JPH04136131A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To manufacture a permanent magnet having high performance at low cost by subjecting the cast ingot of an allay in which rare earth elements, Fe and B are used as material essential components to remelting and casting, subjecting it to specified hot working and thereafter executing heat treatment at a specified temp. CONSTITUTION:R (where R denotes at least one kinds among rare earth elements including Y), Fe and B are used as material essential components. An alloy contg. the above essential components is melted and cast. Next, the cast ingot or the alloy obtd. by executing hot working to the above ingot is remelted and cast. After that, the cast ingot is hot-worked at >=500 deg.C and is then heat-treated at 250 to 1100 deg.C. Furthermore, for attaining its different high coercive force and high performance, after the hot working, it is heat-treated at 750 to 1100 deg.C and is thereafter heat-treated at 250 to 750 deg.C. In this way, the amt. of impurities therein is reduced, by which a fine and uniform columnar structure can be obtd. to the central part of the ingot.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a permanent magnet having magnetic anisotropy due to mechanical orientation. ), Fe.

This invention relates to a method for producing a permanent magnet using B as a basic raw material component.

[Prior art] Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household electrical appliances to peripheral terminal equipment for large computers, and have been used in recent years due to the miniaturization of electrical appliances. With the demand for higher efficiency, permanent magnets are also required to have increasingly higher performance.

A permanent magnet is a material that generates a magnetic field without supplying electrical energy from the outside, and one that has a large coercive force and a high residual magnetic flux density is suitable.

Typical permanent magnets currently in use are alnico cast magnets, ferrite magnets, and rare earth-transition metal magnets, with special emphasis on rare earth-transition metal magnets.
-Co-based permanent magnets and R-Fe-B-based permanent magnets have been extensively researched and developed as permanent magnets with extremely high coercive force and energy product.

Conventionally, there are methods for manufacturing these R-Fe-E based high-strength n and anisotropic permanent magnets, such as the one described above.

(1) First, Japanese Patent Application Laid-open No. 59-46008 and H.S.
Agawa.

ε, Fujimura, N., Togawa, H. Yam.
amoto and Y, Matsu-ura; J, ^
pp1. Phys, Vo1.55(6), 15 Mar
ch 1984. p2083 etc. have an atomic percentage of 8~
A permanent magnet characterized by being a magnetically anisotropic sintered body consisting of 30x of R (where R is at least one rare earth element including Y), 2 to 28% of B, and the balance Fe is produced using a powder metallurgy method. is disclosed to be manufactured by based sintering.

In this sintering method, an alloy ingot is produced by melting and casting, and then pulverized to obtain magnetic powder with 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 complete a molded product. The compact is sintered in argon at a temperature of around 11006C for 1 hour and then rapidly cooled to room temperature.

After sintering, the permanent magnet is heat treated at a temperature of around 1600°C to further improve its coercive force.

Furthermore, regarding the heat treatment of this sintered magnet,
No. 217540, Japanese Unexamined Patent Publication No. 62-165305, etc. disclose the effects of multistage heat treatment.

(2) JP-A-59-211549, R, W, Le
e; Appl.

Phys, Lett, troll, 46(8), 15
April 1985. P790 discloses an R-Fe-B magnet in which fine pieces of melt-spun alloy ribbon with a very fine crystalline magnetic phase are bonded together with a resin.

This permanent magnet is manufactured by making a quenched thin piece with a thickness of about 30 μm using a quenched ribbon manufacturing apparatus used for manufacturing an amorphous alloy, and then kneading the thin piece with a resin and press-molding it.

(3) JP-A-60-100402, R, W, Le
e: Appl.

Phys, Lett, Vol, 46(8), 15 A
pril 1985. For p790, a dense and anisotropic R-Fe-B 6M stone is obtained by using the rapidly cooled flakes used in the method (2) above in a vacuum or in an inert atmosphere using a method called a two-step hot pressing method. This is disclosed.

(4) Japanese Patent Application Laid-Open No. 62-276803 states that R (where R is at least one rare earth element including Y) 8 to
30 atom%, B2 to 28 atom%, Co50 atom% or less,
After melting and spinning an alloy consisting of 115 at. A rare earth-iron permanent magnet is disclosed in which the cast alloy is made magnetically anisotropic by orienting its crystal axis in a specific direction.

[Problem M to be solved by R-ming] The conventional manufacturing methods of R-Fe-B permanent magnets described in (1) to (4) above have the following drawbacks.

The manufacturing method for permanent magnets in (1) requires that the alloy be made into powder, but since R-Fe-B alloys are highly active against oxygen, making them into powder will cause additional oxidation. The oxygen concentration in the sintered body inevitably increases.

Furthermore, when molding the powder, a molding aid such as zinc stearate must be used, and this is removed beforehand during the sintering process, but several percent of the molding aid is This carbon remains in the magnet body in the form of carbon, which is undesirable because it significantly reduces the magnetic performance of the R-Fe-B magnet.

The molded product after press molding with a molding aid added is called a green body, which is extremely brittle and difficult to handle.
Therefore, another major drawback is that it takes a considerable amount of time and effort to neatly line up the pieces in the sintering furnace.

Because of these drawbacks, - in the shell, R-Fe-B
Not only does the production of sintered magnets require expensive equipment, but the production method has poor production efficiency, resulting in high magnet production costs. -The advantages of Fe-B magnets cannot be utilized.

Next, the permanent magnet manufacturing methods (2) and (3) use a vacuum melt spinning device, but this device currently has very low productivity and is expensive.

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

The method (3) for manufacturing permanent magnets is a unique method of using hot press in two stages, but it cannot be denied that it is 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 iHc, making it impossible to produce a practical permanent magnet.

The method (4) for manufacturing permanent magnets does not involve a powder process and only requires one step of hot pressing, so it is the manufacturing method that can simplify the manufacturing process and reduce mass production costs the most.
There were problems in that the casting structure was not uniform enough and the magnetic properties were slightly lower than in the sintering method.

The present invention solves the above-mentioned drawbacks of the prior art, particularly the problem (4) regarding the cast structure and the performance of permanent magnets, and its purpose is to provide a high-performance, low-cost permanent magnet. The purpose of this invention is to provide a method for manufacturing the same.

[Means for Solving the Problems] The method for manufacturing a permanent magnet of the present invention uses R (where R is at least one rare earth element including Y).

Fe and B are used as basic raw material components, and the alloy containing the basic components is melted and cast, and then the cast ingot or the alloy obtained by subjecting the ingot to hot working is melted and cast again.
After casting, the cast ingot is hot worked at a temperature of 500°C or higher, and then heat treated at a temperature of 250 to 1100°C.

In addition, in order to further increase coercive force and improve performance, heat treatment at 750 to 1100 °C after hot working is required.
It is characterized by heat treatment at a temperature of 750°C.

Here, cast ingots include those that have been previously cast twice or more, and alloys obtained by hot working cast ingots include those that have been previously hot worked two or more times, and Also includes those that have been heat treated one or more times after hot working.

As mentioned above, the method of manufacturing permanent magnets by casting has the disadvantage that it is difficult to make the casting structure uniform.

This is because impurities present in the molten metal become solidification nuclei during solidification, and also prevent the growth of columnar crystals from the casting wall, inhibiting the formation of a uniform columnar crystal structure. .

In the present invention, it has been found that by performing remelting and casting, the number of impurity types is reduced, thereby making it possible to obtain a fine and uniform columnar crystal structure up to the center of the ingot.

The preferred composition range of the permanent magnet in the present invention will be explained below.

Rare earths include Y, La, Ce, Pr,
Nd.

Sm, Eu, Gd, Tb, Dy,
Candidates include Ho, Er, Tm, Yb, and Lu, and one or more of these may be used in combination. The highest magnetic performance is obtained with Pr, so Pr, Pr-Nd alloy, Ce-Pr-N
d alloy etc. are used. Small amounts of heavy rare earth elements, e.g. DV
, Tb, etc. are effective in improving coercive force.

The main phase of an R-Fe-B magnet is RaFe+aB. Therefore, if R is less than 8 w, %, the above compound will no longer be formed and high magnetic properties will not be obtained; on the other hand, if R is 30 atomic %
If it exceeds 100%, the nonmagnetic R-rich phase increases and the magnetic properties deteriorate significantly. Therefore, the appropriate range of R is 8 to 30 atomic %. However, for high residual magnetic flux density, preferably R8~25w.

child% is appropriate.

B is an essential element for forming the R2Fe+*B phase, and if it is less than 2 atomic %, it becomes a rhombohedral R-Fe system, so high coercive force cannot be expected, and if it exceeds 28 atomic %, B-rich non- As the magnetic phase increases, the residual magnetic flux density decreases significantly. However, in order to obtain a high coercive force, preferably B
It is better to have 88 atoms or less, and if it is more than 88 atoms, fine R2Fe+a
It is difficult to obtain phase B, and the coercive force is small.

CO is an effective element for increasing the Curie point of the present magnet, but since it reduces the coercive force, it is preferably 50 atomic % or less.

Elements such as Cu, Ag, Au, Pd, and Ga that exist together with the R-rich phase and lower the melting point of the phase have the effect of increasing coercive force. However, since these elements are non-magnetic elements, increasing the amount will reduce the residual magnetic flux density, so it is preferably 6 at % or less.

The temperature during hot working is desirably higher than the recrystallization temperature, preferably 500°C in the R-Fe-B alloy of the present invention.
That's all.

The heat treatment temperature is preferably 250°C or higher in order to clean the grain boundaries and diffuse the initial Fe.
If the phase exceeds 11006C, grains will grow rapidly and the coercive force will be lost, so a temperature lower than that is preferable.

In addition, when performing heat treatment in two or more stages, the temperature in the first stage is preferably 7500C or higher so that the initial Fe diffuses quickly, and in the second stage, the temperature is around the melting point of the R-rich phase at the grain boundaries or below. That is, the temperature is preferably 750°C or lower, and the temperature higher than 250°C is preferable because it takes too much time for the effect of heat treatment to occur.

Next, examples of the present invention will be described.

[Example] [Example 1] A process diagram of the manufacturing method according to the present invention is shown in FIG.

According to this process, an alloy having the composition P r 17F 8765B5Cu I5 was melted and cast using an induction heating furnace in an Albon atmosphere. At this time, rare earth, iron and copper raw materials with a purity of 99.9% were used, and boron was ferroboron.Then, the obtained cast ingot was heated in an Rg'JJ heating furnace in an argon atmosphere. It was melted again and cast.

The structure of the thus obtained cast ingot was a columnar crystal structure, which was uniform and oriented to the center of the ingot.

This is presumed to be due to a decrease in the level of impurities in the ingot. In addition, R2FezB in this ingot
The average grain size of the crystal grains was 17.1 μm.

Next, a sample was cut into a cylindrical shape from this cast ingot, and the sample was fitted into an iron ring to restrain the sides.
Hot pressed to 0%. The press pressure at this time was 0.
2 to 0.8 ton/cm2, and the strain rate is 10-''
~10-'/sec.

Also, during this hot working, the axis of easy magnetization of the crystal was oriented parallel to the direction in which the alloy was pressed.

After that, heat treatment was performed at 1000°C for 24 hours,
Next, it was heat treated at 475°C for 2 hours, then cut and polished, and its magnetic properties were measured.

The magnetic properties and average particle size of this magnet are shown in Table 1 along with the values when remelting and casting were not performed (Comparative Example 1).

Table 1 All magnetic properties are B- at the maximum applied magnetic field of 25 kOe.
)1 Measured using a tracer.

As shown in Table 1, it can be seen that the magnet of the present invention is effective in decreasing the crystal grain size and improving the coercive force by melting and casting the magnet again after having been produced by -times tE. It is also clear that the maximum energy output is improved.

[Example 2] Similarly to Example 1, Pr+vFe76 was produced using an induction heating furnace in an argon atmosphere according to the manufacturing process shown in FIG.
．． An alloy having the composition 5BsCu+,s was melted to produce t4. At this time, rare earth, iron, and copper raw materials with a purity of 99.9% were used as in Example 1, and boron was ferroboron.

Sample 2a was cut out from the cast ingot thus obtained. Additionally, this cast ingot was placed in an iron capsule, degassed, and sealed. This was hot-rolled four times in air at 950°C with a working degree of 30%, so that the final working degree was 76%.

Sample 2b was cut out from the rolled ingot thus obtained.

Next, this rolled ingot was melted again in an argon atmosphere using an M1 heating furnace and cast.

The ingot thus obtained was placed in a S-made cover, degassed, and sealed. This is processed at 950°C with a processing degree of 30
% hot rolling in air four times, and the final workability was 7.
It was set to 6%. And from the rolled ingot,
Sample 2c was cut out.

Next, the ingot that was not hot rolled after the -th melting and casting was melted and cast again. This cast ingot was placed in an iron capsule, degassed and sealed, and hot-rolled at 950°C with a workability of 30% in air four times to achieve a final workability of 76%. Sample 2d was then exposed from the rolled ingot.

Samples 2a, 2b, 2c, and 2d were all heat-treated at 1000°C for 24 hours, and then heat-treated at 475°C for 4 hours.

Table 2 shows the magnetic properties of the four types of samples.

As shown in Table 2, hot rolling significantly improves coercive force in particular, but it is clear that melting and casting again improves magnetic properties, particularly coercive force and maximum energy product. It is.

[Example 3] Similarly to Example 1, an alloy having the composition shown in Table 3 was melted and cast using an induction heating furnace in an argon atmosphere according to the manufacturing process shown in FIG. The raw materials used at this time were also of similar purity. Then, the obtained cast ingot was melted again and cast.

Next, samples were cut into cylindrical shapes from these cast ingots, and the samples were hot-pressed in an argon atmosphere at 1000° C. to a degree of workability of 80% by fitting them into iron rings to restrict the sides. The press pressure at this time is 0
．． 2 to 0.8 ton/cm2, and the strain rate is 10-3
~10-'/sec.

After that, it was heat treated at 1000°C for 24 hours, then at 475°C for 2 hours, then cut and polished, and its magnetic properties were measured.

The magnetic properties of these magnets are shown in Table 4.

Table 4 Table 3 From the above examples, it is clear that permanent magnets whose basic raw material components are R (where R is at least one rare earth element including Y), Fe, and B can be hot worked at 500"C or higher. It becomes anisotropic when heat treated at 250 to 750"C, and the highest (BH)max exceeds 40 MGOe. It is clear that by remelting and casting the processed material, the crystal grains become finer and the magnetic properties, especially the coercive force, are greatly improved.

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

(1) The C-axis orientation rate can be increased, and the residual magnetic flux density B
r could be significantly increased, crystal grains could be made finer, coercive force iHc could be increased, and maximum energy 8'l(B)I)max could be significantly improved.

(2) The manufacturing process is simple, and the cost is low because the unused portion of the cast ingot or hot-worked alloy can be reused.

(3) fi! The concentration of impurities in the stone is low.

(4) Compared to conventional sintering methods, processing man-hours and production investment can be significantly reduced.

(5) Compared to the conventional method of producing IF stones using melt spinning, it is possible to produce magnets with high performance and at low cost.

[Brief explanation of drawings]

Figure 1 shows the R-F of the present invention. This is a diagram. Manufacturing of e-B magnets that's all

Claims (2)

[Claims] (1) A cast ingot obtained by melting and casting an alloy containing R (where R is at least one rare earth element including Y), Fe, and B as basic raw material components, or the above-mentioned cast ingot. After melting and casting the alloy obtained by hot working, the cast ingot was heated to 500°C.
A method for producing a permanent magnet, which comprises hot working at a temperature above and then heat treatment at a temperature of 250 to 1100°C. (2) 750-1100℃ in heat treatment after hot working
2. The method of manufacturing a permanent magnet according to claim 1, wherein the permanent magnet is heat-treated at a temperature of 250 to 750°C.