JP2010219499A - R-t-b based rare earth sintered magnet and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an R-T-B based rare earth sintered magnet for manufacturing an R-T-B based rare earth sintered magnet having high magnetic characteristics, especially, an excellent coercive force with a high yield. <P>SOLUTION: This method for manufacturing an R-T-B based rare earth sintered magnet includes: a treatment process for preparing treated alloy by carrying out HDDR treatment to R-T-B based raw material alloy; a crashing process for preparing alloy powder whose mean particle diameter is equal to or less than 2 μm by crushing the treated alloy; and a sintering process for preparing a sintered body by molding and sintering the alloy powder in a magnetic field. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an R-T-B rare earth sintered magnet and a method for manufacturing the same.

  An R-T-B rare earth sintered magnet (R is at least one element selected from rare earth elements including Y, and T is at least one element of Fe and Co) has excellent magnetic properties. Since Nd, a kind of rare earth element, is abundant in resources and relatively inexpensive, it is used in various electrical devices. The coercive force (HcJ), which is the main characteristic of this RTB-based rare earth sintered magnet, is improved by making the sintered body texture finer. Moreover, the corrosion resistance of the RTB-based rare earth sintered magnet can be improved by refining the sintered body structure.

  R-T-B rare earth sintered magnets are conventionally manufactured by molding and sintering an alloy powder having an average particle diameter of about 5 μm prepared by pulverization. The crystal grain size of the RTB-based rare earth sintered magnet greatly depends on the grain size of the alloy powder before sintering. Accordingly, in order to refine the sintered body structure, it is necessary to use an alloy powder having a smaller particle size.

  Generally, the alloy powder that is a raw material of the sintered body is an alloy produced by a so-called strip casting method in which a melt containing rare earth elements, transition metal elements, boron, and other additives is continuously cooled on a rotating roll. Is prepared by grinding. In the strip casting method, an alloy thin body (RTB-based rare earth compound) having a dendrite structure and a thickness of about 300 μm is formed.

  The columnar crystals forming this dendrite structure have a size of 4 μm or more even in the minor axis direction. For this reason, although it was possible to obtain an alloy powder having an average particle diameter of about 4 to 5 μm by pulverization from an alloy thin body prepared by the strip cast method, it is difficult to obtain an alloy powder finer than that. there were. Further, when classification is performed using a classifier or the like in order to obtain an alloy powder having a smaller average particle diameter, the alloy powder having a larger particle diameter is eliminated, resulting in a significant decrease in yield. It was.

  In order to improve the above problems, it is necessary to use an alloy having a finer structure, and the HDDR method has been proposed as one of the methods (for example, Patent Document 1).

  Conventionally, powder processed by the HDDR method is prone to grain growth if it is molded and sintered as it is, so that the structure of the R-T-B rare earth sintered magnet finally obtained can be sufficiently refined. However, it was difficult to improve magnetic properties such as coercive force. Therefore, it was necessary to use a specific sintering method such as hot pressing or electric current sintering.

JP-A-9-63878

  Accordingly, the present invention provides an RTB-based rare earth sintered magnet that can produce an RTB-based rare earth sintered magnet having high magnetic properties and particularly excellent coercive force in a high yield. It aims at providing the manufacturing method of a magnet. It is another object of the present invention to provide an RTB-based rare earth sintered magnet having high magnetic characteristics and particularly excellent coercive force.

  In order to achieve the above object, the present invention prepares an alloy powder having an average particle size of 2 μm or less by pulverizing the treated alloy by subjecting the RTB-based raw material alloy to HDDR treatment to prepare the treated alloy. Provided is a method for producing an RTB-based rare earth sintered magnet having a pulverization step and a sintering step in which an alloy powder is molded and sintered in a magnetic field to prepare a sintered body.

  According to the present invention, an RTB-based rare earth sintered magnet having excellent magnetic properties can be produced with high yield. The reason why such an effect can be obtained is as follows.

  In the present invention, the R-T-B type raw material alloy is subjected to HDDR treatment to refine crystal grains of the raw material alloy. A sufficiently fine alloy powder is prepared by further pulverizing the processed alloy obtained by the HDDR process. As described above, since sintering is performed using sufficiently fine alloy powder, the structure of the R-T-B rare earth sintered magnet can be refined, and the residual magnetic flux density can be maintained while being maintained. Magnetic force can be improved. Moreover, since both HDDR processing and pulverization are performed, the R-T-B type raw material alloy can be used effectively. Therefore, an R-T-B rare earth sintered magnet having high magnetic properties can be produced with a high yield.

  In the present invention, “R” is at least one element selected from rare earth elements including Y, and “T” is Fe and / or Co. That is, R is at least one element selected from Y (yttrium), La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  The production method of the present invention preferably has a hydrogen storage step of storing hydrogen in the treated alloy before the pulverization step. In the present invention, an R-T-B rare earth sintered magnet is produced through the HDDR-treated treated alloy and fine alloy powder. However, such treated alloy and alloy powder are highly active and easily nitrided. Or they tend to be oxidized. For this reason, it is effective to store hydrogen in the HDDR-processed alloy by the hydrogen storage process as described above. As a result, the active rare earth element is inactivated, and it becomes possible to reduce the formation of nitrides and oxides in the pulverization process and the sintering process, and the residual magnetic flux density of the R-T-B rare earth sintered magnet can be reduced. The coercive force can be further improved while maintaining.

  In the pulverization step of the production method of the present invention, the treated alloy is pulverized to prepare an alloy powder. As a result, it is possible to obtain an RTB-based rare earth sintered magnet having improved orientation and further excellent magnetic properties such as coercive force and residual magnetic flux density.

In the present invention, the constituent component is R (wherein R is at least one element selected from rare earth elements including Y), B, Zr, Co, Fe, and one or two of Al and Cu. The content of each element is
R: 25-37% by mass,
B: 0.5 to 4.5% by mass,
1 type or 2 types of Al and Cu: 0.02-0.5 mass%,
Zr: 0.03 to 0.5 mass%,
Co: 2% by mass or less (excluding 0% by mass),
Fe: the balance,
An RTB-based rare earth sintered magnet having an average grain size of 2 μm or less is provided.

  Such an R-T-B rare earth sintered magnet has an excellent coercive force because it has a suitable composition for realizing high magnetic properties and has sufficiently fine crystal grains. It becomes.

  According to the present invention, an RTB-based rare earth sintered magnet having high magnetic properties and capable of producing an RTB-based rare earth sintered magnet having a particularly excellent coercive force with a high yield is provided. A method for manufacturing a magnet can be provided. In addition, according to the present invention, it is possible to provide an RTB-based rare earth sintered magnet having high magnetic characteristics and particularly excellent coercive force.

It is an electron micrograph which shows an example of the microstructure of the RTB system rare earth sintered magnet which concerns on this embodiment. It is an electron micrograph which shows an example of the microstructure of the conventional RTB system rare earth sintered magnet.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. The manufacturing method of the RTB-based rare earth sintered magnet of the present embodiment includes a preparation step of preparing an RTB-based raw material alloy, and an HDDR process applied to the RTB-based raw material alloy. The HDDR treatment process for preparing the HDDR powder, the hydrogen storage process for storing the hydrogen gas in the HDDR powder, and the grinding for obtaining the alloy powder having an average particle size of 2 μm or less by pulverizing the HDDR powder stored with the hydrogen gas. A step, a sintering step in which the alloy powder is molded and sintered in a magnetic field to obtain a sintered body, and an aging treatment step in which an aging treatment is performed on the sintered body. Details of each step will be described below.

  In the preparation step, an RTB-based raw material alloy which is an RTB-based rare earth compound is prepared by, for example, a strip casting method. The composition of the RTB-based raw material alloy may be the same as that of the finally obtained RTB-based rare earth sintered magnet. Moreover, when employ | adopting 2 alloy method, you may prepare two types of RTB type raw material alloys from which a composition differs. The composition and blending ratio of the RTB-based raw material alloy can be changed as appropriate according to the composition of the target RTB-based rare earth sintered magnet.

  The method for preparing the RTB-based material alloy is not limited to the strip casting method, and for example, a known melting method may be used.

  In the HDDR processing step, HDDR powder (treated alloy) is prepared by subjecting the RTB-based material alloy prepared in the preparation step to HDDR processing. HDDR (Hydrogenation Decomposition Resorption Recombination) can be performed in two stages, for example, (i) hydrogen storage treatment and (ii) dehydrogenation treatment.

  (I) In the hydrogen storage treatment, the RTB-based raw material alloy is held in a hydrogen gas atmosphere at a temperature of 700 to 900 ° C. for 0.5 to 5 hours. As a result, the RTB-based raw material alloy undergoes phase decomposition.

  (Ii) In the dehydrogenation treatment, nitrogen gas is introduced to lower the partial pressure of the hydrogen gas to, for example, 100 Pa or less, and hydrogen is removed from the phase-decomposed RTB-based material alloy. By the dehydrogenation treatment, the RTB-based material alloy is recrystallized.

  The processing conditions such as the temperature and time of the above (i) hydrogen storage treatment and (ii) dehydrogenation treatment can be adjusted according to the composition of the RTB-based material alloy. In addition, when using two or more types of HDDR powders having different compositions, the HDDR process may be performed separately or the HDDR process may be performed together. The HDDR powder obtained by the HDDR process has a texture in which a plurality of recrystallized particles having a particle size of 1 μm or less are gathered.

  In the hydrogen occlusion process, the HDDR powder is occluded with hydrogen by holding the HDDR powder in a hydrogen gas atmosphere. The hydrogen storage step is preferably performed under the conditions of a pressure of 0.05 to 0.25 MPa, a temperature of 20 to 100 ° C., and a holding time of 0.5 to 5 hours in a hydrogen gas atmosphere.

  In the pulverization step, the HDDR powder obtained in the hydrogen storage step is pulverized to prepare an alloy powder. In the pulverization step, the HDDR powder is pulverized in a low oxygen atmosphere until the average particle size becomes 2 μm or less. The average particle diameter of the pulverized alloy powder is 2 μm or less, preferably 1.8 μm or less. Although there is no restriction | limiting in particular in the minimum of the average particle diameter of alloy powder, From a viewpoint of process shortening, Preferably it is 0.5 micrometer or more, More preferably, it is 1.0 micrometer or more. In addition, the average particle diameter of the alloy powder in this embodiment is a volume average particle diameter measured using a commercially available particle size distribution meter.

  The pulverization is preferably performed by adding an additive such as zinc stearate or oleic acid amide in an amount of about 0.01 to 0.3% by mass based on the HDDR powder. Thereby, the orientation at the time of shaping | molding alloy powder can be improved. For the pulverization, a jet mill, ball mill (dry / wet), vibration mill, wet attritor or the like can be used.

  For example, when using a jet mill, coarse grain classification can be performed by using a jet mill equipped with a classifier. Thereby, an alloy powder having a desired average particle size can be easily prepared. In the pulverization method using a jet mill, a high-pressure inert gas (for example, nitrogen gas) is released from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates coarse HDDR powder. This is a method of pulverizing by generating a collision between each other or a target or a container wall.

  In the pulverization step, when plural types of HDDR powders having different compositions are pulverized separately, the pulverized alloy powder is preferably mixed using, for example, a Nauter mill.

In the sintering process, first, the alloy powder prepared in the pulverization process is molded in a magnetic field to produce a compact. Molding in a magnetic field may be performed by pressing at 69 to 196 MPa (0.7 to 2.0 t / cm ² ) in a magnetic field of 955 to 1353 kA / m (12.0 to 17.0 kOe), for example.

  Next, the compact is sintered in a vacuum or an inert gas atmosphere to produce a sintered body. For example, the sintering temperature and the sintering time can be set to 900 to 1100 ° C. and 1 to 5 hours, respectively. Since the sintering conditions in the sintering process greatly affect the coercive force (HcJ) of the R-T-B rare earth sintered magnet, the sintering conditions are appropriately selected according to the composition, pulverization method, particle size, particle size distribution, and the like. It is preferable to set.

  In the aging treatment step, an R-T-B rare earth sintered magnet is obtained by holding the sintered body at a predetermined temperature in a vacuum or an inert gas atmosphere for a predetermined time. The aging treatment may be a two-stage treatment that is held at a temperature of about 800 ° C. and about 500 ° C. for a predetermined time (for example, 0.1 to 5 hours), respectively. (5 hours) It is good also as a 1 step process to hold | maintain. By performing the aging treatment, the coercive force of the RTB-based rare earth sintered magnet can be further improved.

  The RTB-based rare earth sintered magnet obtained by the above-described manufacturing method has a sufficiently fine structure and has excellent magnetic properties (particularly coercive force). In the manufacturing method of the above-described embodiment, an RTB-based rare earth sintered magnet having excellent magnetic properties can be obtained with a high yield. For this reason, the manufacturing method according to the above embodiment has a good yield and is particularly suitable for mass production. In addition, in the manufacturing method of the R-T-B type rare earth sintered magnet of the present embodiment, the atmosphere in each process from the HDDR treatment process to the sintering process is a low oxygen atmosphere having an oxygen concentration of less than 100 ppm. It is preferable.

  Next, a preferred embodiment of the RTB-based rare earth sintered magnet of the present invention will be described. The RTB-based rare earth sintered magnet of this embodiment can be obtained by the above-described manufacturing method. The RTB-based rare earth sintered magnet according to the present embodiment has R as a constituent component (where R is at least one element selected from rare earth elements including Y), B, Zr, and Co. Fe, and one or two of Al and Cu. Here, the “constituent component” is a main component included in the RTB-based rare earth sintered magnet and refers to a component that contributes to the improvement of magnetic properties. That is, the RTB-based rare earth sintered magnet according to the present embodiment may contain inevitable impurities different from the above-described constituents as long as the effect of having an excellent coercive force is not impaired.

  In this R-T-B rare earth sintered magnet, the content of R is 25 to 37% by mass, preferably 28 to 35% by mass, and more preferably 29 to 33% by mass. In addition, “mass%” of each element in the RTB-based rare earth sintered magnet is a mass ratio with respect to the entire RTB-based rare earth sintered magnet.

When the content of R is less than 25% by mass, the amount of R ₂ T ₁₄ B phase, which is the main crystal phase of the R-T-B rare earth sintered magnet, decreases, and α-Fe having soft magnetism Etc. are likely to precipitate, and the excellent coercive force is impaired. On the other hand, when R exceeds 37% by mass, the volume ratio of the R ₂ T ₁₄ B phase, which is the main crystal phase, decreases, and the residual magnetic flux density decreases. In addition, the oxygen content increases due to the reaction between R and oxygen, and accordingly, the R-rich phase effective for improving the coercive force tends to decrease.

  Since Nd and Pr are abundant in resources and relatively inexpensive, the R-T-B rare earth sintered magnet preferably contains at least one element of Nd and Pr as R, and particularly contains Nd. Is preferred. From the viewpoint of improving the coercive force, it is preferable that R includes one or more heavy rare earth elements selected from Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  The content of boron (B) in the R-T-B rare earth sintered magnet is 0.5 to 4.5 mass%, preferably 0.5 to 1.5 mass%, more preferably 0. .8 to 1.2% by mass. When B is less than 0.5% by mass, excellent coercive force is impaired, and when B exceeds 4.5% by mass, the residual magnetic flux density is lowered.

  The content of Zr in the R-T-B rare earth sintered magnet is 0.03 to 0.50 mass%, preferably 0.05 to 0.2 mass%, more preferably 0.1 to 0.1 mass%. 0.15% by mass. Zr contributes to the refinement of the structure because it has the effect of suppressing abnormal grain growth in the sintering process. If Zr is less than 0.03% by mass, the effect of suppressing grain growth cannot be obtained, and if it exceeds 0.50% by mass, high magnetic properties cannot be obtained.

  The RTB-based rare earth sintered magnet contains 0.02 to 0.5 mass% in total of at least one of Al and Cu. When at least one of Al and Cu is contained within this range, the coercive force can be increased, and the corrosion resistance and temperature characteristics can be improved. When Al is contained, the content of Al is preferably 0.03 to 0.3% by mass, and more preferably 0.05 to 0.25% by mass. Moreover, when it contains Cu, content of Cu becomes like this. Preferably it is 0.15 mass% or less (0 is not included), More preferably, it is 0.03-0.12 mass%.

  The content of Co in the RTB-based rare earth sintered magnet is 2% by mass or less (not including 0), preferably 0.1 to 1.0% by mass, more preferably 0.3. It is -0.7 mass%. Co forms the same phase as Fe, but by containing Co, the Curie temperature and the corrosion resistance of the grain boundary phase can be improved.

  The RTB-based rare earth sintered magnet according to the present embodiment is an inevitable impurity in addition to one or two of the above-described R, B, Zr, Co, Fe and Al and Cu, which are essential elements. May be included.

  The content of oxygen (O) in the RTB-based rare earth sintered magnet is preferably as low as possible, and it is more preferable that the RTB-based rare earth sintered magnet does not contain any oxygen. However, it is difficult to manufacture an RTB-based rare earth sintered magnet that does not contain oxygen at all in the manufacturing process. From such a viewpoint, the oxygen content is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and further preferably 0.1% by mass or less.

  The RTB-based rare earth sintered magnet may contain another element different from the above-mentioned essential elements as long as the effect of having an excellent coercive force is not impaired. For example, the coercive force can be further improved by containing Ga in an amount of 0.1 to 0.5% by mass. Examples of elements other than Ga include elements such as Ti, Bi, Sn, Nb, Ta, Si, V, Ag, and Ge. However, from the viewpoint of maintaining high magnetic properties, the content of elements other than Ga is preferably 1% by mass or less, more preferably 0.5% by mass or less, in total.

  The average grain size of the crystal grains of the RTB-based rare earth sintered magnet of the present embodiment is 2 μm or less, more preferably 1.8 μm or less. The lower limit of the average grain size of the crystal grains of the R-T-B rare earth sintered magnet is not particularly limited, but is preferably 0.5 μm or more from the viewpoint of ease of manufacture. The average grain size of the R-T-B rare earth sintered magnet of the present embodiment is the average grain size of the crystal grains in a 50 μm × 50 μm field of view on the observation screen of a scanning electron microscope magnified 2000 times. It can be obtained as a value.

  FIG. 1 is an electron micrograph showing an example of the microstructure of the RTB-based rare earth sintered magnet according to the present embodiment. This RTB-based rare earth sintered magnet is manufactured by the above-described manufacturing method, and the average grain size of crystal grains is 2 μm or less.

  FIG. 2 is an electron micrograph showing an example of the microstructure of a conventional RTB-based rare earth sintered magnet. The R-T-B rare earth sintered magnet shown in FIG. 2 is manufactured using an alloy powder having an average particle diameter of 3 μm obtained by pulverization with a jet mill without performing HDDR treatment. The average particle size exceeds 2 μm.

  Comparing FIG. 1 and FIG. 2, the RTB-based rare earth sintered magnet of the present embodiment is composed of crystal grains that are sufficiently finer than the conventional one. Since it has such a fine structure, the RTB-based rare earth sintered magnet of this embodiment has an excellent coercive force.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, the pulverization step may be performed subsequent to the HDDR treatment step without performing the hydrogen storage step.

  The content of the present invention will be described in more detail using examples and comparative examples, but the present invention is not limited to the following examples.

[Production of RTB-based rare earth sintered magnet]
Example 1
<Preparation process>
An RTB-based material alloy a having the following composition was prepared by a strip casting method.
Nd: 29% by mass
Dy: 1.0 mass%
Co: 1.0 mass%
Cu: 0.1% by mass
Al: 0.1% by mass
Zr: 0.2% by mass
B: 1.0% by mass
Fe and inevitable impurities: balance

  The above-mentioned RTB-based raw material alloy a contained unavoidable impurities (total of 0.1% by mass or less).

<HDDR processing step>
The prepared R-T-B type raw material alloy a was subjected to HDDR treatment to prepare HDDR powder. Specifically, first, the RTB-based raw material alloy a was hydrophase decomposed by holding in a hydrogen gas atmosphere at 800 ° C. for 1 hour. Next, after introducing Ar gas and switching the atmosphere to Ar gas, evacuation is performed to reduce the processing atmosphere under reduced pressure and hold at 800 ° C. for 1 hour to perform dehydrogenation treatment, thereby recrystallized particles. HDDR powder was obtained. The HDDR powder had a texture composed of a plurality of recrystallized particles having a particle size of about 0.2 to 1 μm.

<Hydrogen storage process>
The HDDR powder was held in a hydrogen gas atmosphere under conditions of a pressure of 0.1 MPa and room temperature for 2 hours, and the HDDR powder was allowed to occlude hydrogen.

<Crushing process>
Zinc stearate is added to HDDR powder occluded with hydrogen in an amount of 0.1% by mass based on the entire HDDR powder, and finely pulverized by a jet mill equipped with a classifier using high-pressure nitrogen gas. An alloy powder of 1.5 μm was obtained. The average particle diameter of the alloy powder was measured as a volume average particle diameter using a particle size distribution measuring device (trade name: HELOS & RODOS, manufactured by Nippon Laser Co., Ltd.).

<Sintering process>
The obtained alloy powder was subjected to pressure molding at 147 MPa (1.5 ton / cm ² ) in a magnetic field of 1200 kA / m (15 kOe) to obtain a compact. This molded body was heated in vacuum at 950 to 1050 ° C. for 4 hours to obtain a sintered body. Note that the processing step to the pulverization step were performed in a low oxygen atmosphere.

  The obtained sintered body was subjected to an aging treatment in an Ar atmosphere at 500 ° C. for 1 hour to obtain an RTB-based rare earth sintered magnet of Example 1.

(Example 2)
A sintered body was prepared in the same manner as in Example 1 except that the hydrogen storage step was not performed, and an RTB-based rare earth sintered magnet of Example 2 was obtained.

(Comparative Example 1)
By changing the classification rotation speed of the classifier in the pulverization step, preparing an alloy powder having an average particle size of 2.5 μm, and performing the sintering step using the alloy powder, the same as in Example 1, An R-T-B rare earth sintered magnet of Comparative Example 1 was obtained.

(Comparative Example 2)
By changing the classification rotation speed of the classifier in the pulverization step, preparing an alloy powder having an average particle size of 4.5 μm, and performing the sintering step using the alloy powder, the same as in Example 1, An R-T-B rare earth sintered magnet of Comparative Example 2 was obtained.

(Comparative Example 3)
The same as in Example 1 except that the HDDR treatment was not performed, the classification rotation speed was changed in the pulverization step, an alloy powder having an average particle size of 2.1 μm was prepared, and the sintering step was performed using the alloy powder. Thus, an R-T-B rare earth sintered magnet of Comparative Example 3 was obtained.

(Comparative Example 4)
The same as in Example 1 except that the HDDR treatment was not performed, the classification rotation speed was changed in the pulverization step, an alloy powder having an average particle size of 3.2 μm was prepared, and the sintering step was performed using the alloy powder. Thus, an R-T-B rare earth sintered magnet of Comparative Example 4 was obtained.

(Comparative Example 5)
The same as in Example 1 except that the HDDR treatment was not performed, the classification rotation speed was changed in the pulverization step, an alloy powder having an average particle size of 4.3 μm was prepared, and the sintering step was performed using the alloy powder. Thus, an R-T-B rare earth sintered magnet of Comparative Example 5 was obtained.

Example 3
An RTB-based material alloy b having the following composition was prepared by a strip casting method.
Nd: 31.0% by mass
Co: 1.0 mass%
Cu: 0.1% by mass
Al: 0.1% by mass
Zr: 0.2% by mass
B: 1.0% by mass
Fe and inevitable impurities: balance

  The above-described RTB-based material alloy b contained inevitable impurities (total of 0.1% by mass or less). The same as in Example 1 except that the HDDR treatment process was performed using this RTB-based material alloy b and the sintering process was performed using an alloy powder having an average particle size of 1.3 μm. Thus, the RTB-based rare earth sintered magnet of Example 3 was produced. The average particle size of the alloy powder was adjusted by changing the classification rotation speed in the pulverization step.

Example 4
In the same manner as in Example 3 except that the classifying rotation speed of the classifier in the pulverizing process was changed to prepare an alloy powder having an average particle size of 1.7 μm and the sintering process was performed using the alloy powder. The RTB system rare earth sintered magnet of Example 4 was produced.

(Example 5)
An RTB-based material alloy c having the following composition was prepared by a strip casting method.
Nd: 31.2% by mass
Co: 1.0 mass%
Cu: 0.1% by mass
Al: 0.2 mass%
Zr: 0.2% by mass
B: 1.0% by mass
Ga: 0.3% by mass
Fe and inevitable impurities: balance

  The above-mentioned RTB-based raw material alloy c contained inevitable impurities (total of 0.1% by mass or less). The same as Example 1 except that the HDDR treatment process was performed using this RTB-based material alloy c and the sintering process was performed using an alloy powder having an average particle size of 1.24 μm. Thus, the RTB-based rare earth sintered magnet of Example 5 was produced. The average particle size of the alloy powder was adjusted by changing the classification rotation speed in the pulverization step.

(Example 6)
An RTB-based material alloy d having the following composition was prepared by a strip casting method.
Nd: 31.0% by mass
Co: 1.0 mass%
Cu: 0.1% by mass
Al: 0.3% by mass
Zr: 0.2% by mass
B: 1.0% by mass
Fe and inevitable impurities: balance

  The above-described RTB-based material alloy d contained inevitable impurities (total of 0.1% by mass or less). The same as Example 1 except that the HDDR treatment process was performed using this R-T-B system raw material alloy d and the sintering process was performed using an alloy powder having an average particle diameter of 1.25 μm. Thus, the RTB-based rare earth sintered magnet of Example 6 was produced. The average particle size of the alloy powder was adjusted by changing the classification rotation speed in the pulverization step.

[Evaluation of microstructure]
The cross sections of the R-T-B rare earth sintered magnets of Examples and Comparative Examples prepared as described above were observed with a scanning electron microscope (SEM, magnification: 2000 times). On the SEM observation screen, the particle size of particles in a 50 μm × 50 μm field of view was measured, and the average value of the measured values was used as the crystal particle size of each R-T-B rare earth sintered magnet. The results are shown in Table 1.

[Evaluation of magnetic properties]
Using a B—H tracer, Br (residual magnetic flux density) and HcJ (coercive force) of the rare earth sintered magnets obtained in the respective Examples and Comparative Examples were measured. The obtained results are summarized in Table 1.

  From the results shown in Table 1, the R-T-B rare earth sintered magnets of Examples 1 to 6 have fine crystal grains and have an excellent coercive force while maintaining a sufficient residual magnetic flux density. Was. Moreover, in Examples 1-6, the RTB system rare earth sintered magnet was able to be obtained with a sufficiently high yield. Here, the yield is a value calculated as a mass ratio of the final product (R-T-B system rare earth sintered magnet) to the used material (R-T-B system material alloy).

  On the other hand, the RTB-based rare earth sintered magnets of Comparative Examples 1 and 2 had a large crystal grain size, and the coercive force was inferior to those of Examples 1 and 2. Further, in Comparative Examples 3 to 5 in which the alloy powder was prepared without performing the HDDR process to produce the RTB-based rare earth sintered magnet, it is difficult to sufficiently refine the alloy powder. The diameter became larger than Examples 1-6. Moreover, since the amount of the alloy powder excluded in the pulverization process was large, the yield was low.

Claims (3)

An R-T-B type raw material alloy (R is at least one element selected from rare earth elements including Y, and T is at least one element of Fe and Co) is HDDR processed to prepare a processed alloy. Processing steps to
Crushing the treated alloy to prepare an alloy powder having an average particle size of 2 μm or less;
And a sintering step of preparing the sintered body by forming the alloy powder in a magnetic field and sintering it, and a method for manufacturing the RTB-based rare earth sintered magnet.   The manufacturing method according to claim 1, further comprising a hydrogen storage step of storing hydrogen in the treated alloy before the crushing step. As a constituent component, R (wherein R is at least one element selected from rare earth elements including Y), B, Zr, Co, Fe, and one or two of Al and Cu, Elemental content is
R: 25-37% by mass,
B: 0.5 to 4.5% by mass,
1 type or 2 types of Al and Cu: 0.02-0.5 mass%,
Zr: 0.03 to 0.5 mass%,
Co: 2% by mass or less (excluding 0% by mass),
Fe: balance, R-T-B rare earth sintered magnet having an average grain size of 2 μm or less.