JP7528437B2 - Manufacturing method of RTB based sintered magnet - Google Patents

Description

This disclosure relates to a method for producing R-T-B based sintered magnets.

R-T-B system sintered magnets (R is a rare earth element, and T is Fe or Fe and Co) with an R ₂ Fe ₁₄ B type compound as the main phase are known as the highest performance magnets among permanent magnets, and are used in a variety of motors such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances.

R-T-B based sintered magnets are composed of a main phase consisting mainly of R ₂ Fe ₁₄ B type compounds and a grain boundary phase located at the grain boundaries of this main phase. The R ₂ Fe ₁₄ B type compound that is the main phase is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field, and forms the basis of the characteristics of R-T-B based sintered magnets.

Since the intrinsic coercivity H _cJ (hereinafter simply referred to as "H _cJ ") of an R-T-B based sintered magnet decreases at high temperatures, irreversible thermal demagnetization occurs. In order to avoid irreversible thermal demagnetization, when the magnet is used in a motor or the like, it is required to maintain a high H _cJ even at high temperatures.

It is known that the H _cJ of an R-T-B based sintered magnet is improved when a part of R in the R ₂ Fe ₁₄ B type compound phase is replaced with a heavy rare earth element RH (Dy, Tb, etc.). In order to obtain a high H _cJ at high temperatures, it is effective to add a large amount of the heavy rare earth element RH to the R-T-B based sintered magnet. However, when the light rare earth element RL (Nd, Pr) as R in an R-T-B based sintered magnet is replaced with a heavy rare earth element RH, there is a problem that while the H _cJ is improved, the residual magnetic flux density B _r (hereinafter simply referred to as "B _r ") is reduced. In addition, the heavy rare earth element RH is a scarce resource. For these reasons, there is a demand to reduce the amount of heavy rare earth element RH used.

In recent years, in order to improve the _HcJ of R-T-B based sintered magnets with less heavy rare earth element RH, it has been proposed to supply heavy rare earth element RH such as Tb or Dy to the surface of the R-T-B based sintered magnet and diffuse the heavy rare earth element RH into the magnet. This allows the heavy rare earth element RH to be distributed in a large amount in the main phase outer periphery (near the grain boundaries). By distributing a thin shell layer (RH-enriched layer) of heavy rare earth element RH in the main phase outer periphery (near the grain boundaries), it is possible to suppress a decrease in B _r , and further, since the _HcJ generation mechanism of R-T-B based sintered magnets is of the nucleation type, distributing a thin shell layer of heavy rare earth element RH in the main phase outer periphery (near the grain boundaries) enhances the crystal magnetic anisotropy of the entire crystal grains, preventing the nucleation of reverse magnetic domains, and as a result, improving _HcJ .

Patent Document 1 describes a method in which a powder containing Dy, Tb, etc. is placed on the surface of a sintered body and heated at a temperature lower than the sintering temperature, thereby diffusing Dy, Tb, etc. from the powder into the sintered body.

Patent Document 2 and Patent Document 3 describe a method in which a sintered magnet (sintered body in Patent Document 3) and an evaporation material containing Dy and the like (bulk body in Patent Document 3) are placed apart via a net, and the sintered magnet and the evaporation material are heated to a predetermined temperature, thereby diffusing Dy and the like from the evaporation material into the sintered magnet.

Patent document 4 describes a method in which multiple R-T-B based sintered magnet bodies and multiple RH diffusion sources containing Dy or the like are inserted into a treatment chamber so that they are relatively movable and close to or in contact with each other, and the R-T-B based sintered magnet bodies and the RH diffusion sources are heated while being moved continuously or intermittently within the treatment chamber, thereby diffusing Dy or the like from the RH diffusion sources into the R-T-B based sintered magnet bodies.

JP 2008-147634 A JP 2008-171995 A International Publication No. 2007/102391 International Publication No. 2011/007758

However, according to the method described in Patent Document 1, the heavy rare earth element RH accumulated on the surface of the sintered body diffuses into the interior of the sintered body all at once, leading to the heavy rare earth element RH diffusing even to the vicinity of the center of the main phase in the surface region of the sintered body, resulting in a decrease in B _r . In addition, since a large amount of the heavy rare earth element RH is consumed in the surface region of the sintered body, it becomes difficult to diffuse a sufficient amount of the heavy rare earth element RH from the surface region of the magnet body to the region deeper inside (the central part of the magnet).

According to the methods described in Patent Documents 2 to 4, the heavy rare earth element RH quickly diffuses into the interior of the sintered magnet after colliding with the surface. However, because the heavy rare earth element RH is supplied to the magnet surface successively, when attempting to diffuse a sufficient amount of the heavy rare earth element RH from the surface region of the sintered magnet to a region deeper inside (the central part of the magnet), a relatively thick shell layer of the heavy rare earth element RH may be formed in the main phase of the surface region of the sintered magnet.

As described above, the methods described in Patent Documents 1 to 4 may cause the heavy rare earth element RH to diffuse not only to the outer crust portion of the main phase (near the grain boundaries) but also into the interior of the main phase in the surface layer region of the sintered magnet, or may form a relatively thick shell layer of the heavy rare earth element RH. As a result, it is difficult to say that they necessarily improve _HcJ while sufficiently suppressing a decrease in _Br .

Various embodiments of the present disclosure provide a method for producing a sintered RTB based magnet that reduces the amount of heavy rare earth RH used and has high _HcJ while suppressing a decrease in B _r .

In an exemplary embodiment, the method for producing an R-T-B based sintered magnet according to the present disclosure is to produce an R ₂ Fe ₁₄ magnet containing a light rare earth element RL (RL is at least one element selected from the group consisting of Nd, Pr, and Ce) as the main rare earth element R. The method includes the steps of: preparing a sintered R-T-B based magnet material (T is Fe, or Fe and Co) having B-type compound crystal grains as a main phase; preparing a diffusion source powder formed from a powder of an alloy or compound containing a heavy rare earth element RH (RH is at least one selected from the group consisting of Tb, Dy, and Ho); bringing at least a part of the diffusion source powder into contact with at least a part of the surface of the sintered R-T-B based magnet material; and subjecting the sintered R-T-B based magnet material in contact with the diffusion source powder to a heat treatment at a temperature of 800° C. or higher and lower than the sintering temperature of the sintered R-T-B based magnet material for 30 hours or more, thereby diffusing the heavy rare earth element RH contained in the diffusion source powder from the surface to the inside of the sintered R-T-B based magnet material.

In one embodiment, in the diffusion step, the R-T-B based sintered magnet material in contact with the diffusion source powder is subjected to a heat treatment at a temperature equal to or lower than the sintering temperature of the R-T-B based sintered magnet material for 30 hours to 45 hours.

In one embodiment, in the diffusion step, the R-T-B based sintered magnet material in contact with the diffusion source powder is subjected to a heat treatment at a temperature equal to or lower than the sintering temperature of the R-T-B based sintered magnet material for 35 hours to 40 hours.

In one embodiment, the diffusion source powder is an RHM alloy powder (wherein M is at least one selected from the group consisting of Nd, Pr, Ce, Cu, Ga, Fe, Co, Ni, and Al).

In one embodiment, the diffusion source powder contains Cu.

In one embodiment, the thickness dimension of the R-T-B based sintered magnet material is 1 mm or more and 5 mm or less.

In one embodiment, the step of contacting at least a portion of the diffusion source powder with at least a portion of the surface of the R-T-B based sintered magnet material is a step of adhering at least a portion of the diffusion source powder to at least a portion of the surface of the R-T-B based sintered magnet material.

The present disclosure makes it possible to provide a method for producing a sintered RTB based magnet that reduces the amount of heavy rare earth RH used and has high _HcJ while suppressing a decrease in B _r .

The present inventors have investigated whether it is possible to diffuse the heavy rare earth element RH into the outer shell of the main phase (near the grain boundaries) in the surface region of the R-T-B based sintered magnet by using the method described in Patent Document 1, for example, by contacting the surface of the R-T-B based sintered magnet material with a diffusion source powder containing the heavy rare earth element RH and then subjecting the R-T-B based sintered magnet with the diffusion source powder in contact therewith to a heat treatment in which the heavy rare earth element RH is diffused into the R-T-B based sintered magnet material.

Usually, the longer the heating time in the diffusion step (for example, 5 to 10 hours), the more the heavy rare earth element RH diffuses from the surface region of the magnet into the main phase. Therefore, it has been believed that the longer the heating time, the more the heavy rare earth element RH diffuses from the surface region of the magnet into the main phase, which leads to a decrease in B _r , and furthermore, the more the heavy rare earth element RH is consumed in the surface region, making it difficult to diffuse a sufficient amount of the heavy rare earth element RH to the center of the magnet, thereby preventing an improvement in H _cJ . However, as a result of the investigation, it was found, quite unexpectedly, that when the heating time is 30 hours or more, the heavy rare earth element RH does not diffuse into the main phase, and the heavy rare earth element RH can be diffused to the outer periphery of the main phase (near the grain boundary). It was also found that the heavy rare earth element RH can be diffused from the surface region of the magnet to a region deeper inside (the center of the magnet). Although the detailed mechanism is unclear, it is believed that the heavy rare earth element RH that was once diffused into the main phase is then diffused back into the grain boundaries by heating for a long period of time, and the reversely diffused heavy rare earth element RH is then diffused through the grain boundaries from the surface region of the magnet to a region deeper inside. It is believed that this makes it possible to obtain an R-T-B based sintered magnet that has a high _HcJ while suppressing a decrease in B _r . It was also found that this phenomenon does not occur in the methods described in Patent Documents 2 to 4. This is believed to be because, unlike Patent Document 1, the heavy rare earth element RH is successively newly introduced to the magnet surface.

Patent Document 1 gives a very wide range of diffusion times, from 1 minute to 100 hours, but in the examples it gives a range of 5 hours to 20 hours, with a preferred range of 5 minutes to 8 hours, and particularly 10 minutes to 6 hours. Patent Document 2 also gives diffusion times of 48 hours and 60 hours, but as mentioned above, in the method described in Patent Document 2, the heavy rare earth element RH is successively newly introduced to the magnet surface, and it is not possible to diffuse the heavy rare earth element RH into the outer shell of the main phase (near the grain boundaries) in the surface region of the R-T-B based sintered magnet.

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." In addition, in this disclosure, the "surface region" refers to the region from the magnet surface to a depth of approximately 20 μm.

(Preparing R-T-B based sintered magnet material)
An R-T-B system sintered magnet material (T is Fe or Fe and Co) having, as a main phase, R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (RL is at least one selected from the group consisting of Nd, Pr and Ce) as the main rare earth element R is prepared.

The RTB based sintered magnet material may be any known material, for example, having the following composition:
Rare earth element R: 27.5 to 35.0% by mass,
B (a part of B (boron) may be substituted with C (carbon)): 0.80 to 1.20 mass%,
Ga: 0 to 0.8% by mass,
Additional element M (at least one selected from the group consisting of Al, Cu, Zr, and Nb): 0 to 2 mass %,
T (T is Fe or Fe and Co) and inevitable impurities: the balance.

The rare earth element R mainly contains a light rare earth element RL, but may also contain a heavy rare earth element RH (RH is at least one element selected from the group consisting of Tb, Dy, and Ho).

The R-T-B based sintered magnet material of the above composition can be manufactured by any known manufacturing method. The R-T-B based sintered magnet material may be in the as-sintered state, or may have been subjected to cutting or polishing processing.

In addition, it is preferable that the thickness dimension of the R-T-B based sintered magnet material is 1 mm or more and 5 mm or less. For example, if the magnet is rectangular and 4 mm x 4 mm x 2 mm, the thickness direction is 2 mm. Also, if the dimensions are the same, for example, 2 mm x 2 mm x 2 mm, the thickness direction is 2 mm. If the thickness dimension is less than 1 mm, cracks or breaks may occur due to insufficient strength, and if it exceeds 5 mm, it may be difficult to sufficiently diffuse the heavy rare earth element RH to the center of the R-T-B based sintered magnet material. In addition, the thickness direction does not necessarily have to be the magnetization direction, and the magnetization direction may be in a direction different from the thickness direction.

(Step of Preparing Diffusion Source Powder)
A diffusion source powder formed from a powder of an alloy or compound containing a heavy rare earth element RH (RH is at least one selected from the group consisting of Tb, Dy and Ho) is prepared.

The diffusion source powder is, for example, RHM alloy powder (where M is at least one selected from the group consisting of Nd, Pr, Ce, Cu, Ga, Fe, Co, Ni, and Al).

The method of producing the RHM alloy powder is not particularly limited. The RHM alloy powder may be produced by a method of producing an alloy ribbon by roll quenching and pulverizing the alloy ribbon, or may be produced by a known atomizing method such as centrifugal atomizing, rotating electrode method, gas atomizing, or plasma atomizing. The ingot produced by casting may be pulverized. Typical examples of the RHM alloy powder include DyFe alloy powder, DyAl alloy powder, DyCu alloy powder, TbFe alloy powder, TbAl alloy powder, TbCu alloy powder, DyFeCu alloy powder, TbCuAl alloy powder, TbNdPrCu alloy powder, TbNdCePrCu alloy powder, TbNdGa alloy powder, and TbNdPrGaCu alloy powder. The RHM alloy powder preferably contains Cu. By including Cu, it is possible to diffuse a sufficient amount of the heavy rare earth element RH from the surface region of the sintered R-T-B magnet material to a deeper region (the central portion of the magnet). The particle size of the RHM alloy powder is, for example, 500 μm or less, and as small as about 10 μm.

The compound of the heavy rare earth element RH is one or more selected from RH fluoride, RH acid fluoride, and RH oxide, and these are collectively referred to as RH compounds. RH acid fluoride may be included in RH fluoride as an intermediate substance in the manufacturing process of RH fluoride. The particle size of many available RH compound powders is 20 μm or less, typically 10 μm or less, in terms of the size of the agglomerated secondary particles, and for small ones, the primary particles are about a few μm in size.

(Step of contacting at least a part of the diffusion source powder with at least a part of the surface of the sintered R-T-B based magnet material)
At least a part of the diffusion source powder is brought into contact with at least a part of the surface of the R-T-B based sintered magnet material. There is no particular limit to the method of bringing the diffusion source powder into contact with the surface of the R-T-B based sintered magnet material. Any method may be used as long as at least a part of the diffusion source powder can be attached to at least a part of the surface of the R-T-B based sintered magnet material. Examples include a spray method, an immersion method, and application with a dispenser. The diffusion source powder may also be attached by applying an adhesive to the surface of the R-T-B based sintered magnet material and scattering the diffusion source powder on the surface of the R-T-B based sintered magnet material to which the adhesive has been attached. For example, a method of immersing the R-T-B based sintered magnet material to which the adhesive has been applied in fluidized diffusion source powder, known as a fluidized bed coating process, may be used. An example of application of the fluidized bed coating process will be described below.

The fluidized bed method is a method that has been widely used in the field of powder coating. A heated workpiece is immersed in fluidized thermoplastic powder paint, and the paint is fused to the workpiece surface by the heat. In this example, in order to apply the fluidized bed method to magnets, the above-mentioned diffusion source powder is used instead of the thermoplastic powder paint, and an R-T-B sintered magnet material coated with an adhesive is used instead of the heated coating. Any method can be used to fluidize the diffusion source powder. For example, as one specific example, a method using a container with a porous partition at the bottom will be described. In this example, the diffusion source powder is placed in the container, and air or an inert gas or other gas is pressurized and injected into the container from the bottom of the partition, and the diffusion source powder above the partition can be floated and fluidized by the pressure or air flow.

The R-T-B based sintered magnet material coated with an adhesive is immersed (or placed or passed through) in the diffusion source powder flowing inside the container, thereby adhering the diffusion source powder to the R-T-B based sintered magnet material. The time for which the R-T-B based sintered magnet material coated with an adhesive is immersed is, for example, about 0.5 to 5.0 seconds. By using the fluidized immersion method, the diffusion source powder is fluidized (stirred) inside the container, which prevents relatively large powder particles from being unevenly attached to the magnet surface, or, conversely, relatively small powder particles from being spaced apart and attached to the magnet surface. This allows the diffusion source powder to be more uniformly attached to the R-T-B based sintered magnet material.

(Diffusion process)
The R-T-B based sintered magnet material in contact with the diffusion source powder is heat-treated at a temperature of 800°C or higher and lower than the sintering temperature of the R-T-B based sintered magnet material for 30 hours or more, so that the heavy rare earth element RH contained in the diffusion source powder is diffused from the surface to the inside of the R-T-B based sintered magnet material. If the heating temperature is 800°C or lower, the amount of liquid phase containing the heavy rare earth element RH is too small, so that diffusion into the inside of the R-T-B based sintered magnet is insufficient, and it may not be possible to obtain a high _HcJ . If the heating temperature exceeds the sintering temperature, abnormal grain growth may occur, and _Br and _HcJ may be significantly reduced. The heating temperature is preferably 850°C or higher and 950°C or lower. A higher _HcJ can be obtained. The heat treatment can be performed using a known heat treatment device.

As described above, by performing heating for 30 hours or more, the heavy rare earth element RH can be diffused into the outer periphery of the main phase (near the grain boundaries) in the surface region of the sintered R-T-B magnet, and can be diffused from the surface region of the magnet to a region deeper inside (the center part of the magnet). This makes it possible to obtain a sintered R-T-B magnet that has a high _HcJ while suppressing a decrease in B _r .

The heating time in the diffusion process of the present disclosure starts when the temperature of the R-T-B based sintered magnet material reaches the set temperature (for example, when it reaches 920°C when the set temperature is 920°C) and ends when it falls below the set temperature by more than 20°C (for example, when it falls below 900°C when the set temperature is 920°C). If the heat treatment is performed in two or more stages, the total time should be 30 hours or more. The temperature of the R-T-B based sintered magnet material can be measured, for example, by attaching a thermocouple to the magnet material. The heating time is preferably 30 hours or more and 45 hours or less, and more preferably 35 hours or more and 40 hours or less.

After the diffusion process, the R-T-B sintered magnet may be subjected to a second heat treatment for the purpose of improving its magnetic properties. The temperature, time, and other conditions in the second heat treatment may be those known as heat treatment conditions for sintered magnets (e.g., 500°C for 3 hours). The final magnet dimensions may also be adjusted by machining such as grinding. In this case, this may be done before or after the second heat treatment.

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

Experimental Example 1
(Preparing R-T-B based sintered magnet material)
Each element was weighed so that the R-T-B sintered magnet material had a composition approximately shown by symbol 1-A in Table 1, and the alloy flakes were cast by strip casting to obtain a 0.2-0.4 mm thick raw alloy flakes. The obtained raw alloy flakes were subjected to hydrogen pulverization, followed by heating to 550°C in a vacuum and then cooling to obtain a coarsely pulverized powder. Next, zinc stearate was added as a lubricant to the obtained coarsely pulverized powder in an amount of 0.04% by mass relative to 100% by mass of the coarsely pulverized powder, and mixed. The mixture was then dry-pulverized in a nitrogen gas stream using an airflow pulverizer (jet mill device) to obtain a finely pulverized powder (alloy powder) with a particle size D ₅₀ of 4 μm. The particle size D ₅₀ is the volume center value (volume-based median diameter) obtained by a laser diffraction method using an airflow dispersion method.

Zinc stearate was added as a lubricant at 0.05% by mass relative to 100% by mass of the finely pulverized powder, mixed, and molded in a magnetic field to obtain a green body. 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 for 4 hours (a temperature was selected at which densification by sintering was sufficient) to prepare a number of R-T-B based sintered magnet materials (No. 1-A). The density of the obtained R-T-B based sintered magnet material was 7.5 Mg/ ^m3 or more. Table 1 shows the composition of the obtained R-T-B based sintered magnet material. Each component in Table 1 was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). The oxygen content of the sintered body was measured by gas fusion-infrared absorption method, and it was confirmed to be around 0.1 mass%. The R-T-B based sintered magnet material No. 1-A was cut and machined to obtain a 4.4 mm x 10.0 mm x 11.0 mm rectangular parallelepiped (the 10.0 mm x 11.0 mm surface was perpendicular to the orientation direction, and the 4.4 mm direction was the thickness direction, which is the orientation direction).

(Step of Preparing Diffusion Source Powder)
A diffusion source powder was prepared by atomizing an alloy powder having a composition shown in No. 1-a of Table 2. The particle size of the obtained diffusion source powder was 106 μm or less.

(Step of contacting at least a part of the diffusion source powder with at least a part of the surface of the sintered R-T-B based magnet material)
Next, an adhesive was applied to the entire surface of the R-T-B based sintered magnet material No. 1-A in Table 1. The application method was to heat the R-T-B based sintered magnet material to 60°C on a hot plate, and then apply the adhesive to the R-T-B based sintered magnet material by spraying. PVP (polyvinylpyrrolidone) was used as the adhesive.

Next, the diffusion source powder No. 1-a in Table 2 was attached to the adhesive-coated R-T-B sintered magnet material (No. 1-A). The attachment method was to spread the diffusion source powder in a container, and then attach the diffusion source powder in the container so that it was sprinkled over the entire surface of the adhesive-coated R-T-B sintered magnet material.

(Diffusion process)
Using a tubular gas flow furnace, the R-T-B based sintered magnet material in contact with the diffusion source powder (No. 1-a) was subjected to a heat treatment (diffusion treatment) at 920°C for 36 hours in reduced pressure argon controlled at 200 Pa. The R-T-B based sintered magnet after the diffusion treatment was then subjected to a second heat treatment at 490°C for 6 hours to obtain an R-T-B based sintered magnet (No. 1-1). An R-T-B based sintered magnet (No. 1-2) was produced in the same manner as the R-T-B based sintered magnet No. 1-1, except that the heating time in the diffusion treatment was changed from 36 hours to 10 hours. The magnetic properties of the obtained R-T-B based sintered magnets (No. 1-1 and No. 1-2) were measured using a B-H tracer. The B _r and H _cJ of each sample were measured. The results are shown in Table 3.

As shown in Table 3, by carrying out the heating for 36 hours, a high _HcJ was obtained while suppressing the decrease in B _r .

The cross sections near the magnet surface of No. 1-1 (invention example) and No. 1-2 (comparison example) were observed with a scanning electron microscope (SEM: JEOL JCM-6000) to confirm the presence of a Tb-enriched layer in the main phase crystal grains. As a result, it was confirmed that in the invention example (No. 1-1), a thin Shar phase (RH-enriched layer) of the heavy rare earth element RH (Tb) is distributed in the outer periphery of the main phase in the surface layer region of the R-T-B sintered magnet, whereas in the comparison example (No. 2-1), it was confirmed that the heavy rare earth element RH (Tb) is diffused even near the center of the main phase in the surface layer region of the R-T-B sintered magnet.

In addition, when the amount of Tb in the center of the magnets of No. 1-1 and No. 1-2 was measured, Tb was measured in No. 1-1, but not in No. 1-2.

Experimental Example 2
An R-T-B based sintered magnet material No. 1-A in Example 1 was prepared. Then, diffusion source powders were prepared by atomizing alloy powders having the compositions shown in Nos. 2-a to 2-e in Table 3. The particle size of the obtained diffusion source powders was 106 μm or less.

Next, heat treatment (diffusion treatment) was performed in the same manner as in Example 1, except that the heating time was as shown in Table 5. Furthermore, a second heat treatment was performed on the R-T-B based sintered magnets after the diffusion treatment in the same manner as in Example 1, to obtain R-T-B based sintered magnets (Nos. 2-1 to 2-11). The magnetic properties of the obtained R-T-B based sintered magnets (Nos. 2-1 to 2-11) were measured for B _r and H _cJ using a B-H tracer. The results are shown in Table 5.

As shown in Table 5, when comparing the invention examples and comparative examples (Nos. 2-1 and 2-2, 2-3 and 2-4, 2-5 and 2-6, 2-7 and 2-8, and 2-9 and 2-10) using the same R-T-B based sintered magnet material and diffusion source powder, the invention examples all achieved higher _HcJ while suppressing the decrease in B _r . Also, comparing the invention examples No. 2-9 (heating time: 38 hours) and No. 2-11 (heating time: 45 hours), they have the same magnetic property levels. For this reason, the heating time is preferably 30 hours or more and 45 hours or less, and more preferably 30 hours or more and 40 hours or less.

The R-T-B based sintered magnets obtained through this disclosure can be suitably used in a variety of motors, such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EVs, HVs, PHVs, etc.), motors for industrial equipment, home appliances, etc.

Claims (3)

A step of preparing an R-T-B based _{sintered magnet material (T is Fe or Fe and Co) having, as a main phase, crystal grains of an R2Fe14B type} compound containing a light rare earth element RL (RL is at least one selected from the group consisting of Nd, Pr and Ce) as a main rare earth element R;
providing a diffusion source powder formed from a powder of an alloy including Tb, Nd, Pr, and Cu;
a step of contacting at least a part of the diffusion source powder with at least a part of the surface of the sintered R-T-B based magnet material;
a diffusion step in which the sintered R-T-B based magnet material in contact with the diffusion source powder is heat-treated at a temperature higher than 900°C and lower than 950°C for 30 hours to 45 hours, thereby diffusing the heavy rare earth element RH contained in the diffusion source powder from the surface to the inside of the sintered R-T-B based magnet material;
Including,
The step of contacting at least a portion of the diffusion source powder comprises:
applying an adhesive to a surface of the sintered R-T-B magnet material;
contacting the adhesive with the diffusion source powder;
Including,
In the method for producing a sintered RTB based magnet, the time for the heat treatment is measured from the point when the temperature of the sintered RTB based magnet material reaches a set temperature. The method for producing an R-T-B based sintered magnet according to claim 1, wherein in the diffusion step, the R-T-B based sintered magnet material in contact with the diffusion source powder is subjected to a heat treatment at a temperature equal to or lower than the sintering temperature of the R-T-B based sintered magnet material for 35 to 40 hours. The method for manufacturing an R-T-B based sintered magnet according to claim 1 or 2, wherein the dimension in the thickness direction of the R-T-B based sintered magnet material is 1 mm or more and 5 mm or less.