JPH06151219A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To mold an R-Fe-B cast and hot-worked magnet by conducting a hot bending work. CONSTITUTION:R (provided that R indicates at least a kind of rare-earth elements containing Y), Fe and B are used as a raw material component, the alloy having the aforesaid fundamental component is melted, cast and then the obtained cast ingot is hot-worked at the temperature of 500 deg.C or higher, and a hot bending work is performed on the obtained rolled magnet. In the above-mentioned process, the average crystal particle diameter after hot pressing should be 40mum or less, and besides, the standard deviation of crystal particle diameter distribution should be 15mum or less. Also, the crystal particles of particle diameter three times or more of average crystal particle diameter should not be contained. As a result, generation of cracks due to performance of bending work can be suppressed, and the bending work at high distortional speed can be conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a permanent magnet having magnetic anisotropy due to mechanical orientation, especially R (where R is
Is at least one of rare earth elements including Y), Fe,
The present invention relates to a method for producing a permanent magnet containing B as a raw material basic component.

[0002]

2. Description of the Related Art Permanent magnets are one of the important electric and electronic materials used in a wide range of fields from various household electric appliances to peripheral terminals for large computers.
With the recent demand for miniaturization and high efficiency of electrical products,
Permanent magnets are also required to have higher performance.

The permanent magnet is a material for generating a magnetic field without supplying electric energy from the outside, and a material having a large coercive force and a high residual magnetic flux density is suitable.

Typical permanent magnets currently in use are alnico type cast magnets, ferrite magnets and rare earth-transition metal type magnets, especially R-Co type permanent magnets which are rare earth-transition metal type magnets. The R-Fe-B system permanent magnet has been extensively researched and developed as a permanent magnet having an extremely high coercive force and energy product.

Conventionally, there are the following methods for producing these R—Fe—B type high-performance anisotropic permanent magnets.

(1) First, Japanese Patent Laid-Open No. 59-46008 and M. Sagaw
a, S.Fujimura, N.Togawa, H.Yamamoto and Y.Matsu-ura; J.
Appl.Phys.Vol.55 (6), 15 March 1984, p2083, etc., 8 to 30% R (where R is at least one rare earth element including Y) and 2 to 28% B in atomic percentage. It is disclosed that a permanent magnet characterized by being a magnetic anisotropic sintered body composed of Fe and the balance Fe is manufactured by sintering based on the powder metallurgy method.

In this sintering method, an alloy ingot is produced by melting and casting and crushed to obtain a magnetic powder having an appropriate particle size (several μm). The magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to form a molded body. The molded body is sintered in argon at a temperature of around 1100 ° C for 1 hour,
Then it is rapidly cooled to room temperature. After sintering, the coercive force of the permanent magnet is further improved by heat treatment at a temperature of around 600 ° C.

Regarding the heat treatment of this sintered magnet, Japanese Patent Laid-Open No. 61-217540, Japanese Patent Laid-Open No. 62-165305, etc.
The effect of multi-step heat treatment is disclosed.

(2) JP-A-59-211549 and RWLee; A
Vol. 46 (8), 15 April 1985, p790, ppl.Phys.Lett.Vol.46,8, R- has a resin-bonded fine piece of melt-spun alloy ribbon with a very fine crystalline magnetic phase.
Fe-B magnets are disclosed. This permanent magnet is manufactured by a quenching ribbon production apparatus used for producing an amorphous alloy, by making a quenching thin piece having a thickness of about 30 μm, kneading the thin piece with a resin and press-molding.

(3) Japanese Patent Laid-Open No. 60-100402 and RWLee; A
Vol.46 (8), 15 April1985, p790, ppl.Phys.Lett.Vol.46, the quenching thin piece used in the method of (2) above is described by a method called a two-step hot pressing method in vacuum or in an inert atmosphere. It is disclosed to obtain a dense and anisotropic R-Fe-B magnet.

(4) In Japanese Patent Laid-Open No. 62-276803, R (where R is at least one of rare earth elements including Y) 8
~ 30 atom%, B 2 ~ 28 atom%, Co 50 atom% or less, A
After melting and casting an alloy consisting of less than 15 atom% and the balance of iron and other impurities that are unavoidable in production, the cast ingot is subjected to hot working at a temperature of 500 ° C or higher to refine the crystal grains and the crystals. Disclosed is a rare earth-iron-based permanent magnet characterized by orienting its axis in a specific direction to magnetically anisotropy the cast alloy.

In addition, this method has a drawback that the degree of freedom in shape is low, but in order to compensate for this, a plate-shaped permanent magnet anisotropy by hot working is subjected to hot bending. A method of molding by carrying out is disclosed in JP-A-2-252222.
Japanese Patent Application No. 2-315397. In addition,
Japanese Patent Laid-Open No. 2-297910 discloses a method for producing a radial oriented magnet by orienting a cast alloy by hot rolling and then forming it into an arc shape by pressing. These methods have the property that the magnet material has an extremely brittle R ₂ Fe ₁₄ B intermetallic compound as a main phase, has a grain boundary phase with a low melting point, and is in a semi-molten state at a high temperature, so that the composition is easily deformed. Is used.

[0013]

The conventional methods for manufacturing R-Fe-B based permanent magnets (1) to (4) above have the following drawbacks.

The method for producing a permanent magnet of (1) essentially requires that the alloy be made into powder. However, since the R-Fe-B alloy is very active with respect to oxygen, it cannot be powdered. Oxidation becomes excessive, and the oxygen concentration in the sintered body will inevitably increase.

When molding the powder, it is necessary to use a molding aid such as zinc stearate, which is removed beforehand in the sintering process. However, it remains in the form of carbon in the magnet body, and this carbon remarkably deteriorates the magnetic performance of the R-Fe-B magnet, which is not preferable.

The green body is a green body after press-molding by adding a molding aid, which is very brittle and difficult to handle. Therefore, it takes a great deal of time to neatly put them side by side in the sintering furnace, which is a big drawback.

Due to these drawbacks, generally speaking, not only expensive equipment is required for producing an R--Fe--B system sintered magnet, but also the production method is inferior in production efficiency. Eventually, the manufacturing cost of the magnet increases. Therefore, it is not possible to take advantage of the advantages of the R-Fe-B magnets, which have relatively low raw material costs.

It is also possible to impart radial anisotropy in the step of molding in a magnetic field, but since shrinkage occurs in the subsequent sintering step, the dimensional accuracy is low and the magnet is cracked due to this shrinkage. It has a drawback that it easily occurs and the yield is low. As a means for solving this, a method of bending a plate-shaped sintered magnet by applying a load at a temperature of 900 to 1150 ° C. is disclosed in JP-A-62-262405 and JP-A-1-270210. It is disclosed in the publication. However, in the methods shown in these, since the processing is performed only by the load applied to the mold, the processing takes time and is not practical considering the actual production. Further, since the processing speed cannot be controlled, there is a drawback that cracking is likely to occur.

Next, in the permanent magnet manufacturing methods of (2) and (3), a vacuum melt spinning device is used, but this device is currently very unproductive and expensive.

Since the permanent magnet of (2) is isotropic in principle, it has a low energy product, the squareness of the hysteresis loop is poor, and it is disadvantageous in terms of temperature characteristics and use.

The method (3) for manufacturing a permanent magnet is a unique method in which hot pressing is used in two steps.
It cannot be denied that it is inefficient when actually considering mass production.

Further, according to this method, the crystal grains are remarkably coarsened at a high temperature of, for example, 800 ° C. or higher, which causes a coercive force iH.
c is extremely reduced, and it does not become a practical permanent magnet.

In the method of manufacturing a permanent magnet of (4), hot working may be performed in one step, and since hot working can be performed by sealing the magnet alloy in a capsule, it is not necessary to control the atmosphere at the time of working. Since the whole manufacturing process is simple, the manufacturing cost is low,
Since it does not include a powder process, it has many advantages such as low oxygen content, good corrosion resistance, high mechanical strength, and the ability to manufacture large magnets. However,
Although such a manufacturing method is suitable for mass production of large magnets, it has a low degree of freedom in shape, and in the case of manufacturing magnets with complicated shapes or circular / ring-shaped magnets, processing costs such as cutting and grinding are required. In addition to this, there is a problem that the yield is low and the overall manufacturing cost is high. In addition, plate magnets can be bent, and radial anisotropy can be imparted by matching the radial direction of the curved surface with the plate thickness direction. However, there is a problem that cracks are likely to occur depending on the plate thickness. Regarding this problem, Japanese Patent Application No. 2-315397 discloses that the bending temperature must be 600 to 1500 ° C. and the strain rate must be 0.5 / s or less in order to perform bending without cracking. ing. In addition, the average grain size of the magnet alloy after hot working is set to 40 μm or less so as not to include the step of causing grain growth before bending, so that bending can be performed easily and without causing cracks. What can be done is shown in Japanese Patent Application No. 4-36614.

However, as a result of conducting additional tests with respect to these inventions, the bending work is greatly affected by the crystal grain size and the distribution state of the magnet alloy before the bending work in addition to the above-mentioned conditions. It was found that it is necessary to specify the grain size distribution of the magnet alloy before bending in order to facilitate the processing of. However, Japanese Patent Application No. 4-36614 does not have a detailed description regarding the grain size distribution.

The present invention has the above-mentioned drawbacks of the prior art, particularly (4).
Is to solve the problem regarding the degree of freedom of shape in the permanent magnet of the above, and its purpose is to prevent the occurrence of cracking during bending by specifying the structure of the magnet alloy before bending in detail, and to prevent high strain. An object of the present invention is to provide a high-performance and low-cost manufacturing method of a permanent magnet by enabling bending at a high speed.

[0026]

According to the method for producing a permanent magnet of the present invention, R (where R is at least one of rare earth elements including Y), Fe and B are used as raw material basic components and the basic components are used. In an arc-shaped magnet produced by melting and casting an alloy, then hot working the cast ingot at a temperature of 500 ° C. or higher, and performing hot bending, the average crystal grain size in the magnet alloy after hot working is It is characterized in that the magnet alloy having a size of 40 μm or less and a standard deviation of the crystal grain size distribution of 15 μm or less is bent.

The magnet alloy after hot working has an average crystal grain size of 40 μm or less, and the magnet alloy containing no crystal grains of 3 times the average grain size or more is bent. And

As described above, a magnet obtained by subjecting a cast ingot to hot working has a low degree of freedom in shape, and if the magnet has a complicated shape, the machining cost such as cutting and grinding increases. There was a problem. In addition, the plate magnet can be bent, but the bending speed is
There is a problem that cracks are likely to occur depending on the processing temperature and the plate thickness. In the present invention, the average grain size of the magnet alloy after hot working is 40 μm or less, and the standard deviation of the grain size distribution is 15 μm or less so that cracks easily occur even at a high strain rate. It has been found that the bending process can be performed without the need. Further, in the magnet alloy having the above structure, if the structure does not further include crystal grains having a grain size three times or more of the average crystal grain size, bending after hot working becomes easier, We have found that the occurrence of cracks during processing is suppressed and bending at high strain rates is possible.

The preferable composition range of the permanent magnet in the present invention will be described below.

As rare earths, Y, La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, and Lu are listed as candidates, and one or more of these are used in combination. Since the highest magnetic performance can be obtained with Pr, practically, Pr, P
An r-Nd alloy, a Ce-Pr-Nd alloy, etc. are used.
A small amount of heavy rare earth element, such as Dy or Tb, is effective for improving the coercive force.

The main phase of the R-Fe-B magnet is R ₂ Fe ₁₄ B.
Is. Therefore, if R is less than 8 atomic%, the above compound is no longer formed and high magnetic properties cannot be obtained. On the other hand, when R exceeds 30 atom%, the nonmagnetic R-rich phase is increased and the magnetic properties are remarkably deteriorated. Therefore, the range of R is suitably 8 to 30 atomic%. However, for high residual magnetic flux density, R8 to 25 atomic% is preferable.

B is an essential element for forming the R ₂ Fe ₁₄ B phase, and if it is less than 2 atomic%, a rhombohedral R—Fe system is formed, so that a high coercive force cannot be expected. On the other hand, if it exceeds 28 atomic%, the non-magnetic phase rich in B is increased and the residual magnetic flux density is significantly lowered. However, in order to obtain a high coercive force, B8 atomic% or less is preferable, and if it is more than that, fine R ₂
It is difficult to obtain the Fe ₁₄ B phase, and the coercive force is small.

Co is an element effective in increasing the Curie point of the present system magnet, but since it reduces the coercive force, it is 50
Atomic% or less is good.

An element that is present together with the R-rich phase such as Cu, Ag, Au, Pd, and Ga and that lowers the melting point of that phase has the effect of increasing the coercive force. However, since these elements are non-magnetic elements, the residual magnetic flux density decreases as the amount of these elements increases, so 6 atomic% or less is preferable.

The temperature in hot working is preferably a recrystallization temperature or higher, and is preferably 500 ° C. or higher in the R—Fe—B type alloy of the present invention.

The temperature in bending is required to be 600 ° C. or higher in order to realize processing at a processing speed with high productivity without causing cracks during processing. If the processing temperature exceeds 1050 ° C., there is a high possibility that the coercive force will decrease due to the coarsening of crystal grains, so a temperature below this is desirable.

Next, examples of the present invention will be described.

[0038]

【Example】

(Example 1) Using an induction heating furnace in an argon atmosphere,
Alloys having the compositions shown in Table 1 were melted and cast. At this time, raw materials of rare earth, iron and copper having a purity of 99.9% were used, and ferroboron was used as boron.

The cast ingot thus obtained was placed in an iron capsule, degassed, sealed, and processed at a processing temperature of 950 ° C.
Was hot-rolled. At this time, rolling with a height reduction amount of 30% in one rolling was carried out for 4 passes so that the total working amount became 76%.

During this hot working, the easy magnetization axis of the crystal was oriented so as to be parallel to the rolling direction of the alloy. A plate-like sample having a width of 15 mm, a length of 20 mm and a thickness of 2 mm was cut out from the rolled magnet thus obtained. After heating this plate-shaped sample to 1000 ° C. in an inert gas, the processing speed was 0.800 mm / min (strain rate 4.0 ×
The mold was bent at 10 ⁻⁴ / s) to form an arc magnet having an outer diameter of 22 mm and an inner diameter of 18 mm. At this time, 6 samples were processed per one condition. The results are shown in Table 2. Here, the number of successes means that machining was performed under the same conditions.
It is the number of samples that have been completely bent without cracks.

[0041]

[Table 1]

[0042]

[Table 2]

From these results, it is understood that the magnet alloy after hot working having a standard deviation of the crystal grain size distribution of more than 15 μm has poor workability and cracks are generated during bending.

(Example 2) As in Example 1, alloys having the compositions shown in Table 3 were melted and cast in an argon atmosphere using an induction heating furnace. At this time, as the raw materials of the rare earths, iron, and copper, those having a purity of 99.9% were used as in Example 1, and ferroboron was used as the boron.

The cast ingot thus obtained was placed in an iron capsule, deaerated, sealed, and hot-rolled at a processing temperature of 950 ° C. as in Example 1. At this time, rolling with a workability of 30% was performed four times so that the final workability was 76%.

A width of 10 m is obtained from the rolled magnet thus obtained.
A plate-like sample of m × length 12 mm × thickness 1 mm was cut out. When the average grain size and crystal grain size distribution were determined by observing the structure of this plate sample, the distributions shown in Table 4 were obtained. This plate sample is heated at 1000 ° C in an inert gas.
After heating, the mold was bent under the following three conditions to form an arc-shaped magnet having an outer diameter of 14 mm and an inner diameter of 12 mm.

Condition 1: Strain rate 1.5 × 10 ⁻⁴ / s (processing speed 0.21
6 mm / min) Condition 2: Strain rate 4.0 × 10 ⁻⁴ / s (processing speed 0.57
6 mm / min) Condition 3: Strain rate 7.5 × 10 ⁻⁴ / s (processing speed 1.08
0 mm / min) At this time, 6 samples were processed per one condition. The results are shown in Table 5. Here, the number of successes is the number of samples that have been bent without causing cracks among the 6 samples processed under the same conditions.

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

From these results, it was found that the magnet alloys having a standard deviation of the crystal grain size distribution in the hot-worked magnet alloy of more than 15 μm had poor workability, and cracks occurred especially in bending at a high strain rate. I understand.

(Example 3) As in Examples 1 and 2, alloys having the compositions shown in Table 6 were melted and cast in an argon atmosphere using an induction heating furnace. At this time, as the raw materials of the rare earths, iron and copper, those having a purity of 99.9% were used as in the case of Examples 1 and 2, and ferroboron was used as the boron.

The cast ingot thus obtained was placed in an iron capsule, deaerated, sealed, and hot-rolled at a working temperature of 950 ° C. as in Examples 1 and 2.
At this time, rolling with a workability of 30% was performed four times so that the final workability was 76%.

A width of 10 m is obtained from the rolled magnet thus obtained.
A sample of m × length 40 mm × thickness 4 mm was cut out. When the structure of these samples was observed and the particle size distribution was examined, the standard deviations were all 15 μm or less. This plate sample is placed in an inert gas to 100
After heating to 0 ° C., the mold was bent under the following three conditions to form an arc-shaped magnet having an outer diameter of 25 mm and an inner diameter of 21 mm.

Condition 1: Processing speed 1.20 mm / min (strain speed 3.0
× 10 ^-4 / s) Condition 2: Processing speed 3.00 mm / min (strain speed 7.5)
× 10 ^-4 / s) Condition 3: Processing speed 4.00 mm / min (strain speed 1.0
× 10 ^-3 / s) The results are shown in Table 7. Here, the number of successes is the number of samples for which the bending process has been completed without the generation of cracks due to the process.

[0056]

[Table 6]

[0057]

[Table 7]

From these results, it is found that the magnet alloy after hot working containing crystal grains having a grain size three times or more of the average grain size has poor workability and cracks especially in bending at a high strain rate. It can be seen that

From the above examples, the average crystal grain size is 40 μm.
In the magnet alloy after hot working having a temperature of m or less, the standard deviation of the crystal grain size distribution is set to 15 μm or less, and by performing hot bending, it is possible to prevent cracking during bending, Obviously, bending at a strain rate is possible. Further, by setting the crystal grain size of the magnet alloy after hot working to 40 μm or less and not containing the crystal grains having a grain size three times or more of the average grain size, the processing caused by the coarse crystal grains is performed. Deterioration of sex does not occur,
It is clear that cracking can be prevented from occurring during bending and that processing at a high strain rate becomes possible.

[0060]

As described above, the method for manufacturing a permanent magnet of the present invention has the following effects.

(1) The manufacturing process is simple and the cost is low.

(2) Compared with the conventional sintering method, the processing man-hour and the production investment can be remarkably reduced.

(3) As compared with the conventional method for producing a magnet by the melt spinning method, a high-performance and low-cost magnet can be produced.

(4) A magnet having a shape that was difficult to manufacture by the conventional method for manufacturing a magnet by the hot working method can be manufactured at low cost with high productivity.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor St. Arai 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (72) Inventor Koji Akioka 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Within the corporation

Claims (2)

[Claims] 1. R (where R is at least one of rare earth elements including Y), Fe and B as raw material basic components, an alloy having the basic components is melted and cast, and then a cast ingot is heated to 500 ° C. or higher. In an arc-shaped magnet manufactured by hot working at a temperature of, and hot bending, the average grain size of the magnet alloy after hot working is 40 μm or less, and the standard deviation of the grain size distribution is 15 μm. A method for producing a permanent magnet, which comprises bending the following magnet alloy. 2. The manufacturing of a permanent magnet according to claim 1, wherein bending is performed on a magnet alloy that does not contain crystal grains that are three times or more of the average grain size after hot working. Method.