the surface portion of the unprocessed surface 12b, preventing cracks 16 reaching the interior of the magnet body 10 or stress due to processing strain. Therefore, in the rare earth magnet 1 according to the first embodiment, a decrease in the coercive force of the surface portion of the constituent surface 12 of the magnet body 10 can be suppressed, thereby suppressing deterioration in the magnetic properties of the rare earth magnet 1. Specifically, the rare earth magnet 1 can suppress demagnetization even with a small demagnetizing field and significant demagnetization as the demagnetizing field increases, thereby suppressing a decrease in the residual magnetic flux density. Therefore, when the rare earth magnet 1 is used in a motor, sufficient torque can be obtained.

[0058] Next, a rare earth magnet according to the second embodiment will be further exemplified. Figure 3 (a) is a schematic perspective view showing a rare earth magnet according to a second embodiment. Figure 3 (b) is along Figure 3 (a) is a schematic cross-sectional view of the rare earth magnet taken along line AA. Figure 4 (a) is a schematic perspective view showing a rare earth magnet according to the prior art. Figure 4 (b) is along Figure 4 (a) is a schematic cross-sectional view of the rare earth magnet taken along line AA.

[0059] like Figure 3 (a) and Figure 3 As shown in FIG. 2( b ), the rare earth magnet 1 according to the second embodiment further comprises, in addition to the magnet body 10 according to the first embodiment, a rare earth-rich layer 20 provided on the processed surface 12a of the constituent surface 12 of the magnet body 10 so as to cover the main phase grains 10a. Furthermore, the surface portion of the processed surface 12a of the constituent surface 12 is modified by providing a diffusion layer 40. The rare earth-rich layer 20 is not provided on the unprocessed surface 12b of the constituent surface 12. Furthermore, although not shown, the rare earth magnet 1 further comprises a Ni plating layer or coating film formed by surface treatment on the surface 10s of the magnet body 10 and the surface 20s of the rare earth-rich layer 20.

[0060] on the other hand, Figure 4 (a) and Figure 4 The rare earth magnet 100 shown in the prior art (b) has the following features: Figure 2The conventional magnet body 10 shown further includes a rare-earth-rich layer 20 disposed on the entire processed surface 12a of the magnet body 10, covering the main phase grains 10a. Furthermore, the surface portion of the entire processed surface 12a of the magnet body 10 is modified by the diffusion layer 40. This restores the coercivity of the entire processed surface 12a, thereby suppressing deterioration in the magnetic properties of the rare-earth magnet 100. However, this increases the amount of expensive rare-earth elements used, potentially leading to increased manufacturing costs.

[0061] In contrast, in the rare earth magnet 1 according to the second embodiment, the rare earth-rich layer 20 and the diffusion layer 40 are provided only on the processed surface 12a of the constituent surface 12 of the magnet body 10, and neither the rare earth-rich layer 20 nor the diffusion layer 40 is provided on the unprocessed surface 12b. Therefore, while suppressing an increase in manufacturing costs, the coercive force of the surface portion of the pressurized surface 12a, which is part of the constituent surface 12, can be restored, thereby restoring the magnetic properties of the rare earth magnet 1.

[0062] Therefore, according to the rare earth magnets of the embodiments, it is possible to suppress deterioration of magnetic properties as in the first and second embodiments. In addition, when a rare earth-rich layer is provided on the processed surface of the magnet body as in the second embodiment, it is possible to suppress an increase in manufacturing costs and restore magnetic properties.

[0063] Next, the configuration of the rare earth magnet and the method for producing the same according to the embodiment will be described in detail.

[0064] 1. Magnet

[0065] The magnet body is not particularly limited as long as it contains a rare earth element R1, a transition metal element T, and boron B and includes a main phase. However, it usually includes a main phase and a subphase surrounding the main phase.

[0066] The composition of the magnet base is not particularly limited as long as it contains a rare earth element R1, a transition metal element T, and boron B, and can be arbitrarily selected depending on the intended purpose. However, in the case of an R1-TB magnet base (R1: rare earth element, T: transition metal element, B: boron), from the viewpoint of excellent magnetic properties, a composition in which the rare earth element R1 is 27.0 mass% to 32.0 mass%, boron B is 0.5 mass% to 2.0 mass%, and the remainder consists essentially of the transition metal element T is preferred. This is because, when the rare earth element R1 content is at least the lower limit of this range, precipitation of soft magnetic elements such as α-Fe and a decrease in coercivity can be suppressed. When the rare earth element R1 content is at most the upper limit of this range, an increase in the amount of the secondary phase and a deterioration in corrosion resistance can be suppressed, and a decrease in the volume ratio of the main phase and a decrease in residual magnetic flux density can be suppressed. Furthermore, when the boron B content is equal to or greater than the lower limit of the range, a high coercive force can be obtained, and when the boron B content is equal to or less than the upper limit of the range, a decrease in residual magnetic flux density can be suppressed.

[0067] Among the components of the magnet body, the rare earth element R1 is not particularly limited as long as it is one or more selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Preferred rare earth elements are those primarily composed of one or two selected from Nd and Pr. This is because they offer a good balance of magnetic properties, are abundant in resources, and are relatively inexpensive. Furthermore, the transition metal element T is preferably one or more transition elements, such as Fe or Fe and Co, which are essential.

[0068] The magnet precursor is not particularly limited, and examples thereof include Nd-Fe-B magnet precursors and Pr-Fe-B magnet precursors. The magnet precursor may be an R (rare earth element)-TBM magnet precursor containing an additive element M in addition to a rare earth element R1, a transition metal element T, and boron B. As the additive element M, for example, one or more of Al, Ga, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, Hf, and Mo may be mentioned. Among these additive elements, Nb, Zr, W, and the like, which are high melting point metals, are preferred in terms of their ability to suppress grain growth. Furthermore, the composition of the magnet precursor is not limited to the compositions listed in this specification, and may be other compositions applicable to the present invention.

[0069] The main phase of the magnet body is R2Fe 14 For example, when the magnet body is a Nd-Fe-B magnet body, the main phase is Nd2Fe 14B. The secondary phase of the magnet body is a phase containing more rare earth element R1 than the primary phase, and exists so as to surround the primary phase.

[0070] The regions of the constituent surfaces of the magnet body near the corners thereof are processed surfaces that have undergone removal processing, and the regions of the constituent surfaces that are closer to the center than the regions near the corners are unprocessed surfaces that have not undergone removal processing. Here, the term "corner of the magnet body" refers to the region where at least two of the constituent surfaces of the magnet body intersect.

[0071] The machined surface of the magnet body is not particularly limited as long as it is a surface obtained by subtractive processing. However, subtractive processing generally removes secondary phases, or causes damage or stress, resulting in partial surface deterioration and deterioration of the magnetic properties of that portion. Subtractive processing refers to surfaces newly exposed by subtractive processing of a sintered body prior to forming into a magnet body. Examples include ground surfaces, lapped surfaces, and cut surfaces. The surface roughness Ra of the machined surface of the magnet body is, for example, within a range of 0.1 μm to 10 μm.

[0072] The unprocessed surface of the magnet body is the portion of the surface of the sintered body processed to obtain the magnet body that has not been removed. The surface roughness Ra of the unprocessed surface of the magnet body is, for example, within a range of 0.5 μm to 50 μm.

[0073] The shape of the magnet body is not particularly limited as long as it is a three-dimensional shape with corners. It can be set to the general shape of the magnet body of the rare earth magnet used in the motor of an electric vehicle, etc. For example, polygons such as cubes and rectangular parallelepipeds can be listed. As long as it has corners, it can also be a shape with curved surfaces as the constituent surfaces.

[0074] The size of the magnet body is not particularly limited and can be set to the general size of the magnet body of the rare earth magnet used in the motor of the electric vehicle, etc., but when the shape of the magnet body is a cube or a rectangular parallelepiped, for example, the width (W) is preferably 3 mm or more and 30 mm or less, the length (L) is 5 mm or more and 80 mm or less, and the height (H) is 2 mm or more and 15 mm or less. This is because, when the size of the magnet body is above the lower limit of this range, the influence of shrinkage during sintering of the molded body becomes greater, and the necessity of removing the excess parts of the corners and the vicinity of the sintered body becomes higher. In addition, when the size of the magnet body is below the upper limit of this range, the surface modification effect of the processed surface of the magnet body brought by the rare earth rich layer becomes greater.

[0075] 2. Rare earth-rich layer and diffusion layer

[0076] The rare earth magnet preferably further includes a rare earth rich layer provided on the processed surface of the magnet body. This can restore the coercive force of the surface portion of the processed surface of the magnet body and the magnetic properties of the rare earth magnet.

[0077] The rare earth-rich layer is a layer that remains after a diffusion reaction between the diffusion material and the surface portion of the processed surface of the magnet body, resulting from heat treatment while a diffusion material containing the rare earth element R2 is present on the processed surface of the magnet body. This layer is richer in the rare earth element R2 than the surface portion of the processed surface of the magnet body. Furthermore, during the diffusion reaction between the diffusion material and the surface portion of the processed surface of the magnet body, the rare earth element R2 diffuses from the diffusion material into the surface portion of the processed surface of the magnet body, and the constituent elements of the magnet body diffuse from the surface portion of the processed surface of the magnet body into the diffusion material. Examples of the rare earth-rich layer are not particularly limited, and include, for example, a layer remaining after a diffusion reaction of a film formed on the processed surface of the magnet body by PVD, CVD, or the like, or a layer formed by applying a powdered diffusion material to the processed surface of the magnet body and then undergoing a subsequent diffusion treatment.

[0078] The rare earth element R2 is not particularly limited as long as it is one or more selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among them, rare earth elements mainly composed of one or two selected from Nd, Pr, Ce, Sm, Dy, and Tb are preferred, and rare earth elements mainly composed of one or two selected from Dy and Tb are particularly preferred. This is because the effect of restoring magnetic properties such as coercivity is significant.

[0079] The thickness of the rare earth-rich layer is not particularly limited as long as it is a thickness that can restore the magnetic properties of the rare earth magnet. For example, it is preferably within the range of 0.1 μm to 5 μm. This is because, by having a rare earth-rich layer thickness above the lower limit of this range, the effect of restoring the coercive force of the surface portion of the machined surface of the magnet body can be fully achieved. In addition, by having a rare earth-rich layer thickness below the upper limit of this range, the reduction in residual magnetic flux density caused by the presence of the rare earth-rich layer can be suppressed. When used in a motor, sufficient torque can be obtained, and the amount of rare earth elements used can be reduced, which can reduce unnecessary costs.

[0080] When a rare earth magnet has a rare earth-rich layer, a diffusion layer typically exists on the surface of the machined surface of the magnet body. This diffusion layer is formed by the diffusion of rare earth elements R2 from the diffusion material into the surface of the machined surface of the magnet body. This layer is richer in rare earth elements R2 than the interior of the magnet body. This diffusion layer can further restore magnetic properties such as coercivity.

[0081] The thickness of the diffusion layer is not particularly limited as long as it can restore the magnetic properties of the rare earth magnet. For example, it is preferably within the range of 0.1 μm to 5 μm. This is because when the diffusion layer thickness is at least the lower limit of this range, the effect of restoring coercive force and other properties can be fully achieved. On the other hand, when the diffusion layer thickness is at or below the upper limit of this range, deterioration of magnetic properties due to the diffusion layer can be avoided.

[0082] 3. Rare earth magnets

[0083] The use of rare earth magnets is not particularly limited. Examples of rare earth magnets include motors such as internal magnetic field motors (IPM motors) mounted on electric vehicles such as electric vehicles (EVs) and hybrid vehicles (HVs), actuators for hard disk drives, and motors for mobile phones. Among these, rare earth magnets preferably are used in motors mounted on electric vehicles.

[0084] 4. Manufacturing method of rare earth magnets

[0085] The method for manufacturing a rare earth magnet involved in the embodiment is a method for manufacturing a rare earth magnet involved in the embodiment, which is characterized by comprising: a molding step, in which a raw material powder containing a rare earth element R1, a transition metal element T and boron B is compression-molded into the shape of the above-mentioned magnet original body for making the above-mentioned rare earth magnet to obtain a molded body; a sintering step, in which the above-mentioned molded body is sintered to obtain a sintered body; and a processing step, in which the corners of the above-mentioned sintered body and excess parts near the corners are removed and processed to make the above-mentioned magnet original body.

[0086] Here, the outline of the method for manufacturing the rare earth magnet according to the embodiment is given as an example. Figure 3 A method for producing a rare earth magnet according to the second embodiment shown will be described. Figure 5 It is a diagram schematically showing the flow of a method for producing a rare earth magnet according to the second embodiment. Figure 6 (a)~ Figure 7 (c) is a schematic cross-sectional view showing the main steps of the method for producing a rare earth magnet according to the second embodiment.

[0087] In the method for manufacturing a rare earth magnet according to the second embodiment, first, Figure 5 As shown, rare earth element R1, transition metal element T, boron B and other additive elements are weighed in accordance with the composition of the magnet body of the rare earth magnet to be manufactured, and these raw materials are mixed and placed in a crucible (weighing and mixing process).

[0088] Then, if Figure 5As shown, a crucible is placed in a vacuum melting furnace, and high frequency is applied to the crucible to melt the raw materials and alloy them homogeneously. The molten metal is then poured into a mold to produce an ingot (alloying step).

[0089] Then, if Figure 5 As shown, the ingot is pulverized in several stages using a jet mill or the like to a raw material powder having an average particle size of several microns (pulverization step). At this time, to prevent oxidation of the raw material powder, the powder is protected in a nitrogen and / or argon atmosphere while being pulverized.

[0090] Then, if Figure 5 and Figure 6 As shown in (a), a raw material powder 5 containing a rare earth element R1, a transition metal element T, and boron B is compression-molded into the shape of a magnet base for producing the rare earth magnet according to the second embodiment, thereby obtaining a molded body 50 (molding step). Specifically, the raw material powder 5 is compression-molded in a mold to which a magnetic field is applied. This aligns the crystal orientation of the raw material powder 5 with the direction of the external magnetic field, improving the magnetic properties in the orientation direction.

[0091] Then, if Figure 5 and Figure 6 As shown in (b), the molded body 50 is sintered to obtain a sintered body 60 (sintering step). Specifically, the molded body 50 is sintered in a vacuum sintering furnace to obtain the sintered body 60. At this time, as a result of the shape change accompanying the shrinkage of the molded body 50, the sintered body 60 has excess portions 60c at and near the corners that are unnecessary for the intended magnet body to be produced.

[0092] Then, if Figure 5 As shown, a test is performed to measure the magnetic properties of the sintered body 60, such as the residual magnetic flux density and the coercive force, and the sintered body 60 that passes the test is sent to the next step (magnetic property test step).

[0093] Then, if Figure 5 and Figure 7 As shown in (a), the corners of a sintered body 60 and the surrounding excess portions 60c are ground (removed) to produce a rare earth magnet base 10 (processing step). The newly exposed surface of the sintered body 60 after grinding becomes the processed surface (ground surface) 12a of the magnet base 10, while the surfaces other than the processed surface 12a of the magnet base 10 become the unprocessed surface 12b. The magnet base 10 contains a rare earth element R1, a transition metal element T, and boron B, and comprises primary phase grains (main phase) 10a and a secondary phase 10b surrounding the primary phase grains 10a.

[0094] Then, if Figure 5 and Figure 7 As shown in (b), a heat treatment (heat treatment step) is performed while the diffusion material 30 containing the rare earth element R2 is present on the processed surface 12a of the magnet body 10. Figure 7 As shown in (c), the rare earth element R2 is diffused from the diffusion material 30 to the surface portion of the processed surface 12a of the magnet body 10 to form a diffusion layer 40, thereby modifying the surface portion of the processed surface 12a of the magnet body 10. Furthermore, the diffusion material 30 is allowed to remain after the diffusion reaction with the surface portion of the processed surface 12a of the magnet body 10, thereby forming a rare earth rich layer 20. At this time, for example, when the magnet body 10 is a Nd-Fe-B based magnet body, the rare earth element R2 is diffused into the main phase particles (Nd2Fe 14 B) The surface area of ​​10a diffuses and reacts to form (Nd, R2)2Fe 14 B. Furthermore, the surface of the main phase grains 10a is covered with the Nd-rich layer (rare earth-rich layer) 20. As a result, the coercivity of the surface portion of the processed surface 12a of the magnet body 10 is restored, and the magnetic properties of the magnet body 10 are restored. Furthermore, during the diffusion of the rare earth element R2, cracks 16 that have reached the interior of the magnet body 10 during the grinding process, as well as stress caused by processing strain, are eliminated. Consequently, the coercivity within the magnet body 10 is also restored.

[0095] Then, if Figure 5 As shown, various surface treatments (surface treatment steps) are performed on the magnet body 10 provided with the rare earth rich layer 20 according to the environment in which it is used. Specifically, for example, when the magnet body 10 is a Nd-Fe-B magnet body, which is generally susceptible to rust, Ni plating and / or painting are performed.

[0096] Then, if Figure 5 As shown, the magnet body 10 after surface treatment is inspected (inspection step). Specifically, the dimensions and appearance of the magnet body 10 are inspected. In addition, magnetic properties are measured, corrosion resistance tests are performed, and strength measurements are performed according to product specifications.

[0097] Then, if Figure 5 As shown in FIG. 1 , the magnet body 10 is magnetized (magnetization process). Through the above process, the above-mentioned Figure 3 The rare earth magnet 1 according to the second embodiment shown in FIG. Figure 5 As shown, the manufactured rare earth magnets are packaged and shipped (packing and shipping process).

[0098] In the rare earth magnet manufacturing method according to the second embodiment, the magnet body 10 of the rare earth magnet 1 is produced by grinding only the corners of the sintered body 60 and the excess portions 60c thereabouts. Therefore, the secondary phase 10b is not removed from the surface portion of the unprocessed surface 12b of the magnet body 10, and cracks 16 reaching the interior of the magnet body 10 or stress caused by processing strain are not generated. This suppresses the reduction in coercivity of the surface portion of the constituent surface 12 of the magnet body 10, thereby suppressing the deterioration of the magnetic properties of the rare earth magnet 1. Furthermore, a diffusion layer 40 can be formed only on the surface portion of the processed surface 12a of the magnet body 10, thereby modifying that portion, and a rare earth-rich layer 20 can be formed on the processed surface 12a of the magnet body 10. This can suppress an increase in manufacturing costs while restoring the magnetic properties of the rare earth magnet 1.

[0099] Furthermore, the above Figure 1 The method for manufacturing a rare earth magnet according to the first embodiment shown does not perform a heat treatment step, but performs a surface treatment step and subsequent steps on the magnet body 10 without the rare earth rich layer 20. This method differs from the method for manufacturing a rare earth magnet according to the second embodiment only in the above point.

[0100] Therefore, according to the method for manufacturing a rare earth magnet according to the embodiment, it is possible to suppress deterioration of the magnetic properties of the rare earth magnet. In addition, when a heat treatment step is further included in which a diffusion material containing the rare earth element R2 is applied to the processed surface of the magnet body, it is possible to suppress an increase in manufacturing costs and restore the magnetic properties of the rare earth magnet.

[0101] Next, the details of the method for producing the rare earth magnet according to the embodiment will be described.

[0102] (1) Molding process

[0103] In the molding step, raw material powder containing the rare earth element R1, the transition metal element T, and boron B is compression-molded into the shape of the magnet body for producing the rare earth magnet, thereby obtaining a molded body.

[0104] The composition of the raw material powder is the same as that of the magnet body described in the above-mentioned "1. Magnet body", and therefore its description is omitted here.

[0105] The method for compression molding the raw material powder is not particularly limited, but preferably, the raw material powder is compressed and molded in a mold to which a magnetic field is applied. The method for molding in a magnetic field can be vertical magnetic field pressing, in which a magnetic field is applied perpendicularly to the pressing direction, or parallel magnetic field pressing, in which a magnetic field is applied parallel to the pressing direction. Molding in a magnetic field can be performed, for example, in a magnetic field within a range of 500 kA / m to 2000 kA / m at a pressure within a range of 100 MPa to 200 MPa.

[0106] The shape and size of the compact formed by compression molding of the raw material powder are not particularly limited as long as they are the shape and size of the magnet body used to make rare earth magnets. They are usually determined in accordance with the shape and size of the magnet body and can be determined by considering the shrinkage of the compact during sintering.

[0107] (2) Sintering process

[0108] In the sintering step, the molded body is sintered to obtain a sintered body.

[0109] The sintering atmosphere is preferably a vacuum atmosphere or an inert gas atmosphere such as argon or helium. The sintering temperature and sintering time are not particularly limited and need to be adjusted according to various conditions such as the composition of the raw material powder, the pulverization method during production, and the particle size distribution. For example, sintering for 5 hours at a temperature within the range of 900°C to 1150°C is possible. The heating method used for sintering is not particularly limited and includes resistance heating, high-frequency induction heating, and the like.

[0110] During the sintering process, the compact shrinks as it solidifies. The compact's volumetric shrinkage varies depending on the raw material powder, the compact's molding conditions, and the sintering conditions. However, generally, the sintered compact's dimensions are approximately 70% to 80% of the compact's, and its volume is approximately 50% of the compact's.

[0111] (3) Processing procedures

[0112] In the processing step, the corners of the sintered body and the excess parts near them are removed to produce the magnet base body. Thus, the surface newly exposed by the removal of the sintered body becomes the processed surface of the magnet base body, and the surface other than the processed surface of the magnet base body becomes the unprocessed surface.

[0113] The method for removing the corners of the sintered body and any excess portions near them is not particularly limited as long as it removes a portion of the sintered body, and examples thereof include lapping, grinding, and cutting. The shape and dimensions of the magnet body produced in this processing step are the same as those described in "1. Magnet Body" above, and therefore their description is omitted here.

[0114] (4) Heat treatment process and aging treatment process

[0115] The method for producing a rare earth magnet preferably further comprises a heat treatment step in which a diffusion material containing the rare earth element R2 is present on the processed surface of the magnet base. This is because diffusion of the rare earth element R2 from the diffusion material into the surface portion of the processed surface of the magnet base can modify the surface portion of the processed surface of the magnet base, thereby restoring the magnetic properties of the rare earth magnet.

[0116] The method for making the diffusion material containing the rare earth element R2 present on the processed surface of the magnet body is not particularly limited, and examples include methods of forming a film of the diffusion material on the processed surface of the magnet body by PVD, CVD, etc., methods of forming the diffusion material into a powder and coating the processed surface of the magnet body, etc. More specifically, examples include methods of forming a sputtered film, vapor-deposited film, etc. of the rare earth element R2, or a sputtered film, vapor-deposited film, etc. of an alloy containing the rare earth element R2, etc. on the processed surface of the magnet body by PVD, CVD, etc.; methods of coating the processed surface of the magnet body with powder of the rare earth element R2, powder of a compound such as an oxide, fluoride, oxyfluoride, hydride, hydroxide of the rare earth element R2, or powder of an alloy containing the rare earth element R2; and methods of arranging the magnet body within the powder.

[0117] The rare earth element R2 is the same as the rare earth element R2 described in the above-mentioned “2. Rare earth rich layer and diffusion layer”, and therefore the description thereof is omitted here.

[0118] The atmosphere in which the heat treatment is carried out is preferably, for example, a vacuum atmosphere or an inert gas atmosphere. The temperature of the heat treatment is not particularly limited as long as the magnetic properties of the rare earth magnet can be restored, but is preferably within a range below the sintering temperature of the magnet body, specifically, for example, preferably within a range of 500°C to 1000°C. This is because, by setting the temperature of the heat treatment below the upper limit of these ranges, problems such as structural deterioration of the magnet body and failure to obtain high magnetic properties can be avoided. In addition, by setting the temperature of the heat treatment above the lower limit of the range, the surface modification effect of the processed surface can be fully obtained. The time of the heat treatment is not particularly limited as long as the magnetic properties of the rare earth magnet can be restored, for example, preferably within a range of 10 minutes to 1 hour. This is because, by setting the time of the heat treatment above the lower limit of the range, the surface modification effect of the processed surface can be fully obtained. In addition, by setting the time of the heat treatment below the upper limit of the range, a decrease in productivity can be avoided and the thermal impact on the magnet body can be reduced.

[0119] When a rare earth magnet manufacturing method includes a heat treatment step, it is preferable to further include an aging treatment step. The aging treatment step is a step of aging the magnet body after the heat treatment step. This is because it can optimize the structure of the magnet body and enhance the recovery effect of magnetic properties such as coercive force.

[0120] The atmosphere in which the aging treatment is performed is preferably, for example, a vacuum atmosphere or an inert gas atmosphere. The aging treatment temperature is preferably within a range lower than the heat treatment temperature, specifically, preferably within a range of 400°C to 600°C. This is because magnetic properties such as coercivity can be fully restored. The aging treatment time is preferably within a range of 1 minute to 10 hours.

[0121] Furthermore, in the heat treatment step, the temperature and time of the heat treatment may be optimized so that the heat treatment also serves as the aging treatment, thereby omitting a part or all of the aging treatment step.

[0122] (5) Others

[0123] The method for manufacturing a rare earth magnet according to an embodiment may include the following steps: a recovery step of recovering the rare earth magnet comprising the magnet body described in "1. Magnet Body" from a motor; and a heat treatment step of heat-treating the rare earth magnet while a diffusion material containing the rare earth element R2 is present on the processed surface of the magnet body. This is because a rare earth magnet whose magnetic properties, such as coercive force, have deteriorated due to use in a motor can be regenerated to restore its magnetic properties.

[0124] As the method for producing the rare earth magnet according to the embodiment, a method for producing the rare earth magnet according to the third embodiment will be further exemplified. Figure 8 (a)~ Figure 8 (d) is a schematic cross-sectional view showing the main steps of the method for producing a rare earth magnet according to the third embodiment.

[0125] In the method for manufacturing a rare earth magnet according to the third embodiment, Figure 8 (a) shows that Figure 6 and Figure 7 The sintered body 60 is manufactured in the same manner as the method for manufacturing the rare earth magnet according to the second embodiment shown in FIG. Figure 8 As shown in (b), in the processing step, the corners of the sintered body 60 and the excess portion 60c near them are ground, and the sintered body 60 is cut with two surfaces parallel to the upper surface and the side surface of the sintered body 60, thereby producing the magnet original body 10 in which the sintered body 60 is divided into four parts. Figure 8As shown in (c), in the heat treatment process, the diffusion material 30 containing the rare earth element R2 is heat treated in a state where it is present on the processed surface (polished surface) 12a and the processed surface (cut surface) 12a' of the constituent surface 12 of the magnet body 10. Figure 8 As shown in (d), the rare earth element R2 is diffused from the diffusion material 30 onto the surface portions of the processed surfaces 12a and 12a' of the magnet body 10, thereby forming a diffusion layer 40 and modifying the surface portions of these surfaces. Furthermore, the diffusion material 30 remains after the diffusion reaction, thereby forming a rare earth-rich layer 20.

[0126] In the method for producing a rare earth magnet according to the third embodiment, the secondary phase 10b is not removed from the surface portion of the non-machined surface 12b of the constituent surface 12 of the magnet body 10, excluding the machined surfaces 12a and 12a'. Consequently, no cracks 16 or stress due to machining strain are generated. Furthermore, by modifying the surface portions of the machined surfaces 12a and 12a' of the magnet body 10 and forming the rare earth-rich layer 20, the coercivity of these surface portions can be restored.

[0127] Furthermore, the method for manufacturing the rare earth magnet according to the embodiment is as follows: Figure 5 As in the process of the present invention, in addition to the forming step, sintering step, processing step and heat treatment step, it may also include a weighing and mixing step, an alloying step, a pulverizing step, a magnetic property test step, a surface treatment step, an inspection step, a magnetization step, etc. Furthermore, when the method for manufacturing a rare earth magnet includes an aging treatment step and a surface treatment step, the aging treatment step is a step before the surface treatment step.

[0128] Example

[0129] Hereinafter, the rare earth magnet and the method for producing the same according to the present invention will be described in more detail with reference to examples.

[0130] [Reference Example 1]

[0131] First, a sintered body was prepared before being formed into a Nd-Fe-B magnet base body. Next, all surfaces of the sintered body were polished to obtain a rectangular parallelepiped magnet base body with a width (W) of 5 mm, a length (L) of 20 mm, and a height (H) of 3 mm. This produced a rare earth magnet base body with all constituent surfaces being processed surfaces.

[0132] [Reference Example 2]

[0133] First, the magnet body obtained in Reference Example 1 was prepared and placed within the Nd-containing alloy powder so that all of the magnet body's constituent surfaces were entirely within the Nd-containing alloy powder. This allowed the diffusion material, which included the Nd-containing alloy powder, to be present across all of the magnet body's constituent surfaces.

[0134] Next, the magnet body, with the diffusion material present on all its constituent surfaces, was heat treated in a vacuum atmosphere at 900°C for 30 minutes. The heat-treated magnet body was then aged in a vacuum atmosphere at 550°C for 60 minutes. This produced a rare earth magnet comprising the magnet body and a treated layer of the vapor-deposited film.

[0135] [SEM observation and EPMA measurement]

[0136] The cross section of the boundary between the magnet body and the deposited film in the rare earth magnet of Reference Example 2 was observed using a SEM (scanning electron microscope). The amount of Nd at each position on the cross section was measured using an EPMA (electron probe microanalyzer). Figure 9 These are diagrams showing a SEM image of a cross section of the boundary portion between the magnet body and the processed layer of the vapor-deposited film in the rare earth magnet of Reference Example 2, and an EPMA image of the Nd amount.

[0137] Depend on Figure 9 The SEM image and EPMA image of the Nd content confirm that an Nd-rich layer (rare earth-rich layer) is formed on the machined surface of the magnet body. This suggests that the Nd diffuses into the surface of the machined surface of the magnet body, forming a diffusion layer and modifying the surface of the machined surface of the magnet body.

[0138] [Evaluation of magnetic properties]

[0139] With respect to the rare earth magnets of Reference Examples 1 and 2, JH curves were measured when a demagnetizing field was applied and then removed. Figure 10 (a) is a schematic cross-sectional view showing a BH curve tracer according to JIS C 2501 as a measuring device used for measuring a JH curve, Figure 10 (b) is a diagram showing the procedure of applying a magnetic field when measuring a JH curve.

[0140] In the measurement of the JH curve, first, a magnetic field H of 5 T (magnetic field H ≈ 4000 kA / m) is applied to the rare earth magnet by a pulse magnetization method to magnetize the rare earth magnet. Figure 10 The BH curve tracer shown in (a) is Figure 10As shown in (b), the magnetic field H was changed from +1600 kA / m to a demagnetizing field of -1600 kA / m, and then the magnetic polarization J[T] was measured while the magnetic field H was changed from a demagnetizing field of -1600 kA / m to 0 kA / m. Figure 11 This is a diagram showing JH curves measured for the rare earth magnets of Reference Examples 1 and 2.

[0141] Depend on Figure 11 The JH curve shown confirms that the rare earth magnet of Reference Example 1 demagnetizes even when the demagnetizing magnetic field is small, and demagnetizes more significantly as the demagnetizing magnetic field increases. However, the rare earth magnet of Reference Example 2 does not demagnetize to the same extent as Reference Example 1 when the demagnetizing magnetic field is small. Furthermore, the amount of demagnetization of the rare earth magnet of Reference Example 2 is approximately half that of the rare earth magnet of Reference Example 1. Furthermore, the JH curve of the rare earth magnet of Reference Example 2 confirms that the magnetic polarization J increases to approximately 1.12 T when the magnetic field H is -900 kA / m.

[0142] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims.

Claims

1. A rare earth magnet, characterized in that: A magnet body comprising a main phase containing a rare earth element R1, a transition metal element T, and boron B, wherein a region of a constituent surface constituting the surface of the magnet body near a corner of the magnet body is a processed surface obtained by removal processing, and a region of the constituent surface closer to the center than the region near the corner is a non-processed surface that has not been removed, wherein the corner is a portion where at least two of the constituent surfaces constituting the surface of the magnet body intersect. The rare earth magnet further comprises: a rare earth-rich layer, the rare earth-rich layer being provided on the processed surface of the magnet body, the rare earth-rich layer being a layer remaining after a diffusion reaction between the diffusion material and the surface portion of the processed surface of the magnet body by heat treatment while a diffusion material containing the rare earth element R2 is present on the processed surface of the magnet body, and being a layer enriched in the rare earth element R2 as compared to the surface portion of the processed surface of the magnet body, and A diffusion layer is provided on the processed surface of the magnet body. The diffusion layer is generated by diffusing the rare earth element R2 from the diffusion material to the surface portion of the processed surface of the magnet body. The diffusion layer is a layer in which the rare earth element R2 is enriched compared to the interior of the magnet body. The rare earth rich layer and the diffusion layer are not provided on the non-processed surface.

2. A method for manufacturing a rare earth magnet, which is a method for manufacturing the rare earth magnet according to claim 1, characterized in that: have: A molding step of compressing raw material powder containing a rare earth element R1, a transition metal element T, and boron B into the shape of the magnet body for producing the rare earth magnet to obtain a molded body; a sintering step of sintering the molded body to obtain a sintered body; and The processing step is to remove the excess parts of the corners of the sintered body and the surrounding areas to produce the magnet body. The corner portion refers to a portion where at least two of the constituent surfaces constituting the surface of the sintered body intersect. The manufacturing method also includes a heat treatment process, which is a process of performing heat treatment in a state in which a diffusion material containing the rare earth element R2 is present on the processing surface of the magnet body, thereby generating a diffusion layer by diffusing the rare earth element R2 from the diffusion material to the surface portion of the processing surface of the magnet body, and forming a rare earth-rich layer by allowing the diffusion material to remain after the diffusion reaction with the surface portion of the processing surface of the magnet body.

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