JPH06290919A - Rare earth-iron-boron permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the cavity in a permanent magnet, and to suppress the deterioration in corrosion resistance by a method wherein the friction generating between the mold and raw material powder when a molding operation is conducted is reduced by adding the specific quantity of alkali metal stearate to rare earth-iron-boron permanent magnet alloy coarse powder. CONSTITUTION:This rare earth-iron-boron permanent magnet is mainly composed in atomic % of rare earth element R (among rare-earth elements containing Y, one or two or more elements are combined) of 10 to 25%, B of 1 to 12%, and the remaining part consisting of Fe (a part of Fe is replaced at least with one or more kinds of elements selected from Co, Ni, Al, Nb, Ti, W, Mo, V, Ga, Zn and Si, if necessary). After alkali metal stearate of 0.001 to 0.2wt.% has been mixed to the alloy coarse powder, the mixture is dry- pulverized and the permanent magnet is manufactured. As a result, the lubricating property can be improved by reducing the friction between raw material powder and the wall surface of mold, or between the raw material powder, and the residual carbon quantity can be reduced.

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 a rare earth-iron-boron-based permanent magnet, in which a small amount of a lubricant is added to reduce friction between a die and a raw material powder at the time of molding to improve magnetic characteristics. The present invention relates to a technique for improving the corrosion resistance as well as improving the corrosion resistance.

[0002]

2. Description of the Related Art In recent years, along with the market trend toward miniaturization and weight reduction of electronic equipment and precision equipment, rare earth magnets have been used in many fields in permanent magnets instead of conventional alnico and ferrite magnets. It was Among rare earth permanent magnets, there is an increasing demand for rare earth-iron-boron-based magnets that can obtain a high energy product, and there is a tendency for higher energy products and higher coercive force to be required than ever. Various attempts have been made to improve the magnetic properties of rare earth-iron-boron magnets, and many inventions based on various additive elements have been disclosed. In addition, many inventions of rare earth-iron-boron magnets by superquenching method, which is an alternative to the conventional powder metallurgy method, have been disclosed. Unlike the powder metallurgy method, the ultra-quenching method
It is not practical because it requires hot plastic working such as upsetting or extrusion to obtain a high energy product, which increases manufacturing costs. Therefore, most of the rare earth-iron-boron magnets having the energy product of 30 MGOe or more which are currently put to practical use in the market are manufactured by using the powder metallurgy method.

By the way, in the method for producing the rare earth-iron-boron system sintered magnet by the powder metallurgy method, the rare earth-iron-boron system alloy is dissolved in the target composition and the average particle size thereof is about 1 to 50 μm. A general method is to pulverize the powder into fine powders, then form the powder in a magnetic field, and then perform the steps of sintering and heat treatment. In this step, as a method for obtaining fine powder for molding in a magnetic field from a melt-casting ingot, a method of mechanical grinding using a jaw crusher, a disc mill, a jet mill, a ball mill, etc. 60-633
As disclosed in No. 04, there is a method of occluding hydrogen in a rare earth-iron-boron magnet melting and casting ingot to spontaneously disintegrate it into particles having an average particle diameter of 500 μm or less and finely pulverizing the coarse powder with a jet mill or the like. . This method of occluding hydrogen and pulverizing it to an average particle size of 500 μm or less makes it possible to obtain finely pulverized powder having a predetermined particle size in about 1/4 of the time required for mechanical pulverization. , Crushing efficiency is improved, and now, rare earth-
It is generally used as a method for producing iron-boron magnet powder. In the molding step, the average particle size is 1 to 50 μm
After the finely pulverized powder of No. 1 was filled in the forming space formed by the die and the lower punch, the orientation magnetic field was continuously applied to the raw material powder until the upper punch descended to complete the consolidation of the raw material powder for orientation.

[0004]

However, in the molding of rare earth-iron-boron permanent magnet raw material powder, friction between the inner wall of the die and the raw material powder or the shaped body during molding is great, and sometimes the raw material powder is gold. The die adhered to the inner wall of the die and galling of the die occurred, which required frequent replacement of the die, resulting in a decrease in molding work efficiency and an increase in die cost. Therefore, in order to reduce the friction between the raw material powder and the mold, a method of applying a lubricant such as a higher fatty acid to the wall surface of the mold has been proposed. However, the method of applying the lubricant to the metal wall surface is time-consuming and reduces the work efficiency. The applicant of the present invention has disclosed in JP-A-61-214402 that the average particle diameter is 1 to
Zinc stearate is added to and mixed with 50 μm finely pulverized powder,
A method has been proposed in which molding of this mixed powder is the gist. According to this method, the friction between the raw material powder and the mold can be reduced without lowering the work efficiency. However, careful observation of the permanent magnet according to the method of Japanese Patent Laid-Open No. 61-214402 revealed that the number of cavities present in the permanent magnet was large and such a magnet had poor corrosion resistance. Therefore, the present invention reduces the friction between the mold and the raw material powder during molding to improve the magnetic characteristics, and
The purpose is to reduce the number of cavities in the magnet and prevent deterioration of corrosion resistance.

[0005]

A method of manufacturing a permanent magnet according to the present invention for solving the above-mentioned problems includes a rare earth element R in atomic percentage.
(One or a combination of two or more rare earth elements including Y) is 10 to 25%, boron B is 1 to 12%, and the balance is iron Fe (a part of Fe is Co, Ni, A if necessary).
Rare earth-iron-containing at least one element selected from 1, Nb, Ti, W, Mo, V, Ga, Zn and Si within the range of 0 to 15%) 0.001 to 0.2 wt.% Of stearic acid metal salt is added to the boron-based permanent magnet alloy coarse powder. % Addition and mixing, followed by dry pulverization. Examples of the metal stearate of the present invention include Zn, K, Ca, Al, Fe, Cu, Ni,
At least one element selected from Co can be used.

According to the above-mentioned production method of the present invention, the rare earth element R (one or a combination of two or more rare earth elements including Y) is contained in an atomic percentage of 10 to 25% and the boron B is contained in an amount of 1 to 12%. Is iron Fe (a part of Fe may be Co, Ni, Al, Nb, Ti, W, Mo, V, G
a, Zn, Si can be substituted with at least one or more elements selected from the range of 0 to 15%) as a main component, and the degree of orientation is 99.5% or more, A magnet having 150 or less cavities with a size of 5 μm or more in 1 mm ² of the permanent magnet mirror-polished surface is obtained. In addition, the degree of orientation in the present invention is obtained by a mathematical formula shown in Examples described later.

[0007]

The present invention is different from JP-A-61-214402 in that the stearic acid metal salt is added to the coarse powder. By doing so, the cavities in the magnet were reduced and the deterioration of corrosion resistance was suppressed. It was also confirmed that the degree of orientation was improved as compared with the case where it was added to the fine powder. Although the reason why the present invention can obtain the above effects is not clear, because fine pulverization is performed after adding the metal stearate to the coarse powder, the dispersity of the metal stearate in the fine powder is improved. It is supposed to do. In the present invention, a stearic acid metal salt is adopted as the lubricant, but the group composed of C, H, and O at the other end is used by utilizing the ease of binding of this metal ion and the rare earth-iron-boron magnet alloy. To improve lubricity. As a result, the addition of the metal stearate as a lubricant can be suppressed to a small amount. In this case, the amount of carbon remaining in the magnet is reduced, and the generation of rare earth carbide that adversely affects the magnetic properties can be suppressed.

The details of the present invention will be described below. First, the composition of a magnet melt-casting ingot to be the subject of the present invention contains 10 to 25% rare earth elements (one or a combination of two or more rare earth elements including Y) and 1 to 12 atomic% boron as an essential element. The balance is Fe as a main component, and a part of Fe is optionally Co, Ni, Mn, Al, Nb, Z.
It is a rare earth-iron-boron-based permanent magnet alloy that is substituted with other elements such as r, Ti, W, Mo, V, Ga, Zn, and Si in the range of 0 to 15 atomic%. After breaking this molten cast ingot so that the metal surface is exposed, after storing the broken mass in a closed container, hydrogen gas is supplied into the container to spontaneously collapse the molten cast ingot and the average particle size is 50 to 50. 1000
Make a coarse powder of μm. In order to reduce the activity of the coarse powder against oxidation, the coarse powder may be subjected to dehydrogenation treatment at 100 to 900 ° C. in vacuum or in argon gas after the hydrogen treatment. In addition, the casting ingot may be mechanically crushed by a jaw crusher, a brown mill, or the like to prepare the coarse powder.

Next, metal salt of stearic acid is added to and mixed with the coarse powder, and then finely ground to an average particle size of 1 to 50 μm by a dry grinding machine such as a jet mill. After filling the obtained finely pulverized powder into a molding space formed by a die and a lower punch, an orientation magnetic field is applied to carry out consolidation molding to produce a molded body. The formed body is sintered in a vacuum or in a non-oxidizing atmosphere such as nitrogen or Ar gas at a temperature in the range of 1000 to 1200 ° C., and heat-treated at a temperature in the range of 350 ° C. to the sintering temperature to produce a permanent magnet. To be done.

Next, the reasons for limitation will be described. It is considered that when a stearic acid metal salt is adopted, metal ions are easily bonded to the rare earth-iron-boron magnet powder, and friction is reduced due to lubricity between the bases composed of C, H, and O at the other end. Therefore, addition of a small amount reduces the friction between the raw material powder and the wall surface of the mold and the friction between the raw material powders. The addition amount is 0.001 wt. %, The effect of addition is not sufficient, and 0.20 wt. %, The strength of the molded body is lowered and the molded body is liable to peel off, resulting in difficulty in handling and lack of mass productivity.
0 wt. %. In order to obtain a remarkable addition effect,
02 wt. % Or more, and when high magnetic properties are desired, considering that the carbon content becomes high, 0.08 wt. % Or less is desirable.

Next, regarding the method of adding the metal stearate, the dispersibility of the metal stearate is better by adding and mixing it to the coarse powder and then finely pulverizing it in a dry method than by adding and mixing the fine powder. The effect of improving the magnetic properties, the galling of the mold, and the reduction of the number of cavities present in the magnet are conspicuous. The reduction of the number of cavities also improves the corrosion resistance. Permanent magnet mirror polished surface 1
The number of nests with a size of 5 μm or more in mm ² ,
If the number of cavities with a size of 5 μm or more exceeds 150, the corrosion resistance is significantly reduced.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Example) Nd 30.0 wt. %, Dy
2.0 wt. %, Al 0.3 wt. %, Nb 1.0w
t. %, B 1.0 wt. A magnet alloy having a balance of Fe was subjected to high frequency melting in an inert atmosphere to obtain a cast ingot.
After breaking 1.5 kg of this ingot to 50 mm square or less, the broken mass was inserted into a closed container, hydrogen gas was allowed to flow in for 20 minutes to replace air, and treated with 1 kg / cm ² of hydrogen gas for 2 hours and averaged. The particle size was set to 500 μm or less. 1.2 kg of this coarse powder contained 0.03 wt. % (Example 1), 0.07 wt. % (Example 2), 0.10 wt.
% (Example 3), 0.40 wt. % (Comparative Example 1) zinc stearate was added and mixed with a V-type mixer for 10 minutes. Next, this coarse powder was finely pulverized using a jet mill to obtain a powder having an average particle diameter of 3.8 μm, and a raw material for molding was produced. This raw material powder was filled in a molding space formed by a die and a lower punch, oriented with an orientation magnetic field of about 10 kOe, and pressure-molded at ² ton / cm ² . Molded body 10
Sintering was performed at 80 ° C. for 2 hours, and heat treatment was performed at 600 ° C. for 2 hours to produce a permanent magnet. Tables 1 and 2 show the magnetic characteristics, orientation degree, molded body strength, etc. of these permanent magnets.
Table 3 shows the number of nests having a size of 5 μm or more when the 1 mm ² mirror-polished surface of the permanent magnet was observed under a stereoscopic microscope at a magnification of 50 times.

(Comparative Example 2) Nd 30.0 wt. %, Dy
2.0 wt. %, Al 0.3 wt. %, Nb 1.0w
t. %, B 1.0 wt. A magnet alloy having a balance of Fe was subjected to high frequency melting in an inert atmosphere to obtain a cast ingot.
After breaking 1.5 kg of this ingot into 50 mm square or less, the broken mass was inserted into a closed container, hydrogen gas was introduced for 20 minutes to replace the air, and 1 kg / cm ² of hydrogen gas was used for 2
It was treated for a time so that the average particle diameter was 500 μm or less. 1.2 kg of this coarse powder was finely pulverized using a jet mill to obtain a powder having an average particle size of 4.5 μm, and a raw material for molding was prepared. This raw material powder is filled in a molding space formed by a die and a lower punch, and oriented by an orientation magnetic field of about 10 kOe, and 2 to
Pressure molding was performed at n / cm ² . Molded body at 1080 ℃, 2
Sintering was performed under the condition of time, and heat treatment was performed at 600 ° C. for 2 hours to produce a permanent magnet. Magnetic properties of these permanent magnets, the degree of orientation and strength of the shaped body or the like in Table 1 and Table 2, the number of 5μm or more the size of the nest when the permanent magnet polished mirror surface 1 mm ² was observed 50 magnifications stereomicroscope Is shown in Table 3.

(Comparative Example 3) Nd 30.0 wt. %, Dy
2.0 wt. %, Al 0.3 wt. %, Nb 1.0w
t. %, B 1.0 wt. A magnet alloy having a balance of Fe was subjected to high frequency melting in an inert atmosphere to obtain a cast ingot.
After breaking 1.5 kg of this ingot into 50 mm square or less, the broken mass was inserted into a closed container, hydrogen gas was introduced for 20 minutes to replace the air, and 1 kg / cm ² of hydrogen gas was used for 2
It was treated for a time so that the average particle diameter was 500 μm or less. This coarse powder was finely pulverized using a jet mill to give an average particle size of 3.7.
It was made into a powder of μm. Next, 0.03 wt. % Zinc stearate was added and mixed with a V-type mixer for 10 minutes to prepare a raw material for molding. This raw material powder is filled in a molding space formed by a die and a lower punch, and is oriented by an orientation magnetic field of about 10 kOe, and 2 ton.
Pressure molding was performed at / cm ² . The molded body was sintered under the condition of 1080 ° C. for 2 hours and heat-treated at 600 ° C. for 2 hours to produce a permanent magnet. Magnetic properties of these permanent magnets, the degree of orientation and strength of the shaped body or the like in Table 1 and Table 2, the number of 5μm or more the size of the nest when the permanent magnet polished mirror surface 1 mm ² was observed 50 magnifications stereomicroscope Is shown in Table 3.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

According to the present invention, by reducing the friction between the raw material powder and the wall surface of the mold or the raw material powders, the lubricity is improved, the orientation degree of the permanent magnet is also improved, and its industrial utility value is extremely high. . Further, the addition of the metal stearate can be suppressed to a small amount, the amount of carbon remaining in the magnet can be suppressed, and the nonmagnetic phase can be reduced.

Front Page Continuation (72) Inventor Chitoshi Hagi 5200 Sankejiri, Kumagaya City, Saitama Hitachi Metals Co., Ltd. Kumagaya Plant

Claims (5)

[Claims] 1. A rare earth element R (one or a combination of two or more rare earth elements including Y) is 1 in atomic percentage.
0 to 25%, boron B 1 to 12% and the balance iron Fe
(A part of Fe may be Co, Ni, Al, Nb,
Ti, W, Mo, V, Ga, Zn, Si can be substituted with at least one element selected from the range of 0 to 15%) as a main component, A rare earth-iron-boron-based permanent magnet having a degree of 99.5% or more and 150 or less cavities of 5 μm or more in 1 mm ² of a mirror-polished surface of the permanent magnet. 2. The rare earth-iron-boron-based permanent magnet according to claim 1, wherein the C content is 0.1 wt.% Or less. 3. A rare earth element R (one or a combination of two or more rare earth elements including Y) is 1 in atomic percentage.
0 to 25%, boron B 1 to 12% and the balance iron Fe
(A part of Fe may be Co, Ni, Al, Nb,
Rare earth-iron-boron-based permanent magnet containing as a main component at least one element selected from Ti, W, Mo, V, Ga, Zn, and Si). 0.001 to 0.001 of metal stearate to alloy powder
0.2 wt. %, And mixed and then finely pulverized by a dry method. A method for producing a rare earth-iron-boron based permanent magnet. 4. The amount of the metal stearate added is 0.0
2 to 0.08 wt. % Rare earth according to claim 3
Iron-boron permanent magnet manufacturing method. 5. A metal salt of Zn, K, Ca, Al,
The rare earth element according to claim 3 or 4, wherein at least one element selected from Fe, Cu, Ni, and Co is used.
Iron-boron permanent magnet manufacturing method.