JP7631955B2 - Manufacturing method of RTB based sintered magnet - Google Patents

Description

The present invention relates to a method for producing R-T-B based sintered magnets.

In recent years, there has been high demand for rare earth sintered magnets, and among them, R-T-B sintered magnets (R is a rare earth element and must contain 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 must contain Fe; B is boron) are known as the most high-performance magnets, and are used in a variety of motors and home appliances, including voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), and motors for industrial equipment. R-T-B sintered magnets contribute to energy conservation and reduced environmental impact by making various motors smaller and lighter.

R-T-B based sintered magnets are composed of a main phase consisting mainly of R ₂ T ₁₄ B compounds and a grain boundary phase located at the grain boundaries of this main phase. The R ₂ T ₁₄ B compounds that make up the main phase are ferromagnetic materials with high saturation magnetization and anisotropic magnetic field, and form the basis of the properties of R-T-B based sintered magnets.

At high temperatures, the coercive force H _cJ (hereinafter sometimes simply referred to as "H _cJ ") of an R-T-B based sintered magnet decreases, causing irreversible thermal demagnetization. For this reason, R-T-B based sintered magnets used in electric vehicle motors, in particular, are required to have a high H _cJ .

It is known that in an R-T-B based sintered magnet, when a part of the light rare earth element RL (e.g., Nd or Pr) contained in R in the R ₂ T ₁₄ B compound is replaced with a heavy rare earth element RH (e.g., Tb or Dy), the H _cJ improves. As the amount of RH replaced increases, the H _cJ improves. However, when RL in the R ₂ T ₁₄ B compound is replaced with RH, while the H _cJ of the R-T-B based sintered magnet improves, the remanence B _r (hereinafter sometimes simply referred to as "B _r ") decreases. In addition, since heavy rare earth elements are raw materials with high resource risk, there is a demand to improve the H _cJ by reducing the amount of their use or by not using them at all.

Patent Document 1 discloses that HcJ is improved by heat-treating and diffusing a powder of an alloy containing R1i-M1j (R1 is rare earth elements including Y and Sc, M1 is one or more selected from Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, 15<j≦99, i is the remainder) and 70% by volume or more of an intermetallic compound phase on the surface of an R-T-B based sintered magnet. Patent Document 2 discloses that _HcJ is improved by applying an adhesive to the surface of an R-T- _B based sintered magnet, adhering a powder of an alloy or compound of at least one of Dy and Tb, and heat-treating the magnet.

JP 2008-263179 A International Publication No. 2018/030187

The inventors of the present invention investigated a method of heat treating and diffusing R-M alloy powder on the surface of an R-T-B sintered magnet as described in Patent Document 1, and found that in some cases, multiple protrusions with a height of 0.1 to 0.5 mm were generated on the surface of the sintered body after heat treatment. Further investigation revealed that the protrusions are a mixture of a liquid phase formed by the melting of the R-M alloy and a liquid phase formed from the R-T-B sintered magnet, and that the mixture of liquid phases solidifies to form raised metal pools. The presence of metal pools reduces the machining accuracy in subsequent processes, which increases the number of processes for removing the metal pools, resulting in a problem of reduced productivity.

Therefore, an embodiment of the present disclosure provides a method for manufacturing an R-T-B based sintered magnet that can suppress the occurrence of metal pools while suppressing the deterioration of magnetic properties.

In an exemplary embodiment, a method for producing a sintered R-T-B based magnet according to the present disclosure includes the steps of: preparing an R-T-B based sintered magnet material (R is a rare earth element and must include 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 must include Fe); and producing an R-M-Zr based alloy (R is a rare earth element and must include at least one selected from the group consisting of Nd, Pr, and Ce; M is Al, Cu, Zn, Ga, Fe, Co). , and Ni) and a diffusion step of attaching the R-M-Zr alloy to at least a portion of the surface of the R-T-B based sintered magnet material, and heating the R-M-Zr alloy at a temperature of 700° C. or more and 1100° C. or less in a vacuum or inert gas atmosphere, wherein the R content in the R-M-Zr alloy is 70 mass% or more and 95 mass% or less, the M content is 4.5 mass% or more and 25 mass% or less, and the Zr content is 0.5 mass% or more and 5 mass% or less.
In one embodiment, M of the RM-Zr alloy necessarily contains at least one of Cu and Ga, and the total content of Cu and Ga in M is 80% or more.

According to an embodiment of the present disclosure, a method for manufacturing an R-T-B based sintered magnet can be provided that can suppress the occurrence of metal pools while suppressing the deterioration of magnetic properties.

FIG. 2 is an enlarged cross-sectional view showing a schematic view of a portion of an RTB based sintered magnet. 1B is a cross-sectional view showing a further enlarged schematic view of the dashed rectangular region in FIG. 1A. 1 is a flowchart showing an example of steps in a method for producing a sintered RTB based magnet according to the present disclosure. 1 is a photograph showing the appearance of Sample No. 1-1. 1 is a photograph showing the appearance of Sample No. 1-2. 1 is a photograph showing the appearance of Sample No. 1-3. 1 is a photograph showing the appearance of Sample No. 1-4. 1 is a photograph showing the appearance of Sample No. 1-5. 1 is a photograph showing the appearance of Sample No. 1-6. 1 is a photograph showing the appearance of Sample No. 1-7. 1 is a photograph showing the appearance of Sample No. 1-8.

First, the basic structure of the R-T-B based sintered magnet according to the present disclosure will be described. An R-T-B based sintered magnet has a structure in which powder particles of a raw material alloy are bonded by sintering, and is composed of a main phase consisting mainly of R ₂ T ₁₄ B compound particles, and a grain boundary phase located at the grain boundaries of this main phase.

FIG. 1A is a cross-sectional view showing an enlarged portion of an R-T-B based sintered magnet, and FIG. 1B is a cross-sectional view showing an enlarged portion of the dashed rectangular region in FIG. 1A. In FIG. 1A, an arrow of 5 μm in length is shown as an example for reference as a reference length showing the size. As shown in FIG. 1A and FIG. 1B, the R-T-B based sintered magnet is composed of a main phase 12 mainly made of R ₂ T ₁₄ B compounds, and a grain boundary phase 14 located at the grain boundary portion of the main phase 12. As shown in FIG. 1B, the grain boundary phase 14 includes a two-particle grain boundary phase 14a in which two R ₂ T ₁₄ B compound particles (grains) are adjacent, and a grain boundary triple point 14b in which three R ₂ T ₁₄ B compound particles are adjacent. The typical main phase crystal grain size is 3 μm to 10 μm in average circle equivalent diameter of the magnet cross section. The R ₂ T ₁₄ B compound which is the main phase 12 is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field. Therefore, in an R-T-B based sintered magnet, the B _r can be improved by increasing the abundance ratio of the _{R 2} T ₁₄ B compound which is the main phase 12. In order to increase the abundance ratio of the R 2 T ₁₄ B compound, the amounts of R, T and B in the raw material alloy should be brought closer to the stoichiometric ratio of the R ₂ T ₁₄ B compound (R amount:T amount:B amount=2:14:1).

It is also known that the anisotropic magnetic field of the main phase can be increased while decreasing the saturation magnetization by substituting a part of R in the R ₂ T ₁₄ B compound, which is the main phase, with a heavy rare earth element such as Dy, Tb, or Ho. 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 technique, which can preferentially substitute heavy rare earth elements in the outer shell of the main phase, can efficiently obtain a high _HcJ while suppressing the decrease in saturation magnetization.

On the other hand, it is known that a high _HcJ can also be obtained by controlling the magnetism of the two-particle grain boundary phase 14a. Specifically, by lowering the concentration of magnetic elements (Fe, Co, Ni, etc.) in the two-particle grain boundary phase, the two-particle grain boundary phase can be made closer to non-magnetic, thereby weakening the magnetic coupling between the main phases and suppressing magnetization reversal.

In the manufacturing method of the R-T-B sintered magnet disclosed herein, R and M contained in the R-M-Zr alloy are diffused from the surface of the R-T-B sintered magnet material through the grain boundaries into the interior of the magnet material. As a result of research, the inventors have found that the occurrence of metal pools can be suppressed by further including Zr in a specific range in the alloy powder in which R and M are diffused. Furthermore, it was found that Zr is hardly diffused into the interior of the R-T-B sintered magnet after diffusion. This makes it possible to suppress the occurrence of metal pools while suppressing the deterioration of magnetic properties. This is believed to be because by including Zr in a specific range in the alloy powder to be diffused, it is possible to increase the melting point of the R-M-Zr alloy without diffusing Zr into the interior of the R-T-B sintered magnet. This is believed to make it possible to suppress the occurrence of metal pools by reducing the amount of liquid phase generated from the R-M-Zr alloy during diffusion while suppressing the deterioration of magnetic properties.

The method for producing a sintered R-T-B based magnet according to the present disclosure includes step S10 of preparing a sintered R-T-B based magnet material and step S20 of preparing an R-M-Zr based alloy, as shown in Fig. 2. The order of step S10 of preparing the sintered R-T-B based magnet material and step S20 of preparing the R-M-Zr based alloy may be arbitrary.
As shown in FIG. 2, the method for producing a sintered R-T-B based magnet according to the present disclosure further includes a diffusion step S30 in which an R-M-Zr based alloy is adhered to at least a portion of the surface of the sintered R-T-B based magnet material, and then heated at a temperature of 700° C. or higher and 1100° C. or lower in a vacuum or inert gas atmosphere.

In this disclosure, the R-T-B based sintered magnet before and during the diffusion process is referred to as the "R-T-B based sintered magnet material," and the R-T-B based sintered magnet after the diffusion process is simply referred to as the "R-T-B based sintered magnet."

(Step of preparing R-T-B based sintered magnet material)
In the sintered R-T-B based magnet material, R is a rare earth element that necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce, and the content of R is, for example, 27 mass% to 35 mass% of the entire sintered R-T-B based magnet material. T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si, T necessarily contains Fe, and the content of Fe relative to the entire T is 80 mass% or more.
If R is less than 27 mass%, the liquid phase is not sufficiently generated during the sintering process, and it may be difficult to sufficiently densify the sintered body. On the other hand, if R exceeds 35 mass%, grain growth occurs during sintering, and _HcJ may decrease. R is preferably 28 mass% or more and 33 mass% or less.

The RTB based sintered magnet material has, for example, the following composition range.
R: 27-35 mass%,
B: 0.80 to 1.20 mass%,
Ga: 0 to 1.0 mass%,
X: 0 to 2 mass% (X is at least one of Cu, Nb, and Al);
T: Contains 60 mass% or more.

Preferably, in the R-T-B based sintered magnet material, the molar ratio [T]/[B] of T to B is more than 14.0 and not more than 15.0. A higher H _cJ can be obtained. In the present disclosure, [T]/[B] is the ratio of the analytical value (mass%) of each element constituting T (at least one selected from the group consisting of Fe, Co, Al, Mn, and Si, T necessarily contains Fe, and the content of Fe in the whole of T is 80 mass% or more) divided by the atomic weight of each element, the total value being [T], to the analytical value (mass%) of B divided by the atomic weight of B, [B]. The condition that the molar ratio [T]/[B] exceeds 14.0 indicates that the amount of B is relatively small compared to the amount of T used to form the main phase (R ₂ T ₁₄ B compound). It is more preferable that the molar ratio [T]/[B] is 14.3 or more and 15.0 or less. It is possible to obtain a higher _HcJ . The content of B is preferably 0.9 mass % or more and less than 1.0 mass % of the entire RTB based sintered body.

The R-T-B sintered magnet material can be prepared by a general method for producing R-T-B sintered magnets, such as Nd-Fe-B sintered magnets. For example, a raw alloy produced by a strip casting method or the like is crushed to a particle size D ₅₀ of 2.0 μm to 3.5 μm using a jet mill or the like, and then molded in a magnetic field and sintered at a temperature of 900° C. to 1100° C. to produce a sintered body. By crushing to a particle size D ₅₀ of 2.0 μm to 3.5 μm, a high B _r and a high H _cJ can be obtained. Preferably, the particle size D ₅₀ is 2.5 μm to 3.3 μm. Higher B _r and high H _cJ can be obtained while reducing valuable RH and suppressing deterioration of productivity. The particle size D ₅₀ is the particle size at which the cumulative particle size distribution (volume basis) from the small diameter side becomes 50% in the particle size distribution obtained by the laser diffraction method using the airflow dispersion method. The particle size _D50 can be measured, for example, using a particle size distribution measuring device "HELOS &RODOS" manufactured by Sympatec under the conditions of dispersion pressure: 4 bar, measurement range: R2, and measurement mode: HRLD.

(Step of preparing RM-Zr based alloy)
In the R-M-Zr alloy, R is a rare earth element and necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce. The content of R is 70 mass% or more and 95 mass% or less of the entire R-M-Zr alloy. M is at least one selected from the group consisting of Al, Cu, Zn, Ga, Fe, Co, and Ni. The content of M is 4.5 mass% or more and 25 mass% or less of the entire R-M-Zr alloy. The content of Zr is 0.5 mass% or more and 5 mass% or less of the entire R-M-Zr alloy. Typical examples of the R-M-Zr alloy include a TbNdPrCuZr alloy, a TbNdCePrCuZr alloy, a TbNdGaZr alloy, and a TbNdPrGaCuZr alloy. In addition to the above elements, small amounts of elements such as inevitable impurities, such as Mn, O, C, and N, may be contained.

If R is less than 70 mass%, _HcJ may decrease, and if it exceeds 95 mass%, the alloy powder during the manufacturing process of the R-M-Zr alloy becomes very active. As a result, the alloy powder may be significantly oxidized or ignite. Preferably, the content of R is 80 mass% or more and 90 mass% or less of the entire R-M-Zr alloy. A higher _HcJ can be obtained.
Furthermore, the method for producing a sintered R-T-B based magnet according to the present disclosure can obtain a sintered R-T-B based magnet having high B _r and high H _cJ while reducing the amount of heavy rare earth elements (Tb, Dy, etc.) used. Therefore, the content of the heavy rare earth elements is preferably 10 mass% or more and 20 mass% or less of the entire R-M-Zr based alloy, and more preferably the R-M-Zr based alloy does not contain any heavy rare earth elements.

If M is less than 4.5 mass%, R and M are difficult to introduce into the two-particle grain boundary phase, and H _cJ may not be sufficiently improved, and if it exceeds 25 mass%, the content of R decreases and H _cJ may not be sufficiently improved. Preferably, the content of M is 7 mass% or more and 15 mass% or less of the entire R-M-Zr alloy. A higher H _cJ can be obtained. Moreover, M preferably contains at least one of Cu and Ga, and more preferably contains both Cu and Ga. The total content ratio of Cu and Ga in M is preferably 80% or more. By containing Cu and Ga, a higher H _cJ can be obtained.

If Zr is less than 0.5 mass%, it may not be possible to suppress the occurrence of metal pools in the R-T-B based sintered magnet after diffusion, and if it exceeds 5 mass%, _HcJ may decrease. By including Zr in a specific range in the alloy powder in which R and M are diffused, it is possible to suppress the occurrence of metal pools while suppressing the deterioration of magnetic properties. Preferably, the content of Zr is 0.8 mass% or more and 4 mass% or less, and more preferably, 0.8 mass% or more and 2 mass% or less. It is possible to suppress the occurrence of metal pools while further suppressing the deterioration of magnetic properties.

The method for producing the R-M-Zr alloy is not particularly limited. It may be produced by roll quenching or casting. These alloys may also be pulverized to produce alloy powder. It may also be produced by known atomization methods such as centrifugal atomization, rotating electrode method, gas atomization, and plasma atomization.

(Diffusion process)
The R-M-Zr alloy prepared as described above is attached to at least a part of the surface of the R-T-B sintered magnet material, and a diffusion process is performed in which the alloy is heated in a vacuum or inert gas atmosphere at a temperature of 700°C to 1100°C. As a result, a liquid phase containing R and M is generated from the R-M-Zr alloy, and the liquid phase is diffused from the surface of the sintered magnet material to the inside via the grain boundaries in the R-T-B sintered magnet material. In the diffusion process, the amount of the R-M-Zr alloy attached to the R-T-B sintered magnet material is preferably 1 mass% to 5 mass%, and more preferably, the amount of the R-M-Zr alloy attached to the R-T-B sintered magnet material is 1.5 mass% to 3 mass%. A higher H _cJ can be obtained.

If the heating temperature in the diffusion step is less than 700°C, the amount of liquid phase containing R and M may be too small to obtain a high H _cJ . On the other hand, if the heating temperature exceeds 1100°C, the H _cJ may be significantly reduced. Preferably, the heating temperature in the diffusion step is 800°C or higher and 1000°C or lower. A higher H _cJ can be obtained. Also, preferably, the R-T-B based sintered magnet that has been subjected to the diffusion step (700°C or higher and 1100°C or lower) is cooled from the temperature at which the diffusion step was performed to 300°C at a cooling rate of 15°C/min or higher. A higher H _cJ can be obtained.

The diffusion process can be carried out by placing an R-M-Zr alloy of any shape on the surface of the R-T-B sintered magnet material and using a known heat treatment device. For example, the surface of the R-T-B sintered magnet material can be covered with a powder layer of the R-M-Zr alloy and then the diffusion process can be carried out. For example, a coating process of coating an adhesive on the surface to be coated and a process of attaching the R-M-Zr alloy to the area coated with the adhesive can be carried out. Examples of adhesives include PVA (polyvinyl alcohol), PVB (polyvinyl butyral), and PVP (polyvinylpyrrolidone). When the adhesive is a water-based adhesive, the R-T-B sintered magnet material can be preheated before coating. The purpose of the preheating is to remove excess solvent, control the adhesive strength, and to attach the adhesive uniformly. The heating temperature is preferably 60 to 200°C. In the case of a highly volatile organic solvent-based adhesive, this process may be omitted. Also, for example, a slurry in which the R-M-Zr alloy is dispersed in a dispersion medium may be applied to the surface of the R-T-B sintered magnet material, and the dispersion medium may then be evaporated to allow the R-M-Zr alloy and the R-T-B sintered magnet material to adhere to each other. Examples of the dispersion medium include alcohol (such as ethanol), aldehydes, and ketones.

(Step of carrying out heat treatment)
2, the R-T-B based sintered magnet that has been subjected to the diffusion step is preferably subjected to a heat treatment S40 in a vacuum or inert gas atmosphere at a temperature of 400° C. to 750° C., both inclusive, and lower than the temperature used in the diffusion step. By performing the heat treatment, a higher _HcJ can be obtained.

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

Experimental Example 1
[Preparing R-T-B based sintered magnet material]
Each element was weighed so as to obtain the composition of the R-T-B based sintered magnet material shown in No. 1 of Table 1, and a raw material alloy was prepared by strip casting. Each obtained alloy was coarsely pulverized by hydrogen pulverization to obtain coarsely pulverized powder. Next, the coarsely pulverized powder was finely pulverized by a jet mill. Fine powder with a particle size D ₅₀ of 4.2 μm was obtained by fine pulverization. The obtained finely pulverized powder was molded in a magnetic field to obtain a compact. The molding device used was a so-called perpendicular magnetic field molding device (horizontal magnetic field molding device) in which the magnetic field application direction and the pressure direction are perpendicular to each other. The obtained compact was sintered in a vacuum for 4 hours (a temperature was selected at which densification by sintering would occur sufficiently), and then quenched to obtain a R-T-B based sintered magnet material. The density of the obtained R-T-B based sintered magnet material was 7.5 Mg/m ³ or more.
To determine the composition of the resulting sintered R-T-B magnet material, the contents of Nd, Pr, Dy, B, Co, Al, Cu, Ga, and Tb were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The analysis results are shown in Table 1.

[Step of preparing RM-Zr based alloy]
Each element was weighed so as to obtain the alloy composition shown in No. 1-A to 1-G in Table 2, and the raw materials were melted and ribbon- or flake-shaped alloys were obtained by single-roll ultra-quenching. The compositions of the obtained alloys (RM-Zr alloys and comparative alloys) are shown in Table 2. The components in Table 2 were measured using high-frequency inductively coupled plasma atomic emission spectrometry.

[Diffusion process]
The R-T-B-based sintered magnet material No. 1 in Table 1 was cut and machined into a rectangular parallelepiped of 45 mm x 52 mm x 4 mm. PVA was applied as an adhesive to the entire surface of the processed R-T-B-based magnet material by dipping. Next, an alloy was attached to the entire surface of the R-T-B-based sintered magnet material coated with the adhesive under the conditions shown in Table 3. The amount of alloy attached was adjusted by crushing the alloy in an argon atmosphere using a mortar, passing it through several types of sieves with openings of 45 to 1000 μm, and using alloys with different particle sizes. Then, using a vacuum heat treatment furnace, the alloy and the R-T-B-based sintered magnet material were heated in a reduced pressure argon atmosphere controlled to 100 Pa under the conditions shown in Table 3, and then cooled.

[Heat treatment process]
The sintered R-T-B based magnet material heated in the diffusion step was subjected to a heat treatment at 500° C. in a vacuum heat treatment furnace in reduced pressure argon controlled at 100 Pa. The heating temperatures of the R-M-Zr based alloy and the sintered R-T-B based magnet material in the diffusion step, and the heating temperature of the sintered R-T-B based magnet in the step of carrying out the heat treatment after the diffusion step were each measured using a thermocouple.

[Sample evaluation]
After the heat treatment, each sample was entirely machined using a surface grinder to obtain a rectangular parallelepiped sample (RTB-based sintered magnet) measuring 7.0 mm x 7.0 mm x 7.0 mm. The residual magnetic flux density B _r and coercive force H _cJ of the obtained samples were measured using a B-H tracer. The results are shown in Table 3. The appearance of each sample No. after the diffusion step is shown in Figs. 3 to 10. Fig. 3 is a photograph showing the appearance of No. 1-1, Fig. 4 is a photograph showing the appearance of No. 1-2, Fig. 5 is a photograph showing the appearance of No. 1-3, Fig. 6 is a photograph showing the appearance of No. 1-4, Fig. 7 is a photograph showing the appearance of No. 1-5, Fig. 8 is a photograph showing the appearance of No. 1-6, Fig. 9 is a photograph showing the appearance of No. 1-7, and Fig. 10 is a photograph showing the appearance of No. 1-8.
The number of metal puddles generated on the surface of the R-T-B based sintered magnet in Nos. 1-1 to 1-8 was evaluated. The metal puddles were convex portions of about 0.5 mm or more. No. 1-1, which is a comparative example, generated 9 metal puddles. On the other hand, Nos. 1-2 to 1-4, which are examples of the present invention, obtained high magnetic properties of B _r of 1.450 T or more and H _cJ of 2126 kA/m or more, and furthermore, no metal puddles were generated. Furthermore, No. 1-5, which is a comparative example, obtained high B _r and high H _cJ , but generated 30 or more metal puddles. Furthermore, No. 1-6, which is a comparative example, did not generate metal puddles, but Br decreased. Furthermore, Nos. 1-7 and 1-8, which are comparative examples, obtained high B _r and high H _cJ , but generated 7 and 2 metal puddles, respectively.

Claims (1)

preparing an R-T-B based sintered magnet material (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si, and must contain Fe);
preparing an R-M-Zr alloy (R is a rare earth element, and must contain at least one selected from the group consisting of Nd, Pr, and Ce, M is at least one selected from the group consisting of Al, Cu, Zn, Ga, Fe, Co, and Ni, and must contain at least one of Cu and Ga , and the total content of Cu and Ga in M is 80% or more );
a diffusion step of adhering the R-M-Zr based alloy to at least a part of the surface of the R-T-B based sintered magnet material, and heating the resulting material at a temperature of 700° C. or higher and 1100° C. or lower in a vacuum or inert gas atmosphere;
The method for producing an R-T-B based sintered magnet, wherein the R content in the R-M-Zr based alloy is 70 mass% or more and 95 mass% or less, the M content is 4.5 mass% or more and 25 mass% or less, and the Zr content is 0.5 mass% or more and 5 mass% or less.

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