JP3178848B2 - Manufacturing method of permanent magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a permanent magnet, and more particularly to a method for producing a permanent magnet having a high coercive force without deteriorating magnetic properties as compared with conventional Sm-Co and Nd-Fe-B magnets. To a method for manufacturing a permanent magnet made of a sintered body.

[0003]

2. Description of the Related Art Conventionally known and mass-produced high-performance rare earth permanent magnets such as Sm-Co based magnets and Nd-Fe
-B-based magnets and the like. These magnets contain a rare earth element such as Sm, Nd, etc., as a property developing component. That is, the rare-earth element contained in the magnet body causes a very large magnetic anisotropy derived from the behavior of the 4f electrons in the crystal field, thereby increasing the coercive force and realizing a high-performance magnet. . Such high-performance magnets are mainly used for electrical devices such as speakers, motors, and measuring instruments.

[0004] However, rare earth elements are generally very expensive, and it is necessary to reduce the content of rare earth elements in order to reduce the cost of the above-mentioned high-performance magnet.

As a high-performance magnet material having a reduced rare earth content, a 1-12 based rare earth iron-based intermetallic compound having a ThMn ₁₂ type crystal structure recently formed by using a liquid quenching method has attracted attention. ing. This intermetallic compound
As compared with the conventional intermetallic compounds such as Sm ₂ Co ₁₇ and Nd ₂ Fe ₁₄ B _{1, which} have a small stoichiometric amount of rare earth elements, the raw material cost is low and the ratio of Fe is relatively high. Therefore, it has a large saturation magnetic flux density Bs and a high maximum energy product (BH) _max .

[0006]

It has been reported that the 1-12 type intermetallic compound formed by the liquid quenching method can obtain a large coercive force, while sintering can expect a higher energy product. The problem of the coercive force dropping rapidly in the body is the problem of the American Society of Applied Physics (J.A.).
ppl. Phys. 67.9544 (1990)).

The present invention has been made to solve the above problems, and has been made without reducing magnetic anisotropy.
In particular, it is an object of the present invention to provide a method for manufacturing a permanent magnet made of a sintered body having a high coercive force. [Configuration of the invention]

[0008]

Means and Action for Solving the Problems The present inventors have minimized the use of expensive rare earth elements and have succeeded in reducing the conventional Sm-C
To obtain a permanent magnet with a high coercive force without losing the magnetic anisotropy of the o-based magnet, etc., repeated research and testing by changing the composition and sintering time of rare earth elements, transition metal elements, etc.
As a result of forming various magnet bodies and investigating their characteristics, when the alloy powder adjusted to a certain composition range was sintered and integrated in a short time, a sintered body with extremely high coercive force was obtained and excellent. The present invention has been completed based on the finding that a permanent magnet having improved magnetic properties can be formed.

[0009] That at least one element manufacturing method of a permanent magnet according to the present invention the composition formula _{R x M y Fe 100-x} -y ( wherein R is selected from rare earth elements including Y, M
Is at least one element selected from Si, Cr, V, Mo, W, Ti, Zr, Hf and Al, where x is 4 to 20% and y is 20% or less in atomic%. By sintering the green compact of the alloy powder to be obtained at a temperature lower than the melting point of the alloy powder for 0.8 hours or less, a permanent magnet having a maximum energy product (BH) _max of 17.2 MGOe or more is formed. It is characterized by doing.

The average particle size of the alloy powder is 100 μm.
m or less.

The reasons for limiting the composition of the alloy powder as described above in the method of manufacturing a permanent magnet according to the present invention are as follows.

The R is La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
Rare earth elements of m, Yb, and Lu and Y are mentioned, and one or a mixture of two or more of them is used. R brings about magnetic anisotropy to the magnet body and is added in the range of 4 to 20 atomic% in order to give a high coercive force.

When the added amount of R is less than 4 atomic%, α-
A large amount of Fe or the like precipitates and the coercive force (iHc) is greatly reduced. On the other hand, when the addition amount of R exceeds 20 atomic%, the saturation magnetic flux density (Bs) is greatly reduced, and a large amount of expensive rare earth element is used, which leads to an increase in manufacturing cost. And it becomes disadvantageous.

As the M element, Si, Cr, V, Mo,
One or a mixture of two or more selected from W, Ti, Zr, Hf and Al is used. Rare earth element R
And Fe alone cannot form a stable crystal structure, but by adding the above-mentioned M element within a range of 20 atomic% or less, a rare-earth iron-based tetragonal compound having a stable ThMn ₁₂ type crystal structure can be formed. And enhance the magnetic properties and thermal stability of the magnet.

When the amount of the element M exceeds 20 atomic%,
Since the saturation magnetic flux density (Bs) is greatly reduced, M
The addition amount of the element is set to 20 atom% or less.

Further, by substituting a part of Fe with a transition metal other than Fe, such as Co or Ni, the Curie temperature of the magnet is greatly increased, the thermal stability of the magnet body is improved, and the coercive force is increased. Can be done. However, for example, when 50% by atom or more of iron is replaced with Co, a decrease in crystal magnetic anisotropy and a decrease in coercive force become remarkable.
The substitution amount is desirably 50% or less of Fe in atomic fraction. In order to minimize the amount of expensive Co used, the amount of substitution is preferably within the above range.

Next, a method for manufacturing a permanent magnet according to the present invention will be described.

First, an alloy powder containing predetermined amounts of Fe, R, and M elements is prepared. In this case, the raw material powder is melted by arc melting or high frequency melting and then cast to prepare an alloy having a predetermined composition, and the obtained alloy is pulverized.

As another method for preparing the alloy powder, a mechanical alloying method or a mechanical grinding method for applying alloying by applying mechanical energy to the above-mentioned mixture of the respective element powders of R, M and Fe is employed. You can also. These methods are methods in which a mixture of powders containing R, Fe, and M components is subjected to solid-phase reaction to form an alloy, and specific methods for causing a solid-phase reaction include, for example, a planetary ball mill, a rotary ball mill, Attritor, vibrating ball mill,
A method in which the raw material mixture is charged into a screw ball mill or the like and a mechanical impact is applied to the powder particles is employed.

According to the mechanical alloying method or the like, the raw material powder particles are crushed into flakes, and heterogeneous atoms are mutually diffused at the portions where the flakes are in surface contact with each other, so that the raw material mixture is homogeneously integrated. Is done.

In the case of preparing the alloy powder by any of the above methods, the average particle size of the alloy powder is set to 10% in order to form a denser sintered body having excellent magnetic properties.
It is good to set it to 0 μm or less. The average particle size of the alloy powder is 1
If the thickness exceeds 00 μm, it becomes difficult to obtain a dense sintered body, and magnetic properties such as coercive force are significantly reduced.

The obtained alloy powder is then filled in a mold of a molding machine and pressed to form a compact (compact) having a predetermined shape. Here, a magnet body having a high magnetic flux density can be obtained by applying a magnetic field to the compact at the time of pressurization and aligning the crystal orientation.

The compact thus obtained is then sintered in a vacuum or in an inert gas atmosphere. The temperature as the sintering condition varies depending on the alloy composition, but is usually set to a temperature immediately below the melting point of the alloy powder or a temperature about 100 ° C. lower than the melting point, and preferably in a range of 400 to 1200 ° C.
Note that sinterability is improved by performing a hot press treatment of pressing the molded body at the same time as the heat sintering, so that a denser sintered body can be obtained.

In addition to the ordinary sintering method and hot pressing method as described above, a method of sintering a compact in a short time by so-called electric current sintering can be adopted. That is, while pressing the alloy powder filled in the mold with the punch of the molding machine,
Sintering may be performed by applying a current directly to the compact in a vacuum or an inert gas atmosphere and heating it with Joule.

Regardless of which sintering method is employed, the sintering time must be set within 0.8 hours. If the sintering operation is performed for more than 0.8 hours, the coercive force of the sintered body will be reduced, and the magnetic properties will be reduced.

In order to further enhance the magnetic properties of the sintered body,
After sintering, aging treatment may be performed as necessary. The aging temperature in this case varies depending on the alloy composition,
Usually, a temperature range of about 500 to 1000 ° C. is preferable.

[0027]

Next, the present invention will be described more specifically based on the following examples.

Examples 1-3, Comparative Examples 1-3 As Examples 1-3, high purity Sm, Nd, Er, Zr,
Ti, V, Si, Mo, and Fe powders were prepared to have the compositions shown in Table 1, melted in a high-frequency melting furnace, and then poured into a mold to prepare each ingot. Next, each ingot was finely pulverized by a jet mill to a size having an average particle diameter of 3 μm. Next, each of the obtained alloy powders is filled in a mold of a molding machine, and while being oriented in a magnetic field of 20 KOe, compression molding is performed at a molding pressure of ² ton / cm ² to form a green compact. At a temperature of 1120 ° C. while supplying Sm vapor in an Ar gas atmosphere.
After sintering for 0 minutes, the mixture was rapidly cooled to room temperature, and each obtained sintered body was heat-treated at 740 ° C. for 30 minutes in a vacuum to prepare a magnet body. The residual magnetic flux density (Br), coercive force (iHc), and maximum energy product (BH) _max of each magnet were measured, and the results shown in Table 1 were obtained.

On the other hand, as Comparative Examples 1 to 3, Examples 1 to 3
A magnet body was prepared under the same conditions as in Examples 1 to 3, except that the sintering time was 90 minutes using the ingot prepared in
The magnetic properties were measured. That is, each ingot used in Examples 1 to 3 was finely pulverized to an average particle size of 3 μm, and each obtained powder was oriented in a magnetic field of 20 KOe to form a green compact. A sintering process was performed. Next, after each of the obtained sintered bodies was subjected to a heat treatment at 740 ° C. for 30 minutes, the magnetic properties were measured. The results shown in Table 1 below were obtained.

[0030]

[Table 1]

As is clear from the results shown in Table 1, according to Examples 1 to 3, the sintering time was short, and the stability of the intermetallic compound constituting the magnet body was hardly hindered. It was found that the magnetic properties such as the residual magnetic flux density and the coercive force were superior to those of Nos. 1 to 3, and the maximum energy product (BH) max was greatly improved.

The crystal structures of the magnet bodies prepared in Examples 1 to 3 were measured by an X-ray diffraction method.
It was confirmed that a stable crystal structure of the hMn ₁₂ type was present.

Examples 4-6, Comparative Examples 4-6 As Examples 4-6, high purity Sm, Ti, Al, W,
Cr, Si, and Fe powders were prepared to have the compositions shown in Table 2, melted in a high-frequency melting furnace, and then poured into molds to prepare alloy ingots. Next, each alloy ingot was finely pulverized by a jet mill to an average particle size of 1, 50 and 80 μm, respectively. Next, the obtained alloy powder is filled into a mold formed of an insulating material, and while applying an external magnetic field of 20 KOe to the mold, compression molding is performed by a punch formed of a conductive material to form a compact. Electric power was supplied to the compact through the punch, and the compact was sintered by the generated Joule heat. Here, the sintering operation was performed in an Ar atmosphere, and the energization time was 2 minutes.

The residual magnetic flux density (Br), coercive force (iHc) and maximum energy product (BH) max of each of the obtained sintered bodies were measured, and the results shown in Table 2 were obtained.

On the other hand, as Comparative Examples 4 to 6, Examples 4 to 6
A sintered body was prepared under the same conditions as in Examples 4 to 6, except that the average particle size of the pulverized alloy powder was set to 150, 200, and 300 μm, respectively, using the ingots prepared in the above, and the magnetic properties were similarly measured. It measured and obtained the result shown in the following Table 2.

[0036]

[Table 2]

As is clear from the results shown in Table 2, in Examples 4 to 6, since the average particle size of the alloy powder is set to 100 μm or less, a dense sintered body having a stable crystal structure can be obtained. . Therefore, a permanent magnet having high magnetic properties could be formed.

On the other hand, in Comparative Examples 4 to 6, since the densification of the sintered body did not proceed sufficiently, the coercive force was 1 to 3 KOe.
It was about.

[0039] As Examples 7-9 Examples 7-9, the average particle diameter of 0.5mm of Sm, P
r, Nd powder, F having an average particle size in the range of 5 to 40 μm
e, Co, and Ti powders were each prepared to have the composition shown in Table 3 to prepare a raw material mixture, and each obtained raw material mixture was put into a ball mill, and pulverized and mixed in an Ar gas atmosphere for 60 hours. The raw material powder was alloyed with a mechanical alloy.

Next, each of the obtained alloy powders is filled in a molding die formed of an insulating material, and the alloy powder is pressed and compressed by a conductive punch in an Ar gas atmosphere. The molded body was heated by electric current and sintered to prepare magnet bodies of Examples 7 to 9. Note that the energization time was set to 2 minutes. Next, the magnetic properties of each of the obtained magnet bodies were measured in the same manner as in Examples 1 to 6, and the results shown in Table 3 were obtained.

[0041]

[Table 3]

As is clear from the results shown in Table 3, in Examples 7 to 9, sintering was performed in a very short time by electric current sintering, and a stable compound phase was formed. It was found that a permanent magnet having excellent magnetic properties and particularly high coercive force (iHc) was obtained.

[0043]

As described above, according to the method of the present invention,
Since the sintering time is set short, stable ThMn ₁₂
A rare-earth iron-based tetragonal compound having a type crystal structure is formed, and a permanent magnet excellent in magnetic properties such as coercive force can be provided.

Continuation of front page (56) References JP-A-1-175205 (JP, A) JP-A-59-215460 (JP, A) JP-A-64-67902 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) H01F 1/04 H01F 1/08 C22C 38/00 303

Claims (1)

(57) [Claims] 1. A composition formula _{R x M y Fe 100-x} -y ( at least 1 wherein R is selected from rare earth elements including Y
Seed element, M is Si, Cr, V, Mo, W, Ti, Z
at least one element selected from the group consisting of r, Hf, and Al, where x is 4 to 20% and y is 20% or less in atomic%. By sintering at a temperature lower than the melting point for a time of 0.8 hours or less, the maximum energy product (BH) _max is 17.2.
A method for producing a permanent magnet, comprising forming a permanent magnet of MGOe or more.