JPH07211568A - Rare earth permanent magnet manufacturing method - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing an R-Co rare earth permanent magnet having high characteristics by controlling the reaction of carbon and oxygen, which adversely affects the magnetic characteristics of the fine powder in the fine pulverization step. To do. [Structure] In a fine pulverizing step in a manufacturing process of an R-Co rare earth permanent magnet by a sintering method, a coarse powder of 500 μm or less is cooled to a temperature of −5 ° C. or less and finely pulverized using a ball mill. A magnetic field is pressed using the powder to obtain a compact, and the compact is heat-treated to obtain an R-Co rare earth permanent magnet having high magnetic properties.

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 an R--Co rare earth permanent magnet by a sintering method.

[0002]

2. Description of the Related Art Conventionally, permanent magnets have been used as a main component material of electronic devices in various fields such as various electric products, small precision devices, motors and actuators.
Therefore, the permanent magnet material is one of the major component materials for electric, electronic and communication devices. On the other hand, due to recent demands for miniaturization and high efficiency of equipment, permanent magnets having high characteristics are also required. There is a great demand for R-Co rare earth magnets, which are permanent magnets having high characteristics capable of meeting these requirements and also having very good temperature characteristics. A general manufacturing method of the R-Co rare earth permanent magnet by a sintering method is to melt and cast a raw material metal to obtain an alloy ingot, and then finely pulverize the alloy ingot to about several μm, and then obtain the alloy ingot. The fine powder is subjected to compression molding in a magnetic field, sintering, and heat treatment to obtain a permanent magnet. In practice, after-treatments such as processing, rustproofing, and painting are often performed thereafter. However, in the method for producing an R—Co rare earth permanent magnet by the sintering method, when the alloy ingot is crushed to obtain a fine powder, the specific surface area increases, and the active element of rare earth is used. Therefore, the conventional pulverization method has a problem that impurities such as oxygen and carbon cannot be avoided. Due to the mixing of impurities, there is a drawback in that the squareness of the demagnetization curve is deteriorated in the permanent magnet characteristics, that is, the maximum energy product is decreased, the residual magnetic flux density is decreased, and the coercive force is decreased. .

[0003]

SUMMARY OF THE INVENTION In order to overcome such drawbacks, the object of the present invention is to suppress the mixing of impurities such as oxygen and carbon in the fine pulverization process, thereby making it possible to obtain rare earths having high magnetic properties. It is to provide a manufacturing method of a permanent magnet.

[0004]

The present invention provides R and Co (where R is at least one rare earth element containing Y).
After melting each metal of the alloy composition of the R-Co permanent magnet containing as a main component by high frequency to produce an alloy ingot, the alloy ingot is coarsely crushed to a predetermined particle size to obtain a coarse powder. In the method for producing a rare earth permanent magnet, which comprises the step of finely pulverizing the coarse powder to produce a fine powder for sintering, a step of finely pulverizing the coarse powder after cooling it to a temperature of −5 ° C. or lower. A method for manufacturing a rare earth permanent magnet, which comprises:

[0005]

A feature of the present invention is that the temperature is -5 ° C. or lower in the fine pulverization step in the manufacturing process of the R-Co rare earth permanent magnet by the sintering method. The effect of this is as follows. Is thought to be. In the manufacturing process of the R—Co based permanent magnet by the sintering method, fine powder finely pulverized to about several μm is generally required as a raw material for sintering. Therefore, it is generally used to crush the alloy ingot produced by the casting process with a crusher. However, as pulverization progresses and the powder particle size becomes smaller, the specific surface area increases and the area exposed to the outside becomes larger. The surface exposed to the outside has the opportunity to contact and react with the atmosphere gas or various impurities contained in the atmosphere gas in the atmosphere, or with solvent molecules in the solvent or various impurities contained in the solvent. As a result, the increase in the area of the powder increases the amount of impurities in the sintered body and adversely affects the magnetic properties of the product. Further, during the pulverization, heat is generated both locally and locally, and the reaction on the surface of the powder exposed to the outside is promoted. In the case of the R-Co rare earth permanent magnet, since it contains a chemically active rare earth element, a reaction is likely to occur, particularly a reaction with oxygen and carbon occurs, and the amount of oxygen which is an impurity in the sintered body, As the carbon content increases, the magnetic properties deteriorate. According to the present invention, in the fine pulverizing step, by pulverizing the coarse powder at a low temperature of -5 ° C or lower, reaction acceleration due to heat generation on the powder surface exposed to the outer surface is suppressed, and The magnetic properties are improved by making it possible to reduce the amount of impurities such as oxygen and carbon. According to the present invention, the residual magnetic flux density Br and the coercive force can be reduced by suppressing the mixing of impurities such as oxygen and carbon in the manufacturing process of the R-Co rare earth permanent magnet, especially in the pulverization process.
_A method for manufacturing a rare earth permanent magnet having improved magnetic properties such as _I Hc and energy product (BH) max can be obtained.

[0006]

EXAMPLES Hereinafter, the method for producing the R—Co rare earth permanent magnet of the present invention will be described in detail with reference to examples.

FIG. 1 is a diagram showing the relationship between the fine grinding temperature and the magnetic characteristics. FIG. 2 is a diagram showing the relationship between the fine pulverization temperature and the squareness. In the present invention, in the step of finely pulverizing the R-Co rare earth permanent magnet of the present invention, -30 ° C, -15 ° C,
The experimental method and its results were conducted to cool the coarse powder at each temperature of −5 ° C., obtain a fine powder, take a sample, and confirm the effects of press molding and heat treatment in a predetermined magnetic field. Will be explained. In the embodiment, 2 R-Co magnets are used.
5.5 wt% Sm-14.0 wt% Fe-, 5.1 wt
% Cu-2.5 wt% Zr and balance Co alloy composition were selected, and each element was weighed so as to obtain this alloy composition. After that, 3 kg of an alloy ingot was cast by high-frequency melting under a condition of Ar atmosphere and casting the molten alloy into a copper casting mold. Next, this alloy ingot was coarsely pulverized by a disc mill to an average particle diameter of 500 μm or less to obtain coarse powder. Then, using a vortex type ball mill, with a cooling device −
The coarse powder was cooled at 5 ° C, -15 ° C, and -30 ° C and pulverized for 30 minutes. The finely pulverized powder thus obtained was subjected to 1.
Molded with a mold at a pressure of 5 ton / cm ² and the outer diameter φ
Thirty samples of 10 mm in height and 10 mm in height were collected at each temperature. Next, this green compact was sintered in vacuum at 1210 ° C. for 30 minutes, then solution-treated at 1200 ° C. for 1 hour in an Ar atmosphere, and then rapidly cooled to room temperature. Subsequently, as an aging treatment, the sintered body was held at 800 ° C. for 2 hours and then cooled from 800 ° C. to 400 ° C. at a cooling rate of 1 ° C./min. Then, it was rapidly cooled to obtain a sintered magnet. Further, as a comparative example, fine pulverization is performed at room temperature and a temperature of 5 ° C.,
The results were evaluated. In the comparative example, coarse powder crushed to an average particle size of 500 μm or less was treated at room temperature and 5 ° C. and finely crushed, and then 30 samples of each sample were prepared under the same conditions as those of the present invention. The magnetic properties of 30 of each sample were measured and evaluated as an average value. Table 1 shows the analysis results of the amount of impurity oxygen and the amount of carbon in the sintered body for the present invention example and the comparative example.
Shown in. Samples 30 of the present invention and comparative example
Table 2 shows the magnetic characteristics of the average values of the individual pieces.

[0008]

[Table 1]

[0009]

[Table 2] From this, it can be seen that both the amounts of oxygen and carbon impurities in the sintered magnet of the present invention are smaller than those of the comparative example. Also, B
The samples of the present invention and the comparative example were measured with a -H tracer, and the results of magnetic measurement of the samples are shown in FIGS. 1 and 2. Each of the plots in FIG. 1 and FIG.
The average value of 0 pieces was used. From this, the coercive force _I H of the example of the present invention
It can be seen that c and the squareness ratio Hk / _I Hc (Hk is a magnetic field when Br × 90%) are improved.

In the examples, only the Sm ₂ Co ₁₇ system was described as the R—Co rare earth permanent magnet. However, in addition to this, SmCo ₅ system, or part or all of Sm is Y and other rare earths. Various R—Co rare earth permanent magnets substituted with elements, for example, Ce, Pr, Nd, etc. can be targeted. Therefore, the present invention is not limited to the examples.

[0011]

As described above, in the fine pulverization step,
By finely pulverizing the coarse powder cooled to 5 ° C. or less, the reaction of carbon and oxygen, which adversely affects the magnetic properties of the finely pulverized fine powder, is suppressed, and the magnetic properties of the magnet are improved. As described above, according to the present invention, the RC having high magnetic characteristics is provided.
It has become possible to provide a method for manufacturing an o-based rare earth permanent magnet.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a fine pulverization temperature and magnetic characteristics. Figure 1
(A) is a figure which shows the relationship between a fine pulverization temperature and an energy product: (BH) max. FIG. 1B is a diagram showing the relationship between the fine pulverization temperature and the residual magnetic flux density: Br. FIG. 1 (c) milling temperature and the coercive force: graph showing the relationship between _I Hc.

FIG. 2 is a diagram showing a relationship between fine pulverization temperature and squareness: Hk / _I Hc × 100.

Claims (1)

[Claims] 1. A metal of an alloy composition of an R—Co based permanent magnet containing R and Co (where R is at least one kind of rare earth element including Y) as a main component is melted by high frequency to melt an alloy ingot. After manufacturing, the alloy ingot is roughly crushed to a predetermined particle size to obtain a coarse powder, and then the coarse powder is finely crushed to produce a fine powder for sintering. A method for producing a rare earth permanent magnet, which comprises a step of cooling the coarse powder to a temperature of −5 ° C. or lower and then finely pulverizing the coarse powder.