JPH04287304A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To realize an R-Fe-B sintered magnet manufacturing method which does not cause any deterioration with lapse of time during the manufacturing process, can stably manufacture formed or sintered bodies having a high strength, etc., and can improve the moisture resistance and stability of produced magnets. CONSTITUTION:The nitride contained in the raw material powder is changed in quality by bringing the powder into contact with an atmosphere containing moisture of, preferably, 0.01g/l or more so as to prevent the occurrence of deterioration with lapse of time during the manufacturing process.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to permanent magnets, especially R-F magnets.
e-B system (R is at least one rare earth element including Y)
The present invention relates to a method for manufacturing a sintered magnet.

0002

[Prior Art] R-Fe-B sintered magnets are made by grinding powder alloys obtained by the reduction diffusion method or alloy powders obtained by pulverizing alloys obtained by the melting method into 1 to 20 μm particles. It is obtained by pulverizing it, molding it while orienting it in a magnetic field, sintering it, and subjecting it to heat treatment.

[0003] Such R-Fe-B based sintered magnets have advantages such as inexpensive raw materials and greater magnetic properties than conventional SmCo based magnets, but on the other hand, they have the property of being extremely susceptible to rust. . For this reason, when it becomes fine powder during the process, its surface area becomes large and the fine powder is very easily oxidized and difficult to handle.

[0004] In order to improve these points, R-Fe
-B-based sintered magnets are generally manufactured by handling them in a non-oxidizing gas such as N2. However, it is difficult to completely seal the process equipment, especially in the case of mass production, and there is a possibility that fine powder and green compacts are more or less exposed to oxygen and moisture in the air.

[0005] Until now, it has been thought that contact with oxygen and moisture in the air increases the amount of oxygen inside the magnet and deteriorates the magnetic properties. A proposal has been made (Japanese Unexamined Patent Publication No. 62-625
No. 03, etc.). It is also believed that the amount of oxygen varies depending on the degree of exposure to oxygen and moisture in the air, which causes variations in not only the magnetic properties but also the dimensions, strength, and moisture resistance of the magnet.

[0006]

[Problems to be Solved by the Invention] However, when the compact comes into contact with moisture in the air after forming and before sintering, even if the amount of oxygen in the resulting sintered magnet is maintained at a constant value, forming The strength of the body and the strength of the sintered body may not be sufficient, the dimensions of these or the sintered body may vary, sintering defects such as cracks and chips may occur, and the moisture resistance and stability of the magnet may be insufficient. It was found that there was a decline.

The main object of the present invention is to facilitate process control, have high strength of molded bodies and sintered bodies, have stable strength and dimensions of sintered bodies, and prevent sintering defects such as cracks and chips. It is an object of the present invention to provide a method for manufacturing an R-Fe-B based sintered magnet that does not cause molding, exhibits good and stable forming or sintering properties, has high moisture resistance and stability, and has stable quality.

[0008]

[Means for Solving the Problems] Such objects are achieved by the present invention as described in (1) to (3) below.

(1) Molding the raw material powder to obtain a molded body,
In a method for producing a permanent magnet in which a permanent magnet containing R (wherein R is at least one rare earth element including Y), Fe, and B is obtained by sintering this compact, the raw material powder before forming is moistened. A method for producing a permanent magnet, the method comprising: bringing it into contact with a permanent magnet.

(2) The raw material powder is mixed with 0.01 g of moisture/
1. The above (
1) The method for manufacturing a permanent magnet.

(3) The method for producing a permanent magnet according to (2) above, in which the permanent magnet is brought into contact with the atmosphere for 3 seconds or more.

0012

[Operation] The present invention is based on the knowledge that the amount of N in the raw material alloy has a large effect on the aging of the powder during the process and the corrosion resistance of the magnet body.

[0013] In R-Fe-B based sintered magnets, the finer the particle size of the fine powder, the better the coercive force and magnetization performance of the magnet.
If the particles become too fine, the degree of oxidation will increase and the coercive force will deteriorate.
Degree is often used. However, when comparing the change over time in the amount of O2 during the process, it was found that even with the same particle size, the amount of N in the composition has a large effect. This seems to have been overlooked in the past because R-Fe-B sintered magnets allow up to several thousand ppm of oxygen. However, the biggest effect of N in the composition is that it changes the properties of the powder and green compact every moment due to moisture in the air.
This causes variations in the quality of the magnets.

[0014]N in the raw material alloy is provided by the raw metal, particularly the rare earth metal, which is the raw material. It is believed that N is present in the form of rare earth nitride RN. Rare earth nitrides are stable even at high temperatures and remain after the melting process. When an alloy containing residual N is pulverized, the nitrides do not change or deteriorate since the pulverization is usually carried out in an atmosphere of N2 or a solvent. However, once it comes into contact with air after pulverization, nitrides undergo the following reaction, become a gas, diffuse into the air, become rare earth hydroxides, and remain in the powder or green compact as rare earth oxides. It came to be.

RN +3H2 O→NH3 ↑+R(
OH)3 This reaction is known as a chemical reaction of rare earth elements, but the nitrides in the alloy at several tens to hundreds of ppm can affect the strength of the molded body, the sintered dimensions, the strength, and even the reliability of the final product. It was unforeseen that this would lead to this.

[0016]Furthermore, the following points can be cited as reasons why such problems are confused and the influence of nitrides in the process has not been regarded as a problem until now. In other words, when analyzing nitrides, it is difficult to quantify the trace amount of N discussed here unless the sample is crushed in an inert gas and then measured without exposing it to air. In addition, nitrides are reduced because they are exposed to air to a greater or lesser extent during manufacturing. Furthermore, since N2 gas is used to prevent oxidation during the process, N is adsorbed onto the powder. Unlike N in nitrides, these adsorbed N2 do not adversely affect processes or products. Furthermore, since it is a trace amount of nitride, even if the above reaction occurs, the amount of ammonia generated is trace and difficult to detect. For these reasons, even though the amount of N in the product itself was a problem, the negative effects of nitrides during the process were not considered a problem in the past. When this happens, the generation of ammonia can be detected as an odor.

Therefore, in the present invention, in order to change the quality of the nitride in the raw material powder in advance so that it does not exist in the molded product, and to eliminate the aging deterioration during the process due to contact between the nitride and moisture, The raw material powder and moisture are brought into contact with each other in advance.

Regarding N in sintered magnets, there have been proposals to regulate the amount of N in the product, as in the above-mentioned publication. However, this is due to magnetic properties,
As in the present invention, there has been no attempt to reduce the amount of N by deactivating nitrides in the raw material and to improve the moisture resistance and stability of the powder and the magnet body obtained therefrom.

[0019]

[Specific structure] The permanent magnet of the present invention comprises R, Fe and B.
Contains R (R is at least one rare earth element including Y) 27-38, Fe51-72, B
0.5 to 4.5, and further contains unavoidable impurities, and the nitrogen content is 250 ppm or less.

[0020] When the R content decreases, an iron-rich phase precipitates and the coercive force decreases.

Furthermore, as the R content increases, the residual magnetic flux density decreases. When the content of B decreases, the coercive force decreases. Furthermore, as the B content increases, the residual magnetic flux density decreases. In addition, 30% by weight or less of Fe is C
It may be replaced with o. Furthermore, Al, Cr, Mn, Mg
, Si, Cu, C, Nb, Sm, W, V, Zr, Ti,
Additive elements such as Mo can improve the coercive force by adding a small amount, but if the amount exceeds 6% by weight, the residual magnetic flux density decreases.

[0022] If the nitrogen content is 250 ppm or less, especially 10 to 250 ppm, the moisture resistance of the R-Fe-B permanent magnet can be improved, and in particular rust can be prevented by improving the moisture resistance caused by the magnet body itself. You can. In addition, the oxygen content is 6000 ppm or less, especially 2500 to 45
00 ppm is preferable.

The permanent magnet of the present invention has a main phase with a substantially tetragonal crystal structure. The particle size of this main phase is 1
The thickness is preferably about 100 μm. It usually contains a non-magnetic phase of 1 to 50% by volume.

In the present invention, the nitrogen level in the magnet is controlled by bringing the raw material powder into contact with water in advance, and it is preferable to use a raw material with a relatively low nitrogen content. The amount of N in the raw material is 500 ppm or less, especially 10 to 2
00 ppm is preferred. If it exceeds 500ppm,
This is because the moisture contact treatment increases the amount of oxygen too much.

The raw material used may be a powder alloy obtained by a reduction diffusion method. Such powder is 1
It is obtained as a particle size of about 0 to 500 μm.

Alternatively, an alloy having a desired composition may be cast to obtain an ingot, and the obtained ingot may be coarsely pulverized to a particle size of approximately 10 to 500 μm using a stamp mill, a hydrogen storage pulverization method, or the like.

[0027] In these, the amount of oxygen in the alloy is 50~
It is preferably 2000 ppm or less, particularly 50 to 500 ppm. Note that the amount of N and O may be measured by the melting-thermal conductivity detection method in an inert gas.

Next, these are pulverized to a particle size of about 0.5 to 5 μm, particularly about 2 to 5 μm, using a jet mill, a ball mill, or the like. At this time, it is preferable to carry out the jet milling in an N2 atmosphere, and the ball milling in a solvent such as acetone, alcohol, or toluene.

The obtained powder is preferably compacted in a magnetic field. In this case, it is preferable that the magnetic field strength is 10 kOe or more and the molding pressure is about 0.5 to 3 t/cm2.

[0030] Next, the molded body is heated to 1000 to 1200°C.
Sinter for 0.5 to 5 hours and quench. Note that the sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. After this, aging treatment is performed at 500 to 900° C. for 1 to 5 hours, preferably in an inert gas atmosphere.

[0031] In such a case, the raw material powder, especially the finely pulverized powder, has a concentration of 0.01 g/1 or more, usually 0.0 g/1, before molding.
Exposure to an atmosphere containing 1 g/1 to 0.1 g/1 of moisture. The ambient temperature is 20 to 50°C, and the contact time with the atmosphere is 3 seconds or more, usually about 5 seconds to 12 hours. For contact with the atmosphere, especially in the case of fine powder, it is sufficient to expose the raw material powder to the atmospheric air stream little by little for a relatively short period of time. Alternatively, a large amount of treated powder may be left still and subjected to atmospheric treatment for a relatively long period of time.

As described above, in the present invention, the nitrides in the raw material powder are removed by reacting with water in advance, so that the moldability or sinterability and the stability thereof are reduced due to the reaction of the nitrides with water. Inhibiting factors or factors inhibiting the corrosion resistance and stability of the magnet are removed.

[0033]

[Examples] The present invention will be explained below with reference to Examples.

Example 1 An alloy ingot having a composition of 30Nb3Dy65.8Fe1.2B in weight percent was produced by a melting method in an Ar gas atmosphere. By changing the starting materials, the N content of the ingot was changed as shown in Table 1 below. These ingots were magnetized through the usual sintering process of crushing, coarse pulverization, fine pulverization, molding in a magnetic field, sintering, and heat treatment.

[0035] In this case, the coarse pulverization was carried out by the hydrogen absorption method, and the coarsely pulverized powder had an average particle size of 30 μm. In addition, fine pulverization is performed using N
2 The average particle size of the finely pulverized powder was set to 3 μm using a jet mill in an air stream. This powder was placed in a magnetic field of 10 keO for 1
．． It was pressurized at a pressure of 5 tons/cm2 and molded in a magnetic field. During the process, contact with air is blocked, and the finely pulverized powder is
The samples were brought into contact with an atmosphere having a moisture content (g/1) shown in Table 1 for 5 seconds at 25° C. with stirring.

After that, the molded body was heated to 1100°C in an Ar atmosphere.
℃ for 3 hours, and after quenching, sintered at 600℃ in an Ar atmosphere.
Aged for 3 hours at ℃, 11mm 7 diameter x 4mm
Obtained a magnet.

Strength of molded body and strength of sintered body after contact with moisture (
Table 1 shows the average value of 5 samples. The strength of the molded body is 2
Measurement was performed at 5°C and relative intensity of 55%. Further, Table 1 shows the results of measuring the amount of N and the amount of O in the sintered body by gas analysis. Gas analysis was based on melting-thermal conductivity detection in an inert gas.

[0038]

[Table 1]

From the results shown in Table 1, the effects of the present invention are clear. In addition, the N content in the raw material is 400 ppm.
In the above products, an ammonia odor could be confirmed after contact with water.

Example 2 In weight percent, 31.5Nd1.5Dy65.8Fe1.
An alloy powder having a composition of 2B was obtained by a reduction diffusion method. On this occasion,
The nitrogen content of the alloy powder was changed as shown in Table 2. This was finely pulverized using the Ar+N2 jet stream pulverization method, and 20 kg of the finely pulverized powder was exposed to a moisture atmosphere of 0.015 g/1 (relative humidity 65%) at 25°C for 8 hours.
Similarly, molding was performed in a magnetic field. It was made into a magnet through sintering and heat treatment processes. Table 2 shows the strength of the molded body.

[0041]

[Table 2]

From the results shown in Table 2, the effects of the present invention are clear.

Example 3 Electrolytic Ni plating was applied to the magnet produced in Example 1 to a thickness of 10 μm.
provided. Next, a humidity test was conducted at 85° C. and 85% for 500 hours, and the results are shown in Table 3.

[0044]

[Table 3]

From the results shown in Table 3, the effects of the present invention are clear.

[0046]

According to the present invention, changes in the pulverized powder over time due to moisture in the air are reduced, and stable production can be achieved. Furthermore, the strength of the molded body during compaction is improved, and a product without deterioration of strength over time and without chips or cracks can be obtained. The moisture resistance of the magnet body is improved, and a highly reliable product can be obtained. After moisture treatment, the powder and molded body can be handled in the air, which is extremely advantageous for mass production.

Claims (3)

[Claims] Claim 1: A raw material powder is molded to obtain a molded body, and this molded body is sintered to form a permanent magnet containing R (wherein R is at least one rare earth element containing Y), Fe, and B. A method for producing a permanent magnet, characterized in that the raw material powder before molding is brought into contact with moisture. 2. The method for producing a permanent magnet according to claim 1, wherein the raw material powder is brought into contact with an atmosphere having a moisture content of 0.01 g/1 or more. 3. The method for manufacturing a permanent magnet according to claim 2, wherein the permanent magnet is brought into contact with the atmosphere for 3 seconds or more.