JPH04240703A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a permanent magnet which is formed of a sintered compact having a remarkably high coercive force without decreasing a magnetic anisotropy as compared with the conventional Sm-Co or Nd-Fe-B magnet. CONSTITUTION:A pressed powder compact of alloy powder which is expressed by the composition formula RxMyFe100-x-y (R is at least one kind of element selected among rare earth elements which include Y, M is at least one kind of element selected among Si, Cr, V, Mo, W, Ti, Zr, Hf and Al, x is 4-20 atomic% and y is 20 or less atomic %) is sintered at the temperatures less than the melting point of the alloy powder for 0.8 hours or shorter.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention relates to a method of manufacturing a permanent magnet, and in particular, it has a high coercive force without deteriorating magnetic properties compared to conventional Sm-Co-based or Nd-Fe-B-based magnets. The present invention relates to a method of manufacturing a permanent magnet made of a sintered body.

0003

[Prior Art] Sm-Co magnets and Nd-F are known high-performance rare earth permanent magnets that have been mass-produced.
Examples include e-B magnets. These magnets include Sm, Nd
Rare earth elements such as these are contained as properties-expressing components. In other words, the rare earth elements contained in the magnet body bring about a very large magnetic anisotropy derived from the behavior of 4f electrons in the crystal field, which increases the coercive force and realizes a high-performance magnet. . Such high-performance magnets are mainly used in electrical equipment such as speakers, motors, and measuring instruments.

However, rare earth elements are generally very expensive, and in order to reduce the cost of high-performance magnets as described above, it is necessary to reduce the content of rare earth elements.

Recently, 1-12 rare earth iron intermetallic compounds having a ThMn12 type crystal structure formed using a liquid quenching method have attracted attention as high-performance magnetic materials with reduced rare earth content. There is. This intermetallic compound has a lower stoichiometric amount of rare earths than conventional intermetallic compounds such as Sm2Co17 and Nd2Fe14B1 that make up the magnet body, so the raw material cost is low, and the Fe ratio is relatively high. Therefore, it has a large saturation magnetic flux density Bs and a high maximum energy product (BH) max.

[0006]

[Problems to be Solved by the Invention] While it has been reported that the 1-12 series intermetallic compound formed by the liquid quenching method has a large coercive force, sintering is expected to yield a higher energy product. The problem that the coercive force rapidly decreases in the body was reported in the Journal of the American Society of Applied Physics (J.A.
ppl. Phys. 67.4954 (1990)) etc.

The present invention has been made to solve the above-mentioned problems.
It is an object of the present invention to provide a method for manufacturing a permanent magnet made of a sintered body having a particularly high coercive force. [Structure of the invention]

[0008]

[Means and effects for solving the problem] The present inventors have solved the problem by suppressing the amount of expensive rare earth elements used and
In order to obtain a permanent magnet with high coercive force without impairing the magnetic anisotropy of o-based magnets, we repeated research tests by changing the composition of rare earth elements, transition metal elements, etc. and sintering time.
As a result of forming various magnetic bodies and investigating their properties, it was found that when alloy powders adjusted to a certain composition range were sintered and integrated in a short period of time, a sintered body with extremely high coercive force was obtained, which was an excellent result. The present invention was completed based on the knowledge that it is possible to form a permanent magnet with magnetic properties.

That is, the method for producing a permanent magnet according to the present invention has the composition formula RxMyFe100-x-y (wherein R is at least one element 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, and x is 4 to 20% and y is 20% or less in atomic %). A green compact of the indicated alloy powder is sintered at a temperature below the melting point of the alloy powder for 0.8 hours or less.

[0010] Furthermore, the average particle size of the above alloy powder is 100 μm.
It is recommended to set it to less than m.

The reason why the composition of the alloy powder is limited as described above in the method for producing a permanent magnet according to the present invention is as follows.

[0012] The R mentioned above is La, Ce, Pr, Nd.
, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Examples include rare earth elements Yb, Lu, and Y, and one or a mixture of two or more of these may be used. R is added in a range of 4 to 20 at % in order to bring magnetic anisotropy to the magnet body and impart high coercive force.

[0013] When the amount of R added is less than 4 at%, α-
A large amount of Fe etc. precipitates and the coercive force (iHc) decreases significantly. On the other hand, if the amount of R added exceeds 20 atomic percent, the saturation magnetic flux density (Bs) will decrease significantly and a large amount of expensive rare earth elements will be used, leading to an increase in manufacturing costs. And you will be at a disadvantage.

[0014] M elements include Si, Cr, V, Mo, and W.
, Ti, Zr, Hf and Al, or a mixture of two or more thereof is used. Originally, a stable crystal structure cannot be formed only with the rare earth elements R and Fe, but
By adding the above M element in a range of 20 atomic % or less, it is possible to form a rare earth iron-based tetragonal compound having a stable ThMn12 type crystal structure, which improves the magnetic properties and thermal stability of the magnet. be able to.

[0015] When the amount of M element added exceeds 20 atomic %,
Since the saturation magnetic flux density (Bs) will decrease significantly, M
The amount of the element added is set to 20 atomic % or less.

[0016] Furthermore, by substituting a part of Fe with a transition metal other than Fe such as Co or Ni, the Curie temperature of the magnet can be significantly increased, the thermal stability of the magnet body can be improved, and the coercive force can be increased. can be done. However, if more than 50 atomic % of iron is replaced with Co, for example, the decrease in magnetocrystalline anisotropy and, as a result, the decrease in coercive force becomes significant.
The amount of substitution is desirably 50% or less of Fe in terms of atomic fraction. Furthermore, in order to suppress the amount of expensive Co used as much as possible, 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 explained.

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, then cast to prepare an alloy having a predetermined composition, and the resulting alloy is pulverized.

[0019] As another method for preparing the alloy powder, a mechanical alloying method or a mechanical grinding method is employed in which mechanical energy is applied to the mixture of the R, M, and Fe element powders to form an alloy. You can also do that. These methods are methods in which a mixture of powders containing R, Fe, and M components is subjected to a solid phase reaction to form an alloy.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 is adopted in which the raw material mixture is placed in a screw ball mill or the like and a mechanical impact is applied to the powder particles.

[0020] According to this mechanical alloying method, raw material powder particles are crushed into flakes, and the raw material mixture is homogeneously integrated by mutually diffusing different atoms at the parts where the flakes are in surface contact with each other. be done.

[0021] In addition, when preparing the alloy powder by any of the above methods, the average particle size of the alloy powder is set to 10 to form a sintered body that is denser and has excellent magnetic properties.
It is preferable to set it to 0 μm or less. The average particle size of the alloy powder is 1
This is because if it exceeds 00 μm, it becomes difficult to obtain a dense sintered body, and magnetic properties such as coercive force are significantly reduced.

[0022] The obtained alloy powder is then filled into a mold of a molding machine and pressurized to form a molded body (green compact) of a predetermined shape. By applying a magnetic field to the compact during pressurization to align the crystal orientation, a magnet having a high magnetic flux density can be obtained.

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

[0024] In addition to the usual sintering method and hot press method as described above, a method of sintering the molded body in a short time by so-called electric sintering can also be employed. In other words, while the alloy powder filled in the mold is pressurized and molded by the punch of the molding machine,
Sintering may be performed by directly applying electricity to the molded body in a vacuum or in an inert gas atmosphere to perform Joule heating.

Regardless of which sintering method is used, 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 decrease, resulting in a decrease in magnetic properties.

[0026] Furthermore, in order to further enhance the magnetic properties of the sintered body,
After sintering, aging treatment may be performed as necessary. The aging treatment temperature in this case varies depending on the alloy composition, but
Usually, a temperature range of about 500 to 1000°C is preferred.

[0027]

EXAMPLES Next, the present invention will be explained in more detail based on the following examples.

Examples 1-3, Comparative Examples 1-3 Examples 1-3
High purity Sm, Nd, Er, Zr, Ti, V, S
Ingots were prepared by blending i, Mo, and Fe powders into the compositions shown in Table 1, melting them in a high-frequency melting furnace, and pouring them into molds. Next, each ingot was pulverized to an average particle size of 3 μm using a jet mill. Next, each of the obtained alloy powders is filled into a mold of a molding machine, and while oriented in a magnetic field of 20 KOe, compression molding is performed at a molding pressure of 2 tons/cm2 to form a green compact. While supplying Sm vapor in an Ar gas atmosphere, sintering was performed at a temperature of 1120°C for 30 minutes, then rapidly cooled to room temperature, and each of the obtained sintered bodies was further heat-treated in a vacuum at a temperature of 740°C for 30 minutes. A magnet was prepared. And the residual magnetic flux density (Br
), coercive force (iHc), and maximum energy product (BH
)max was measured, and the results shown in Table 1 were obtained.

On the other hand, as Comparative Examples 1 to 3, Examples 1 to 3
Magnets were prepared under the same conditions as in Examples 1 to 3, except that the ingot prepared in was used and the sintering time was 90 minutes.
Its 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, each of the obtained powders was oriented in a magnetic field of 20 KOe to form a green compact, and then pulverized at 1120° C. in an Ar gas atmosphere. A sintering process was performed. Next, each of the obtained sintered bodies was heat-treated at 740° C. for 30 minutes, and then the magnetic properties were measured, and 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 is short and the stability of the intermetallic compound constituting the magnet body is less likely to be inhibited. It was found that magnetic properties such as residual magnetic flux density and coercive force were superior to those of Examples 1 to 3, and in particular, the maximum energy product (BH) max was significantly improved.

[0032] When the crystal structures of the magnet bodies prepared in Examples 1 to 3 were measured by X-ray diffraction, all of them showed T.
It was confirmed that a stable crystal structure of hMn12 type exists.

Examples 4-6, Comparative Examples 4-6 Examples 4-6
As, high purity Sm, Ti, Al, W, Cr, Si,
Fe powder was mixed into the composition shown in Table 2, melted in a high frequency melting furnace, and then poured into a mold to prepare each alloy ingot. Next, each alloy ingot was 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 made of an insulating material, and while an external magnetic field of 20 KOe is applied to the mold, compression molding is performed using a punch made of a conductive material to form a green compact. The green compact was sintered by the Joule heat generated by passing electricity through the punch. Here, the sintering operation was performed in an Ar atmosphere, and the current application time was 2 minutes.

Then, the residual magnetic flux density (Br), coercive force (iHc) and maximum energy product (
BH)max was measured and the results shown in Table 2 were obtained.

On the other hand, as Comparative Examples 4 to 6, Examples 4 to 6
Sintered bodies were prepared under the same conditions as in Examples 4 to 6, except that the ingots prepared in 1. The results shown in Table 2 below were obtained.

[0036]

[Table 2]

[0037] As is clear from the results shown in Table 2, in Examples 4 to 6, the average particle size of the alloy powder was set to 100 μm or less, so a sintered body that was dense and had a stable crystal structure could be obtained. . Therefore, permanent magnets with high magnetic properties could be formed in both cases.

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

Examples 7 to 9 As Examples 7 to 9, Sm, P with an average particle size of 0.5 mm
r, Nd powder, F with an average particle size in the range of 5 to 40 μm
A raw material mixture was prepared by blending e, Co, and Ti powders to the compositions shown in Table 3, and each of the obtained raw material mixtures was put into a ball mill, and pulverized and mixed for 60 hours in an Ar gas atmosphere to obtain each powder. The raw material powder was alloyed by mechanical alloying.

Next, each of the obtained alloy powders is filled into a mold made of an insulating material, and at the same time, the alloy powders are compressed and molded using a conductive punch in an Ar gas atmosphere, and at the same time, the alloy powders are compressed through the punch. The molded bodies were sintered by heating with electricity to prepare magnet bodies of Examples 7 to 9. Note that the current application 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]

[0042] As is clear from the results shown in Table 3, in Examples 7 to 9, the sintering process was performed in an extremely short time by energization sintering, and a stable compound phase was formed. It has been found that permanent magnets with excellent magnetic properties, particularly high coercive force (iHc), can be obtained in both cases.

[0043]

[Effects of the Invention] As explained above, according to the method of the present invention,
Stable ThMn1 due to short sintering time
A rare earth iron-based tetragonal compound having a type 2 crystal structure is formed, and a permanent magnet can be provided that has particularly excellent magnetic properties such as coercive force.

Claims (1)

[Claims] [Claim 1] Compositional formula RxMyFe100-x-y
(In the formula, R is at least one element selected from rare earth elements including Y, M is Si, Cr, V, Mo, W, Ti,
A green compact of an alloy powder containing at least one element selected from Zr, Hf, and Al, in which x is 4 to 20% and y is 20% or less in atomic %, is A method for producing a permanent magnet, comprising sintering at a temperature below the melting point for 0.8 hours or less.