JPH03196601A - Permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a high quality and low-cost magnet by casting a material composed mainly of rear earth elements (including Y), transition metal, and boron into a copper mold to form a magnet having a macro composition in a columnar structure; and make the magnet anisotropic. CONSTITUTION:A magnetic material, composed of rear earth elements (including Y), transition metal, and boron, is cast into a copper mold to form an anisotropic magnet, which has a macro composition in a columnar form. That is, the cast magnet is subjected to a hot process to make it anisotropic. The magnet is then heat-treated for a sufficient coercive force. According to this method, a high quality magnet is obtained with high productivity simply by heat-treating an ingot without pulverization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a permanent magnet whose main components are a rare earth element, a transition metal, and boron, and a method for manufacturing the same.

[Conventional technology]

Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers.

With the recent demand for smaller and more efficient electrical products,
Permanent magnets are also required to have increasingly higher performance. Typical permanent magnets currently in use are alnico, hard ferrite, and rare earth-transition metal magnets. In particular, R-Co permanent magnets, which are rare earth-transition metal magnets, and R
Since -Fe-B permanent magnets provide high magnetic performance, much research and development has been carried out on them.

Conventionally, there are methods for manufacturing these R-Fe-B permanent magnets as shown in the following documents.

(1) A sintering method based on powder metallurgy.

(References 1 and 2) (2) A quenched thin strip with a thickness of about 30 um is made using a quenched ribbon production device used to manufacture amorphous alloys, and the quenched thin section is made into a magnet using a resin bonding method using the melt spinning method. (References 3, 4) (3) A method of mechanically orienting the rapidly cooled flakes used in method (2) above using a two-step hot press method, (References 45 and 5) ) Here, Document 1: JP-A-59-46008: Document 2:
M, Sagawa, S, Fujimura, N, T
ogawa, H.

Yamamoto, and Y, Matsuura:
J, Appl, Phys, Vol, 5516115Ma
roh 1984. p2083゜Reference 3: Unexamined Japanese Patent Publication No. 1983-
Publication No. 211549: Document 4: R, W, Lee; A
ppl, Phys, Lett, Vol, 45 (81°1
5 April 1985. p790; Document 5: Japanese Unexamined Patent Publication No. 60-100402 Next, the above conventional method will be explained.

First, in the sintering method (1), an alloy ingot is produced by melting and casting, and then pulverized to obtain magnet powder with an appropriate particle size (several μm). Magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to complete a molded product. The compact was sintered in argon at a temperature of around 1100°C for 1 hour.
It is then rapidly cooled to room temperature. After sintering, the coercive force is improved by heat treatment at a temperature of around 600°C.

In the resin bonding method (2) using quenched flakes by the melt spinning method, first, a quenched ribbon of R-Fe-B alloy is produced at an optimal rotation speed of a quenched ribbon manufacturing apparatus. Obtained thickness 3
A ribbon-like thin strip of 0 um is an aggregate of crystals with a diameter of 1000 Å or less, is brittle and easily broken, and since the crystal grains are distributed in the same direction, it is also magnetically isotropic. This ribbon is crushed to an appropriate particle size, mixed with resin, and press-molded.

The manufacturing method of (3) is to process the ribbon-like quenched ribbon or flake in (2) by a method called a two-step hot pressing method in vacuum or in an inert atmosphere to produce dense and anisotropic R-Fe-B. This is what you get from magnets.

Uniaxial pressure is applied during this pressing process.

The easy axis of magnetization is oriented parallel to the pressing direction, making the alloy anisotropic.

In addition, the crystal grains of the ribbon-like ribbon produced by the initial melt spinning method are made smaller than the grain size at which they exhibit the maximum coercive force, and the grains become coarser during the subsequent hot pressing. This is done so that the particle size is optimal.

[Problem to be solved by the invention]

Although it is possible to manufacture permanent magnets whose main components are rare earth elements, iron, and poron using the conventional techniques described above, these manufacturing methods have the following drawbacks.

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, oxidation becomes even more intense when they are turned into powder. The oxygen concentration in the body is inevitably high, and when the powder is compacted, compacting aids, such as zinc stearate, must be used, which are removed beforehand during the sintering process. , the dispersion in the forming aid will remain in the magnet body in the form of carbon, and this carbon will significantly increase the R-Fe
- It is undesirable because it lowers the magnetic performance of the B alloy.

The molded body that has been press-formed with a forming aid added is called a green body, which is very brittle and difficult to handle, so it can take a lot of effort to neatly line it up and put it into the sintering furnace. This is a big drawback. Because of these drawbacks, manufacturing R-Fe-B permanent magnets for boat fishing not only requires expensive equipment, but also has low production efficiency, resulting in high magnet manufacturing costs. turn into.

Therefore, it cannot be said that this is a method that can take advantage of the advantages of R-Fe-B magnets, which have relatively low raw material costs.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very poor productivity and is expensive.

The method (2) using resin bonding is isotropic in principle, resulting in a low energy product, and the squareness of the hysteresis loop is also poor, which is disadvantageous in terms of temperature characteristics and usage.

Method (3) is a unique method that uses a hot press in two stages, but it cannot be denied that it is extremely inefficient when considering actual mass production.

Furthermore, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force i Hc, making it impossible to produce a practical permanent magnet.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to provide a high-performance, low-cost rare earth-iron permanent magnet and a method for manufacturing the same.

[Means for Solving the Problems] The permanent magnet of the present invention is a magnet whose main components are a rare earth element (including Y), a transition metal, and boron, and the macrostructure of the magnet is cast using a copper mold. It is a permanent magnet characterized by columnar crystals and anisotropy.

Therefore, the first method for producing permanent magnets is to produce magnets whose main components are rare earth elements (including Y), transition metals, and boron, by casting using a Cn mold.
A method for manufacturing a permanent magnet, characterized in that the macrostructure of the magnet is made into columnar crystals, and then heat treated at a temperature of 250° C. or higher, the macrostructure of the magnet is made into columnar crystals, and the magnet is magnetically hardened. The second method for manufacturing magnets is to orient the crystal axes of the crystal grains in a specific direction by hot working at a temperature of 500°C or higher after casting using a copper mold, and then hot working at a temperature of 500°C or higher. A method for producing a permanent magnet, characterized in that the magnet is made anisotropic by hot working, and a third method for producing a permanent magnet is a method for producing a permanent magnet after hot working in the second production method. , a method for producing a permanent magnet characterized in that it is magnetically hardened by heat treatment at a temperature of 250° C. or higher.

[Function] As mentioned above, the sintering method and the quenching method, which are methods for producing rare earth-iron magnets, each have major drawbacks such as difficulty in powder control through pulverization and poor productivity.

In order to improve these drawbacks, the present inventors undertook research on magnetization in the bulk state, and first, in the composition range of magnets whose basic components are rare earth elements, transition metals, and boron, Cn
It was discovered that sufficient coercive force could be obtained by casting using a mold, making the macrostructure into fine columnar crystals, making it anisotropic by hot working, and then applying heat treatment. That is,
(1) By making the macrostructure during casting into fine columnar crystals, in-plane anisotropy (I
It is possible to produce a magnet with a degree of orientation of the easy-to-ify axis of 70%).

(2) By forming the casting macrostructure into fine columnar crystals, uniaxial anisotropy due to hot working is promoted, and the degree of orientation of the axis of easy magnetization is considerably increased.

(3) As a result of (1) and (2), high-performance magnets can be manufactured without going through the powder state, which is difficult to control, so strict atmosphere control is no longer necessary for heat treatment, improving magnet productivity, and improving equipment. Costs can also be significantly reduced.

The optimal composition of conventional R-Fe-B magnets is R+sFe ttB s as typified by Document 2.

This composition shifts to the side rich in RlB compared to the composition R21, tFesx4Bs, s, in which the main phase RtFe+4B compound is expressed as an atomic percentage. This is explained from the point that in order to obtain a coercive force, not only the main phase but also non-magnetic phases such as an R-rich phase and a B-rich phase are required.

However, in the case of the appropriate composition according to the present invention, the peak value of the coercive force exists where the B content shifts to the side where there is less B. In this composition range, the coercive force is drastically reduced in the case of the sintering method, so it has not been much of a problem so far.

However, when a casting method is used, it is easier to obtain a coercive force on the low B side than the stoichiometric composition, and it is difficult to obtain it on the high B side.

These points can be considered as follows. First of all, whether a sintering method or a casting method is used, the coercive force mechanism itself is 1uc.
It follows the leation model. This can be seen from the fact that the periodization curves for both of them show a steep rise like Sm Co *.

The coercive force of this type of magnet is basically based on a single domain model. That is, in this case, if the R5Fe+J compound having large magnetocrystalline anisotropy is too large, it will have domain walls within the grains, so the reversal of magnetization will easily occur due to the movement of the domain walls, and the coercive force will be small.

On the other hand, when the particles become smaller and exceed a certain size, each particle no longer has a domain wall, and the reversal of magnetization proceeds only by rotation, so the coercive force increases.

In other words, in order to obtain an appropriate coercive force, Rs Fe 14
It is necessary that the B phase has an appropriate particle size. A suitable particle size is around 10 gm, and in the case of a sintered type, the particle size can be adjusted by adjusting the powder particle size before sintering.

However, in the case of the casting method, the size of the crystal grains of the R□Fe+4B compound is determined at the stage of solidification from molten metal, so it is necessary to pay attention to the composition and solidification process.

The material that has the biggest influence on solidification is the material of the mold.
22 (Reference 6) shows examples of iron molds and ceramic molds, but in the present application, this is limited to copper molds. this is,
This is because copper has excellent thermal conductivity, is highly efficient at cooling molten metal, and is the perfect material for creating uniform, fine crystals.

Next, regarding the composition, if B is contained in an amount of 8 at % or more, the size of the RF e 14B phase after casting tends to become coarse, and it is difficult to obtain a coercive force unless the cooling speed is faster than usual.

On the other hand, in the low boron region, crystals can be easily refined by adjusting the mold, casting temperature, etc. From a different perspective, this region can be said to be a Fe-rich phase compared to RwFe+aB, and in the solidification stage, Fe first appears as primary crystals, followed by a peritectic reaction.

R*F e 14B phase appears. At this time, since the cooling speed is much faster than the equilibrium reaction, the R*Fe+J phase solidifies around the primary Fe. Since this composition range contains less B, it goes without saying that the typical composition of the sintered type is R+aF e yyB
Rich phases such as a can be almost ignored in quantity.

The heat treatment is for diffusing primary Fe to reach an equilibrium state, and the coercive force is largely dependent on the diffusion of this Fe phase.

Next, the meaning of using columnar crystals in the macrostructure in the present invention will be described.

As mentioned above, there are two effects of using columnar crystals, one of which is to increase in-plane anisotropy during casting, and the other is to improve performance during hot working.

First, to explain the former, when the intermetallic compound Rz Fe+48 (R is a rare earth), which is the source of magnetism in water-based magnets, develops columnar crystals, its easy magnetization axis C-axis lies in a plane perpendicular to the columnar crystals. It has the property of being distributed, that is, C
The axis is not in the direction of columnar crystal growth, and the in-plane anisotropy is distributed only in the plane perpendicular to the axis. Naturally, this magnet has higher performance than one using an isotropic equiaxed product as the macrostructure, and is very advantageous. However, even if columnar crystals are used, the grain size must be fine due to coercive force, and the lower the B side, the better.

Next is the latter, which further enhances the anisotropy effect of hot working. The degree of orientation of the anisotropic magnet is expressed as kl-A = Bx/J (Bx"+ By" +
When defined as Bz"l x 100 (%) (Bx, By, and Bz are the residual magnetic flux densities in the x, y, and z directions, respectively), the isotropy is approximately 60% and the in-plane anisotropy is 70%.Thermal The anisotropy effect (orientation increase effect) due to preliminary processing exists regardless of the degree of orientation of the processed material, but the higher the degree of orientation of the source material, the higher the degree of orientation of the final processed material. Increasing the degree of orientation of the base material by using the above is effective in ultimately obtaining a high-performance anisotropic magnet.The preferred composition range of the permanent magnet according to the present invention will be described below.

Rare earths include Y, La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ha, Er, Tm, Yb, L
u is listed as a candidate, and one or more of these may be used in combination. The highest magnetic performance is obtained with Pr.

Therefore, Pr, Pr-Nd alloy, Ce-Pr-
Nd alloy or the like is used. Further, small amounts of additive elements, such as heavy rare earth elements such as Dy and Tb, Al, Mo, and Si, are effective in improving the coercive force.

The main phase of the R-Re-B magnet is R1Fe+4B. Therefore, if R is less than 8 at %, the above compound is no longer formed and a cubic crystal structure having the same structure as α-iron is formed, so that high magnetic properties cannot be obtained.

On the other hand, if R exceeds 30 atomic %, the nonmagnetic R-rich phase increases and the magnetic properties deteriorate significantly.

Therefore, a suitable range for R is 8 to 30 atomic %.

However, since it is a cast magnet, it is preferably R8~258~
It has 25 atoms.

B is an essential element for forming the RxFexB phase, and if it is less than 2 atom%, it will become a rhombohedral R-Fe system, so high coercive force cannot be expected, and if it exceeds 28 atom%, a B-rich nonmagnetic phase will form. As the residual magnetic flux density increases, the residual magnetic flux density decreases significantly. However, for a cast magnet, B88 atoms or less are preferable; if it is larger than that, it is difficult to obtain a fine RxFe+4B phase, and the coercive force becomes small.

Ce is an effective element for increasing the Curie point of water-based magnets, and basically replaces Fe sites to create R2C014.
B is formed, but this compound has a small crystal anisotropy magnetic field, and as the amount increases, the coercive force of the magnet as a whole becomes smaller. Therefore, IK can be considered as a permanent magnet.
In order to provide a coercive force of Oe or more, the content is preferably within 50 atomic %.

AI has the effect of increasing coercive force. (Reference 7: Zh
ang Maocai et al., Proceedingsof
the 8th International Wor
kshop on Rare-Farth Magne
ts, 1985, p5411 This document 7 shows the effect on sintered magnets, but this effect also exists on cast magnets. However, A
Since I is a non-magnetic element, increasing the amount added lowers the residual magnetic flux density, and if it exceeds 15 atomic %, the residual magnetic flux density becomes lower than hard ferrite, so that it cannot fulfill its purpose as a rare earth magnet. Therefore, the amount of AI added is 15
It is preferably less than atomic %.

Next, examples of the present invention will be described.

[Example] A process diagram of the manufacturing method according to the present invention is shown in FIG.

First, according to the process diagram of FIG. 1, an alloy having the composition shown in Table 1 is melted in an induction furnace and cast into a copper mold to form columnar crystals.

Next, in order to harden the ingot magnetically, it was heated to 1000°C.
x 24 hours + 500℃ x 2 hours annealing treatment 6 In the case of a cast type, if cutting and grinding are performed at this stage,
This is an in-plane anisotropic magnet that utilizes the anisotropy of columnar crystals.

In the case of an anisotropic type, hot working is first performed before annealing treatment, and then annealing is performed.

In this example, hot pressing was used as the hot working method.

The processing temperature was 1000°C.

Next, Pr+4Fes2B4 had the highest performance among them.
and Nd, 9FettB, which is the optimal composition of the sintering method in Reference 2.
Regarding s, a comparison was made between one in which fine columnar crystals were formed using a copper mold and one in which ordinary columnar crystals were formed using an iron mold. The results are shown in Table 3, and Table 4 shows the grain size after hot working measured on the composition and mold side.

Table 1 Table 3 Table 4 It can be seen that this is related to the grain refinement effect.

By forming columnar crystals using the present invention, all magnetic properties such as coercive force iHe, maximum energy product (BH) =, orientation degree etc. is found to be superior.

【Effect of the invention〕

According to the permanent magnet and the manufacturing method thereof of the present invention as shown in the above, a high-performance magnet can be obtained by simply heat-treating a cast ingot without pulverizing it, and productivity can be improved. It is something.

[Brief explanation of drawings]

FIG. 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention. Below Up

Claims (4)

[Claims] (1) In a magnet whose main components are rare earth elements (including Y), transition metals, and boron, the macrostructure of the magnet cast using a copper mold is columnar and anisotropic. Permanent magnet. (2) In a method for manufacturing a magnet whose main components are rare earth elements (including Y), transition metals, and boron, the magnet is cast using a copper mold to have a columnar crystal structure, and then 2
A method for producing a permanent magnet, characterized in that it is magnetically hardened by heat treatment at a temperature of 50° C. or higher. (3) In a method for manufacturing magnets whose main components are rare earth elements (including Y), transition metals, and boron, crystal grains are 1. A method for producing a permanent magnet, which comprises orienting the crystal axis of a permanent magnet in a specific direction to make the magnet magnetically anisotropic. (4) In a method for manufacturing a magnet whose basic components are rare earth elements (including Y), iron, and boron, after casting using a copper mold, hot working at a temperature of 500°C or higher, then 250°C
A method for producing a permanent magnet, characterized in that it is magnetically hardened by heat treatment at a temperature above.