JPH06283318A - Manufacture of rare-earth permanent magnet - Google Patents

Abstract

PURPOSE:To reduce the impurity phase of a main phase forming alloy so as to obtain high magnetic characteristics by mixing the powder of an R-T-B alloy composed mainly of R2T14B of an R-T-B permanent magnet with the powder of an R-T alloy containing a large amount of R and having a low melting point. CONSTITUTION:In the manufacturing method of an R-T-B rare-earth permanent magnet constituted mainly of a main phase composed mainly of an R2T14B intermetallic compound (R represents one or two or more kinds of rare-earth elements including Y and T represents one or two or more kinds of transition metals), the magnet is manufactured by mixing the powder of an R-T alloy containing >=45wt.% R in the powder of an R-T-B alloy containing 1.0-1.20wt.% B and 25-30wt.% R by 8-15wt.% and molding the mixture. Then the molded body is sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing an RTB-based rare earth permanent magnet containing a rare earth element R, a transition metal T and boron B as main components.

[0002]

2. Description of the Related Art When an RTB rare earth permanent magnet is manufactured by a powder metallurgical method, it is generally manufactured by steps such as weighing of raw materials, making an ingot by melting, crushing, molding, sintering and heat treatment. The dissolution is performed in Ar or in vacuum. The pulverization is divided into coarse pulverization and fine pulverization depending on the process. Coarse crushing is performed with a stamp mill, jaw crusher, brown mill, disk mill, and fine crushing is performed with a jet mill, vibration mill, ball mill, or the like. Both are performed in a non-oxidizing atmosphere using an organic solvent or an inert gas to prevent oxidation. For forming, vertical magnetic field forming (pressurizing direction and magnetic field applying direction are parallel) or horizontal magnetic field forming (pressurizing direction and magnetic field applying direction are vertical) are used for improving orientation degree and anisotropy. Sintering is performed in an inert gas such as Ar or He or in a vacuum. The heat treatment is performed in the range of 400 to 800 ° C., though it depends on the type and composition of the element used.

The structure of the magnet manufactured by the powder metallurgical method as described above is mainly composed of the main phase R ₂ T ₁₄ B phase, a non-magnetic phase called R rich phase, and RT ₄ B called B rich phase. _Four
Phase and R oxide phase. As for the magnetic characteristics, a high residual magnetic flux density Br and a high coercive force iHc are realized by surrounding the R ₂ T ₁₄ B phase, which is the main phase responsible for magnetism, with a non-magnetic R rich phase and separating the magnetic coupling. . The B-rich phase and the R oxide phase play a role of suppressing grain growth and increasing coercive force.

[0004]

An ideal structure for obtaining high magnetic properties is a structure in which the R-rich phase evenly surrounds the R ₂ T ₁₄ B phase in a thin and fine structure. It is necessary to approach a structure that satisfies the conditions such that the crystal grain size is uniform and the R ₂ T ₁₄ B phase, which is a magnetic phase, has a high volume occupancy.
However, the sintering is liquid phase sintering in which the R-rich phase having a low melting point becomes a liquid phase to accelerate the sintering, and in the conventional method, a relatively high temperature is required to improve the sinterability. It was However, when the sintering temperature is raised, crystal grains grow and the residual magnetic flux density Br improves, but the structure becomes non-uniform and the coercive force iHc and squareness deteriorate. Conversely, if the sintering temperature is lowered, the sinterability is lowered, and the coercive force iHc and the squareness are improved, but Br is lowered. In any case, the maximum energy product (B
H) _Does not improve _max .

As a countermeasure for this, Japanese Patent Publication No. 1-19461
No. ₂ has a low R content with R ₂ T ₁₄ B as the main phase.
An R-T-B alloy powder (R-rich phase forming alloy powder) having a higher R content and a lower melting point than the alloy powder is separately prepared and mixed with the B alloy powder (main phase forming alloy powder). There is a proposal of a manufacturing method using the alloy powder. This is because by using the RTB-based alloy powder having a low melting point, the sintering temperature is lowered without impairing the sinterability, iHc is improved without sacrificing Br, and the maximum energy product (BH )
_It improves _max . However, such low R and high R
In the production method of producing and mixing the two types of alloy powders, the soft magnetic phase such as α-Fe or R rich phase is generated because the peritectic reaction in the solidification process of the main phase forming alloy having low R is incomplete. Crystallization occurs and magnetic properties are deteriorated.

That is, a manufacturing method using a mixed powder of the main phase forming alloy powder and the R-rich phase forming alloy powder is effective for improving the magnetic properties, but at the same time, α- which crystallizes in the main phase forming alloy. It is important to reduce impurity phases other than R ₂ T ₁₄ B phase, which is the main phase, such as Fe, R-rich phase (RT), B-rich phase (RT ₄ B ₄ ). In order to reduce this impurity phase, it is considered that the main phase forming alloy is subjected to heat treatment for solid phase diffusion (hereinafter referred to as homogenization treatment).
The effect of disappearance of these impurity phases greatly differs depending on the composition. That is, the composition of the main phase forming alloy must be set within a range in which the diffusion effect by the heat treatment of impurities is large. In view of the above problems, it is an object of the present invention to reduce the impurity phase of the main phase forming alloy and obtain high magnetic properties.

[0007]

The inventors of the present invention have found that the impurity phase such as α-Fe crystallized in the main phase forming alloy is B in the alloy.
Amount and R amount are 1.0 wt% ≦ B ≦ 1.2 wt%, 25 wt% ≦ R ≦ 3
It was found that if it is set to 0 wt%, most of it can be eliminated by solid phase diffusion by homogenization treatment. Further, in order to set the composition of the main phase forming alloy within the above range, it is necessary to add no B to the R rich phase forming alloy in order to suppress the excessive generation of the non-magnetic B rich phase. I found out that. Further, by using the RT alloy powder as the R-rich phase forming alloy,
It has been found that the sintering can be performed at a temperature lower than that of the conventional one, so that it is possible to control to bring the structure closer to an ideal structure. That is, the present invention relates to a main phase mainly composed of an R ₂ T ₁₄ B-based intermetallic compound (R is one or more kinds of rare earth elements including Y, T is one or more kinds of transition metals) and R
In the method for manufacturing an RTB rare earth permanent magnet having a rich phase as a main constituent phase, 1.0 wt% ≦ B ≦ 1.20 wt
%, 25 wt% ≤ R ≤ 30 wt% R-T-B alloy powder to 45 wt% ≤ R RT alloy powder 8 to 1
This is a method for producing a rare earth permanent magnet, which is formed and sintered after being added and mixed in the range of 5 wt%.

In the present invention, T of the RT alloy powder is preferably Fe. R-T-B type alloy powder and R-
Regarding the mixing method of the T-based alloy powder, coarsely crushed R-
The T-B alloy powder and the R-T alloy powder are mixed and then finely pulverized, followed by molding, or the coarsely crushed R-T-B alloy powder and R-T alloy powder are finely pulverized, After that, it is preferable to mix and mold either.

[0009]

In the present invention, the main phase forming alloy RT-
By limiting the composition of the B-based alloy powder, it is possible to reduce the impurity phases such as the α-Fe phase, and the composition of the main phase forming alloy becomes approximately R ₂ T ₁₄ B. To limit the composition of the main phase forming alloy to the range of the present invention, R-rich phase forming alloy is
It is necessary to use an RT alloy powder that does not include If B is added to the RT alloy powder, B becomes excessive as a whole composition after mixing the RTB alloy powder and the RT alloy powder, so that B rich phase (RT ₄ B ₄ phase ) Is generated and coarsens. Since R is consumed to generate the B-rich phase, R becomes deficient, and the Nd-rich phase that effectively functions as a liquid phase decreases, so the magnetic characteristics are not improved. Also, by separately preparing and using an RT-T alloy powder having a low melting point and a high R content, the RT phase necessary for liquid phase sintering can be effectively utilized and the sintering temperature can be lowered. Further, it becomes easy to control and homogenize the structure such as the crystal grain size after sintering, and the coercive force can be improved without reducing the residual magnetic flux density Br so much.

The B content and R content in the main phase forming alloy are 1.0 wt% ≦ B ≦ 1.2 wt% and 25 wt% ≦ R ≦ 3.
Set to 0 wt%. When the amount of B is less than the above range, α-Fe is not diffused unless the homogenization treatment is performed for a long time, and an impurity phase such as the R ₂ T ₁₇ phase of the soft magnetic phase is precipitated, which is a factor that deteriorates the magnetic properties. Becomes When the amount of B exceeds the above range, a B-rich phase (RT ₄ B ₄ phase) is generated, and R is consumed for this generation, so that R becomes deficient and α-Fe is easily generated. That is, when the amount of B exceeds the above range, the impurity phase such as α-Fe phase is likely to crystallize as in the case of decreasing R,
Even if a homogenizing treatment by heat treatment is performed, it cannot be completely diffused, which causes a decrease in magnetic characteristics. Therefore, 1.0 wt%
≦ B ≦ 1.2 wt% is set. Next, when the amount of R is less than the above range, the amount of α-Fe crystallized increases, and when the amount of R exceeds the above range, a large amount of fine R-rich phase remains, and the oxidation becomes severe in the subsequent pulverization process. Any of these causes deterioration of magnetic characteristics. Therefore, 25 wt% ≦ R ≦ 3
It is set to 0 wt%.

The R content of the R-rich phase forming alloy is 45% by weight.
That is all. This is because if R is less than 45 wt%, the liquid phase required for sintering is insufficiently formed and a dense sintered body cannot be obtained. As the transition metal T which is a component of the R-rich phase forming alloy, conventionally used Fe, Co, Ni and the like can be used, but Ni tends to deteriorate the sinterability and reduce the magnetic properties. Fe and Co are desirable. As described above, the mixing amount of the powder of the R-rich phase forming alloy with the RT alloy powder is 8 to 15 wt% with respect to the RTB alloy powder which is the main phase forming alloy in which the R amount and the B amount are set. To do. When the mixing amount of the RT alloy powder is reduced so that the total R amount after mixing becomes constant, the sinterability,
The coercive force iHc decreases, and when it is less than 8 wt%, the decrease is remarkable. Therefore, the mixing amount is 8 wt% or more. Also, R
When the mixing amount is increased to increase the rich phase, iH
Although c increases, if it exceeds 15 wt%, the effect of improving iHc decreases and Br decreases remarkably. Therefore, the mixing amount of the R-rich phase is set in the range of 8 to 15 wt%.

Regarding the mixing method of the R-T-B type alloy powder and the R-T type alloy powder, each alloy is roughly pulverized, then mixed at a predetermined ratio, and further finely pulverized, and each alloy is finely pulverized. It is desirable to use one of the methods of later mixing to a predetermined ratio. Both mixing methods have their respective advantages. The former tends to increase the density and the residual magnetic flux density Br is high, and the latter is difficult to increase the density, but the coercive force iHc is high.

[0013]

EXAMPLES Example 1 Main phase forming alloys having different B contents shown in Table 1 (indicated as main phase in the table) by Nd, B having a purity of 95% or more and electrolytic iron and by high frequency melting, and R A rich phase forming alloy (indicated as R phase in the table) was prepared.

[0014]

[Table 1]

Of the ingots, each of the main phase forming alloys was homogenized at 1100 ° C. × 20 H and coarsely pulverized to obtain an R-T-B type alloy powder having an average particle size of 15 to 25 μm. After melting and cooling the R-rich phase forming alloy,
This was coarsely pulverized to obtain an RT-T alloy powder having an average particle size of 15 to 25 μm. The RT alloy powder was mixed with the RT alloy powder at a compounding ratio of 10 wt%, and this was finely pulverized by a jet mill using N ₂ as a pulverizing medium so that the average particle diameter was 2 to 5 μm. The obtained finely pulverized powder was subjected to transverse magnetic field molding in a magnetic field of 10 KOe at a molding pressure of ² ton / cm ² . The compact was sintered in vacuum at 1080 ° C. × 2H. The sintered body was subjected to a primary heat treatment of 900 ° C x 2H in an Ar atmosphere and then 6
A second heat treatment of 00 ° C. × 1H was performed. Table 2 shows the measurement results of the magnetic properties of the permanent magnets obtained by the above procedure and using the main phase forming alloys having different B contents. The permanent magnets produced by the production method of the present invention all have high magnetic characteristics, and in particular, the amount of B in the main phase forming alloy is 1.0 to 1.2 w.
Remarkably high magnetic properties are obtained in the range of t%.

[0016]

[Table 2]

(Example 2) Nd and D having a purity of 95% or more
The main phase forming alloys shown in Table 3 and the R rich phase forming alloys having different R contents were produced by high frequency melting using y, B and electrolytic iron.

[0018]

[Table 3]

Using such an ingot, an RTB alloy powder was prepared in the same manner as in Example 1, and the RT alloy powder was mixed at a compounding ratio of 10 wt%. This was finely pulverized by a jet mill using N ₂ as a pulverizing medium so that the average particle size was 2 to 5 μm. The obtained finely pulverized powder was subjected to transverse magnetic field molding in a magnetic field of 10 KOe at a molding pressure of ² ton / cm ² . The compact was sintered in vacuum at 1080 ° C. × 2H. Sintered body is A
60 after performing a primary heat treatment of 900 ° C x 2H in an r atmosphere
A secondary heat treatment of 0 ° C. × 1H was performed. Table 4 shows the measurement results of the magnetic properties and sintered body densities of the permanent magnets having different R contents in the R-rich phase forming alloy obtained by the above procedure.
As shown in Table 4, if the R amount is 45 wt% or more, it can be used as a permanent magnet, but if it is less than 45 wt%, it does not shrink and cannot be used as a permanent magnet.

[0020]

[Table 4]

(Example 3) Nd and D having a purity of 95% or more
Main phase forming alloys shown in Table 5 and R rich phase forming alloys were produced by high frequency melting using y, B and electrolytic iron.

[0022]

[Table 5]

The RTB alloy powder was prepared in the same manner as in Example 1, and the RT alloy powder was mixed at a compounding ratio of 10 wt%. This was finely pulverized by a jet mill using N ₂ as a pulverizing medium so that the average particle size was 2 to 5 μm. The finely pulverized powder obtained is molded under a magnetic field of 10 KOe at a molding pressure of 2 ton / c.
Transverse magnetic field molding was performed at m ² . Molded body is 1100 ° C in vacuum
Sintering was performed at 2H. 900 ° C in Ar atmosphere
After the primary heat treatment of × 2H, the secondary heat treatment of 600 ° C. × 1H was performed. Table 6 shows the mixing ratios and the measurement results of the magnetic properties of the obtained permanent magnets. From Table 6, Ni in the RT type alloy powder
It can be seen that the coercive force is reduced by adding.

[0024]

[Table 6]

(Example 4) Nd and D having a purity of 95% or more
Main phase forming alloys shown in Table 7 and R rich phase forming alloys were produced by high frequency melting using y, B and electrolytic iron.

The RTB-based alloy powder was prepared in the same manner as in Example 1, and the RTB alloy powder had a total R content of 29.
Mixing was performed so that 1 wt% was constant. This was finely pulverized by a jet mill using N ₂ as a pulverizing medium so that the average particle size was 2 to 5 μm. The obtained finely pulverized powder was subjected to transverse magnetic field molding in a magnetic field of 10 KOe at a molding pressure of ² ton / cm ² .
The molded body was sintered at 1100 ° C. × 2H in vacuum. The sintered body was subjected to a first heat treatment at 900 ° C. × 2H in an Ar atmosphere and then a second heat treatment at 600 ° C. × 1H. Table 8 shows the compounding ratio and the measurement result of the magnetic characteristics of the obtained permanent magnet. Particularly high magnetic properties are obtained when the mixing ratio is 8 wt% or more.

[0027]

[Table 7]

[0028]

[Table 8]

(Example 5) Nd and D having a purity of 95% or more
Main phase forming alloys shown in Table 9 and R rich phase forming alloys were produced by high frequency melting using y, B and electrolytic iron.

[0030]

[Table 9]

R-T-B type alloy powder (Ingot No.
22) was prepared in the same manner as in Example 1, and the RT alloy powder (Ingot No. 23) was mixed in a compounding ratio of 10, 12.5,
They were mixed at 15.0 and 17.5 wt%. This was finely pulverized by a jet mill using N ₂ as a pulverizing medium so that the average particle size was 2 to 5 μm. 10 KOe of the finely pulverized powder obtained
In a magnetic field of ² ton / cm ² at a forming pressure. The molded body was sintered at 1100 ° C. × 2H in vacuum. The sintered body was subjected to a first heat treatment at 900 ° C. × 2H in an Ar atmosphere and then a second heat treatment at 600 ° C. × 1H. Table 1
The results of measurement of the compounding ratio and the magnetic characteristics of the obtained permanent magnet are shown in 0. It can be seen from Table 10 that the magnetic properties are all high.

[0032]

[Table 10]

(Example 6) Nd and D having a purity of 95% or more
The main phase forming alloys shown in Table 11 and the R rich phase forming alloys were produced by high frequency melting using y, B and electrolytic iron.

[0034]

[Table 11]

Using this ingot, the main phase forming alloy was homogenized at 1100 ° C. × 20 H, and then coarsely pulverized to obtain an RTB-based alloy powder. The R-rich phase forming alloy was melt-cooled and then coarsely pulverized to obtain an R-T alloy powder. This coarse powder was mixed at a compounding ratio of 10 wt%, and this was pulverized by a jet mill using N ₂ as a pulverizing medium so as to have an average particle size of 2 to 5 μm. The obtained finely pulverized powder was subjected to transverse magnetic field molding in a magnetic field of 10 KOe at a molding pressure of ² ton / cm ² . The compact was sintered in vacuum at 1080 ° C. × 2H. The sintered body was subjected to a first heat treatment at 900 ° C. × 2H in an Ar atmosphere and then a second heat treatment at 600 ° C. × 1H. The magnetic properties of the sintered body obtained by the above procedure are shown in Table 12 as coarse powder mixture.
A coarse powder of the main phase forming alloy and a coarse powder of the R rich phase forming alloy were finely pulverized by a jet mill using N ₂ as a pulverizing medium so as to have an average particle size of 2 to 5 μm at a compounding ratio of 10 wt%. In the procedure after mixing and molding, the magnetic characteristics of the permanent magnet produced in the same manner as the coarse powder mixing were changed to fine powder mixing.
Shown in. When coarse powder is mixed, the density is high and Br, (BH)
max is high, and iHc is high in the case of fine powder mixing.

[0036]

[Table 12]

[0037]

According to the present invention, by mixing the R-T-B alloy powder mainly composed of R ₂ T ₁₄ B and the R-T alloy powder having a high R content and a low melting point, It is possible to obtain a rare earth permanent magnet having a reduced impurity phase and excellent magnetic properties.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Furushiro 5200 Sankejiri, Kumagaya-shi, Saitama, Hitachi Metals Co., Ltd. Magnetic Materials Research Center (72) Inventor Shigeho Tanigawa 5200 Sankejiri, Kumagaya, Saitama Hitachi Metals Co., Ltd., Kumagaya Plant

Claims (4)

[Claims] 1. An R ₂ T ₁₄ B-based intermetallic compound (R is one or more rare earth elements including Y, and T is one of transition metals.
One or more) and a main phase mainly composed of R-rich phase and a main constituent phase of the R-T-B rare earth permanent magnet, 1.0 wt% ≤ B ≤ 1.20 wt%, 25 wt% ≤R≤
45 wt% ≦ 30 wt% of R-T-B based alloy powder
A method for producing a rare earth permanent magnet, which comprises adding and mixing R-T based alloy powder which is R in a range of 8 to 15 wt%, followed by molding and sintering. 2. The method for producing a rare earth permanent magnet according to claim 1, wherein T of the RT alloy powder is Fe. 3. A coarsely crushed RTB-based alloy powder and R
The method for producing a rare earth permanent magnet according to claim 1 or 2, wherein the -T alloy powder is mixed, finely pulverized, and then molded. 4. A coarsely crushed RTB-based alloy powder and R
The method for producing a rare earth permanent magnet according to claim 1, wherein each of the -T alloy powders is pulverized and then mixed and molded.