JPH05339684A - Permanent magnet alloy and its manufacture - Google Patents

Abstract

PURPOSE:To improve the performance of a magnet, in a sintered magnet allay expressed by R-Fe-Co-M, by specifying the constitutional ratio of R and executing specified heat treatment and classificational circulating pulverization. CONSTITUTION:A sintered magnet alloy essentially consisting of rare earth elements, iron and boron expressed by R-Fe-Co-M is constituted in such a manner that the constitutional ratio of rare earth elements R is regulated to, by weight, 27 to 32%, and a part of Dy among R is regulated to <=1.5%. 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 alpha iron precipitated at the time of its solidification to re-enter into solid solution is used. Coarse powder is classificationally circulated and pulverized, and its size distribution is sharpened. In this way, high performance cab be 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 methods for manufacturing this magnet: an ultra-quenching method and a sintering method. The ultra-quenching magnet is a high energy-product permanent magnet obtained by hot-plasticizing a ribbon or powder obtained by using a method such as a melt spinning method and magnetically anisotropy. 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. Less than the following. Further, 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.
For this reason, an anisotropic magnet produced by the ultra-quenching method is a voice coil model.
It has been attracting attention as a magnet for magnets. However, anisotropic ultra-quenched magnets have a complicated manufacturing process and require large-scale equipment for performing hot plastic working, so that the manufacturing cost is higher than that of sintered magnets. 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 characteristics of sintered rare earth-iron-boron magnets, particularly the maximum energy product. In order to increase the maximum energy product of the sintered rare earth-iron-boron magnet, Nd2Fe1 which has the magnetism as a permanent magnet.
Make the volume ratio of the 4B phase magnet as high as possible,
And the rare earth-rich second phase that is responsible for the coercive force is Nd2
It is known that it is sufficient to disperse the Fe14B phase around the minimum and evenly. Various attempts have been made to realize the above basic concept in a practical magnet body. For example, in JP-A-63-99502, the amount of oxygen is 30
A means for achieving high energy product is disclosed in which the content of rare earth in the alloy is set to 0 ppm or less and 13 atomic% or less. However, in order to set the amount of oxygen in the magnet to 300 ppm, it is necessary to suppress the amount of oxygen in the raw material used, and it is necessary to use expensive raw materials, and to prevent the mixing of oxygen from the crucible during melting. Therefore, it requires complicated equipment such as flotation and melting, which is not suitable for industrial production. On the other hand, Japanese Patent Application Laid-Open No. 63-48805 discloses a method in which a rare earth-rich phase which is a second phase is prepared by a melt spinning method, which is mixed with an alloy having a composition close to that of the Nd2Fe14B phase which is a main phase and is sintered. There is. However, the melt spinning method is industrially expensive, and the phase close to the main phase is α
-There is a problem that high coercive force cannot be obtained due to poor pulverizability due to precipitation of iron and 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 80-
When set to 120 ° C, assuming a temperature coefficient of coercive force of this system magnet of -0.55 to -0.65% / ° C, an intrinsic coercive force of at least 95% of residual magnetic flux density at room temperature is required. is there. 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. Although the addition of Dy improves the Ha of the main phase and is extremely effective in improving the coercive force, the magnetic moment of Dy is coupled to the magnetic moments of Fe, Nd, and Pr in a ferriferromagnetic manner. It has the drawback of significantly reducing the saturation magnetization of the magnet. In order to eliminate the drawbacks of Dy, the amount of Dy added should be kept to a minimum and Nb, Al, Zr, W,
Many inventions in which Mo and other elements are added in combination are also disclosed. The role of the added elements is to suppress grain growth in the sintering process or to improve the coercive force by improving the interface between the rare earth-rich phase and the main phase.
However, 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 composite addition is utilized, Dy of about 1.5% by weight is necessary. Made it difficult to obtain a higher energy product in a sintered magnet than in an ultra-quenched magnet. In view of the above background, an object of the present invention is to provide a high energy-product rare earth-iron-boron-based permanent magnet having a high coercive force and a high residual magnetic flux density even in a composition region of low rare earth and low Dy. ..

[0003]

[Means for Solving Problems] In order to solve the above problems,
According to the present invention, a melt cast ingot containing Dy of 1.5 wt% or less as an alloy component is heat-treated at 900 ° C. or higher in a non-oxidizing atmosphere and rapidly cooled to 700 ° C. or lower at a cooling rate of 50 ° C./min or higher, By crushing the ingot to an average particle size of 3 to 7 microns, and further setting the abundance ratio of the coarse particles of 10 microns or more contained in the crushed powder to 10% or less, the average crystal grain size of the sintered body becomes 3 to 10 The sintered body has an oxygen content of 2000 to 500 ppm, a specific coercive force of 95% or more of the residual magnetic flux density, and a squareness ratio of 94% or more. It was also found that a rare earth-iron-boron sintered magnet having excellent thermal stability can be obtained. In the present invention, the heat treatment of the ingot at 900 ° C. or higher causes the soft magnetic α-precipitated during melting and casting.
It is effective for re-dissolving Fe in the main phase, and particularly in the alloy having a small Dy content in the present invention, in the equilibrium state, there is an α-iron precipitation region in a wide temperature range, so that the magnetic properties are improved. It is also an extremely effective means for controlling the average particle size during pulverization. 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 narrows, so that the effect is not remarkable. Therefore, the rare earth content is set to 32% by weight or less. 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, 10% or more of unpulverized coarse powder of 10 microns or more is present in the fine powder after pulverization. Naturally, in a magnet body obtained by molding and sintering such fine powder, % Or more of coarse particles are present. 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 7 microns,
Further, it was found that the existence probability of the coarse powder of 10 microns or more was set to 10% or less and the raw material powder of the sintered magnet having a sharp particle size distribution was obtained. 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 micron or more is that when the average particle size is 3 micron or less, the amount of oxygen increases, the reduction of the residual magnetic flux density and the reduction of the energy product cannot be avoided, and the specific surface area of the powder increases, which results in the molding process. This is because the handling becomes difficult industrially. In the present invention, R other than Dy is Nd or Pr.
Conventionally known elements such as the above can be used. In the present invention, the reason why the B content is set to 0.9% or more is that if it is less than 0.9% by weight, the magnetic properties, particularly coercive force and Hk are remarkably lowered due to the precipitation of the Nd2Fe17 phase. The reason for setting below is NdFe4B when it exceeds 1.2% by weight.
This is because the precipitation of four phases reduces the pulverizability and makes it difficult to obtain a raw material powder having a sharp particle size distribution. In the present invention, the additional element represented by M is effective in suppressing the growth of the crystal grain size during sintering or promoting the densification. However, the addition of more than 1.5% by weight deteriorates the magnetic properties, so 1.5% by weight
Below.

[0004]

The present invention will be described in detail with reference to the following examples. (Example 1) Alloys having different compositions of Dy contents were prepared by making the total amount of rare earths constant by high frequency melting and further setting the amount of Co to 5% by weight. These cast ingots were heated to 1150 ° C
It heat-processed in vacuum for 4 hours, and was rapidly cooled in Ar stream. The rapidly cooled ingot was self-disintegrated in a hydrogen stream in advance for about 20 minutes.
After making a coarse powder of 0 micron, it was subjected to dry jet mill grinding in a nitrogen stream. During crushing, coarse powder is circulated from the lower part of the classification zone in the crushing chamber and repeatedly crushed to obtain an average particle size of about 5
Micron fines were obtained. Mold this fine powder in a magnetic field and
After sintering in vacuum at 100 ° C. for 2 hours, heat treatment was performed in Ar at 600 ° C. for 2 hours to measure magnetic properties. The results are shown in FIG. 1 in comparison with an ingot magnet 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.
9.5 wt%, Dy 0.8 wt%, B 1.05 wt%, Co 3 wt%, Nb 0.5 wt%, the balance Fe alloy is melted by high frequency and cast to make an ingot. did. Half of the ingot was heat-treated at 1100 ° C. in the same manner as in Example 1, and then pulverized by cyclic sinter 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.
Tables 1 and 2 show the results of carrying out the present invention in comparison with comparative examples.

[0006]

[Table 1]

[0007]

[Table 2]

Example 3 An alloy having the composition shown in Table 3 was 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.

[0009]

[Table 3]

[0010]

[Table 4]

(Example 4) Nd 31% by weight, Dy1.
3% by weight, 0.6% by weight of Al, 0.8% by weight of Nb, and 1.05% by weight of boron were used to prepare molten ingots with various amounts of cobalt added. This ingot is 1150 ℃
After being heat-treated in a vacuum for 4 hours, it was cooled in an Ar stream. After that, coarse powder was formed by the same process as in Example 1, and then a sintered magnet was formed in the same manner as in Example 1, and the magnetic properties, the oxygen content of the sintered body, and the average particle size were examined. The results are shown in Tables 5 and 6.

[0012]

[Table 5] Note: Comparative Example 2 was not heat-treated at 1150 ° C.

[0013]

[Table 6]

(Example 5) 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, 1.1% by weight of boron, 5% by weight of cobalt, and the balance of Fe was heat-treated in vacuum at 1100 ° C. for 4 hours and then in an Ar stream. Cooled. After that, the same treatment as in Example 1 was performed to make coarse powder, and then cyclic pulverization was performed 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, and the magnetic characteristics were examined. The results are shown in Figure 2. From FIG. 2, the average particle size of the fine powder is 3 to 7 μm.
High coercive force was obtained and the oxygen content of the sintered body was 5
It can be reduced to 000 ppm or less.

[0015]

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

Front Page Continuation (72) Inventor Katsuhiko Furujo 5200 Sankejiri, Kumagaya-shi, Saitama, Hitachi Metals Co., Ltd. Magnetic Materials Research Laboratory (72) Inventor Masaaki Tokunaga 5200 Sankejiri, Kumagaya, Saitama Hitachi Metals Co., Ltd.

Claims (10)

[Claims] 1. A rare earth represented by R-Fe-Co-BM.
In a sintered magnet alloy containing iron and boron as main constituent elements, the constituent ratio of the rare earth element R is 27% by weight or more and 32% by weight or less, and Dy of R is 1.5% by weight or less. Characteristic permanent magnet alloy. 2. The permanent magnet alloy according to claim 1, wherein B is 0.9 wt% or more and 1.2 wt% or less, and Co is 0 to 10 wt% or less. 3. M is Ti, Zr, V, Mo, W, Nb,
One or more selected from H, Al, Cu, Ni, Cr, and Mn, and the total addition amount thereof is 1.5
The permanent magnet alloy according to claim 1 or 2, wherein the content is less than or equal to wt%. 4. The average crystal grain size is not less than 3 microns and not more than 10 microns, and the oxygen content of the sintered body is 2000 to 5000 p.
The permanent magnet alloy according to claim 1, which is pm. 5. The intrinsic coercive force after heat treatment is 95% or more of the value of the residual magnetic flux density, and the squareness ratio (Hk value divided by the intrinsic coercive force) is 94% or more. The permanent magnet alloy according to any one of to 4. 6. 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 claim 1, wherein the cast ingot is 900 A method for producing a permanent magnet alloy, which comprises heat-treating for 2 hours or more in a non-oxidizing atmosphere at a temperature of not less than 1 ° C and not more than 1250 ° C. 7. The crushed average particle size of the alloy powder during crushing is 3 to.
The method for producing a permanent magnet alloy according to claim 5, wherein the probability of existence of the coarse powder having a size of 7 microns is 10% or less. 8. The method for producing a permanent magnet alloy according to claim 5, wherein coarse powder of 10 μm or more is separated at the time of pulverization, and the coarse powder is circulated and pulverized. 9. The average crystal grain size of the sintered body is 3 μm or more and 10 μm or less, and the oxygen content of the sintered body is 2000-5.
It is 000 ppm, The permanent magnet in any one of Claims 5-7. 10. The intrinsic coercive force after heat treatment is 95% or more of the value of the residual magnetic flux density, and the squareness ratio (Hk value divided by the intrinsic coercive force) is 94% or more. The permanent magnet according to any one of to 9.