JPH05339683A - Permanent matnet alloy and its manufacture - Google Patents

Abstract

PURPOSE:To improve the performance of a magnet, in a sintered magnet allay expressed by R-Fe-B-M, by specifying the constitutional ratio of R and executing specified heat treatment and classificational circulating pulverization. CONSTITUTION:In a sintered magnet allay essentially consisting of rare earth elements, iron and baron expressed by R-Fe-B-M, the constitutional ratio of rare earth elements R is regulated to, by weight, 27 to 32%, a part of R is substituted by <=1.5% Dy, and the balance is substantially constituted of Nd and Pr. Then, this allay having a low rare earth content is subjected to heat treatment in the temp. range of 900 to 1150 deg.C, and the ingot obtd. by allowing alphairon precipitated at the time of its solidification to re-enter into solid solution is used. Coarse powder is classficationally circulated and pulverized at the time of its pulverization, and its size distribution is sharpened. In this way, high performance is imparted to the rare earth-iron-boron magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-iron-boron system sintered magnet. In particular, the present invention relates to a permanent magnet that requires a high energy product, such as a magnet for a voice coil motor used in an external magnetic storage device of a computer, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Rare earth-iron-boron magnets are used in voice coil motors, which are external magnetic storage devices for computers. There are two manufacturing methods of this magnet, an ultra-quenching method and a sintering method. The ultra-quenching magnet is made into a high energy product permanent magnet by hot-plasticizing a ribbon or powder obtained by means of a melt spinning method or the like to magnetically anisotropy it. As described in JP-A-59-64739, this permanent magnet basically does not require the step of crushing the alloy during the manufacturing process, so that the amount of oxygen contained as impurities in the magnet is usually 2000 ppm or less. Since the particle size of each crystal forming the magnet is as small as 1 micron or less, a high energy product and a high coercive force can be obtained. Therefore, the anisotropic quenching anisotropic magnet has attracted attention as a magnet for a voice coil motor. However, the anisotropic ultra-quenched magnet has a complicated manufacturing process and requires large-scale equipment for performing hot plastic working, so that the manufacturing cost is higher than that of the sintered magnet and there is a problem. Sintered rare earth magnets are used in various applications including magnets for voice coil motors, and the demand for them is increasing year by year. On the other hand,
Research and development have been actively conducted to improve the magnetic properties of sintered rare earth-iron-boron magnets, especially the maximum energy product. In order to increase the maximum energy product of the sintered rare earth-iron-boron magnet, the volume ratio of the Nd ₂ Fe ₁₄ B phase, which is responsible for the magnetism of the permanent magnet, in the magnet should be as high as possible and should be maintained. It is also known that the rare earth-rich second phase, which is responsible for the magnetic force, may be dispersed around the Nd ₂ Fe ₁₄ B phase in a minimum and uniform manner. Various attempts have been made to realize the above basic concept in a practical magnet body. For example, Japanese Patent Application Laid-Open No. 63-99502 discloses a means for increasing the energy product by setting the oxygen content to 300 ppm or less and the rare earth content in the alloy to 13 atomic% or less. However, the amount of oxygen in the magnet should be 3
In order to set the content to 00 ppm, it is necessary to suppress the amount of oxygen in the raw material used, and it is necessary to use an expensive raw material. In addition, in order to prevent oxygen from being mixed from the crucible or the like at the time of melting, floating melting, etc. It requires complicated equipment and is industrially problematic. On the other hand, in JP-A-63-48805, the second
There is disclosed a method in which a rare earth-rich phase, which is a phase, is produced by a melt spinning method, mixed with an alloy having a composition close to that of a main phase, Nd ₂ Fe ₁₄ B phase, and sintered. However, the melt spinning method has a problem that it is industrially expensive and that a phase close to the main phase cannot obtain a high coercive force due to poor pulverizability due to precipitation of α-iron or the like. The rare earth-iron-boron magnet used as a voice coil motor generally has an intrinsic coercive force of 12 kOe or more, but the operating environment is 8
When set to 0 to 120 ° C. When the temperature coefficient of coercive force of the present system magnet is assumed to be −0.55 to −0.65% / ° C., the intrinsic coercive force of at least 95% of the residual magnetic flux density at room temperature is is necessary. In order to satisfy this requirement, it has been attempted to replace a part of the rare earth element with about 2% by weight of Dy.

[0003]

The addition of Dy is the main phase of H
It is extremely effective for improving a and coercive force, but D
Since the magnetic moment of y has a ferriferromagnetic coupling with the magnetic moments of Fe, Nd, and Pr, there is a drawback that the saturation magnetization of the magnet is significantly reduced. For the purpose of eliminating the drawbacks of Dy, Nb, Al, Zr, W, Mo and other elements are added in combination to minimize the amount of Dy added and to obtain a practically necessary coercive force. Many inventions have been disclosed. Although the role of the elements added in combination is not necessarily uniform, the effect of improving coercive force can be obtained by suppressing grain growth in the sintering process or improving the interface between the rare earth-rich phase and the main phase. But,
In order to obtain an intrinsic coercive force of 95% or more with respect to the residual magnetic flux density at room temperature even if the effect of such complex addition is utilized,
Dy needs to be about 1.5% by weight, which makes it difficult to obtain a higher energy product in the sintered magnet than in the ultra-quenched magnet.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention uses Dy of 1.5% by weight or less as an alloy component.
90 melt-casting ingot containing
After heat treatment at 0 ° C. or higher and rapid cooling to 700 ° C. or lower at a cooling rate of 50 ° C./min or more, the ingot has an average particle size of 3 to 7
Oxygen in the sintered body is 3 to 10 microns when the average crystal grain size of the sintered body is 3 to 10 microns by crushing to a micron and further setting the existence ratio of the coarse powder of 10 microns or more contained in the pulverized powder to 10% or less. In the magnetic properties after the heat treatment, the intrinsic coercive force is 9% of the residual magnetic flux density.
It was found that a rare earth-iron-boron sintered magnet having a high energy product of 5% or more and a squareness ratio of 94% or more and excellent thermal stability can be obtained. In the present invention, the heat treatment of the ingot at 900 ° C. or higher is effective for re-dissolving the soft magnetic α-Fe precipitated during the melting and casting in the main phase,
In particular, in the alloy of the present invention having a small Dy content, in the equilibrium state, since there is a precipitation region of α-iron in a wide temperature range, it is an extremely effective means for improving the magnetic properties and controlling the average particle size during grinding. . The heat treatment of the ingot at 900 ° C. or higher is effective for the alloy having a Dy content of 1.5% by weight, but the effect is not remarkable when the Dy content exceeds 2%. Further, as the rare earth content increases, the α-Fe precipitation temperature region becomes narrower, so that the effect is not remarkable, and it is extremely effective for an alloy having a rare earth content of 32% by weight. By crushing the ingot that has been heat-treated at 900 ° C. or higher, the crushing efficiency is improved and the particle size distribution of the crushed powder can be sharpened as compared with the case where the heat treatment is not performed. However, by itself, there is 10% or more of finely pulverized coarse particles of 10 microns or more in the fine powder after pulverization. Naturally, 10% or more is naturally present in the magnet body obtained by molding and sintering such fine powder. There are coarse particles of. The coarse particles reduce the squareness ratio of the magnet, that is, substantially reduce Hk. In the present invention, in order to solve such a problem, at the time of pulverization, a fine powder of 10 microns or less and a coarse powder of 10 microns or more are separated, and the coarse powder is circulated and pulverized in a pulverizer so that the average particle diameter is 3 to It was found that the raw material powder of the sintered magnet having a sharp particle size distribution was obtained by setting the probability of existence of the coarse powder of 7 microns and 10 microns or more to 10% or less. In the present invention, the reason for defining the average particle size of the pulverized powder as 7 microns or less is that the value of the intrinsic coercive force obtained when the average particle size exceeds 7 microns is 95% or less of the value of the residual magnetic flux density. The reason for defining as 3 microns or more is that when the average particle size is 3 microns or less, the amount of oxygen increases, a decrease in residual magnetic flux density and a decrease in energy product are unavoidable, and the specific surface area of the powder increases This is because the handling becomes industrially difficult in the process and the like. The reason why the amount of B is set to 0.9% or more in claim 2 is that the precipitation of the Nd ₂ Fe ₁₇ phase significantly reduces the magnetic properties, especially the coercive force and Hk at 0.9% by weight or less. 1.2% by weight is the reason why the amount is less than .2% by weight
This is because the precipitation of the NdFe ₄ B ₄ phase deteriorates the pulverizability and it is difficult to obtain a raw material powder having a sharp particle size distribution. The additional element of claim 3 is effective in suppressing the growth of the crystal grain size during sintering or promoting the densification. However, addition of more than 1.5% by weight deteriorates magnetic properties.

[0005]

The present invention will be described in detail with reference to the following examples. (Example 1) The total amount of rare earths was made constant by high frequency melting,
Alloys having different Dy contents were melted. These cast ingots were heat treated in a vacuum at 1100 ° C. for 4 hours,
It was rapidly cooled in an air stream. The rapidly cooled ingot was self-disintegrated in a hydrogen stream to make a coarse powder of about 200 microns,
Dry jet mill pulverization was performed in a nitrogen stream. When crushing,
Coarse powder is circulated from the lower part of the classification zone in the grinding chamber to repeat grinding. A fine powder with an average particle size of about 5 microns was obtained. This fine powder was molded in a magnetic field, sintered in vacuum at 1100 ° C. for 2 hours, and then heat-treated in Ar at 600 ° C. for 2 hours to measure magnetic properties. The results are shown in FIG. 1 in comparison with a magnet made of an ingot in which an alloy having the same composition was not heat-treated. It can be seen that high coercive force can be obtained by performing heat treatment on the ingot.

(Example 2) Nd was reduced to 2 by high frequency melting.
An alloy composed of 9.5% by weight, 0.8% by weight of Dy, 1.05% by weight of B, 0.5% by weight of Nb, and the balance of Fe was high-frequency melted and cast to prepare an ingot. Half of the ingot was heat-treated at 1100 ° C. in the same manner as in Example 1, and then pulverized by circulation, sintered and heat-treated in the same steps to obtain a permanent magnet.
On the other hand, half of the ingots were subjected to normal crushing in one pass without heat treatment for comparison and without self-disintegration in a hydrogen atmosphere and then cyclic crushing. Table 1 and Table 2
The results of carrying out the present invention are shown in comparison with Comparative Examples.

[0007]

[Table 1]

[0008]

[Table 2]

Example 3 Alloys having the compositions shown in Table 3 were melt-cast by high frequency melting. Table 4 shows the results of measuring the magnetic properties of the cast ingot which was heat-treated in the same manner as in Example 1 and then crushed, sintered and heat-treated in the same manner as in Example 1.

[0010]

[Table 3]

[0011]

[Table 4]

(Example 4) Nd 31% by weight, Dy1.
A cast ingot composed of 1% by weight, 0.3% by weight of Al, 0.4% by weight of Mo, and the balance Fe was heat-treated in vacuum at 1100 ° C. for 4 hours and then cooled in an Ar stream. Thereafter, the same treatment as in Example 1 was carried out to make coarse powder, and then cyclic pulverization was carried out by a dry jet mill using a nitrogen stream. During crushing, the crushing conditions were variously changed to change the average particle size of the crushed powder. Thereafter, these fine powders were used as sintered magnets in the same manner as in Example 1 to examine the magnetic characteristics. The results are shown in Figure 2. As shown in FIG. 2, a high coercive force can be obtained when the average particle size of the fine powder is 3 to 7 μm, and the oxygen content of the sintered body can be reduced to 5000 ppm or less.

[0013]

According to the present invention, a permanent magnet of a high energy-product rare earth-iron-boron system having a high coercive force and a residual magnetic flux density even in a composition region of low rare earth and low Dy, which has hitherto been insufficient. It is possible to manufacture magnets.

[Brief description of drawings]

FIG. 1 shows the effect of heat treatment of an ingot according to the present invention by the relationship between the amount of Dy in the alloy and magnetic properties.

FIG. 2 is a graph showing the effect of circulating pulverization according to the present invention, in terms of the average particle size of pulverized powder, the amount of oxygen in a sintered body, and the magnetic properties.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location // H01F 1/053 (72) Inventor Katsuhiko Furujo 5200 Sankejiri, Kumagaya-shi, Saitama Hitachi Metals Co., Ltd. Magnetic Materials Research Laboratory (72) Inventor Masaaki Tokunaga 5200 Mikashiri, Kumagaya, Saitama Hitachi Metals Co., Ltd.

Claims (8)

[Claims] 1. A rare earth represented by R-Fe-BM, iron,
In sintered magnet alloys containing boron as the main constituent element,
32% by weight when the composition ratio of the rare earth element R is 27% by weight or more
The following is a permanent magnet alloy characterized in that part of R is replaced by Dy of 1.5% by weight or less and the balance R is substantially Nd and Pr. 2. The permanent magnet alloy according to claim 1, wherein
A permanent magnet alloy, characterized in that B is 0.9% by weight or more and 1.2% by weight or less. 3. The permanent magnet alloy according to claim 1, wherein M is Ti, Zr, V, Mo, W, Nb, Hf, A.
1, 1 or 2 or more selected from Cu, Ni, Cr and Mn, and the total addition amount thereof is 1.5% by weight.
A permanent magnet alloy characterized by the following: 4. A method for producing a permanent magnet, which comprises melting, casting, crushing, forming in a magnetic field, sintering, and heat treating the permanent magnet alloy according to any one of claims 1 to 3, wherein the cast ingot is 90
A method for producing a permanent magnet, which comprises performing a heat treatment at 0 ° C. or more and 1200 ° C. or less in a non-oxidizing atmosphere for 2 hours or more. 5. The method for producing a permanent magnet alloy according to claim 1, wherein the pulverized average particle size of the alloy powder during pulverization is 3 to 3.
The method for producing a permanent magnet is characterized in that the existence of coarse particles of 10 microns or more is set to 7% or less and the probability of existence of the coarse powder is 10% or less. 6. The method for producing a permanent magnet according to any one of claims 1 to 5, wherein coarse particles of 10 microns or more are separated during pulverization and the coarse particles are circulated and pulverized. 7. The permanent magnet alloy according to any one of claims 1 to 4, wherein the average crystal grain size of the sintered body is 3 microns or more and 10 microns or less, and the oxygen content of the sintered body is 2000 to 5000 ppm. A permanent magnet characterized by being present. 8. The permanent magnet alloy according to any one of claims 1 to 7, wherein the intrinsic coercive force after heat treatment is 95% or more of the value of the residual magnetic flux density, and the squareness ratio (the value of Hk is inherent A value obtained by dividing by a coercive force) is 94% or more.