JP2003342618A - Method for manufacturing anisotropic rare-earth magnet powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved technique on a method for manufacturing a magnet powder in a simplified process, which is used for manufacture of an Nd-Fe-B-based bonded magnet, and produces a magnet with high performance due to own anisotropy. <P>SOLUTION: This method for manufacturing the magnet powder comprises preheating a metal tube filled with a rapidly quenched powder so as to hold it in an atmosphere having a lower temperature than the crystallization temperature of a magnet alloy, to make the temperature of the rapidly quenched powder reach approximately the atmospheric temperature, then heating it to 650-900°C and uniaxially compressing it. Thereby the method provides the magnet powder while preventing the particles from coarsening. Alternatively, the method for manufacturing the magnet powder is characterized by uniaxially compressing the powder at such a working speed as to adjust the strain rate defined by ln(L<SB>0</SB>/L)/T (wherein, L<SB>0</SB>indicates a height of the metal tube before compression; L indicates a height of the metal tube after compression; and T indicates a compression time (second)), into a range of 0.5-3.0 per second, to increase a degree of the anisotropy. Both of the methods are preferably jointly performed. <P>COPYRIGHT: (C)2004,JPO

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 Nd-Fe-B rare earth magnet alloy powder having anisotropy. The present invention also relates to a bonded magnet using the magnet powder having this anisotropy.

[0002]

2. Description of the Related Art Nd-Fe-B magnets have high magnetic properties and are therefore widely used as parts of motors constituting various OA equipment and AV equipment. As is well known, Nd-Fe-B based magnets are roughly classified into sintered magnets, hot-worked magnets and bonded magnets depending on the mode of use.

Among these, the bonded magnet is manufactured by a process of mixing magnet powder and a resin binder and molding, so that a product having a high degree of freedom in shape and high dimensional accuracy can be obtained. It is an advantage. OA mentioned above
Bonded magnets are often used because motor parts for equipment and AV devices must be thin and precise.

However, most of the current bonded magnets are isotropic magnets in which the crystal orientation is random, and they have a smaller energy product of the magnet component itself than anisotropic magnets. In addition, the volume occupancy of the magnetic phase of the bonded magnet may be low due to the inclusion of the binder, and the energy product of the magnet is 20 to 30 that of a sintered magnet or a hot-worked magnet.
The current situation is that it has stopped at about%.

Therefore, it is required to increase the energy product of the bonded magnet, and various methods have been studied. As an example, there is a technique of using a powder of a Nd-Fe-B hot-worked magnet pulverized and used as a material for a bonded magnet (J.App1.Phys., 64, 10, 5293- 529
Five). According to this technique, a bonded magnet having an energy product higher than that of a conventional isotropic bonded magnet can be obtained, but the manufacturing process is complicated, and thus it is difficult to increase the cost.

The Applicant has found that Nd-Fe-B system magnet alloys are
Utilizing the characteristic that magnetic anisotropy is generated when plastically deformed while hot, and with the intention of providing a method for manufacturing a bonded magnet in which the process is simplified and the cost is reduced, the development is advanced. A powder obtained from a quenched ribbon of a —Fe—B based magnet alloy was filled in a metal container, and the inside of the container was evacuated or made an inert gas atmosphere, and the container was sealed at a temperature of 6
A method for producing a magnetic alloy powder having anisotropy by causing plastic deformation by uniaxially compressing at 50 to 900 ° C. and then opening the container has been established and has already been disclosed (JP-A-10-199717). ).

This method does not pass through a material once densified unlike the known method described above.
Not only has the process been improved in that it has become simpler, but the aggregate of magnet alloy powder obtained after plastic deformation is
It is also advantageous in that it can be crushed more easily than the alloy mass obtained when the known method is followed. However, in industrial implementation, it has become an issue to simplify the process of filling powder into a metal container-vacuum suction-sealing-and simplifying the production amount of one batch.

The applicant has solved this problem by using a heating press capable of controlling the atmosphere, and has already proposed this (Japanese Patent Laid-Open No. 11-233323). That is, the proposed technique is to fill a metal cylinder with a quenching powder obtained from an ultra-quenching ribbon of an Nd-Fe-B-based magnet alloy and place it in a heating press capable of controlling the atmosphere, in a non-oxidizing atmosphere, at a temperature of 65
At 0 to 900 ° C., the metal cylinder is uniaxially compressed by the upper and lower punches in the axial direction to be crushed, and the particles of the magnet alloy are plastically deformed to anisotropy. It consists of taking out and crushing.

The method of manufacturing this magnet powder simplifies the process in that the metal cylinder is not required to be hermetically sealed, and accordingly, the manufacturing cost can be reduced. It was experienced that the magnetic properties of the resulting magnet powder deteriorated when attempted to be significantly larger. Upon investigating the cause, it was found that during heating up to uniaxial compression processing, the particles of the magnet alloy powder become coarse and the effect of ultra-quenching is diminished.

That is, while the ultra-quenched powder is filled in a metal cylinder and placed in a heating press capable of controlling the atmosphere, while waiting for the processing temperature to rise to 650 to 900 ° C., the inside of the filled powder is Although the temperature is still low, the powder in the outer portion close to the metal cylinder reaches a temperature exceeding the crystallization temperature, and coarsening progresses. Therefore, it is necessary to avoid such a situation and realize the temperature rise to 650 to 900 ° C. The crystallization temperature is approximately 500 ° C. although it varies slightly depending on the alloy composition, and therefore the time of exposure to high temperatures exceeding that temperature must be shortened as much as possible.

On the other hand, the increase in the anisotropy due to the uniaxial compression processing makes it possible to obtain a magnet powder having higher magnetic characteristics by enhancing the effect, and also the deterioration of the magnetic characteristics due to the coarsening of the particles. Can be compensated for,
It is desirable to find more effective processing conditions for increasing the anisotropy. From such a viewpoint, the inventors have found that if the strain rate during uniaxial compression is too slow, anisotropy does not occur, but if it is too fast, it is rather disadvantageous, and there is an appropriate range between them. I found that.

[0012]

The object of the present invention, which was established based on the new knowledge obtained by the inventors, is to provide an anisotropic magnet alloy powder using the above-mentioned atmosphere-controllable hot press. By improving the manufacturing method, uniaxial compression processing was performed to prevent grain coarsening in the manufacturing process, and one or both of processing at an appropriate strain rate to increase anisotropy was realized. Another object of the present invention is to provide a method for producing anisotropic magnet alloy powder for bonded magnets. It is also included in the object of the present invention to provide a bonded magnet using the powder of the magnet alloy.

[0013]

In the method for producing anisotropic magnet powder for a bonded magnet according to the present invention, the method of heating up to uniaxial compression is improved by Nd-Fe-B.
A metal cylinder filled with quench powder obtained from a super-quenched ribbon of a system magnet alloy was uniaxially compressed along with the metal cylinder in a non-oxidizing atmosphere in a non-oxidizing atmosphere using a hot press capable of controlling the atmosphere. In the method of producing magnet powder by taking out and crushing it after plastic deformation is caused in the particles of the magnet alloy, the metal cylinder filled with the ultra-quenching powder is placed in an atmosphere at a temperature lower than the crystallization temperature of the magnet alloy. After carrying out preheating for holding, the particles are heated to a temperature of 650 to 900 ° C. and uniaxially compressed to prevent coarsening of the particles to obtain a magnet powder.

In the method for producing anisotropic magnet powder for a bonded magnet according to the present invention, the one paying attention to the strain rate in uniaxial compression is a method for producing magnet powder comprising the same steps as those described above for heating temperature. In, the uniaxial compression speed is expressed as ln (L ₀ / L) / T [where L _{0 is} the height of the metal cylinder before compression, L is the height of the metal cylinder after compression, and T is the compression time (second )] Is adjusted so that the strain rate is in the range of 0.5 to 3.0 / sec, and the magnetic powder is obtained by increasing the degree of anisotropy. To do.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The preheating temperature is preferably a temperature close to the crystallization temperature of a magnet alloy, but should not be higher than that. As described above, the crystallization temperature is 500.
Since it is around 0 ° C, it is generally appropriate to select from the range of 500 ± 20 ° C. The above-described selection of the heating method and the selection of the processing conditions are effective in either one, but if both are performed together, those effects are obtained together, and the results are even better.

The bonded magnet of the present invention is formed by mixing the anisotropic magnet powder produced as described above with a resin binder and applying a magnetic field to the mixture to orient the magnet material powder. Consists of. Selection of the binder and molding method, and molding in a magnetic field may be performed according to known techniques.

As the Nd-Fe-B magnet alloy used in the method for producing anisotropic rare earth magnet powder of the present invention, an alloy having a composition represented by the following formula is preferable. RxFe (100-xyzw) CoyBzTw (wherein R is a rare earth element containing Y, T is Ga,
Si, Al, C, Ni, Cu, Zn, In, Mn, N
It is one or more elements selected from b, Ta and Ti. x = 12.5 to 16.0, y = 0 to 10,
z = 4.8 to 6.5, w = 0 to 1)

The reason why the composition of the magnet alloy is limited as described above has been explained in the above-mentioned Japanese Patent Laid-Open No. 11-233323, but a brief re-recording is as follows.

When x is less than 12.5, the coercive force of the magnet is too small to be practical. If it exceeds 16, the energy product will decrease. When z is less than 4.8, the coercive force is low,
If it exceeds 6.5, plastic working becomes difficult. Since the addition of Co raises the Curie temperature, the heat resistance of the magnet is improved, but when y exceeds 10, the magnetization decreases.

The minor addition of component "T" helps improve the magnetic properties, either coercivity, remanence or maximum energy product. However, in general, the addition of more than 1% is not preferable because the decrease in magnetization becomes large. The effect of addition depends on the type of element: Ga, Si, and Al improve the residual magnetization, and Cu and Zn increase the coercive force. Therefore, the type and amount of the optional additional element should be selected according to the characteristics required for the magnet as a product.

In the production of the anisotropic magnet powder of the present invention,
The process of obtaining the ultra-quenched ribbon and its crushing can be carried out according to known techniques. In order to effectively exert the anisotropy by plastic working, it is desirable to make the crystal grain size of the ultra-quenched ribbon as fine as 0.1 to 1 μm, as described above in the disclosure of the invention. It is as follows. In addition, regarding the filling of the ultra-quenched powder into the metal cylinder and the uniaxial compression performed under heating, the above description of the invention is directly applied. However, JP-A-11-233323
Since the description of the compression ratio and the processing rate of No. 1 did not include consideration from the viewpoint of strain rate, the present invention supplements those findings.

The uniaxial compression processing under a controlled atmosphere, that is, under a non-oxidizing atmosphere is carried out in the state where the ultra-quenched powder is heated to a temperature of 650 to 900 ° C., as described above. At a low temperature of less than 650 ° C., anisotropy is not sufficiently achieved and a high energy product cannot be obtained. On the other hand, 90
At temperatures above 0 ° C, the coercive force of the alloy will be low.

The preheating prior to the heating in the hot press, which characterizes the invention, is advantageously carried out in another preheating device, such as a muffle furnace. For example, as shown in Examples described later, the temperature of the preheating furnace is set to 500
The temperature of the heating press was kept constant at 720 ° C, and when the temperature inside the powder filled in the metal cylinder reached about 500 ° C, it was transferred to the heating press for processing. It is a method of waiting until it reaches an appropriate temperature.

[0024]

[Example] [Example 1] In atomic%, Nd: 13.33%,
Fe: 74.96%, Co: 6.06% and B: 5.
An alloy with a composition of 65% is heated to 150 by high frequency heating.
A molten metal at 0 ° C. was formed, and this was poured onto a copper single roll rotating at a peripheral speed of 24 m / sec to obtain a super-quenched ribbon. This ribbon was crushed to a particle size of 300 μm or less to obtain an ultra-quenched powder. The magnetic properties were measured using a vibrating sample magnetometer (VSM) for the easy axis and the hard axis. The results are as follows, and this magnet powder was magnetically isotropic and had low characteristics. Remanent magnetization Br (kG): [easy axis] 2.8 [hard axis] 2.9 Coercive force iHc (Oe): [easy axis] 5.8 [hard axis] 5.8

A cylindrical container having a bottom and made of a mild steel plate having a thickness of 5 mm was filled with 10 kg of the above ultra-quenched powder, and the container was covered.
The lid was fitted and fixed to the edge of the cylinder. This was placed in a heating press capable of controlling an atmosphere according to a conventional method (that is, as a comparative example), and an atmosphere of argon gas was set. Heated. The temperature of the outer circumference of the container,
The temperature at the center of the filled powder was estimated by simulation and recorded in a graph. This graph is shown in Figure 1.
Shown in. 100 minutes after the start of heating, the temperature of the central part of the powder is 7
Since the temperature was close to 00 ° C., it was uniaxially compressed (compression ratio: 2.5), taken out, cooled, and the container was opened, and the anisotropy powder was recovered and pulverized to a particle size of 300 μm or less.

The powder thus obtained was hardened with wax while being oriented in a magnetic field of 15 kOe to obtain a sample for measuring magnetic properties. The magnetic properties of this sample were as follows. Remanent magnetization Br (kG): [easy axis] 11.5 [hard axis] 3.0 Coercive force iHc (Oe): [easy axis] 14.0 [hard axis] 6.0

Next, an epoxy resin was mixed with the magnet powder at a ratio of 2% by weight, and the mixture was filled in a mold and set in a magnetic field press. While applying a magnetic field of 15 kOe to orient the magnet powder, it was pressed at a pressure of ²⁰ ton / cm ² to obtain a compression molded body. This molded body was heated in an argon atmosphere at 150 ° C. for 1 hour to cure the epoxy resin and obtain a bonded magnet. The characteristics of the obtained bonded magnet were measured with a BH tracer, and the following results were obtained. Remanent magnetization Br: 8.7 kG Coercive force iHc: 13 Oe Maximum energy product [BH] max: 18 MGOe

The above metal container filled with ultra-quenched powder was placed in a muffle furnace set at a temperature of 500 ° C. (as an example), and the temperatures at the outer periphery of the container and the center of the powder were also simulated. Estimated. 180
Since it was thought that the whole temperature had almost reached the set value after a lapse of minutes, the temperature was transferred to a heating press having a set temperature of 720 ° C. to continue heating, and the temperatures of the outer peripheral portion and the powder center were estimated.
These estimates are as seen in the graph of FIG.

After heating for 240 minutes in the hot press,
Since it was estimated that the whole temperature reached the set temperature of 720 ° C., an anisotropic powder was obtained by performing uniaxial compression, taking out, cooling and pulverizing. The conditions of compression and crushing are the same as those described above. Of the obtained powder,
The magnetic properties of the magnetic field oriented sample were as follows. Remanent magnetization Br (kG): [easy axis] 13.0 [hard axis] 2.0 Coercive force iHc (Oe): [easy axis] 15.0 [hard axis] 7.0

Using this magnet powder, a bonded magnet was manufactured in the same manner as described above, and its magnetic characteristics were measured.
The results are as follows, and it was confirmed that the magnetic characteristics were improved by the method of the present invention. Remanent magnetization Br: 9.5 kG Coercive force iHc: 14 Oe Maximum energy product [BH] max: 22 MGOe

Compared with the case of placing in a 720 ° C. atmosphere with a heating press from the beginning, first, preheating in a muffle furnace at 500 ° C. and then transferring to a heating press and heating to 720 ° C. yielded a magnet powder of The magnetic characteristics are good, and the performance of the bonded magnet is also excellent accordingly. Even though the heating time was extended (100 minutes → 240 minutes), such improvement was seen.
When the temperature is higher than the crystallization temperature, the particles become coarser,
This is because, while the magnetic properties deteriorate, if the temperature is lower than the crystallization temperature, it can be avoided even if the heating time is long.

[Example 2] In Example 1, a small container having a capacity of 1 kg was used as a mild steel cylindrical container, and the powder was heated by placing it in a heating press set at 720 ° C from the beginning. did. Since it was empirically known that a heating time of 30 minutes was sufficient, uniaxial compression processing was performed after the lapse of that time. Here, the strain rate defined by the above equation is calculated as 0.1, 0.2, 0.5, 1.0,
The compression was performed at 3, 5, 7 and 10 / sec.

The maximum energy product [BH] max of the obtained anisotropy magnet powder was measured, and the relationship with the strain rate was plotted to obtain the graph of FIG. In this case, in the strain rate range of 0.5 to 3.0 / sec, 38 to 40M
A high maximum energy product of GOe was achieved. If the strain rate is not taken into consideration, the value does not reach 30 MGOe, so the effect of the strain rate during uniaxial compression on the magnetic properties is significant.

The reason for this is considered as follows. First, if the strain rate at the time of plastic working is high, there is no room for particles to grow during that period, and in that respect, a high strain rate acts advantageously. This fact has been confirmed by examining the correlation between coercive force and strain rate. On the other hand, as for the change in stress, when the strain rate increases, the slip between metal atoms decreases, which is disadvantageous to the magnetic properties. As described above, in plastic working, a factor that works favorably when the strain rate increases and a factor that works unfavorably coexist.
High magnetic properties can be obtained in the region of intermediate strain rate where one of these factors does not work strongly.

[0035]

Industrial Applicability When an anisotropic magnet powder is produced by the embodiment of the present invention which employs preheating below the crystallization temperature, it is possible to use a closed container, which is a benefit of the production method previously proposed. The benefit of being able to obtain magnet powder with highly anisotropic magnetic properties in an unnecessarily simplified process, while avoiding possible particle coarsening, especially when working in large batches It is possible to avoid deterioration of magnetic properties. On the other hand, according to the manufacturing method in which the plastic working is performed at an appropriate strain rate, which is another aspect of the present invention, the performance potentially possessed by the magnet alloy can be fully exhibited. If you combine these two aspects,
It is possible to obtain a large amount of magnet powder with excellent magnetic properties,
Therefore, a bonded magnet having high performance can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is data of a comparative example of the present invention, showing the temperature of the powder container and the internal temperature of the powder in the case where the pre-heating is not performed in the heating prior to the plastic working of the ultra-quenched powder and the atmosphere at the direct processing temperature is placed A graph showing the change over time.

FIG. 2 is data of an example of the present invention, and is a graph showing temporal changes in temperature of the powder container and the internal temperature when preheating is performed in heating prior to plastic working of ultra-quenched powder.

FIG. 3 is a graph showing the data of Examples and Comparative Examples of the present invention, showing the relationship between the strain rate during plastic working of ultra-quenched powder and the magnetic properties of the obtained magnet powder.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01F 1/06 H01F 1/06 A 1/08 1/04 H (72) Inventor Shinji Nakayama Nagoya City, Aichi Prefecture F-Term in the Technical Development Laboratory, Daido Steel Co., Ltd., Ni-chome 30-30, Daido-cho, Minami-ku (reference) 4K017 AA04 BA06 BB01 BB06 BB07 BB08 BB09 BB12 BB13 DA04 EA03 4K018 AA27 BA18 BC08 BD01 GA04 KA46 5E040 AA04 BB03 CA01 HB06 HB07 HB07 HB07 HB07 HB07 HB07

Claims (5)

[Claims] 1. A quenching powder obtained from an ultra-quenching ribbon of Nd-Fe-B based magnet alloy is filled in a metal cylinder and heated in a non-oxidizing atmosphere using a heating press capable of controlling the atmosphere. In the method of producing magnet powder by uniaxially compressing the whole metal cylinder in the axial direction to cause plastic deformation of the particles of the magnet alloy, and then taking out and crushing the metal cylinder, the metal cylinder filled with the ultra-quenching powder is replaced with the magnet alloy. After performing preheating to maintain the atmosphere at a temperature lower than the crystallization temperature of
A method for producing anisotropic magnet powder for a bonded magnet, characterized in that magnet powder is obtained by preventing particle coarsening by heating at a processing temperature of 0 to 900 ° C. and performing uniaxial compression. 2. The ambient temperature of preheating is 500 ± 20 ° C.
The manufacturing method according to claim 1, which is carried out by selecting from the range. 3. A quenching powder obtained from an ultra-quenching ribbon of Nd-Fe-B magnet alloy is filled in a metal cylinder and heated in a non-oxidizing atmosphere using a hot press capable of controlling the atmosphere. In the method of producing magnet powder by uniaxially compressing the metal cylinder in the axial direction to generate plastic deformation in the particles of the magnet alloy, and then taking out and pulverizing the particles, the processing speed is set to ln (L ₀ / L) / T [where L _{0 is} the height of the metal cylinder before compression, L is the height of the metal cylinder after compression, T is the compression time (seconds)], and the strain rate is 0.5 to 3. A method for producing anisotropic magnet powder for a bonded magnet, characterized in that the degree of anisotropy is increased to obtain the magnet powder by adjusting the content to be within a range of 0 / sec. 4. The Nd—Fe—B magnet alloy having the composition represented by the following formula is used.
Method for producing anisotropic rare earth magnet powder of. RxFe (100-xyzw) CoyBzTw (wherein R is a rare earth element containing Y, T is Ga,
Si, Al, C, Ni, Cu, Zn, In, Mn, N
It is one or more elements selected from b, Ta and Ti. x = 12.5 to 16.0, y = 0 to 10,
z = 4.8 to 6.5, w = 0 to 1) 5. The anisotropic magnet powder produced by the method according to claim 1, is mixed with a resin binder, and a magnetic field is applied to this mixture to orient the powder of the magnet material. Bonded magnet molded in the state.