R-t-b sintered magnet

Abstract

An R-T-B sintered magnet containing 26.5 mass% or more and 31.5 mass% or less of R (R is a rare earth element and contains at least one or two elements selected from the group consisting of Nd and Pr), 0.40 mass% or more and 1.50 mass% or less of M (M is at least one element selected from the group consisting of Ga, Cu, Zn, Al and Si and must contain Cu), 0.85 mass% or more and 0.94 mass% or less of B, 61.5 mass% or more of T (T is Fe and Co, 90% or more of T is Fe in mass ratio), and the balance of Fe and unavoidable impurities. The Nd / Pr alloy satisfies the following conditions: 0.05-0.30% by mass of O, 0.20% by mass or less of Tb, and 0.30% by mass or less of Dy, and satisfies the following formula: the concentration of one or both selected from the group consisting of Nd and Pr and the concentration of Cu gradually decrease from the surface toward the depth direction within a range from the surface to a depth of 200 [mu] m. 26.0 mass% < = ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb])-12 ([O] + [C]) < = 27.7 mass%

Description

Technical Field

[0001] This invention relates to R-T-B system sintered magnets. Background Technology

[0002] R-T-B sintered magnets (where R is at least one rare earth element, T is Fe or a combination of Fe and Co, and B is boron) are known to be the highest-performing permanent magnets. Therefore, R-T-B sintered magnets are used in a wide variety of motors in various fields, including electric vehicles (EVs, HVs, PHVs), renewable energy sources such as wind power generation, home appliances, and industrial applications. R-T-B sintered magnets are indispensable materials for the miniaturization, lightweighting, high efficiency, and energy saving (improving energy efficiency) of these motors. Furthermore, the use of R-T-B sintered magnets in drive motors for electric vehicles helps reduce greenhouse gases such as carbon dioxide (by reducing fuel consumption and emissions) and thus prevent global warming by replacing internal combustion engine vehicles with electric vehicles. In this way, R-T-B sintered magnets will make a significant contribution to achieving a clean energy society.

[0003] R-T-B series sintered magnets are mainly composed of R2T 14 The structure consists of grains composed of type B compounds and grain boundary phases located at the grain boundaries of these grains (e.g., Patent Document 1). Patent Document 1 discloses a rare-earth sintered magnet characterized by containing R2T. 14 B main phase grains, and two adjacent R2T grains 14 B is a two-particle grain boundary phase between the main phase grains, the thickness of which is more than 5 nm and less than 500 nm, and it is composed of a phase with a magnetic field different from that of a strong magnet.

[0004] R2T constituting the grain 14 Type B compounds are ferromagnetic materials with high saturation magnetization and magnetocrystalline anisotropy, exhibiting the characteristics of R-T-B sintered magnets.

[0005] R-T-B series sintered magnets possess coercivity H at high temperatures. cJ (Hereinafter referred to as "H") cJ The magnet's viscosity decreases, leading to irreversible thermal demagnetization. Therefore, particularly in R-T-B sintered magnets used in electric vehicle motors, it is required to maintain high H₂ even at high temperatures. cJ That is, it has a higher H at room temperature cJ .

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent documents Japanese Patent Application Publication No. 2014-209546 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] It can be seen that if heavy rare earth elements RH (mainly Tb and Dy) are used to replace R2T 14 In type B compounds, the light rare earth elements RL (mainly Nd and Pr) are H cJ Improve. However, H cJ Another aspect of the improvement is R2T. 14 The saturation magnetization of the B-type compound phase decreases, thus a remanent magnetic flux density B exists. r (Hereinafter referred to as "B") r This issue needs to be mitigated. Furthermore, due to the inherently low resource quantity of Tb and limited production locations, there are issues such as unstable supply and price fluctuations. Therefore, it is necessary to minimize the use of Tb (reduce usage as much as possible) to suppress B. r The reduction, while obtaining high H cJ .

[0011] The rare-earth sintered magnet disclosed in Patent Document 1 is believed to reduce the amount of heavy rare-earth elements such as Tb and RH used, while also suppressing H at high temperatures. cJ The magnetic properties (B) are reduced, but compared to sintered magnets containing the heavy rare earth element RH, the magnetic properties (B) are improved. r and H cJ (Poor) In recent years, especially in electric motors for electric vehicles, there has been a demand for further improvements in B. r and H cJ .

[0012] Therefore, one embodiment of the present invention aims to provide an R-T-B sintered magnet that can reduce the amount of heavy rare earth element RH such as Tb and further improve B r and H cJ .

[0013] Problem-solving methods

[0014] Method 1 of the present invention is an R-T-B sintered magnet, which contains:

[0015] R: 26.5% by mass and less than 31.5% by mass (R is a rare earth element, including one or two selected from the group consisting of Nd and Pr).

[0016] M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al and Si, and must include Cu).

[0017] B: ≥0.85% by mass and ≤0.94% by mass, and

[0018] T: 61.5% by mass or more (T is Fe and Co, and by mass ratio, more than 90% of T is Fe).

[0019] And satisfy:

[0020] O: ≥0.05% by mass and ≤0.30% by mass

[0021] Tb: less than 0.20% by mass, and

[0022] Dy: less than 0.30% by mass

[0023] And it satisfies the following equation (1).

[0024] From the surface to a depth of 200 μm, the concentration of one or both of the Nd and Pr groups, along with the Cu concentration, gradually decreases from the surface along the depth direction.

[0025] 26.0% mass ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) ≤ 27.7% mass (1)

[0026] Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C expressed in mass% respectively.

[0027] The second embodiment of the present invention is an R-T-B sintered magnet according to the first embodiment, wherein M must contain Ga, the content of Ga is 0.3% by mass or more, and the Ga concentration does not gradually decrease from the surface to a depth of 200 μm.

[0028] The effects of the invention

[0029] According to embodiments of the present invention, an R-T-B sintered magnet can be provided, which can reduce the amount of heavy rare earth element RH such as Tb, while further improving B r and H cJ . Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a process example of a method for manufacturing an R-T-B sintered magnet according to an embodiment of the present invention. Detailed Implementation

[0031] In order to reduce the amount of heavy rare earth elements used and improve the magnetic properties (especially B) in R-T-B sintered magnets, the inventors have developed a method to reduce the amount of heavy rare earth elements used and improve the magnetic properties (especially B). r and H cJThey then devoted themselves to research. It was later discovered that the B content of R-T-B sintered magnets is higher than that of R2T. 14 When compound B has a low stoichiometric composition ("low boron"), the improvement in magnetic properties due to grain boundary diffusion of rare earth element R and metallic element M is enhanced. Furthermore, it is known that in R2T... 14 In compound B, the same effect can be obtained even if part of B is replaced by carbon (C). Further research shows that substitution of R2T as the main phase... 14 In compound B, the carbon (C) of B combines with rare earth oxides at the grain boundaries during the sintering process, forming rare earth oxygen-carbon compounds (R-O-C compounds) at the grain boundaries. Furthermore, it is known that the atomic ratio in this case is R:(C,O) = 1:1. If such R-O-C compounds are formed at the grain boundaries, they constitute R2T as the main phase. 14 The C content of compound B decreases accordingly. As mentioned above, even R2T 14 In compound B, a portion of the B atoms can be replaced by C atoms, yet the "low boron" effect can still be achieved. Therefore, R2T, which constitutes the main phase... 14 The reduced C content in compound B effectively decreases the total amount of B and C. Furthermore, the formation of R-O-C compounds at grain boundaries means that a portion of the rare earth element R contained in the raw alloy is consumed by the formation of R-O-C compounds. Additionally, R-O-C compounds (rare earth oxides) include both R-O compounds (rare earth oxides) and R-C compounds (rare earth carbides).

[0032] Based on the above, the inventors envisioned that when rare earth element R and metallic element M diffuse from the surface of a low-boron R-T-B sintered body inward, in order to optimize the magnetic performance improvement effect brought about by diffusion, it is necessary to control the thickness and structure of the grain boundaries. For this purpose, the contents of R, O, and C need to satisfy an appropriate relationship. Furthermore, the inventors envisioned that by controlling the content of R appropriately, the magnetic performance improvement effect brought about by the grain boundary diffusion of R and M in a low-boron R-T-B sintered magnet can be enhanced. Based on these insights, the inventors found that by introducing R (Nd and Pr) and Cu from the surface of an R-T-B sintered magnet composed of a specific composition that satisfies Equation (1) described later and controls the contents of B and M (Ga, Cu, Zn, Al, and Si) to appropriate amounts, an R-T-B sintered magnet with excellent magnetic properties can be obtained, thus completing the invention of this embodiment.

[0033] The following is a detailed description of the R-sintered magnet (hereinafter referred to as "sintered magnet") according to the embodiments.

[0034] <R-T-B series sintered magnets>

[0035] R-T-B series sintered magnets contain:

[0036] R: 26.5% by mass and less than 31.5% by mass (R is a rare earth element, including one or two selected from the group consisting of Nd and Pr).

[0037] M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al and Si, and must include Cu).

[0038] B: ≥0.85% by mass and ≤0.94% by mass, and

[0039] T: 61.5% by mass or more (T is Fe and Co, and by mass ratio, more than 90% of T is Fe).

[0040] and satisfy

[0041] O: ≥0.05% by mass and ≤0.30% by mass

[0042] Tb: less than 0.20% by mass, and

[0043] Dy: less than 0.30% by mass.

[0044] It is desirable that the content of heavy rare earth elements (RH), especially Tb and Dy, in sintered magnets is lower than before. Sintered magnets can also be RH-free. In other words, the lower limit for the RH content in sintered magnets is 0% by mass.

[0045] The content of Tb is preferably limited to less than 0.10% by mass.

[0046] In addition, the content of Dy is preferably limited to less than 0.20% by mass.

[0047] Sintered magnets satisfy the following equation (1).

[0048] 26.0% mass ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) ≤ 27.7% mass (1)

[0049] Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O], and [C] represent the contents of Nd, Pr, Ce, La, Dy, Tb, O, and C, expressed as mass% respectively. Furthermore, when the sintered magnet does not contain any one or more of Nd, Pr, Ce, La, Dy, Tb, O, and C, the content of the missing element is substituted into equation (1) as "0 mass%".

[0050] By adjusting the contents of R (especially Nd, Pr, Ce, La, Dy, Tb), O, and C in the sintered magnet to satisfy the above formula (1), high B content can be obtained. r and H cJ The C (carbon) content in the sintered magnet is preferably 0.05% by mass or more and 0.18% by mass or less. Furthermore, the C content can be adjusted by the amount of lubricant added during crushing and forming.

[0051] The preferred formulation (1) is 26.0% by mass or more and 27.5% by mass or less, more preferably 26.3% by mass or more and 27.4% by mass or less, and particularly preferably 27.0% by mass or more and 27.4% by mass or less. This can further reduce the amount of heavy rare earth elements such as Tb used (RH), while simultaneously obtaining high B content. r and H cJ .

[0052] A detailed description of the composition of each component in sintered magnets.

[0053] (R: 26.5% by mass or more and 31.5% by mass or less)

[0054] R is a rare earth element, consisting of one or two elements selected from the group consisting of Nd and Pr. The content of R is above 26.5% by mass and below 31.5% by mass. If the R content is below 26.5% by mass, densification during sintering may be difficult; if it is above 31.5% by mass, the principal phase ratio decreases. r There is a possibility of reduction. The content of R is preferably 26.8% by mass or more and 30.0% by mass or less. If R is within this range, a higher B content can be obtained. r .

[0055] (M: ≥0.40% by mass and ≤1.50% by mass)

[0056] M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must contain Cu. The content of M (the total content of Ga, Cu, Zn, Al, and Si) is 0.40% by mass or more and 1.50% by mass or less. If M is within this range, high H can be achieved. cJ .

[0057] In sintered magnets, M must contain Cu, and preferably also Ga, which can further improve H. cJ .

[0058] Furthermore, the inventors' research has yielded the following new findings: Compared to sintered magnets manufactured by diffusion processes involving the diffusion of one or two elements selected from the group consisting of Nd and Pr, and a portion or all of Cu and Ga, a significantly higher H can be achieved by manufacturing the sintered body containing 0.3% by mass or more Ga, with the total amount of Ga derived from the raw materials (in other words, included in the alloy for sintered magnets), followed by diffusion of one or two elements selected from the group consisting of Nd and Pr, and Cu. cJ That is, in the sintered magnet of the present invention, M must contain Cu and Ga, the Ga content is 0.3% by mass or more, and preferably, the Ga concentration does not gradually decrease from the surface to the depth in the range from the surface to a depth of 200 μm. The statement that the Ga concentration does not gradually decrease from the surface to the depth means that the process of diffusion from the magnet surface to the interior of the magnet using a diffusion source containing Ga has not been performed.

[0059] As described above, Cu preferably originates from Cu that diffuses from the surface of the sintered body through a diffusion process following the sintering process, which can improve H. cJ The total amount of Cu contained in a sintered magnet can come from diffusion, but a portion of the Cu can also come from the raw materials.

[0060] The preferred contents of Ga, Cu, Zn, Al and Si are as follows.

[0061] Ga: Above 0.3% by mass and below 0.80% by mass

[0062] Cu: above 0.1% by mass and below 0.70% by mass

[0063] Zn: ≥0.2% by mass

[0064] Al: 0% by mass or more and 0.8% by mass or less, and

[0065] Si: 0% by mass or more and 0.2% by mass or less.

[0066] (B: 0.85% by mass or more and 0.94% by mass or less)

[0067] The content of boron (B) is 0.85% by mass or more and 0.94% by mass or less. By including B within the scope of this invention, sintered magnets can achieve high hydrogen content (H). cJ Preferably, the content is 0.85% by mass or more and 0.90% by mass or less, more preferably 0.87% by mass or more and 0.88% by mass or less, thereby further improving H. cJ .

[0068] (O: ≥0.05% by mass and ≤0.30% by mass)

[0069] The O content is 0.05% by mass or more and 0.30% by mass or less. By including O within the scope of this invention, sintered magnets can achieve high H... cJ .

[0070] (Tb: less than 0.20% by mass)

[0071] The Tb content is 0.20% by mass or less, preferably 0.10% by mass or less. By including Tb, the H of the sintered magnet can be increased. cj However, if it contains an excess, then B r Reduce. Due to the scarcity of Tb resources and the limited availability of production sites, it is desirable to minimize the amount used, preferably by eliminating Tb (in other words, Tb content of 0% by mass).

[0072] (Dy: less than 0.30% by mass)

[0073] The Dy content is 0.30% by mass or less, preferably 0.20% by mass or less. It can also be Dy-free (in other words, the Dy content can be 0% by mass). Similar to Tb, the presence of Dy can increase the H content of the sintered magnet. cj However, if it contains an excess, then B r reduce.

[0074] (T: 61.5% by mass or more)

[0075] T is composed of Fe and Co, and by mass ratio, more than 90% of T is Fe.

[0076] The sintered magnet contains more than 61.5% by mass of titanium, which can improve the sintering quality. r It is particularly preferred that the balance of the sintered magnet composition is T and unavoidable impurities. For example, if it is a sintered magnet containing R, M, B, O and C, but not Tb, Dy and any added elements described later, then it is preferred that the balance of R, M, B, O and C is T and unavoidable impurities.

[0077] Furthermore, the presence of Co as a component of T can improve corrosion resistance; however, if the ratio of Co to T content exceeds 10%, high B content may not be achieved. r .

[0078] In sintered magnets, Cr, Mn, La, Ce, Sm, Ca, Mg, etc., are unavoidable impurities commonly found in neodymium-praseodymium alloys (Nd-Pr), electrolytic iron, ferroboron, etc. In addition, N (nitrogen) is an example of an unavoidable impurity contained in the manufacturing process.

[0079] Furthermore, the sintered magnet of the embodiment may contain one or more other elements (arbitrarily added elements). For example, Ag, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, Pb, Bi, etc., may be contained in small amounts (approximately 0.1% by mass each). Such elements may be contained in a total of, for example, approximately 1.0% by mass. If this level is reached, it is sufficient to obtain a magnet with high H at high temperatures. cJ R-T-B system sintered magnets.

[0080] In the sintered magnet of the embodiment, the concentration of one or both of Nd and Pr, selected from the group consisting of Nd and Pr, gradually decreases from the surface to the depth within a range from the surface to a depth of 200 μm. In addition, the Cu concentration also gradually decreases from the surface to the depth within a range from the surface to the depth of 200 μm. This sintered magnet with such a concentration distribution is obtained during the manufacture of the sintered magnet by using a diffusion source containing one or both of Nd and Pr, and Cu, to perform a process of diffusion from the magnet surface towards the interior of the magnet.

[0081] The magnetic properties of the sintered magnet can be improved by performing a diffusion process during the manufacturing of the sintered magnet.

[0082] Furthermore, it is preferable that the Ga concentration does not gradually decrease from the surface to a depth of 200 μm. In other words, it is preferable not to perform a process that uses a diffusion source containing Ga for diffusion.

[0083] The concentrations of Nd, Pr, and Cu from the surface to a depth of 200 μm can be confirmed by performing line analysis using energy-dispersive X-ray spectroscopy (EDX) on a cross-section of the sintered magnet, from the magnet surface toward the vicinity of the magnet's center, for a depth up to 200 μm. Furthermore, it is preferable to measure on a cross-section perpendicular to the surface and at least 200 μm from the end of the surface. During line analysis, to avoid measuring within 200 μm of the outer perimeter of the measurement cross-section, measurements are performed in a direction orthogonal to the surface (the outer perimeter of the measurement cross-section) within a region at least 200 μm from the end of the measurement cross-section.

[0084] The concentration of Ga can also be confirmed through the same measurement.

[0085] <Manufacturing Method of R-T-B System Sintered Magnets>

[0086] The following describes an embodiment of the manufacturing method of the R-T-B sintered magnet of the present invention.

[0087] The manufacturing method of this embodiment, such as Figure 1As shown, the process may include the following steps: step S10 of preparing an R-T-B sintered body; step S20 of preparing an R1-M alloy; step S30 of performing a first heat treatment; and step S40 of performing a second heat treatment. Step S30 involves contacting at least a portion of the R1-M alloy with at least a portion of the surface of the R-T-B sintered body, performing a first heat treatment in a vacuum or inert gas atmosphere at a temperature of 700°C or higher and 950°C or lower, thereby causing R1 and M to diffuse into the interior of the magnet (diffusion step). Step S40 involves performing a second heat treatment on the R-T-B sintered magnet that has undergone the first heat treatment, in a vacuum or inert gas atmosphere, at a temperature of 400°C or higher and 750°C or lower, and at a temperature lower than the first heat treatment temperature. Each of these steps will be described in detail below.

[0088] (Process for preparing R-T-B system sintered bodies)

[0089] First, the composition of the R-T-B system sintered body (hereinafter referred to as "sintered body") will be explained.

[0090] One of the characteristics of the sintered body used in this embodiment is that the R, oxygen, carbon, and other components contained in the sintered body are adjusted to produce a sintered magnet that ultimately satisfies the aforementioned formula (1). Therefore, in this sintered body, it is preferable to prepare a sintered body that satisfies the following relationships: 0.85 mass% ≤ [B] ≤ 0.94 mass%, 25.8 mass% ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb] - 12([O] + [C]) ≤ 27.5 mass%, and 0.05 mass% ≤ [O] ≤ 0.30 mass%. By performing the diffusion process described later on such a sintered body, R and M, etc., will not diffuse excessively into the interior of the sintered body, and grain boundary diffusion can be greatly promoted.

[0091] The sintered body prepared in this process, for example, has the following composition: Contains

[0092] R: 26.3% by mass or more and 31.3% by mass or less (R is a rare earth element, including one or two selected from the group consisting of Nd and Pr).

[0093] B: ≥0.85% by mass and ≤0.94% by mass

[0094] T: 61.5% by mass or more (T is Fe and Co, and by mass ratio, more than 90% of T is Fe).

[0095] M: 0.40% by mass or more and 1.50% by mass or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al and Si, and must include Cu).

[0096] Tb: less than 0.20% by mass, and

[0097] Dy: less than 0.30% by mass.

[0098] The preferred allowance consists of T and unavoidable impurities.

[0099] Secondly, the preparation method of the sintered body will be explained.

[0100] First, after preparing the R-T-B series sintered magnet alloy (hereinafter referred to as "sintered magnet alloy"), the alloy is coarsely crushed by means of, for example, hydrogen crushing.

[0101] Examples of manufacturing methods for alloys used in sintered magnets are given. Alloy ingots can be obtained by ingot casting, where a metal or alloy with a pre-adjusted composition is melted and solidified in a mold. Alternatively, alloys can be produced by rapid cooling of a molten metal or alloy with a pre-adjusted composition in contact with a single-roll, double-roll, rotating disk, or rotating cylindrical mold, resulting in a rapidly solidified alloy. Thin-sheet alloys can also be manufactured using other rapid cooling methods such as centrifugal casting.

[0102] In embodiments of the present invention, alloys manufactured by either ingot casting or quenching can be used, but alloys manufactured by quenching methods such as strip casting are preferred. The thickness of alloys produced by quenching is typically in the range of 0.03 mm to 1 mm, and they are in sheet form. The alloy melt solidifies from the surface in contact with the cooling roller (roller contact surface), and crystals grow columnarly along the thickness direction from the roller contact surface. Compared to alloys produced by conventional ingot casting (mold casting), quenched alloys have a finer microstructure and smaller grain diameter due to rapid cooling. Furthermore, the grain boundary area is larger. The R-rich phase expands significantly within the grain boundaries, thus quenching is superior in terms of R-rich phase dispersion. Therefore, hydrogen pulverization easily causes fracture at the grain boundaries. By hydrogen pulverizing the quenched alloy, the size of the hydrogen-pulverized powder (coarse powder) is reduced to, for example, 1.0 mm or less. The resulting coarse powder is then pulverized, for example, using a jet mill.

[0103] In this embodiment, the pulverization conditions are adjusted to ensure that the oxygen content of the final sintered magnet is within a specific range (0.05% by mass or more and 0.30% by mass or less). In jet pulverization, pulverization is performed in an inert atmosphere such as nitrogen. Pulverization can also be performed in a humidified atmosphere, for example. It is preferable to reduce the powder particle size (average particle size d50 of 2.0 μm or more and 10.0 μm or less, more preferably d50 of 2.0 μm or more and 8.0 μm or less, further preferably average particle size of 2.0 μm or more and 4.5 μm or less, and even more preferably average particle size of 2.0 μm or more and 3.5 μm or less). By reducing the powder particle size, a high H₂ content can be obtained. cJ.

[0104] Furthermore, the average particle size (d50) is measured by airflow dispersion laser diffraction (according to JIS Z 8825: 2013 revision). That is, in this specification, the average particle size means the cumulative particle size distribution (volume standard) from the smallest particle size side that becomes 50% of the particle size (median diameter).

[0105] Micropowders used for sintering bodies can be made from a single raw material alloy (single raw material alloy) or by mixing two or more raw material alloys (mixing method), provided that the conditions described above are met.

[0106] In a preferred embodiment, after pressing the above-mentioned micro powder into a powder molded body in a magnetic field, the powder molded body is sintered to obtain an R-T-B system sintered body.

[0107] In the fabrication of powder molded articles, from the viewpoint of suppressing oxidation during pressing in a magnetic field, methods of forming powder molded articles by pressing in an inert gas atmosphere or by wet pressing are preferred. In particular, in wet pressing, the surface of the particles constituting the powder molded article is coated with a dispersant such as an oil, suppressing contact with oxygen and water vapor in the atmosphere. Therefore, oxidation of the particles by the atmosphere can be prevented or suppressed before, during, or after the pressing process. Thus, the oxygen content of the sintered magnet can be easily controlled within a specified range. In wet pressing in a magnetic field, a slurry containing a dispersion medium mixed with micro-powder is prepared, fed into the cavity of a mold in a wet pressing apparatus, and pressed into shape in a magnetic field.

[0108] Sintering of the powder-formed body is preferably carried out at a temperature between 950°C and 1150°C. To prevent oxidation during sintering, the residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. The resulting sintered body can be heat-treated. The heat treatment conditions, such as the heat treatment temperature and time, can be those known to be applicable.

[0109] Furthermore, the sintered body may be prepared using known methods such as the PLP (Press-Less Process) method described in Japanese Patent Application Publication No. 2006-19521, without the need for forming or other processes.

[0110] (The process of preparing R1-M alloy)

[0111] In this embodiment, R1 and M are diffused from the surface of the sintered body into its interior. Therefore, an alloy containing these elements as diffusion targets is prepared (referred to as "R1-M alloy").

[0112] First, the composition of the R1-M alloy will be described. R1 in the R1-M alloy is a rare earth element, selected from one or two elements in the group consisting of Nd and Pr. The content of R1 is preferably 65% ​​by mass or more and 95% by mass or less of the total R1-M alloy, more preferably 70% by mass or more and 95% by mass or less. M in the R1-M alloy is at least one element selected from the group consisting of Ga, Cu, Zn, Al, and Si, and must include Cu. In a preferred embodiment, M is at least one element selected from the group consisting of Cu, Zn, and Si, and must include Cu. The content of M is preferably 5% by mass or more and 35% by mass or less of the total R1-M alloy, more preferably 5% by mass or more and 30% by mass or less of the total R1-M alloy.

[0113] The shape and size of R1-M alloys are not particularly limited and can be arbitrary. R1-M alloys can be in the form of films, foils, powders, blocks, particles, etc.

[0114] Secondly, the manufacturing method of R1-M alloy will be explained.

[0115] R1-M alloys can be prepared using methods for producing raw material alloys commonly used in the manufacture of sintered magnets, such as die casting, strip casting, single-roll superquenching (melt spin quenching), and atomization. Alternatively, R1-M alloys can be prepared by pulverizing the aforementioned alloy using known pulverizing methods such as a needle mill.

[0116] (The process of performing the first heat treatment (diffusion process))

[0117] At least a portion of the R1-M alloy is brought into contact with at least a portion of the surface of the sintered body prepared by the aforementioned method, and a first heat treatment is performed in a vacuum or inert gas atmosphere at a temperature of 700°C or higher and 950°C or lower (first heat treatment temperature). The first heat treatment is a process for diffusing R1 and M into the interior of the sintered body (i.e., a diffusion process). Through the heat treatment, a liquid phase containing R1 and M is generated from the R1-M alloy, and the elements forming the liquid phase diffuse from the surface of the sintered body through the grain boundaries in the sintered body into the interior of the sintered body.

[0118] If the first heat treatment temperature is below 700℃, the amount of liquid phase containing R1 and M will be too small to obtain high H. cJ On the other hand, if the temperature is above 950℃, then H... cJ The possibility of reduction. The first heat treatment temperature is preferably above 850°C and below 950°C, so as to obtain higher H. cJFurthermore, it is preferable to cool the sintered body that has undergone the first heat treatment (700°C or higher and 950°C or lower) from the first heat treatment temperature to 300°C at a cooling rate of 5°C / min or higher, thereby enabling the formation of higher H+. cJ More preferably, the cooling rate is 15°C or higher per minute.

[0119] The first heat treatment can be performed by depositing an R1-M alloy of any shape on the surface of the sintered body using a known heat treatment apparatus. For example, the first heat treatment can be performed by covering the surface of the sintered body with a powder layer of R1-M alloy. For example, the first heat treatment can be performed by coating the surface of the sintered body with a slurry in which R1-M alloy is dispersed in a dispersion medium, allowing the dispersion medium to evaporate and bringing the R1-M alloy layer into contact with the sintered body. Examples of dispersion media include alcohols (ethanol, etc.), aldehydes, and ketones. Alternatively, for example, an R1-M alloy film can be formed on the surface of the sintered body using a known sputtering apparatus, and the first heat treatment can be performed. Furthermore, when introducing the heavy rare earth element RH into the sintered body, in addition to using an R1-M alloy containing RH, it is also possible to deposit fluorides, oxides, oxyfluorides, etc. of the heavy rare earth element RH together with the R1-M alloy on the surface of the sintered body and perform the first heat treatment. Fluorides, oxides, and oxyfluorides of the heavy rare earth element RH, for example, include TbF3, DyF3, Tb2O3, Dy2O3, TbOF, and DyOF.

[0120] The placement of the R1-M alloy is irrelevant as long as at least a portion of the R1-M alloy is in contact with at least a portion of the sintered body.

[0121] (The process of performing the second heat treatment)

[0122] For sintered bodies that have undergone the first heat treatment, a second heat treatment is performed in a vacuum or inert gas atmosphere at a temperature of 400°C or higher and 750°C or lower, which is lower than the temperature of the first heat treatment. In this invention, this heat treatment is referred to as the second heat treatment. By performing the second heat treatment, high H can be obtained. cJ If the temperature of the second heat treatment is higher than the temperature of the first heat treatment, or if the second heat treatment temperature is lower than 400°C or higher than 750°C, then a high H cannot be obtained. cJ The possibility.

[0123] Example

[0124] Raw materials containing each element were weighed to produce an R-T-B sintered body with the composition shown in Table 1 (Nos. A to H), and alloys were produced by thin-strip continuous casting. The resulting alloys were coarsely pulverized using a hydrogen pulverization method to obtain coarse powder. Next, zinc stearate, as a lubricant, was added to the coarse powder and mixed. Then, dry pulverization was performed using an air jet mill (jet mill) in a nitrogen atmosphere to obtain micro-powder (alloy powder) with an average particle size d50 of 3 μm.

[0125] For the micronized powder, zinc stearate as a lubricant is added to the micronized powder, and after mixing, it is shaped in a magnetic field to obtain a powder molded body. Furthermore, the forming apparatus uses a so-called right-angle magnetic field forming apparatus (transverse magnetic field forming apparatus) where the direction of magnetic field application is orthogonal to the direction of pressure. The obtained powder molded body is sintered in a vacuum at a temperature above 1000°C and below 1090°C (a temperature selected for each sample where sufficient densification can occur by sintering) for 4 hours to obtain an R-T-B sintered body. The density of the obtained R-T-B sintered body is 7.5 Mg / m³. 3 The composition of the obtained R-T-B sintered bodies is shown in Table 1. The components in Table 1 were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, the O (oxygen) content was measured using a gas analyzer based on gas melting-infrared absorption, and the C (carbon) content was measured using a gas analyzer based on combustion-infrared absorption. The composition of the R1-M alloy (Table 2) was also measured using the same methods.

[0126]

surface

[0127]

[0128] Weigh the raw materials of each element to make the R1-M alloy approximately as shown in Table 2, No. a. Melt these raw materials and obtain the alloy in strip or sheet form by single-roll ultraquenching (melt spin quenching). After pulverizing the obtained alloy in an argon atmosphere using a mortar, pass it through a sieve with a mesh size of 425 μm to prepare the R1-M alloy. The composition of the obtained R1-M alloy is shown in Table 2.

[0129]

surface

[0130]

[0131] The R-T-B sintered bodies No. A to H in Table 1 were cut and ground to form cubes of 7.4 mm × 7.4 mm × 7.4 mm. Next, 3% by mass of R1-M alloy (No. a) was dispersed on all surfaces of the R-T-B sintered bodies No. A to H, relative to 100% of the R-T-B sintered body. The R-T-B sintered magnet No. 1 shown in Table 3 was produced using the R-T-B sintered body No. A in Table 1 and the R1-M alloy No. a in Table 2 after a diffusion process. Nos. 2 to 8 are described similarly.

[0132] Subsequently, the magnets were heat-treated at 900°C for 4 hours in a reduced pressure argon atmosphere controlled at 50 Pa (first heat treatment), and then cooled to room temperature. Then, they were heat-treated at 480°C for 3 hours in a reduced pressure argon atmosphere controlled at 50 Pa (second heat treatment), and then cooled to room temperature to produce R-T-B sintered magnets (No. 1 to 8).

[0133] The composition of the obtained R-T-B sintered magnets and the values ​​of the intermediate part of formula (1) (i.e., [Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) are shown in Table 3. The components in Table 3 were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, the O (oxygen) content was measured using a gas analyzer based on gas melting-infrared absorption, and the C (carbon) content was measured using a gas analyzer based on combustion-infrared absorption.

[0134] Furthermore, the composition of Table 3 is as follows.

[0135] The contents of Ce, La, Dy and Tb are below the detection limit, therefore the R content is calculated in addition to the Nd content and Pr content.

[0136] Since the contents of Zn and Si are below the detection limit, the M content is calculated in addition to the Cu, Ga, and Al contents.

[0137] Even assuming the presence of Zr and other elements detected in the sintered body, and a maximum of about 1% by mass of other elements, the balance T (Fe, Co) is still higher than 61.5% by mass.

[0138] The obtained R-T-B sintered magnets were machined to produce 7mm×7mm×7mm magnet samples. Magnetic properties (BH) were measured using a BH tracker. r and H cJThe measurement results are shown in Table 3. Additionally, line analysis was performed using EDX on the cross-sections of magnets No. 1–8, from the magnet surface to near the center of the magnet. For No. 1–8, it was confirmed that the Pr and Cu concentrations gradually decreased from the surface towards the depth (from the magnet surface towards the center of the magnet) within a range of 200 μm from the magnet surface. Furthermore, for No. 1–8, it was confirmed that the Ga concentration gradually decreased from the surface towards the depth within a range of 200 μm from the magnet surface.

[0139]

surface

[0140]

[0141] As shown in Table 3, Examples No. 2, 3, 5, and 6 of this invention do not contain Tb, and their residual magnetic flux density (B) r The value is above 1.40T, and the coercivity (H) cJ The value is above 1300 kA / m. Thus, while reducing the amount of heavy rare earth elements (Tb) and RH used, it is also possible to obtain a product with high B... r and high H cJ R-T-B system sintered magnets. In contrast, comparative examples (Nos. 1, 4, 7, and 8), where the concentrations of M and B deviate from the scope of this invention, although a remanent magnetic flux density (B) was obtained... r (High B with a capacity of 1.40T or more) r However, coercivity (H cJ Below 1300 kA / m, high H was not obtained. cJ .

[0142] This application is accompanied by a priority claim based on Japanese Patent Application No. 2023-074816, filed on April 28, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. An R-T-B system sintered magnet, comprising: R: ≥26.5% by mass and ≤31.5% by mass, of which, R is a rare earth element, consisting of one or two elements selected from the group consisting of Nd and Pr. M: 0.40% by mass or more and 1.50% by mass or less, wherein M is at least one selected from the group consisting of Ga, Cu, Zn, Al and Si, and must contain Cu; B: ≥0.85% by mass and ≤0.94% by mass; and T: 61.5% by mass or more, of which T is Fe and Co, with more than 90% of T by mass being Fe. And satisfy: O: ≥0.05% by mass and ≤0.30% by mass Tb: less than 0.20% by mass, and Dy: less than 0.30% by mass And it satisfies the following equation (1). From the surface to a depth of 200 μm, the concentrations of one or both of the Nd and Pr groups, and the Cu concentration, gradually decrease from the surface towards the depth. 26.0% mass ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) ≤ 27.7% mass (1) Here, [Nd], [Pr], [Ce], [La], [Dy], [Tb], [O] and [C] are the contents of Nd, Pr, Ce, La, Dy, Tb, O and C expressed in mass% respectively.

2. The R-T-B sintered magnet according to claim 1, wherein, As M, it must contain Ga, with a Ga content of 0.3% by mass or more, and the Ga concentration must not gradually decrease from the surface to a depth of 200 μm.

Images