Method for manufacturing R-T-B sintered magnet

Abstract

To provide a method for manufacturing an R-T-B based sintered magnet that has high Br and high HcJ and is excellent in corrosion resistance while using Ce.SOLUTION: A method for manufacturing an R-T-B based sintered magnet according to the present disclosure includes: a step of preparing an R1-T-B based sintered magnet material; a step of preparing an R2-M based alloy; and a diffusion step of heating the R1-T-B based sintered magnet material and the R2-M based alloy at a temperature equal to or higher than 700°C and equal to or lower than 1,100°C in vacuum or an inert gas atmosphere and diffusing R2 and M into the R1-T-B based sintered magnet material. In the R1-T-B based sintered magnet material, a content ratio of Ce in R1 is equal to or more than 5 mass% and equal to or less than 25 mass%, and the relationships of 25.8 mass%≤([Nd]+[Pr]+[Ce]+[Dy]+[Tb]-(9×[O]+12×[C])≤27.3 mass% and 0.08 mass%≤[O]≤0.30 mass% are satisfied.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an R-T-B sintered magnet.

Background Art

[0002] An R-T-B sintered magnet (where R is a rare earth element, including at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si, and necessarily includes Fe, and B is boron) is composed of a main phase of a compound having an R 2 Fe 14 B-type crystal structure, a grain boundary phase located at the grain boundary portion of this main phase, and a compound phase generated by the influence of trace additive elements and impurities. The R-T-B sintered magnet has a high residual magnetic flux density B r (hereinafter, may be simply referred to as "B r ") and a high coercive force H cJ (hereinafter, may be simply referred to as "H cJ ") and is known as the highest performance magnet among permanent magnets.

[0003] Therefore, R-T-B sintered magnets are used in various motors in the automotive field such as electric vehicles (EV, HV, PHV), the renewable energy field such as wind power generation, the household electric appliance field, and the industrial field. The R-T-B sintered magnet is an essential material for reducing the size and weight of these motors and improving their efficiency and energy savings (improvement of energy efficiency). In addition, the R-T-B sintered magnet is used in the drive motor for electric vehicles, and by replacing internal combustion engine vehicles with electric vehicles, it also contributes to preventing global warming by reducing greenhouse gas emissions such as carbon dioxide (reduction of fuel and exhaust gas). Thus, the R-T-B sintered magnet greatly contributes to the realization of a clean energy society.

[0004] In the R-T-B sintered magnet, R 2 T 14When a part of the light rare earth element RL (e.g., Nd or Pr) contained in R in the B compound is substituted with a heavy rare earth element RH (RH is at least one of Tb and Dy), H cJ is known to improve. As the substitution amount of RH increases, H cJ improves. However, when RL in R 2 T 14 in the B compound is substituted with RH, the H of the R-T-B sintered magnet cJ improves while the residual magnetic flux density B r decreases. In addition, since heavy rare earth elements are raw materials with high resource risks, it is required to reduce their usage amount or improve H cJ without using them.

[0005] Patent Document 1 describes that by heat-treating at least a part of the surface of an R-T-B sintered magnet material with a specific composition in contact with at least a part of an R2-Ga alloy, RH, Pr, and Ga are diffused. Thereby, while reducing the content of RH, high B r and high H cJ can be obtained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The method described in Patent Document 1 suppresses the content of heavy rare earth elements while achieving high B r and high H cJIt is worth noting that an R-T-B sintered magnet can be obtained. However, in recent years, the demand for R-T-B sintered magnets is expected to increase significantly in the future, especially for motors used in electric vehicles. Therefore, from the perspective of effective utilization of resources and cost reduction, not only the content of heavy rare earth elements but also other elements should be considered. It is necessary to use rare earth elements in a well-balanced manner without being biased towards the use of heavy rare earth elements, including other rare earth elements. As a specific means, it is possible to use Ce, which is relatively abundant among rare earth elements. In particular, it is effective to use Ce instead of Nd or Pr, which are the main elements in R-T-B sintered magnets. However, it is known that when Ce or the like is used instead of Nd or Pr, the magnetic properties are significantly reduced. In addition, since R-T-B sintered magnets contain Nd and Fe as main components, they are prone to rust. Therefore, it is also required to improve the corrosion resistance.

[0008] Embodiments of the present disclosure provide a method for manufacturing an R-T-B sintered magnet that maintains high B r and high H cJ while using Ce and has excellent corrosion resistance.

Means for Solving the Problems

[0009] The method for manufacturing an R-T-B sintered magnet of the present disclosure, in an exemplary embodiment, includes a step of preparing an R1-T-B sintered magnet material (where R1 is a rare earth element, including at least Nd, Pr, and Ce, and T is Fe or Fe and Co), a step of preparing an R2-M alloy (where R2 is a rare earth element, necessarily including at least one of Tb and Dy and at least one of Nd and Pr, and M is at least one selected from the group consisting of Cu, Ga, Fe, Co, Ni, and Al), and a diffusion step of heating the R1-T-B sintered magnet material and the R2-M alloy in a vacuum or an inert gas atmosphere at a temperature of 700°C or higher and 1100°C or lower to diffuse R2 and M into the R1-T-B sintered magnet material. In the R1-T-B sintered magnet material, the content ratio of Ce in R1 is 5 mass% or more and 25 mass% or less. When the content of Nd (mass%) in the R1-T-B sintered magnet material is [Nd], the content of Pr (mass%) is [Pr], the content of Ce (mass%) is [Ce], the content of Dy (mass%) is [Dy], the content of Tb (mass%) is [Tb], the content of O (mass%) is [O], and the content of C (mass%) is [C], the relationship 25.8 mass% ≦ ([Nd] + [Pr] + [Ce] + [Dy] + [Tb] - (9×[O] + 12×[C]) ≦ 27.3 mass% and 0.08 mass% ≦ [O] ≦ 0.30 mass% is satisfied.

[0010] In an embodiment, in the R1-T-B sintered magnet material, the content of B is 0.88 mass% or more and 0.97 mass% or less of the entire R1-T-B sintered magnet material.

[0011] In an embodiment, in the R2-M alloy, R2 is 65 mass% or more and 97 mass% or less of the entire R2-M alloy, and M is 3 mass% or more and 35 mass% or less of the entire R2-M alloy.

Advantages of the Invention

[0012] According to an embodiment of the present disclosure, while using Ce, high B r and high H cJIt is possible to provide a method for manufacturing an R-T-B sintered magnet that maintains excellent corrosion resistance.

Brief Description of the Drawings

[0013]

Fig. 1A

Fig. 1B

Fig. 2

Embodiments for Carrying Out the Invention

[0014] First, the basic structure of the R-T-B sintered magnet according to the present disclosure will be described. The R-T-B sintered magnet has a structure in which powder particles of a raw material alloy are bonded by sintering, and mainly consists of an R 2 T 14 main phase composed of B compound particles and a grain boundary phase located at the grain boundary portion of this main phase.

[0015] Fig. 1A is a cross-sectional view schematically showing an enlarged part of an R-T-B sintered magnet, and Fig. 1B is a cross-sectional view schematically showing an enlarged area within the dashed rectangle of Fig. 1A. In Fig. 1A, as an example, an arrow with a length of 5 μm is described for reference as a reference length indicating the size. As shown in Fig. 1A and Fig. 1B, the R-T-B sintered magnet mainly consists of an R 2 T 14 main phase 12 composed of B compound and a grain boundary phase 14 located at the grain boundary portion of the main phase 12. Also, as shown in Fig. 1B, the grain boundary phase 14 includes a two-particle grain boundary phase 14a where two R 2 T 14 B compound particles (grains) are adjacent, and a grain boundary triple point 14b where three R 2 T 14 B compound particles are adjacent. The typical main phase crystal grain size is 2.5 μm or more and 10 μm or less as the average value of the equivalent circle diameter of the magnet cross-section. The main phase 12 is R 2 T 14Compound B is a ferromagnetic material with high saturation magnetization and anisotropy magnetic field. Therefore, in the R-T-B sintered magnet, by increasing the abundance ratio of the R 2 T 14 B compound which is the main phase 12, B r can be improved. For increasing the abundance ratio of the R 2 T 14 B compound, the amounts of R, T, and B in the raw material alloy may be made close to the stoichiometric ratio of the R 2 T 14 B compound (R amount: T amount: B amount = 2:14:1).

[0016] Also, by substituting a part of R in the R 2 T 14 B compound which is the main phase with heavy rare earth elements such as Dy, Tb, and Ho, it is known that the anisotropy magnetic field of the main phase can be increased while reducing the saturation magnetization. In particular, since the outer shell of the main phase in contact with the two-particle grain boundary phase is likely to be the starting point of magnetization reversal, the heavy rare earth diffusion technology capable of preferentially substituting heavy rare earth elements in the outer shell of the main phase can efficiently obtain a high H cJ while suppressing the decrease in saturation magnetization.

[0017] In the method for manufacturing an R-T-B sintered magnet according to the present disclosure, R2 and M contained in the R2-M alloy are diffused from the surface of the R-T-B sintered magnet material through the grain boundaries into the magnet material interior. The present inventors have studied in detail a method of heating the R1-T-B sintered magnet material and the R2-M alloy to diffuse R2 and M into the R1-T-B sintered magnet material interior. As a result, it has been found that when diffusing at least one of Tb and Dy and at least one of Nd and Pr in an R2-M alloy containing Ce in a specific range into an R-T-B sintered magnet material containing Ce, the corrosion resistance is improved. As shown in the examples described later, when diffusion is not performed, the effect of improving the corrosion resistance due to containing Ce is not recognized, and rather, it may deteriorate. On the other hand, as a cause of the improvement in corrosion resistance by diffusing the R2-M alloy into the material containing Ce, it is considered that a Ce-M compound of Ce in the material and the M element of the R2-M alloy is formed in the grain boundary phase by diffusion, and the corrosion resistance is improved for some reason. Furthermore, as a result of investigations, the inventors have found that in order to optimize the effect of improving the magnetic properties by diffusion, it is necessary to control the thickness and composition of the grain boundaries, and for this purpose, the contents of R, O, and C need to satisfy an appropriate relationship. This is because C, which had substituted for B in the R 2 -T 14 -B compound, combines with rare earth oxides in the grain boundaries during the sintering process, changing the amount of C in the main phase, and thereby changing the main phase ratio and the thickness of the grain boundaries. As a result of further investigations, the inventors have found that when the content of Nd (mass%) is [Nd], the content of Pr (mass%) is [Pr], the content of Ce (mass%) is [Ce], the content of Dy (mass%) is [Dy], the content of Tb (mass%) is [Tb], the content of O (mass%) is [O], and the content of C (mass%) is [C], for an R1-T-B system sintered magnet material adjusted to the range of 25.8 mass% ≦ ([Nd] + [Pr] + [Ce] + [Dy] + [Tb]) - (9 × [O] + 12 × [C]) ≦ 27.3, when R2 and M are diffused, the diffusion of R2 and M can proceed appropriately (while maintaining a high B r and improving H cJ ). Thus, it is possible to provide a method for manufacturing an R-T-B system sintered magnet that maintains a high B r and a high H cJ while using Ce and has excellent corrosion resistance.

[0018] <Method for manufacturing an R-T-B system sintered magnet> Hereinafter, embodiments of the method for manufacturing an R-T-B system sintered magnet of the present disclosure will be described.

[0019] As shown in FIG. 2, the manufacturing method in this embodiment may include a step S10 of preparing an R1-T-B system sintered magnet material, a step S20 of preparing an R2-M system alloy, and a diffusion step S30. The step S30 is a diffusion step of heating the R1-T-B system sintered magnet material and the R2-M system alloy in a vacuum or an inert gas atmosphere at a temperature of 700°C or higher and 1100°C or lower to diffuse R2 and M into the R1-T-B system sintered magnet material. In the present disclosure, the R-T-B sintered magnet before and during the diffusion process is referred to as the "R-T-B sintered magnet material", and the R-T-B sintered magnet after the diffusion process is simply referred to as the "R-T-B sintered magnet". Hereinafter, each of these steps will be described in more detail.

[0020] (Step of preparing the R1-T-B sintered magnet material) First, the composition of the R1-T-B sintered magnet material will be described.

[0021] The characteristic point of the R1-T-B sintered magnet material used in this embodiment is that it contains Ce in R1, the content ratio of Ce in R1 is set to 5 mass% or more and 25 mass% or less, and the amounts of R1, oxygen, carbon, etc. contained in the R1-T-B sintered magnet material are adjusted to satisfy the relationship of 25.8 mass% ≤ ([Nd] + [Pr] + [Ce] + [Dy] + [Tb] - (9 × [O] + 12 × [C]) ≤ 27.3 mass% and the relationship of 0.08 mass% ≤ [O] ≤ 0.30 mass%. Preferably, an R1-T-B sintered magnet material satisfying the relationship of 0.05 mass% ≤ [C] ≤ 0.18 mass% is prepared. By performing the diffusion process described later on such an R1-T-B sintered magnet material, it becomes possible to appropriately progress the diffusion of R2 and M inside the R1-T-B magnet material while improving the corrosion resistance.

[0022] The R1-T-B sintered magnet material prepared in this step has, for example, the following composition. R1: 26.6 mass% or more and 31.5 mass% or less (R1 is a rare earth element and contains at least Nd, Pr, and Ce.), B: 0.8 mass% or more and 1.0 mass% or less, Preferably, it is 0.88 mass% or more and 0.97 mass% or less of the entire R1-T-B sintered magnet material, and the effects such as Ce content are particularly remarkable. M: 0 mass% or more and 1.0 mass% or less (M is at least one selected from the group consisting of Ga, Cu, Zn, and Si) M1: 0 mass% or more and 2.0 mass% or less (M1 is at least one selected from the group consisting of Al, Ti, V, Cr, Mn , Ni, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi) The balance is T (T is Fe or Fe and Co), and inevitable impurities.

[0023] Note that the content ratio of Ce in R1 is 5 mass% or more and 25 mass% or less. Further, preferably, the content ratio of Nd in R1 is 50 mass% or more.

[0024] Next, a method for preparing the R1-T-B-based sintered magnet material will be described.

[0025] First, after preparing an alloy for an R-T-B-based sintered magnet, the alloy is roughly pulverized by, for example, a hydrogen pulverization method or the like.

[0026] A method for manufacturing an alloy for an R-T-B-based sintered magnet will be exemplified. An alloy ingot can be obtained by an ingot casting method in which a metal or alloy previously adjusted to have the above-described composition is melted and poured into a mold and solidified. Alternatively, an alloy may be produced by a strip casting method in which a molten metal or alloy previously adjusted to have the above-described composition is brought into contact with a single roll, double roll, rotating disk, or rotating cylindrical mold or the like and rapidly cooled to produce a rapidly solidified alloy. Further, a flaky alloy may be produced by another rapid cooling method such as a centrifugal casting method.

[0027] In the embodiment of the present disclosure, alloys produced by either the ingot method or the rapid cooling method can be used, but it is preferable to use an alloy produced by a rapid cooling method such as the strip casting method. The thickness of the alloy produced by the rapid cooling method is usually in the range of 0.03 mm to 1 mm and has a flake shape. By hydrogen-pulverizing the obtained alloy, the size of the hydrogen-pulverized powder (roughly pulverized powder) can be made, for example, 1.0 mm or less. The roughly pulverized powder thus obtained is pulverized by a jet mill.

[0028] Jet mill pulverization is carried out in an inert atmosphere such as nitrogen. The pulverization may be carried out, for example, using a jet mill in a humid atmosphere.

[0029] The fine powder used for producing the R1-T-B system sintered magnet material may be produced from one kind of raw material alloy (single raw material alloy) as long as the above-mentioned conditions are satisfied, or may be produced by a method (blending method) of mixing two or more kinds of raw material alloys.

[0030] In a preferred embodiment, after producing a powder compact from the above-mentioned fine powder by pressing in a magnetic field, this powder compact is sintered. In pressing in a magnetic field, it is preferable to form the powder compact by pressing in an inert gas atmosphere or wet pressing from the viewpoint of suppressing oxidation. In particular, in wet pressing, the surface of the particles constituting the powder compact is coated with a dispersant such as an oil agent, and contact with oxygen and water vapor in the atmosphere is suppressed. Therefore, it is possible to prevent or suppress the particles from being oxidized by the atmosphere before, after, or during the pressing process. For this reason, it is easy to control the oxygen content within a predetermined range. When performing wet pressing in a magnetic field, a slurry in which a dispersion medium is mixed with the fine powder is prepared, supplied to the cavity in the mold of the wet pressing apparatus, and press-molded in a magnetic field.

[0031] Next, the compact is sintered to obtain an R1-T-B system sintered magnet material. The sintering of the compact is preferably carried out at a pressure of 0.13 Pa (10 -3 Torr) or less, more preferably 0.07 Pa (5.0×10 -4 Torr) or less, in the temperature range of 1000 °C to 1150 °C. In order to prevent oxidation during sintering, the residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. The obtained sintered body (R1-T-B system sintered magnet material) may be subjected to heat treatment. Heat treatment conditions such as the heat treatment temperature and heat treatment time can adopt known conditions.

[0032] (Step of preparing the R2-M alloy) First, the composition of the R2-M alloy will be described. In the R2-M series alloy, R2 is a rare earth element, which necessarily contains at least one of Tb and Dy and at least one of Nd and Pr. M is at least one selected from the group consisting of Cu, Ga, Fe, Co, Ni, and Al. Preferably, R2 is 65 mass% or more and 97 mass% or less of the entire R2-M series alloy, and M is 3 mass% or more and 35 mass% or less of the entire R2-M series alloy. More preferably, R2 is 85 mass% or more and 95 mass% or less of the entire R2-M series alloy, and M is 5 mass% or more and 15 mass% or less of the entire R2-M series alloy. A higher H cJ can be obtained. The content of Tb and Dy in R2 is preferably 3 mass% or more and 24 mass% or less of the entire R2-M series alloy. Also, the content of Pr in R2 is preferably 65 mass% or more and 86 mass% or less of the entire R2-M series alloy. Also, M preferably necessarily contains at least one of Ga and Cu. A higher H cJ can be obtained. Preferably, the content of Pr in the R2-M series alloy is 50 mass% or more of the entire R2. More preferably, R2 consists only of Pr and Tb. By containing Pr, diffusion in the grain boundary phase is likely to proceed, so that Tb can be diffused more efficiently, and a higher H cJ can be obtained.

[0033] The shape and size of the R2-M series alloy are not particularly limited and are arbitrary. The R2-M series alloy can take the form of a film, foil, powder, block, particles, etc.

[0034] Next, a method for producing the R2-M series alloy will be described.

[0035] The R2-M series alloy can be prepared using a method for producing a raw material alloy employed in a general method for manufacturing an R-T-B series sintered magnet, such as die casting, strip casting, single roll super rapid solidification method (melt spinning method), atomization method, etc. Also, the R2-M series alloy may be one obtained by pulverizing the alloy obtained as described above by known pulverizing means such as a pin mill.

[0036] (Diffusion process) A diffusion process is performed in which the R1-T-B-based sintered magnet material prepared by the aforementioned method and the R2-M-based alloy are heated in a vacuum or an inert gas atmosphere at a temperature of 700°C or higher and 1100°C or lower, and R2 and M are diffused into the R1-T-B-based sintered magnet material. As a result, a liquid phase containing R2 and M is generated from the R2-M-based alloy, and the liquid phase is diffused and introduced from the surface to the inside of the sintered body via the grain boundaries in the R1-T-B-based sintered magnet material. At this time, it is preferable to increase the content of the heavy rare earth element RH (preferably Tb) contained in the R1-T-B-based sintered magnet material within an extremely small range of 0.05 mass% or more and 0.30 mass% or less. Thereby, while suppressing the consumption amount of the heavy rare earth element RH, an extremely high H cJ improvement effect can be obtained. In order to increase the content of RH contained in the R1-T-B-based sintered magnet material by 0.05 mass% or more and 0.30 mass% or less, various conditions such as the amount of the R2-M-based alloy, the heating temperature during the treatment, the particle diameter (when the R2-M-based alloy is in particle form), and the treatment time may be adjusted. Among these, by adjusting the amount of the R2-M-based alloy and the heating temperature during the treatment, the introduction amount (increase amount) of the heavy rare earth element RH can be controlled relatively easily.

[0037] In this specification, for example, "increasing the content of Tb by 0.05 mass% or more and 0.30 mass% or less" means that in terms of the content expressed in mass%, the numerical value increases by 0.05 or more and 0.30 or less. For example, if the content of Tb in the R1-T-B-based sintered magnet material before the diffusion process is 0.50 mass% and the content of Tb in the R-T-B-based sintered magnet after the diffusion process is 0.60 mass%, it means that the content of Tb has been increased by 0.10 mass% through the diffusion process. Whether the content (RH amount) of at least one of Tb and Dy is increased by 0.05 mass% or more and 0.30 mass% or less can be calculated by measuring the RH amount in the R1-T-B-based sintered magnet material before the diffusion process and the R-T-B-based sintered magnet after the diffusion process (measuring the RH amount in the whole and determining how much the RH amount has increased before and after). Also, when there is a concentrated portion of the R2-M-based alloy on the surface of the R-T-B-based sintered magnet after diffusion, it is desirable to measure the RH amount after removing the concentrated portion by cutting or the like.

[0038] When the heating temperature is less than 700 °C, for example, the amount of the liquid phase containing Tb, Pr, and M is too small to obtain a high H cJ On the other hand, when it exceeds 1100 °C, H cJ may decrease. Preferably, it is 850 °C or more and 980 °C or less. A higher H cJ can be obtained.

[0039] The diffusion treatment process may be carried out using a known heat treatment apparatus by disposing an R2-M-based alloy of an arbitrary shape on the surface of an R1-T-B-based sintered magnet material. For example, the surface of the R1-T-B-based sintered magnet material may be covered with a powder layer of the R2-M-based alloy and heat-treated. For example, after applying a slurry in which the R2-M-based alloy is dispersed in a dispersion medium to the surface of the R1-T-B-based sintered magnet material, the dispersion medium may be evaporated to bring the R2-M-based alloy into contact with the R1-T-B-based sintered magnet material. Examples of the dispersion medium include alcohol (such as ethanol), aldehyde, and ketone. Further, the heavy rare earth element RH may be introduced by disposing not only the R2-M-based alloy but also a fluoride, oxide, oxyfluoride, etc. of the heavy rare earth element RH together with the R2-M-based alloy on the surface of the R-T-B-based sintered magnet. That is, any method may be used as long as the light rare earth element RL and M can be simultaneously diffused together with the heavy rare earth element RH. Examples of the fluoride, oxide, and oxyfluoride of the heavy rare earth element RH include TbF 3 , DyF 3 , Tb 2 O 3 , Dy 2 O 3 , Tb 4 OF, Dy 4 OF.

[0040] (Heat treatment process) The R-T-B-based sintered magnet after the diffusion treatment process may be heat-treated in a vacuum or an inert gas atmosphere at a temperature of 450°C or higher and 750°C or lower and at a temperature lower than the temperature implemented in the diffusion treatment. By performing the heat treatment, a high H cJ can be obtained.

Example

[0041] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0042] Example 1 [Step of preparing an R1-T-B-based sintered magnet material] Each element was weighed so as to have the composition of the R1-T-B system sintered magnet material shown in No. A to J of Table 1, and a raw material alloy was produced by the strip casting method. Each of the obtained alloys was coarsely pulverized by the hydrogen pulverization method to obtain coarsely pulverized powder. Next, the coarsely pulverized powder was pulverized in a nitrogen gas stream using an air jet mill (jet mill device) to obtain finely pulverized powder with a particle size D 50 : 3.3 μm. The obtained finely pulverized powder was mixed with a dispersion medium to prepare a slurry. The slurry was formed in a magnetic field to obtain a formed body. Note that, as the forming device, a so-called right-angle magnetic field forming device (horizontal magnetic field forming device) in which the magnetic field application direction and the pressing direction are orthogonal was used. The obtained formed body was sintered in a vacuum at 1020 °C or higher and 1060 °C or lower (a temperature at which sufficient densification by sintering occurs was selected), and then rapidly cooled to obtain an R1-T-B system sintered magnet material. The density of the obtained R1-T-B system sintered magnet material was 7.5 Mg / m 3 or higher. The results of the components of the obtained R-T-B system sintered magnet material are shown in Table 1. Note that the contents of Nd, Pr, Ce, Dy, B, Co, Al, Cu, Ga, and Tb were measured using high-frequency inductively coupled plasma optical emission spectrometry (ICP-OES), and the contents of C, O, and N were measured using a gas analyzer by the gas fusion-infrared absorption method. Further, the value of [Nd] + [Pr] + [Ce] + [Dy] + [Tb]) - (9 × [O] + 12 × [C]) and the value of the content ratio of Ce in R1 ([Ce] / [Nd] + [Pr] + [Ce] + [Dy] + [Tb]) in the R1-T-B system sintered magnet material are shown in Table 1.

[0043]

Table 1

[0044] [Step of preparing R2-M system alloy] Each element was weighed so as to have the composition of the alloy shown in No. a of Table 2, and these raw materials were melted to obtain alloy powder by the disk atomization method. The composition of the obtained alloy powder is shown in Table 2. Note that each component in Table 2 was measured using high-frequency inductively coupled plasma optical emission spectrometry.

[0045]

Table 2

[0046] [Diffusion process] The R1-T-B series sintered magnet materials of No. A to J in Table 1 were cut and machined to form cubes of 7.2 mm × 7.2 mm × 7.2 mm. Next, 3 mass% of the R2-M series alloy (No. a) was sprayed on the entire surface with respect to 100 mass% of the R1-T-B series sintered magnet materials of No. A to J.

[0047] [Heat treatment process] The R1-T-B series sintered magnet material heated in the diffusion process was heat-treated at 900 °C for 4 hours in reduced-pressure argon controlled to 50 Pa using a vacuum heat treatment furnace, and then cooled to room temperature. Thereby, an R-T-B series sintered magnet subjected to the first heat treatment was obtained. Further, the heat-treated R-T-B series sintered magnet was heat-treated at 480 °C or higher and 520 °C or lower for 1 hour in reduced-pressure argon controlled to 50 Pa and then cooled to room temperature to produce R1-T-B series sintered magnets (No. 1 to 10).

[0048] For each sample after heat treatment, the entire surface was machined using a surface grinding machine to obtain a cube-shaped sample of 7.0 mm × 7.0 mm × 7.0 mm. The obtained sample was measured for the residual magnetic flux density B r and the coercive force H cJ using a B-H tracer. Thereafter, demagnetization was performed by heat treatment at 350 °C for 3 hours in reduced-pressure argon controlled to 50 Pa using a vacuum heat treatment furnace, and then the entire surface was machined using a surface grinding machine to be processed into a cube shape of 6.9 mm × 6.9 mm × 6.9 mm. The obtained sample was taken out every 0, 12, 24, 48, 96, 144, and 216 hours under the conditions of a temperature of 125 °C, a relative humidity of 85% RH, and 0.2 MPa using a high-accelerated life test device, and the maximum wear amount was measured. The results are shown in Table 3. Here, the corrosion resistance improvement effect is that when the wear amount is with an absolute value of 0.006 mg / cm 2 more than decrease in the case of Ce content with the same B amount of the material, it is marked as ○, with an absolute value of 0.006 mg / cm 2The case of the above increase was represented as ×, and the other cases were represented as △.

[0049]

Table 3

[0050] As shown in Table 3, in the inventive examples (No. 2, 4, 6, 8, 10), although the magnetic properties are reduced by containing Ce, all of them have B r of 1.40 T or more and H cJ of 1800 kA / m or more. While keeping the Tb amount low, even when Nd or Pr is replaced with Ce, high B r and high H cJ are maintained.

[0051] Regarding the corrosion resistance, in the sintered magnet material (the materials in Table 3), the wear amount is almost the same or rather larger in any material B amount when containing Ce compared to those not containing Ce, and the corrosion resistance is reduced. On the other hand, after diffusion, a result with a smaller wear amount than that of the material was obtained. Furthermore, the wear amount becomes smaller when containing Ce compared to those not containing Ce, and particularly, the corrosion resistance improvement effect is large in those with a B amount of 0.97 mass% or less.

Claims

1. A step of preparing an R1-T-B-based sintered magnet material (where R1 is a rare earth element, including at least Nd, Pr, and Ce, and T is Fe or Fe and Co); A step of preparing an R2-M-based alloy (where R2 is a rare earth element, necessarily including at least one of Tb and Dy and at least one of Nd and Pr, and M is at least one selected from the group consisting of Cu, Ga, Fe, Co, Ni, and Al); A diffusion step of heating the R1-T-B-based sintered magnet material and the R2-M-based alloy in a vacuum or an inert gas atmosphere at a temperature of 700°C or higher and 1100°C or lower to diffuse R2 and M into the R1-T-B-based sintered magnet material, In the R1-T-B-based sintered magnet material, the content ratio of Ce in R1 is 5 mass% or more and 25 mass% or less. When the content of Nd (mass%) in the R1-T-B-based sintered magnet material is [Nd], the content of Pr (mass%) is [Pr], the content of Ce (mass%) is [Ce], the content of Dy (mass%) is [Dy], the content of Tb (mass%) is [Tb], the content of O (mass%) is [O], and the content of C (mass%) is [C], then 25.8 mass% ≤ ([Nd] + [Pr] + [Ce] + [Dy] + [Tb] - (9 × [O] + 12 × [C]) ≤ 27.3 mass%, and the relationship of 0.08 mass% ≤ [O] ≤ 0.30 mass% is satisfied, A method for manufacturing an R-T-B-based sintered magnet.

2. The method for manufacturing an R-T-B-based sintered magnet according to Claim 1, wherein in the R1-T-B-based sintered magnet material, the content of B is 0.88 mass% or more and 0.97 mass% or less of the entire R1-T-B-based sintered magnet material.

3. The method for manufacturing an R-T-B-based sintered magnet according to Claim 1, wherein in the R2-M-based alloy, R2 is 65 mass% or more and 97 mass% or less of the entire R2-M-based alloy, and M is 3 mass% or more and 35 mass% or less of the entire R2-M-based alloy.

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