R-Fe-B-BASED SINTERED MAGNET AND METHOD FOR MANUFACTURING SAME

Abstract

The present invention provides an R-Fe-B-based sintered magnet which is characterized in that: R, B, Co, Ga, M1, M2, O, C, N, and Fe are contained at a specific ratio; the grain boundary phase includes an R-Fe(Co)-(Ga, M1) phase that contains the elements at a specific ratio; and when [Fe] is the concentration of Fe atoms with respect to the total amount of the elements in the phase, [Co] is the concentration of Co atoms with respect to the total amount of the elements in the phase, [Ga] is the concentration of Ga atoms with respect to the total amount of the elements in the phase, and [M1] is the concentration of M1 atoms with respect to the total amount of the elements in the phase, the relational expression 4.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.8 is satisfied.　It is possible to obtain an R-Fe-B-based sintered magnet that achieves both high Br and high HcJ at the minimum necessary Ga content by increasing the utilization efficiency of Ga.

Description

R-Fe-B sintered magnet and method for manufacturing the same

[0001] This invention relates to an R-Fe-B sintered magnet that achieves both high Br and high HcJ with a low Ga content, and to a method for manufacturing the same.

[0002] R-Fe-B sintered magnets (sometimes referred to as Nd magnets) are functional materials essential for energy conservation and high performance, and their application range and production volume are expanding year by year. For example, they are used in drive motors in hybrid and electric vehicles, motors for electric power steering in automobiles, and motors for air conditioner compressors. In these various applications, the high coercivity (HcJ) of R-Fe-B sintered magnets is a major advantage for withstanding use in high-temperature environments, but further improvements in HcJ are required to operate motors in even harsher environments.

[0003] Conventionally, R2T is a method for increasing the HcJ of Nd magnets. 14 To improve the crystalline magnetic anisotropy of the B phase, methods have been employed in which a portion of R is replaced with heavy rare earth elements such as Dy and Tb. On the other hand, considering the resource risks associated with rare elements such as Dy and Tb, there has been active development of methods to improve HcJ without using heavy rare earth elements, and various methods have been proposed, such as refining the main phase crystal grains and controlling the structure of the grain boundary phase.

[0004] For example, Japanese Patent Publication No. 2019-050284 (Patent Document 1) discloses that by using Ga as an essential element and forming a structure containing a face-centered cubic XZ phase and an R-O-C-N phase at the grain boundaries, it is possible to obtain an R-T-B system permanent magnet that has high HcJ and residual magnetic flux density (Br) while suppressing the heavy rare earth content, and further exhibits good strength, electrical resistance of the grain boundary phase, or sintering stability.

[0005] Furthermore, Japanese Patent Publication No. 2018-028123 (Patent Document 2) discloses a method for obtaining an R-T-B sintered magnet having high Br and high HcJ while reducing the content of heavy rare earth elements, by bringing an R-Cu-Ga-Fe-A alloy containing Ga into contact with at least a part of the surface of an R-T-B-M sintered body and heat-treating it to supply alloy components into the inside of the magnet.

[0006] Japanese Patent Publication No. 2019-050284 Japanese Patent Publication No. 2018-028123

[0007] However, the R-T-B permanent magnet described in Patent Document 1 above requires the addition of Ga, but in recent years, export restrictions have been imposed by Ga-producing countries, and Ga has become a resource procurement risk. Therefore, from the perspective of obtaining sufficient coercivity with the minimum necessary amount of Ga added, this is not satisfactory.

[0008] Furthermore, the invention described in Patent Document 2 improves coercivity by introducing an R-Cu-Ga-Fe-A alloy with a low Ga concentration into a sintered magnet. However, this presents a problem in that it increases manufacturing costs due to the additional steps of coating the R-Cu-Ga-Fe-A alloy onto the magnet and heat-treating it to introduce the element into the magnet.

[0009] The present invention has been made in view of the above problems, and aims to provide an R-Fe-B sintered magnet that can achieve both high Br and high HcJ with the minimum necessary Ga content by increasing the utilization efficiency of Ga in an R-Fe-B sintered magnet.

[0010] The present inventors, after diligent research to solve the above problems, have found that by including a predetermined composition of R-Fe(Co)-(Ga,M1) phase in the grain boundary phase (where R is one or more elements selected from rare earth elements, and M1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), and by optimizing the concentrations of R, Fe, Co, Ga, and M1 in this R-Fe(Co)-(Ga,M1) phase, it is possible to obtain an R-Fe-B sintered magnet having high Br and high HcJ while reducing the amount of Ga used, thus completing the present invention.

[0011] Therefore, the present invention provides the following R-Fe-B sintered magnet and a method for manufacturing the same. 1. The composition is as follows: 12.5 to 17.0 atomic% R (where R is one or more elements selected from rare earth elements, with Nd being essential), 4.5 to 6.0 atomic% B, 10 atomic% or less Co, 0.1 to 1.0 atomic% Ga, 0.1 to 3.0 atomic% M1 (where M1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), 0.05 to 1.0 atomic% M2 (where M2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), 1.5 atomic% or less O, 0.1 to 1.5 atomic% C, 0.5 atomic% or less N, and the remainder Fe, with R2(Fe, (Co)) 14 An R-Fe-B sintered magnet containing a main phase which is an intermetallic compound B and a grain boundary phase, wherein the grain boundary phase includes an R-Fe(Co)-(Ga,M1) phase having a composition of 25-35 atomic% R, 2.0-8.0 atomic% Ga, 2.0-8.0 atomic% M1, 8.0 atomic% or less Co, and the remainder Fe, and when the concentration of Fe atoms in the R-Fe(Co)-(Ga,M1) phase is [Fe], the concentration of Co atoms is [Co], the concentration of Ga atoms is [Ga], and the concentration of M1 atoms is [M1], the following relation (1) is satisfied: 4.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.8 ... (1). 2. The R-Fe-B sintered magnet according to 1, wherein the concentration of Ga atoms [Ga] and the concentration of M1 atoms [M1] in the above R-Fe(Co)-(Ga,M1) phase satisfy the following relationship (2) 0 < [Ga] / [M1] ≤ 2.0 ... (2). 3. The above R-Fe(Co)-(Ga,M1) phase is La6Co9(Co 0.5 Ga 0.5) An R-Fe-B sintered magnet according to 1 or 2 having a 4Ga type crystal structure. 4. An R-Fe-B sintered magnet according to any one of 1 to 3, wherein the concentration of element M1 relative to the constituent elements in the main phase is lower than the concentration of element M1 [M1] in the R-Fe(Co)-(Ga,M1) phase. 5. An R-Fe-B sintered magnet according to any one of 1 to 4, wherein the grain boundary phase contains an R-Fe(Co)-M1 phase in addition to the R-Fe(Co)-(Ga,M1) phase. 6. When the concentration of Fe atoms in the above R-Fe(Co)-M1 phase is [Fe]', the concentration of Co atoms is [Co]', and the concentration of M1 atoms is [M1]', the following relationship (3) 8.0 ≤ ([Fe]' + [Co]') / [M1]' ≤ 12.0 ... (3) is satisfied, the R-Fe-B sintered magnet described in 5. 7. A method for manufacturing an R-Fe-B sintered magnet according to any one of 1 to 6, comprising: a melting step to obtain a main alloy having a composition of 12.0 to 16.5 atomic percent of R, 5.0 to 6.5 atomic percent of B, 10 atomic percent or less of Co, 0.1 to 1.0 atomic percent of Ga, 0.05 to 1.0 atomic percent of M2, and the remainder Fe; and an auxiliary alloy having a composition of 20 to 40 atomic percent of R, 30 atomic percent or less of Co, 3 atomic percent or less of B, 15 to 35 atomic percent of M1, and the remainder Fe; a coarse grinding step to prepare powders of the main alloy and the auxiliary alloy; a fine powder preparation step to obtain a mixed alloy fine powder by mixing the main alloy powder and the auxiliary alloy powder in a predetermined ratio; a molding step to obtain a molded body by molding the mixed alloy fine powder in a magnetic field; and a sintering step to obtain a sintered body by sintering the molded body. A method for manufacturing an R-Fe-B sintered magnet, characterized in that the mixing ratio of the main alloy and the auxiliary alloy in the above-mentioned fine powder preparation step is 85 to 97% by mass of the main alloy and 3 to 15% by mass of the auxiliary alloy. 8. The method for manufacturing an R-Fe-B sintered magnet according to 7, wherein the above-mentioned fine powder preparation step comprises a mixing step of mixing the main alloy powder and the auxiliary alloy powder to prepare a mixed alloy powder, and a fine grinding step of finely grinding the mixed alloy powder to obtain fine powder. 9. The method for manufacturing an R-Fe-B sintered magnet according to 7, wherein the above-mentioned fine powder preparation step comprises a fine grinding step of finely grinding the main alloy powder and the auxiliary alloy powder respectively to obtain main alloy fine powder and auxiliary alloy fine powder, and a mixing step of mixing the obtained main alloy fine powder and auxiliary alloy fine powder to prepare a mixed alloy fine powder.10. A method for manufacturing an R-Fe-B sintered magnet according to any one of 7 to 9, wherein M1 in the auxiliary alloy contains at least Al and Si.

[0012] According to the present invention, it is possible to obtain an R-Fe-B sintered magnet that achieves both high Br and high HcJ with the minimum necessary Ga content by increasing the utilization efficiency of Ga.

[0013] This is an electron microscope image of the cross-section of the R-Fe-B sintered magnet fabricated in Example 2, observed parallel to the magnetization direction.

[0014] The element R constituting the R-Fe-B sintered magnet of the present invention is one or more elements selected from rare earth elements, and Nd is essential. Preferred rare earth elements are Nd, Pr, La, Ce, Gd, Dy, Tb, and Ho, with Nd, Pr, Dy, and Tb being particularly preferred, and Nd and Pr being even more preferred. In addition, the magnet may contain R elements introduced into it by grain boundary diffusion after sintering as part of the R element.

[0015] The R element content is preferably 12.5 atomic% or more, and more preferably 13.0 atomic% or more, from the viewpoint of suppressing the crystallization of α-Fe in the raw alloy during manufacturing and ensuring sufficient densification. Although it is difficult to eliminate α-Fe even with homogenization, within the above range, it is possible to suppress a significant decrease in HcJ and prismaticity of the R-Fe-B sintered magnet. The same applies when the raw alloy is manufactured by the strip casting method, which makes it difficult for α-Fe to crystallize. In addition, it is possible to prevent insufficient densification of the R-Fe-B sintered magnet due to a decrease in the amount of liquid phase consisting mainly of R components, which plays a role in promoting densification during the sintering process described later, as this reduces sinterability. On the other hand, R2Fe in the sintered magnet 14 From the viewpoint of preventing a decrease in the proportion of phase B and a reduction in Br, the R content is set to 17 atomic percent or less, preferably 15.5 atomic percent or less, and more preferably 15 atomic percent or less.

[0016] The Fe content, which is the remainder of the other elements, is preferably 70 atomic % or more, more preferably 75 atomic % or more, from the viewpoint of obtaining a higher Br. Also, the content of Fe is not particularly limited, but R2Fe 17 From the viewpoint of suppressing deterioration of squareness and decrease of HcJ due to precipitation of the phase, it is preferably 82 atomic % or less, more preferably 80 atomic % or less.

[0017] The B content is 4.5 to 6.0 atomic %, the preferred content is 4.7 to 5.7 atomic %, and more preferably 5.0 to 5.5 atomic %. When the B content is less than 4.5 atomic %, the proportion of the formed R2T 14 The proportion of the B phase becomes low, Br decreases significantly, and at the same time, R2T 17 The phase is formed, resulting in deterioration of squareness. On the other hand, when the B content exceeds 6.0 atomic %, the R-Fe(Co)-(Ga, M1) phase described later cannot be sufficiently formed, and sufficient coercive force cannot be obtained. Note that a part of B may be substituted with C.

[0018] The R-Fe-B-based sintered magnet of the present invention can contain Co, N, and O in addition to the above R, Fe, and B, and can also contain Ga, M1, M2, and C.

[0019] Co can substitute a part of Fe in each phase such as the R2(Fe,(Co)) 14 B phase and the R-Fe(Co)-(Ga, M1) phase. The Co content is 10 atomic % or less, preferably 5 atomic % or less, more preferably 2 atomic % or less with respect to the entire sintered magnet from the viewpoint of stably obtaining a high HcJ, but is preferably 0.1 atomic % or more, more preferably 0.3 atomic % or more from the viewpoint of obtaining the effect of improving the Curie temperature and corrosion resistance.

[0020] The Ga content is 0.1 to 1.0 atomic%, preferably 0.2 to 0.7 atomic%, and more preferably 0.3 to 0.5 atomic%, from the viewpoint of obtaining good coercivity while keeping it to the minimum necessary. If the Ga content exceeds 1.0 atomic%, it is undesirable because the resource procurement risk increases and the Br content decreases significantly. On the other hand, if the Ga content is less than 0.1 atomic%, the formation of the R-Fe(Co)-(Ga,M1) phase, described later, becomes insufficient, and sufficient coercivity cannot be obtained.

[0021] M1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi, and its content is 0.1 to 3.0 atomic%, preferably 0.4 to 2.0 atomic%, and more preferably 0.8 to 1.4 atomic%. If the content of M1 exceeds 3.0 atomic%, the Br content decreases significantly, which is undesirable. On the other hand, if the content of M1 is less than 0.1 atomic%, the formation of the R-Fe(Co)-(Ga,M1) phase, described later, becomes insufficient, and sufficient coercivity cannot be obtained.

[0022] M2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, and its content is 0.05 to 1.0 atomic%, preferably 0.1 to 0.6 atomic%, and more preferably 0.2 to 0.5 atomic%. If the M2 content exceeds 1.0 atomic%, the M2 boride phase and M2 carbide phase are formed in excess, which reduces the amount of B and C needed to form the main phase, leading to a decrease in the Br due to the decrease in the main phase ratio, and consequently to R2Fe 17 The formation of this phase worsens the kyphosis. On the other hand, if the M2 content falls below 0.05 atomic%, the effect of suppressing abnormal grain growth during the sintering process is not obtained.

[0023] The oxygen content is 1.5 atomic percent or less, preferably 1.0 atomic percent or less, and more preferably 0.5 atomic percent or less, from the viewpoint of obtaining a high HcJ content. The lower the oxygen content, the better, and ideally the lower limit is 0 atomic percent. However, as an unavoidable impurity introduced during manufacturing, it may contain 0.1 atomic percent or more of oxygen.

[0024] The carbon (C) content is 0.1 to 1.5 atomic percent, preferably 0.2 to 1.0 atomic percent or less, from the viewpoint of obtaining a high HcJ. The carbon (C) originates from the raw materials and lubricants added to improve the orientation of the fine powder during magnetic field molding. By adding lubricants in an amount such that the carbon content is 0.1 atomic percent or more, sufficient orientation can be obtained during the molding process, and Br can be increased. On the other hand, if the carbon content exceeds 1.5 atomic percent, sufficient HcJ cannot be obtained, which is undesirable.

[0025] From the viewpoint of obtaining good HcJ, the N content is 0.5 atomic% or less, preferably 0.4 atomic% or less, and more preferably 0.3 atomic% or less. A lower N content is preferable, and ideally the lower limit is 0 atomic%. However, as an unavoidable impurity introduced during manufacturing, 0.1 atomic% or more of N may be present.

[0026] The microstructure of the R-Fe-B sintered magnet of the present invention includes R2(Fe,(Co)) 14 The B intermetallic compound is included as the main phase. The grain boundary phase includes the R-Fe(Co)-(Ga,M1) phase. Furthermore, the grain boundary phase may also include other phases such as the R-Fe(Co)-M1 phase, M2 boride phase, and M2 carbide phase. The M2 boride phase suppresses abnormal grain growth by inhibiting the growth of the main phase crystal grains during sintering, and high coercivity can be obtained. The M2 carbide phase suppresses grain growth of the main phase crystal grains during sintering and can also fix the impurity element carbon, thereby suppressing the decrease in coercivity. In addition, phases of compounds that are unavoidable impurities introduced during the manufacturing process, such as R carbides, R oxides, R nitrides, R-OCN compounds, R halides, and R acid halides, may be included, but Br and H cJ From the viewpoint of suppressing a decrease in quality, it is preferable to keep the content of these impurities to a minimum.

[0027] The above-mentioned R-Fe(Co)-(Ga,M1) phase satisfies the following relation (1) when the concentration of R atoms is [R], the concentration of Fe atoms is [Fe], the concentration of Co atoms is [Co], the concentration of Ga atoms is [Ga], and the concentration of M1 atoms is [M1] relative to the total amount of R, Fe, Co, Ga, and M1 in the R-Fe(Co)-(Ga,M1) phase, preferably satisfies the following relation (1a), and more preferably satisfies the following relation (1b). 4.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.8 ... (1) 6.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.5 ... (1a) 6.5 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.0 ... (1b) By keeping the concentrations of each atom within the range that satisfies these relationships, high coercivity can be obtained without decreasing Br.

[0028] Furthermore, it is preferable that the R-Fe(Co)-(Ga,M1) phase satisfies the following relation (2) between [Ga] and [M1], more preferably the following relation (2a), and even more preferably the following relation (2b). 0 < [Ga] / [M1] ≤ 2.0 ... (2) 0.5 < [Ga] / [M1] ≤ 1.5 ... (2a) 0.7 < [Ga] / [M1] ≤ 1.0 ... (2b) By having [Ga] and [M1] within these ranges, sufficient coercivity can be obtained in the R-Fe(Co)-(Ga,M1) phase while efficiently utilizing Ga without excessive consumption of Ga.

[0029] Furthermore, the R concentration [R], Co concentration [Co], Ga concentration [Ga], and M1 concentration [M1] of the above R-Fe(Co)-(Ga,M1) phase are 25 atomic% ≤ [R] ≤ 35 atomic%, 0 atomic% ≤ [Co] ≤ 8.0 atomic%, 2.0 atomic% ≤ [Ga] ≤ 8.0 atomic%, and 2.0 atomic% ≤ [M1] ≤ 8.0 atomic%, respectively, and more preferably 27 atomic% ≤ [R] ≤ 33 atomic%, 0 atomic% ≤ [Co] ≤ 2.0 atomic%, 3.0 atomic% ≤ [Ga] ≤ 5.0 atomic%, and 3.0 atomic% ≤ [M1] ≤ 5.0 atomic%. The remainder is Fe, and the Fe concentration [Fe] is preferably 41 atomic% ≤ [Fe] ≤ 71 atomic%, and more preferably 55 atomic% ≤ [Fe] ≤ 67 atomic%. Because the concentrations of each element are within this range, an R-Fe(Co)-(Ga,M1) phase is formed that efficiently utilizes Ga and M1, thereby increasing coercivity.

[0030] The above R-Fe(Co)-M1 phase preferably satisfies the following relationship (3), more preferably satisfies the following relationship (3a), and even more preferably satisfies the following relationship (3b), where the concentration of Fe atoms is [Fe]', the concentration of Co atoms is [Co]', and the concentration of M1 atoms is [M1]' relative to the total amount of R, Fe, Co, and M1 in the R-Fe(Co)-M1 phase. 8.0 ≤ ([Fe]' + [Co]') / [M1]' ≤ 12.0 ... (3) 9.0 ≤ ([Fe]' + [Co]') / [M1]' ≤ 11.0 ... (3a) 9.5 ≤ ([Fe]' + [Co]') / [M1]' ≤ 10.5 ... (3b) With each element having such a relationship, sufficient coercivity can be more reliably obtained without excessively increasing the amount of Ga in the magnet.

[0031] Here, the composition of the grain boundary phase R-Fe(Co)-(Ga,M1) and R-Fe(Co)-M1 can be confirmed using EDS (Energy Dispersive X-ray Spectrometer) and WDS (Wavelength Dispersive X-ray Spectrometer). It is generally known that when C analysis is performed using an EDS device equipped with a SEM (Scanning Electron Microscope) or a WDS device equipped with an EPMA (Electron Probe Microanalyzer), contamination is superimposed on the analytical values. Therefore, in this invention, the composition of R-Fe(Co)-(Ga,M1) and R-Fe(Co)-M1 is calculated as the concentration relative to the total amount of elements R, Fe, Co, Ga, and M1 for the analytical values ​​of each phase.

[0032] Furthermore, to identify the R-Fe(Co)-(Ga,M1) phase and the R-Fe(Co)-M1 phase, it is preferable to confirm them by obtaining ED (electron diffraction) patterns, etc. Both the R-Fe(Co)-(Ga,M1) phase and the R-Fe(Co)-M1 phase are tetragonal, and La6Co9(Co 0.5 Ga 0.5 It has a 4Ga type crystal structure.

[0033] Furthermore, the average grain size (μm) of the rare earth sintered magnet of the present invention in a plane parallel to the magnetization direction is not particularly limited, but from the viewpoint of obtaining sufficient HcJ, it is preferably 4.0 μm or less, more preferably 3.0 μm or less, and from the viewpoint of obtaining sufficient orientation within an appropriate range of lubricant addition, it is preferably 1.2 μm or more, more preferably 1.8 μm or more. In the present invention, the average grain size is defined as the median area diameter obtained from a histogram showing the particle size distribution, which plots the ratio of the area occupied by the crystal grains at every 1 μm interval between particles for the equivalent circle diameter of each individual particle.

[0034] Incidentally, the measurement of the equivalent circle diameter of the particles described above can be performed, for example, by the following procedure. First, after polishing the cross-section of the sintered magnet until it becomes a mirror surface, a cross-section selectively etched for the grain boundary phase is immersed in an etching solution such as, for example, Birella solution (a mixed solution with a mixing ratio of glycerin: nitric acid: hydrochloric acid = 3:1:2) and observed with a laser microscope. Next, based on the obtained observation image, the cross-sectional area of each particle is measured by image analysis, and the diameter as an equivalent circle is calculated. The average crystal grain size may be, for example, the average of a total of about 2,000 particles in 20 different images. The apparatus for measurement is not particularly limited, but for example, a 3D measurement laser microscope (manufactured by Olympus Corporation, LEXT OLS 4000) can be used, and image analysis software (manufactured by Mitani Corporation, WinROOF) can be used for image analysis.

[0035] In conventional R-Fe-B sintered magnets, even if the addition amount of the M1 element is increased, the ratio of M1 in the grain boundary phase R-Fe(Co)-(Ga,M1) does not increase, and the amount of Ga cannot be reduced. On the other hand, according to the present invention, the ratio of M1 can be increased. The reason is that in the manufacturing method of this magnet, as described later, the master alloy contains Ga while the auxiliary alloy uses a two-alloy method using an alloy that does not contain Ga but contains M1. That is, by using such a technique, the diffusion of the M1 element into the main phase during the sintering process is suppressed compared to the case of being made from one type of alloy, and it is considered that the M1 element is concentrated in the grain boundary phase. As a result, the M1 concentration in R-Fe(Co)-(Ga,M1) formed in the grain boundary phase increases, and it is considered that the amount of Ga required to form R-Fe(Co)-(Ga,M1) can be less than that in the conventional case, achieving more efficient use of Ga.

[0036] As described above, the structure of the R-Fe-B sintered magnet of the present invention contains R2(Fe,(Co)) 14The B intermetallic compound is contained as the main phase, and it is preferable that the concentration of the M1 element with respect to the constituent elements in this main phase is lower than the concentration [M1] of the M1 element in the above R—Fe(Co)—(Ga, M1) phase. If the concentration of the M1 element in the main phase is within this range, the above R—Fe(Co)—(Ga, M1) phase is sufficiently formed, and a higher HcJ can be more surely achieved.

[0037] Next, a method for manufacturing the R—Fe—B sintered magnet of the present invention will be described below. Each step in manufacturing the R—Fe—B sintered magnet of the present invention includes a melting step of melting raw materials to obtain a main alloy and an auxiliary alloy, a coarse pulverization step of coarsely pulverizing the main alloy and the auxiliary alloy having a predetermined composition to prepare alloy powder, a fine powder preparation step of obtaining fine mixed alloy powder in which both alloys are mixed at a predetermined ratio from the main phase alloy powder and the auxiliary alloy powder obtained in the coarse pulverization step, a molding step of powder molding the fine mixed alloy powder under the application of a magnetic field to obtain a molded body, and a sintering step of sintering the molded body to obtain a sintered body.

[0038] First, in the above melting step, metals or alloys as raw materials for each element are weighed so as to have the predetermined composition in the present invention described above, and for example, the raw materials are melted by high-frequency melting and then cooled to produce the above main alloy and auxiliary alloy. For example, these raw material alloys can be obtained by melting in a vacuum or an inert gas, preferably in an Ar atmosphere, and then casting into a flat mold or a book mold, or by strip casting. In this case, the main alloy has a composition of 12.0 to 16.5 atomic % of R, 5.0 to 6.5 atomic % of B, 10 atomic % or less of Co, 0.1 to 1.0 atomic % of Ga, 0.05 to 1.0 atomic % of M2, and the balance Fe, and the auxiliary alloy has a composition of 20 to 40 atomic % of R, 30 atomic % or less of Co, 3 atomic % or less of B, 15 to 35 atomic % of M1, and the balance Fe.

[0039] The R content in the main alloy is 12.0 to 16.5 atomic%, preferably 13.0 to 15.0 atomic%, and more preferably 13.5 to 14.5 atomic%. If the R content in the main alloy is less than 12.0 atomic%, a sufficient R-rich phase cannot be formed in the alloy, the dispersibility of the R-rich phase in the final magnet decreases, and high coercivity cannot be obtained. Also, if the R content in the main alloy exceeds 16.5 atomic%, the Br of the final magnet decreases. On the other hand, the R content in the auxiliary alloy is 20 to 40 atomic%, preferably 30 to 38 atomic%, and more preferably 33 to 37 atomic%. If the R content in the auxiliary alloy is less than 20 atomic%, R²T will be present in the auxiliary alloy. 17 The precipitation of the phase reduces the HcJ and prismatic properties of R-Fe-B sintered magnets. On the other hand, when the R content exceeds 40 atomic percent, the Br of the sintered magnet decreases.

[0040] From the viewpoint of obtaining good angularity, the content of B in the main alloy is 5.0 to 6.5 atomic%, preferably 5.2 to 6.0 atomic%, and more preferably 5.4 to 5.8 atomic%. If the content of B in the main alloy is less than 5.0 atomic%, R2T is present in the alloy. 17 If a ferromagnetic phase of the same magnitude is formed, the angularity of the final magnet deteriorates. Also, if the B content in the main alloy exceeds 6.5 atomic percent, the R-Fe(Co)-(Ga,M1) phase cannot be sufficiently formed, and high coercivity cannot be obtained. On the other hand, the B content in the auxiliary alloy is 3 atomic percent or less, preferably 1 atomic percent, and more preferably 0 atomic percent, as described above. If the B content in the auxiliary alloy exceeds 3 atomic percent, it is necessary to reduce the B content in the main alloy in order to obtain a predetermined sintered magnet composition, but this is unsuitable from the viewpoint of maintaining the lower limit of the B content in the main alloy.

[0041] From the viewpoint of obtaining good HcJ, the Co content in the main alloy is 10 atomic% or less, preferably 3 atomic% or less, and more preferably 0 atomic%. On the other hand, from the viewpoint of obtaining good HcJ, the Co content in the auxiliary alloy is 30 atomic% or less, preferably 20 atomic%, and more preferably 15 atomic% or less.

[0042] The Ga content in the main alloy is 0.1 to 1.0 atomic%, preferably 0.2 to 0.8 atomic%, and more preferably 0.3 to 0.5 atomic%. If the Ga content in the main alloy is less than 0.1 atomic%, the R-Fe(Co)-(Ga,M1) phase cannot be sufficiently formed, and high coercivity cannot be obtained. Furthermore, if the Ga content in the main alloy exceeds 1.0 atomic%, the Br of the final magnet decreases, and the Ga concentration in the R-Fe(Co)-(Ga,M1) phase increases, reducing the utilization efficiency of Ga. On the other hand, if Ga is included in the auxiliary alloy, the Ga concentration in the R-Fe(Co)-(Ga,M1) phase also increases, reducing the utilization efficiency of Ga; therefore, Ga is not included in the auxiliary alloy.

[0043] The M1 content in the auxiliary alloy is 15 to 35 atomic percent, preferably 20 to 33 atomic percent, and more preferably 25 to 31 atomic percent, from the viewpoint of increasing the M1 concentration in the R-Fe(Co)-(Ga,M1) phase and obtaining good HcJ. If the M1 content in the auxiliary alloy is less than 15 atomic percent, the M1 concentration in the R-Fe(Co)-(Ga,M1) phase cannot be increased and sufficient HcJ cannot be obtained. Also, if the M1 content in the auxiliary alloy exceeds 35 atomic percent, some of the M1 element diffuses into the main phase and lowers the Br. The M1 contained in the auxiliary alloy is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi. However, from the viewpoint of stably forming the R-Fe(Co)-(Ga,M1) phase and obtaining high coercivity, it is preferable to include at least one of Al or Si. On the other hand, even if the main alloy contains M1, some of the M1 atoms solid-solve in the main phase and reduce Br, so the main alloy does not contain M1.

[0044] The M2 content in the main alloy is 0.05 to 1.0 atomic%, preferably 0.2 to 0.8 atomic%, and more preferably 0.3 to 0.5 atomic%. If the M2 content in the main alloy is less than 0.05 atomic%, the effect of suppressing abnormal grain growth of the main phase crystal grains during the sintering process cannot be obtained. Furthermore, if the M2 content in the main alloy exceeds 1.0 atomic%, the Br, HcJ, and prismatic properties of the final magnet decrease. On the other hand, if M2 is included in the auxiliary alloy, the effect of suppressing abnormal grain growth cannot be sufficiently obtained, so M2 is not included in the auxiliary alloy.

[0045] The Fe content in the main alloy is the remainder of the other elements as described above, but from the viewpoint of obtaining high Br and high HcJ, it is preferably 73 to 83 atomic%, more preferably 75 to 82 atomic%, and even more preferably 77 to 81 atomic%. Similarly, the Fe content in the auxiliary alloy is the remainder of the other elements as described above, but from the viewpoint of obtaining high Br and high HcJ, it is preferably 20 to 40 atomic%, more preferably 25 to 38 atomic%, and even more preferably 30 to 35 atomic%.

[0046] In the above coarse grinding process, both the main alloy and the auxiliary alloy can be ground using, for example, a jaw crusher, a brown mill, a pin mill, or hydrogenation grinding. In the case of alloys made by strip casting, hydrogenation grinding is usually applied to obtain coarse powder with a size of, for example, 0.05 to 3 mm, and especially 0.05 to 1.5 mm.

[0047] The above-mentioned fine powder preparation step only needs to be able to obtain a mixed alloy fine powder in which both alloys are mixed in a predetermined ratio from the main phase alloy powder and auxiliary alloy powder obtained in the coarse grinding step as described above, and the fine grinding step and the mixing step can be carried out in an appropriate combination. For example, the following two procedures can be exemplified. The first procedure includes a mixing step of mixing the main alloy powder and the auxiliary alloy powder to prepare a mixed alloy powder, and a fine grinding step of finely grinding the mixed alloy powder to obtain fine powder. The second procedure includes a fine grinding step of finely grinding the main alloy powder and the auxiliary alloy powder respectively to obtain main alloy fine powder and auxiliary alloy fine powder, and a mixing step of mixing the obtained main alloy fine powder and auxiliary alloy fine powder to prepare a mixed alloy fine powder.

[0048] In the above-mentioned fine powder preparation step, the mixing ratio of the main alloy and auxiliary alloy is 85 to 97% by mass of the main alloy and 3 to 15% by mass of the auxiliary alloy, preferably 90 to 95% by mass of the main alloy and 5 to 10% by mass of the auxiliary alloy. For mixing, for example, a V-type mixer or a rocking mixer can be used. If the main alloy content exceeds 97% by mass and the auxiliary alloy content is less than 3% by mass, the formation of the R-Fe(Co)-(Ga,M1) phase will be insufficient and sufficient coercivity cannot be obtained. Also, if the main alloy content is less than 85% by mass and the auxiliary alloy content exceeds 15% by mass, the Br will decrease significantly. In addition, in one or both of the above-mentioned mixing step and / or fine grinding step, it is preferable to add 0.05 to 0.30% by mass of lubricant relative to the weight of the alloy powder, and more preferably 0.08 to 0.20% by mass of lubricant, for the purpose of improving the degree of orientation. In this case, there are no particular limitations on the lubricant, but examples include fatty acids such as stearic acid, alcohols, esters, and metal soaps.

[0049] The above fine grinding process is preferably carried out in a gas atmosphere such as nitrogen gas or Ar gas, but oxygen may also be introduced into the gas atmosphere and its concentration controlled. The specific method of introducing oxygen is not particularly limited. Known methods such as jet mill grinding can be applied to the fine grinding.

[0050] In the manufacturing method of the present invention, the average particle size of the fine powder in the fine grinding step is not necessarily limited, but it is preferable to grind it so that it is in the range of 0.5 to 4.0 μm. In this case, a more preferable average particle size of the fine powder is 1.2 to 3.5 μm, and even more preferably 1.8 to 3.0 μm, and the average particle sizes of the main alloy powder and the auxiliary alloy powder may differ within the above average particle size range. The lower limit of 0.5 μm is set from the viewpoint of suppressing oxidation and nitriding of the fine powder and obtaining good HcJ, and the upper limit of 4.0 μm is set from the viewpoint of obtaining sufficient HcJ. The average particle size of the powder refers to the median diameter in the volume-based particle size distribution measured by laser diffraction / scattering method.

[0051] A molded body is obtained by a molding process in which the mixed alloy fine powder prepared in this manner is compacted in an applied magnetic field, and an R-Fe-B sintered magnet is obtained by a sintering process in which the molded body is heat-treated to form a sintered body. In the molding process, a magnetic field of 400 to 1600 kA / m is applied, and the alloy powder is compacted in a compression molding machine while being oriented in the direction of the easy magnetization axis. At this time, the density of the molded body is 2.8 to 4.2 g / cm³. 3 It is preferable to have a molded body density of 2.8 g / cm³, in other words, from the viewpoint of ensuring the strength of the molded body and obtaining good handling properties. 3 It is preferable to have the above, while on the other hand, from the viewpoint of obtaining suitable Br by ensuring good particle orientation during pressurization while obtaining sufficient molded body strength, the molded body density should be 4.2 g / cm³. 3 The following is preferable. Furthermore, molding is preferably carried out in a gas atmosphere such as nitrogen gas or Ar gas in order to suppress oxidation of the alloy fine powder.

[0052] In the above sintering step, the molded body obtained in the molding step is sintered in a high vacuum or in a non-oxidizing atmosphere such as Ar gas. The sintering is preferably carried out at a temperature range of 900°C to 1250°C, particularly 1000°C to 1150°C, for 0.5 to 5 hours. The sintered body after sintering is preferably cooled to a temperature of 400°C or lower, more preferably 300°C or lower, and even more preferably 200°C or lower. The cooling rate is not particularly limited, but until the upper limit of the above range is reached, it is preferably 5°C / min or higher, more preferably 15°C / min or higher, and preferably 100°C / min or lower, and more preferably 50°C / min or lower.

[0053] A heat treatment step may be performed on the obtained sintered body. This heat treatment step preferably consists of two stages: a high-temperature heat treatment step in which the sintered body, cooled to a temperature of 400°C or lower, is heated to a temperature of preferably 700°C or higher, more preferably 800°C or higher, and preferably 1100°C or lower, more preferably 1050°C or lower, and then cooled again to 400°C or lower; and a low-temperature heat treatment step in which, after the high-temperature heat treatment step, the body is heated to a temperature in the range of 400 to 600°C and then cooled to 300°C or lower, preferably 200°C or lower. Furthermore, the heat treatment atmosphere at this time is preferably a vacuum or an inert gas atmosphere such as Ar gas.

[0054] The heating rate in the high-temperature heat treatment process is not particularly limited, but is preferably 1°C / min or more, more preferably 2°C / min or more, and preferably 20°C / min or less, and more preferably 10°C / min or less. The holding time after heating to the high-temperature heat treatment temperature is preferably 1 hour or more, preferably 10 hours or less, and more preferably 5 hours or less. After heating, the material is cooled to preferably 400°C or less, more preferably 300°C or less, and even more preferably 200°C or less. The cooling rate at this time is not particularly limited, but until the upper limit of the above range is reached, it is preferably 1°C / min or more, more preferably 5°C / min or more, and preferably 100°C / min or less, and more preferably 50°C / min or less.

[0055] In the low-temperature heat treatment step following the high-temperature heat treatment step, the cooled sintered body is heated to a temperature preferably of 400°C or higher, more preferably of 430°C or higher, and preferably of 600°C or lower, and more preferably of 550°C or lower. The heating rate in the low-temperature heat treatment step is not particularly limited, but is preferably 1°C / min or higher, more preferably 2°C / min or higher, and preferably 20°C / min or lower, and more preferably 10°C / min or lower. The holding time after heating to the low-temperature heat treatment temperature is preferably 0.5 hours or higher, more preferably 1 hour or higher, and preferably 50 hours or lower, and more preferably 20 hours or lower. The cooling rate after heating is not particularly limited, but until the upper limit of the above range is reached, it is preferably 1°C / min or higher, more preferably 5°C / min or higher, and preferably 100°C / min or lower, more preferably 80°C / min or lower, and even more preferably 50°C / min or lower. The sintered body after heat treatment is then usually cooled to room temperature.

[0056] Furthermore, the conditions in the high-temperature heat treatment process and the low-temperature heat treatment process can be appropriately adjusted within the above-mentioned range, depending on the composition, such as the type of M1 element and the content of other elements, impurities, in particular the concentration of impurities caused by the atmospheric gas during manufacturing, and sintering conditions, as well as other variations caused by manufacturing processes other than the high-temperature and low-temperature heat treatment.

[0057] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0058] [Examples 1-16, Comparative Examples 1-11] Rare earth metals (Nd, Pr, or didium), electrolytic iron, Co, and other metals and alloys were weighed to obtain the compositions shown in Tables 1 and 2 below. The alloys were melted in a high-frequency induction furnace in an argon atmosphere, and thin strips of the main alloy and auxiliary alloy were prepared by a strip casting method in which the molten alloy was cooled on a water-cooled copper roll.

[0059]

[0060]

[0061] Next, the two alloy strips prepared above were subjected to coarse grinding by hydrogenation to obtain coarse powder, after which the main alloy and auxiliary alloy were mixed in the ratios shown in Tables 3 and 4. Subsequently, 0.10% by mass of stearic acid was added to this mixed alloy powder as a lubricant and mixed, and then finely ground in a jet mill under a nitrogen atmosphere to an average particle size of 3.0 μm. The oxygen concentration in the jet mill system during grinding was kept below 10 ppm. After that, these fine powders were filled into a mold of a molding apparatus equipped with an electromagnet in a nitrogen gas atmosphere, and pressure molded perpendicular to the magnetic field while being oriented in a magnetic field of 15 kOe (1.19 MA / m). The resulting compacted body was sintered in a vacuum at 1030 to 1080°C for 5 hours and cooled to below 200°C at a rate of 20°C / min. The obtained sintered body was subjected to high-temperature heat treatment at 900°C for 2 hours, cooled to below 200°C at a rate of 20°C / min, and then subjected to low-temperature heat treatment at 470°C for 3 hours, and cooled to below 200°C at a rate of 20°C / min.

[0062] The center of each sintered body was cut into a rectangular parallelepiped shape measuring 18 mm × 15 mm × 12 mm to obtain sintered magnets, and the magnetic properties of each sintered magnet were measured using a B-H tracer. Tables 3 and 4 show the values ​​for Examples 1 to 16 and Comparative Examples 1 to 11. The mass percentage of oxygen in each sintered magnet was measured by inert gas fusion infrared absorption spectroscopy, the mass percentage of nitrogen by inert gas fusion thermal conduction spectroscopy, and the mass percentage of carbon by combustion infrared absorption spectroscopy. When the atomic percentages were calculated by combining these with the mass percentages of metal elements obtained by ICP analysis, the oxygen concentration was 0.4 atomic%, the carbon concentration was 0.4 atomic%, and the nitrogen concentration was 0.4 atomic% in all magnets.

[0063] Next, the grain boundary phase in an arbitrary 50 μm × 50 μm region of the cross-section parallel to the magnetization direction of each magnet was measured using a WDS apparatus to determine the composition ratio of the R-Fe(Co)-(Ga,M1) phase, and the values ​​of ([Fe] + [Co]) / ([Ga] + [M1]) and [Ga] / [M1] were calculated. The presence or absence of the R-Fe(Co)-M1 phase, and if the R-Fe(Co)-M1 phase is present, the value of ([Fe]' + [Co]') / [M1]' are also shown in Tables 3 and 4. Furthermore, the cross-section parallel to the magnetization direction of the sintered body prepared in Example 2 after low-temperature heat treatment was observed using an electron microscope. The electron microscope image (backscattered electron image) is shown in Figure 1. In Figure 1, A is the R-Fe(Co)-(Ga,M1) phase (a 6-13-1 phase containing Ga), and B is the R-Fe(Co)-M1 phase (a 6-13-1 phase that does not contain Ga).

[0064]

[0065]

[0066] As shown in Tables 3 and 4, when the composition ratio of the R-Fe(Co)-(Ga,M1) phase satisfies 4.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.8, Br is 1.31 T or higher and HcJ is 1400 kA / m or higher, indicating that high properties can be obtained for both Br and HcJ. Furthermore, especially when the R-Fe(Co)-M1 phase is present in addition to the R-Fe(Co)-(Ga,M1) phase, HcJ was 1400 kA / m or higher even with a low Ga content of 0.1 atomic% in the magnet. These results are thought to be due to the concentration of the M1 element added from the auxiliary alloy at the grain boundaries, effectively improving coercivity.

[0067] Furthermore, Table 5 shows the composition ratios of the main phase, R-Fe(Co)-(Ga,M1) phase, and Nd, Pr, Fe, Co, B, Ga, Cu, and Al of the R-Fe(Co)-M1 phase, as analyzed by a WDS instrument in Example 2 and Comparative Example 2.

[0068]

[0069] In Example 2, the M1 ratio of the R-Fe(Co)-(Ga,M1) phase is high, and the R-Fe(Co)-M1 phase is also formed, whereas in Comparative Example 2, only the R-Fe(Co)-(Ga,M1) phase is formed, and it can be seen that the Ga ratio is high and the M1 ratio is low. Thus, magnets with a high M1 ratio in the R-Fe(Co)-(Ga,M1) phase possess both high Br and high Hcj, and can be applied to various applications as high-performance magnets.

Claims

1. The composition consists of 12.5 to 17.0 atomic% R (where R is one or more elements selected from rare earth elements, with Nd being essential), 4.5 to 6.0 atomic% B, 10 atomic% or less Co, 0.1 to 1.0 atomic% Ga, 0.1 to 3.0 atomic% M1 (where M1 is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, and Bi), 0.05 to 1.0 atomic% M2 (where M2 is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), 1.5 atomic% or less O, 0.1 to 1.5 atomic% C, 0.5 atomic% or less N, and the remainder Fe, with R2(Fe, (Co)) 14 An R-Fe-B sintered magnet comprising a main phase which is an intermetallic compound B and a grain boundary phase, wherein the grain boundary phase includes an R-Fe(Co)-(Ga,M1) phase having a composition of 25 to 35 atomic% R, 2.0 to 8.0 atomic% Ga, 2.0 to 8.0 atomic% M1, 8.0 atomic% or less Co, and the remainder Fe, and the R-Fe-B sintered magnet is characterized in that, when the concentration of Fe atoms is [Fe], the concentration of Co atoms is [Co], the concentration of Ga atoms is [Ga], and the concentration of M1 atoms is [M1] relative to the total amount of R, Fe, Co, Ga, and M1 in the R-Fe(Co)-(Ga,M1) phase, the following relation (1) satisfies: 4.0 ≤ ([Fe] + [Co]) / ([Ga] + [M1]) ≤ 7.8 ... (1).

2. The R-Fe-B sintered magnet according to claim 1, wherein the concentration of Ga atoms [Ga] and the concentration of M1 atoms [M1] in the above R-Fe(Co)-(Ga,M1) phase satisfy the following relation (2): 0 < [Ga] / [M1] ≤ 2.0 ... (2).

3. The above R-Fe(Co)-(Ga,M1) phase is La6Co9(Co 0.5 Ga 0.5 ) The R-Fe-B sintered magnet according to claim 1, having a 4Ga type crystal structure.

4. The R-Fe-B sintered magnet according to claim 1, wherein the concentration of element M1 relative to the constituent elements in the main phase is lower than the concentration [M1] of element M1 in the R-Fe(Co)-(Ga,M1) phase.

5. The R-Fe-B sintered magnet according to claim 1, wherein the grain boundary phase contains an R-Fe(Co)-M1 phase in addition to the R-Fe(Co)-(Ga,M1) phase.

6. The R-Fe-B sintered magnet according to claim 5, satisfying the following relationship (3): 8.0 ≤ ([Fe] ≤ ([Fe] ≤ [Co] ≤) / [M1] ≤ 12.0 ... (3), where the concentration of Fe atoms is [Fe] ≤ [Co 7. A method for manufacturing an R-Fe-B sintered magnet according to any one of claims 1 to 6, comprising: a melting step to obtain a main alloy having a composition of 12.0 to 16.5 atomic% R, 5.0 to 6.5 atomic% B, 10 atomic% or less Co, 0.1 to 1.0 atomic% Ga, 0.05 to 1.0 atomic% M2, and the remainder Fe; and an auxiliary alloy having a composition of 20 to 40 atomic% R, 30 atomic% or less Co, 3 atomic% or less B, 15 to 35 atomic% M1, and the remainder Fe; a coarse grinding step to prepare powders of the main alloy and the auxiliary alloy; a fine powder preparation step to obtain a mixed alloy fine powder by mixing the main alloy powder and the auxiliary alloy powder in a predetermined ratio; a molding step to obtain a molded body by molding the mixed alloy fine powder in a magnetic field; and a sintering step to obtain a sintered body by sintering the molded body. A method for manufacturing R-Fe-B sintered magnets, characterized in that the mixing ratio of the main alloy and auxiliary alloy in the above-mentioned fine powder preparation step is 85 to 97% by mass of the main alloy and 3 to 15% by mass of the auxiliary alloy.

8. The method for manufacturing an R-Fe-B sintered magnet according to claim 7, wherein the above-mentioned fine powder preparation step includes a mixing step of mixing the main alloy powder and the auxiliary alloy powder to prepare a mixed alloy powder, and a fine grinding step of finely grinding the mixed alloy powder to obtain fine powder.

9. The method for manufacturing an R-Fe-B sintered magnet according to claim 7, wherein the above-mentioned fine powder preparation step includes a fine grinding step of finely grinding the main alloy powder and the auxiliary alloy powder respectively to obtain main alloy fine powder and auxiliary alloy fine powder, and a mixing step of mixing the obtained main alloy fine powder and the auxiliary alloy fine powder to prepare mixed alloy fine powder.

10. The method for manufacturing an R-Fe-B sintered magnet according to claim 7, wherein M1 in the auxiliary alloy contains at least one of Al and Si.

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