JPS62198103A - Rare earth-iron permanent magnet - Google Patents

Abstract

PURPOSE:To provide a cast rare earth-iron permanent magnet which does not need grinding, sintering and is inexpensive by casting an alloy which has rare earth element including Y, B, Co and iron, and then heat treating at specific temperature or higher. CONSTITUTION:An alloy which contains 8-25, 2-8 and up to 40atom% of R, B and C, the residue of iron and other unavoidable impurities in production is melted, so cast that the cast macrostructure is a columnar crystal, and a cast ingot is heat treated at 500 deg.C or higher to be magnetically cured. The main phase of the obtained R-Re-B magnet is R2Fe14B. If the R is 8atom% or less, this compound is not formed, and since it become the same cubic structure as alpha-iron, high magnetic property is not obtained. If the R exceeds 25atom%, the magnetic property that nonmagnetic R-rich phase content is not large is remarkably reduced. If the B is less than 2atom%, the alloy becomes rhombic structure in R-Fe alloy, and high coercive force is not obtained. If the B is 8atom% or higher, the coercive force in the cast state cannot be obtained. The Co is a useful element to raise Curie point and to improve temperature characteristic, and up to 40atom% of the Co is proper due to low cost and easy workability.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to rare earth-iron permanent magnets.

[Conventional technology]

Conventionally, R-? The following five methods have been reported for manufacturing -B type magnets.

+11 Sintering method based on powder metallurgy (Reference 1).

(2) A quenched ribbon used to produce an amorphous alloy is used to produce a quenched thin piece with a thickness of about 50 μm, and the thin piece is made into a magnet using a resin binding method (Reference 2).

+3) A method in which the same flakes used in method +21 are mechanically aligned using a two-step hot press method (Reference #2).

References 1. M, Sagawa, S, F'ujim
ura, N, TogawaH, Yamamoto an
d Y, Matsuura; , T, Appl, Ph
ys.

Vol, 55(6), 15 Maroh 1981i
, P2O85Reference 2. R,W,Lee;A
ppl, Phys, nett, Vo146(8),
15 Apτ111985. The above-mentioned conventional technology will be explained in conjunction with the P79'0 document. 1s.

In the sintering method (1), an alloy ingot is produced by melting and casting, and is crushed into magnet powder having a particle size of about 6 μm. Magnetic powder is mixed with a binder, which serves as a molding aid, and press-molded in a magnetic field to complete a molded product. The compact is sintered in argon at a temperature around 1100° C. for 1 hour and then rapidly cooled at room temperature. After sintering, 600
Coercive force is further improved by heat treatment at a temperature around ℃.

(2) First, R-
Make Fe-B@-gold quenched ribbon. The resulting thinness.

The band is ribbon-shaped with a thickness of 50 μm and a diameter of 100 μm.
Polycrystals with less than 0 points are gathered. The ribbon is brittle and easily cracked, and since the crystal grains are distributed in the same direction, it is also magnetically isotropic. 7 tb can be made by making the stiff ribbon into an appropriate particle size, kneading it with resin, and press-molding it.

In the manufacturing method (3), first, a ribbon-like quenched ribbon or piece of ribbon is heated in a vacuum or in an inert atmosphere for about 70 minutes.
Preheat at 0°C and place in a press mold made of graphite or other heat-resistant material. Uniaxial pressure is applied when the ribbon reaches the desired temperature. Although the temperature and time are not specified, the conditions for achieving sufficient plasticity are T = 725 ± 250 °C,
A suitable pressure is about PN2,41;on/d.

At this stage, although the magnet is slightly oriented in the pressing direction, it is generally isotropic. The next hot press is carried out in a flood with a large area. most commonly 7
Press at 17 tons for a few seconds at 00°C. Then, the axis of easy magnetization of the sample becomes oriented parallel to the shiveless direction at the initial thickness of 14, and the alloy becomes anisotropic.

These steps are performed using a two-step hot press method (two-at-one).
ags hot-press procedure
), a dense and anisotropic R-Fe-B magnet can be produced by this method. In addition, the ribbon M crystal grains made by the first melt spinning method are made smaller than the grain size when they exhibit the maximum coercive force.
Afterward, the crystal grains are coarsened during hot pressing so that they have the optimum grain size.

[Problems to be Solved by the Invention] Although R-Fe-B magnets can be manufactured using the above-mentioned conventional techniques, manufacturing methods using these techniques have the following drawbacks. There is. In the sintering method (1), it is essential to turn the alloy into powder, but since R-Fe-B alloys are very active against oxygen, turning them into powder makes the acid ratio even more severe. The oxygen concentration in the sintered body inevitably increases. Also, when molding the powder, a molding aid such as zinc stearate must be used, and this is removed in advance during the sintering process, or some percentage of it is contained in the magnet. remains in the form of carbon 1
cormorant. This carbon significantly reduces the magnetic performance of R-kP'e-B. The molded body after press molding without the molding aid is called a green body. This is very fragile and difficult to handle. Therefore, another major drawback is that it takes a considerable amount of effort to neatly arrange them in the sintering furnace.

Because of these drawbacks, generally speaking, the production of R-Fe-B sintered magnets does not only require expensive equipment, but also has low production efficiency and low magnet production costs. It gets expensive. Therefore, it cannot be said that this is a manufacturing method that can fully take advantage of the low raw material costs of R-Fe-B magnets.

Production methods (2) and (3) use a vacuum melt spinning device. This equipment is currently very unproductive and expensive. In (2), since it is isotropic in principle, the energy product is low, and the squareness of the hysteresis loop is not good, so it also has a negative effect on temperature characteristics.

It is also disadvantageous in terms of use. What is the method for (3)?

Although this method uses a hot press in two stages, it is a unique method, but it cannot be denied that it is extremely inefficient when considering mass production.

The method of manufacturing an R-Fe-B magnet according to the present invention solves these drawbacks, and its purpose is to:
Our goal is to provide low-cost, high-performance magnets.

[Means to solve the problem]

The permanent magnet of the present invention relates to a rare earth iron-based permanent magnet, and specifically R is 8 to 25 atoms.

An alloy consisting of 2 to 8 atoms of B, ~40% Co, and the remainder iron and other unavoidable impurities is completely melted, and the casting is left so that the macrostructure of the casting becomes a columnar crystal. It is characterized by magnetically hardening the ingot by heat-treating it at a temperature of 500°C or more, and in order to make a resin magnet, the strain on the crystal lattice is reduced by hydrogen pulverization.

Characterized by the fact that it mixes with organic resin and rubber,
For low cost [1 fat bond magnetization, it is characterized by being mixed with ferrite powder.

As mentioned above, the existing methods of manufacturing rare earth-iron permanent magnets, the sintering method and the quenching method, each have major drawbacks such as difficulty in powder control through pulverization and poor productivity.

In order to improve these drawbacks, the present inventors began research on an alloy that can obtain coercive force in the bulk state, and found that it is possible to obtain coercive force in the bulk state with the above composition. At this time, it is easier to obtain coercive force if the casting structure is columnar crystals, and an anisotropic magnet can be obtained by utilizing the anisotropy of columnar crystals, so it is also possible to use equiaxed crystals. He invented a permanent magnet with high performance. Since there is no need to crush the cast ingot, the sintering method does not require any strict atmosphere control, and a furnace with high mass productivity such as a belt furnace can be used for heat treatment, greatly reducing equipment costs. Similar studies include Hiroaki Miho et al.
Japan Institute of Metals, 1985 Autumn Lecture, Purchase number (5
714, )), but this research not only differs in the composition range from the present invention, but also makes no mention of changes in performance due to macrostructure, and is significantly inferior to the present invention in terms of performance. Also after being magnetically hardened.

In the case of this system, secondary processing to obtain the desired shape is also possible, with bending strength and strength compared to conventional samarium cobalt rare earth magnets.
Since the compressive strength is high, it is very difficult to use.The present invention can also be applied to AT fat bonded magnets.

Resin-bonded type R using the rapid cooling method of the prior art (2) mentioned above
-Fe-B magnets have major drawbacks of low performance and high cost. In addition, Nd, as represented by Reference 1,
With high B compositions such as Fe, Bl, etc., even if a coercive force iHc of about 10 KOe is obtained by sintering, the coercive force iHc decreases to about I KOe when crushed for resin bonding, making it difficult to make a good resin bonded magnet. do not have. However, in the alloy of the present invention, if hydrogen pulverization is used, which causes less strain on the crystal lattice, a considerable coercive force can be maintained even in the powder state.
Since magnetic field orientation is also possible, it is also possible to create anisotropic resin magnets. Even with resin-bonded magnets, in the case of injection molding using thermoplastic resin, etc., kneading and magnetic field orientation at high temperatures of 2Co to 500°C are required, but ordinary simple six-element R-
In the case of Fθ-B magnets, one Curie point is only about 500° C., making orientation difficult at high temperatures. In the case of this system, even if the gold is increased by one point by adding cobalt, both the bulk and powder states are more easily maintained than iHc or additive-free compositions, so resin-bonded magnets can be easily manufactured by injection molding. .

Existing injection molded magnets are made of ferrite (BI (product: 1 to 1.5)
MGOe) and saurium cobalt (BH product 6 to 12
0e). However, the ferrite type has advantages and disadvantages, such as low cost but low performance, and samarium cobalt type high performance but high cost, and there is no intermediate magnet between the two. Due to the recent trend towards lighter, thinner, shorter and smaller metals, although the performance of the Siphelite type is lacking,
In many fields, the samarium cobalt type is not only cost-effective, but also too expensive to replace. In these fields, appropriate performance can be easily obtained at low cost by mixing the present magnet powder and ferrite powder and injection molding the powder. For ferrite powder, the Curie point temperature is approximately 450°C, and for simple five-element R-Pe-B powder, the Curie point difference is nearly 150°C, making it difficult to simultaneously knead and orient the mixed powder. Total 10
Even if the iH decreases by about 15%, it becomes a practical problem.
There is no drop in c, and it has a straight high rise, almost the same as cucumber single point sima ferrite, so it can be treated as a single powder.

Since these R-Fe-B powders for resin binding are easily oxidized, they can be surface-treated before being kneaded with the resin to prevent oxidation and to enhance the bonding force with the resin. When mixed with ferrite powder, similar surface treatment is required for the ferrite powder due to its bonding strength with the resin.

The composition of a conventional R-Fe=B magnet is R, gFe, and 7 Bg, as typified by reference 1 mentioned above.
-Composition R+t, tF'eat, a13s of the main phase R, Fe, and 4B compounds of the Fe-B magnet expressed in atomic percentages,
It has shifted to the side rich in both R and B elements compared to o.

This means that in order to obtain coercive force, not only the main phase but also Rrich
However, in the composition according to the present invention, on the contrary, a peak value exists where the amount of B is shifted to the side where there is less B. In this composition range, the coercive force is reduced by the sintering method, so this has not been considered a problem until now. However, in the bulk state immediately after casting, a high coercive force can be obtained only in this composition range, and a sufficient coercive force cannot be obtained in the normal B-rich side. This means that some change has occurred in the coercive force mechanism, and this is the reason why hydrogen milling produces powder with a practically sufficient coercive force of kW. It is thought that the legacy became possible.

The use of columnar crystals as a permanent magnet material has been used not only for alnico magnets but also for samarium-cobalt magnets, which are rare earth magnets.
It has been announced as an application to resin bonded samarium cobalt magnets (T, Shimoda et al., Pr0ceθdi
ngs of the fifth jnterhat
ianalWorkshop on Rare Ear
th-Cobalt Pern+orentMagre
ts, 1981, P595).

In the present invention as well, obtaining columnar crystals in a cast state is an important point for producing a high-performance magnet. That is, the process of obtaining coercive force through heat treatment is due to diffusion, and like samarium cobalt, it is easier to obtain coercive force with columnar crystals. Furthermore, this type of magnet.

Since the axis of easy magnetization is oriented in a plane perpendicular to the columnar crystals, it is possible to create an in-plane anisotropic magnet by using columnar crystals.

The reasons for limiting the composition of the permanent magnet according to the present invention will be explained below. Rare earths include Y, La, Oe, Pr, and Nd.

Ss, Fu, Gd, Tb, Dy, Ho, In, Tm, Y
b, Lu are listed as candidates, and one or more of these may be used in combination. The highest magnetic properties are obtained with Pr. Therefore, Pr practically.

Pr-H6 alloy, Ce-Pr-Nd alloy, etc. are used.

Further, a small amount of a substituent element such as heavy rare earth elements such as Dy-Tb, Mo, 81, etc. is effective in improving the coercive force.

The main phase of the R-Fe-B magnet is R21Pe, B.

Therefore, if R is less than 8 atoms, the above compound is no longer formed and the structure becomes a q-cubic crystal structure, which is the same as that of α-iron, so that high magnetic properties cannot be obtained. - If R exceeds 25 atoms, the magnetic properties, which do not have a large amount of non-magnetic Rrich phase, will be significantly degraded. Therefore, a suitable range is 8 to 25 atom %.

B is an essential element for forming all the R and Fe14B phases, and if it is less than two atoms, it becomes a rhombohedral R-Fe system, so a high coercive force cannot be obtained. However, if 8 or more atoms are added, as in the conventional sintered magnet, the coercive force in the cast state cannot be obtained.

Therefore, a suitable range for the amount of B is 2 to 8 atoms.

CO is an element useful for raising the Curie point and improving temperature characteristics, but it tends to reduce the coercive force as the amount increases. Furthermore, when the Co content is increased, the low cost and ease of processing, which are the characteristics of this magnet, are lost. From these points of view, a suitable range for Cot is 4° at %.

[Example 1] A manufacturing process diagram according to the present invention is shown in FIG. First, an alloy with a desired composition is melted in an induction furnace, and iron is cast to form columnar crystals. The ingot is then magnetically hardened.
Annealing treatment is performed in a temperature range of 5Co to 1,050 tl. In the case of a cast type, if cutting and grinding are performed at this stage, it will become an in-plane anisotropic magnet that takes advantage of the anisotropy of columnar crystals. In the case of the resin bonded type, it is made of 18-8 stainless steel (In) at room temperature, and is ground by holding it in a hydrogen gas atmosphere of about 50 atm for about 24 hours in a high-pressure container. When mixing ferrite powder, After mixing and surface treatment at this stage, it is kneaded with resin and injection molded.

A resin-bonded magnet was prepared by melting the composition shown in the following table and pulverizing a cast in-plane anisotropic magnet with hydrogen using the method shown in FIG. 1, followed by kneading 4 weight widths of epoxy resin.

Table 1 Note that all annealing was performed at 1000° C. for 2 hours. The results obtained are shown in Table 2.

Table 2 also shows an example in which N(L, Feyy Bs (a typical composition of the prior art) was subjected to the same treatment as a comparative example).

[Example 2] Cel N d4 F in atomic ratio! ”4 F e61A
An alloy having a composition represented by 4400H1B4 (this alloy has a Curie temperature of 450°C) was subjected to hydrogen pulverization in the same manner as in Example 1, and then 60w of strontium ferrite powder was obtained.
After mixing with t% in an organic solvent to prevent oxidation, the following surface treatment f was performed. First, the powder was treated with PH10 potassium dichromate to form a film of 0rlO on the surface of the powder, and then treated with a silane coupling agent. ◎Next, 90wt% of the mixed powder and nylon 12 (1wt%) were added. 2
After kneading at 50° C., the mixture was subjected to magnetic field injection molding.

The performance obtained is as follows.

Br=4.5KG Mc=4°0KG (BH)a+ax=42 MGOe It can be seen that the performance of the sintered ferrite magnetic sintered magnet was achieved by the injection molding method.

〔Effect of the invention〕

As described above, according to the invention, it is possible to obtain a coercive force in the bulk state in a composition range where a coercive force of 1Hc could not be obtained with the conventional sintering method, and there is no need for powder sand, sintering, etc. A rare earth-iron permanent magnet is obtained. Furthermore, with hydrogen pulverization, coercive force is maintained even in the powder state, so a high-performance, low-cost resin-bonded magnet can be obtained.If this powder is mixed with ferrite powder, a resin-bonded magnet with higher performance than ferrite pound magnets can be obtained. Coupled magnets are easily obtained.

[Brief explanation of drawings]

The first one is a manufacturing process diagram of the present invention'/) R-Fe-B magnet. Above and 1 other person

Claims (3)

[Claims] (1) In terms of atomic percentage, R8 to 25% (R is at least one rare earth element including Y), B2 to 8%, Co
After melting the alloy consisting of ~40% and the balance consisting of iron and other impurities unavoidable in manufacturing, and casting the cast ingot so that the cast macrostructure becomes a columnar crystal, the cast ingot is
A rare earth-iron permanent magnet characterized by being magnetically hardened by heat treatment at a temperature of ℃ or higher. (2) The rare earth-iron permanent magnet according to claim 1, wherein the magnet powder obtained by pulverizing the ingot is kneaded with an organic resin or rubber as it is or after an appropriate surface treatment. (3) The rare earth-iron permanent magnet according to claim 2, characterized in that it is mixed with ferromagnetic ferrite powder.