JP3053344B2 - Rare earth magnet manufacturing method - Google Patents

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 permanent magnet, in particular, a sintered Nd-based magnet.

[0002]

2. Description of the Related Art Rare-earth sintered magnets have recently been in high demand due to their high magnetic properties, despite being very expensive compared to ferrite and the like. Among them, Nd-based magnets are particularly becoming the mainstream of rare-earth magnets because of their higher magnetic properties and lower cost than Sm-based magnets.

[0003] Nd-based sintered magnets are manufactured by powder metallurgy and undergo the following steps. That is, an alloy is prepared by melting to have a predetermined composition, the alloy is pulverized to obtain a fine powder of 1 to 20 μm, the fine powder is molded in a magnetic field, and sintering and heat treatment are performed. Become.

[0004] Techniques used for obtaining fine powder include a ball mill, an attritor mill, a vibration mill and a jet mill.
The vibration mill generally has no reactivity with the rare earth magnet alloy or is slurried and pulverized using an organic solvent having low reactivity. Therefore, the work process becomes complicated,
There are many disadvantages such as the danger of explosion due to ignition and reaction of the organic solvent due to the reaction with the metal, and it cannot be said that this method is very suitable as a method for pulverizing alloys for rare earth magnets.

On the other hand, a jet mill that performs pulverization using a supersonic gas stream changes the gas to be used to an inert gas, thereby reducing oxidation of fine powder which is a problem in producing rare earth magnets. This method is also suitable as a method for finely pulverizing alloys for rare earth magnets because it can be minimized, and has been actively used in the production of rare earth magnets, especially Sm-based magnets.

However, when a jet mill is applied to the production of an Nd-based magnet and then finely pulverized, the production efficiency is significantly reduced because the pulverization amount per unit time, that is, the pulverizing ability, is lower than that of an Sm-based magnet. There was a problem.

[0007]

When the alloy for Nd-based magnets is finely pulverized by a jet mill, the production efficiency of the fine pulverization step is remarkably reduced due to poor pulverizing ability. There was a problem that efficiency could not be obtained. In the present invention, in view of the problems related to the production of Nd-based sintered magnets, a high-performance Nd-based magnet having high coercivity, high residual magnetization and high remanence is realized by establishing a new production method. It is something to offer.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors consider that there is a difference in the crushing ability between the Sm-based magnet and the Nd-based magnet, and thus the Nm manufactured through the melting step.
We thought that the metallographic structure of the alloy for d-based magnets might affect the pulverization process, which is the subsequent process, and focused on the melting process and the metallographic structure after melting, and as a result, the crystals in the alloy after melting When fine pulverization is performed with a jet mill using an alloy in which fine rare earth element oxides having a diameter of 1 μm or less are dispersed and precipitated inside the particles, the pulverization ability is improved, and Nd
The present invention has been completed by making it possible to manufacture a system magnet with high production efficiency.

The gist of the present invention is that the formula R _x (Fe _1-a Co _a ) _y B _z T
_b (where R is at least one of the rare earth elements including Y, T represents a transition metal other than Fe and Co , x is 11 to 16%, y is 70 to 85%, and z is 4 to 9%, b is 0
４4%, and a is 0 ≦ a ≦ 0.2). In the method for producing a rare earth magnet, the temperature of the molten metal is set to a temperature higher than the melting point of the alloy by 50 ° C. to 200 ° C. And a diameter of 1 within the crystal grains in the alloy after casting.
Alloys containing fine rare earth oxides less than μm
Pulverized by jet mill using supersonic gas flow
And sintering the rare earth magnet.

Hereinafter, the present invention will be described in detail. The composition formula of the rare earth permanent magnet alloy to which the present invention is applied is R _x (Fe _1-a C
o _a ) _y B _z T _b , where R is La, Ce, P containing Y
r, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
one or more rare earth elements selected from r, Tm, Yb and Lu, and T is Al, Si, Ti, V,
Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, M
o, Sn, Hf, Ta, and W are selected.

The weight percentage x is 11-16%, y is 70-85%,
z is 4 to 9%, b is 0 to 4%, and a is 0 ≦ a ≦
0.2. In this composition, if the amount x of R is less than 11%, α-Fe precipitates and the coercive force is remarkably reduced, which is not preferable. If it exceeds 16%, the residual magnetization is undesirably low.

If the amount z of B is less than 4%, the coercive force is remarkably reduced due to the precipitation of the Nd ₂ Fe ₁₇ phase, which is not preferable.
Exceeding the range is not preferable because the amount of the nonmagnetic phase NdFe ₄ B ₄ increases and the residual magnetization decreases.

A represents the ratio of Fe to Co, and F
The residual magnetization can be increased by substituting e with Co. However, if the amount of a exceeds 0.2, the coercive force is remarkably reduced, which is not preferable. If y is less than 70%, the residual magnetization becomes low, and if y exceeds 85%, the coercive force decreases, which is not preferable.

The additional element T is used for increasing the coercive force. However, if b exceeds 4%, the effect of increasing the coercive force is weakened, and the residual magnetization is significantly reduced, which is not preferable.

Next, the manufacturing method of the present invention will be described. Nd-based magnets are usually manufactured through the steps of melting, coarse pulverization, fine pulverization, molding, sintering, and aging. In the melting step, the temperature of the molten metal is adjusted to prevent the reaction between the molten metal and a crucible made of alumina or the like. It was common to melt at a temperature higher than the melting point by 50 ° C. and cast it into a mold to form an alloy. However, the temperature of the molten metal was raised by about 50 ° C. to 200 ° C. higher than the melting point of the alloy, and When casting by introducing oxygen into the molten metal by accelerating the reaction with a crucible made of alumina or the like, fine rare earth element oxides having a diameter of 1 μm or less are contained inside the crystal grains in the alloy as shown in FIG. When the alloy has a dispersed and precipitated alloy structure, and the alloy is finely pulverized with a jet mill using a supersonic gas stream , the pulverizing ability is remarkably improved, resulting in high production efficiency. That Nd-based magnets can be manufactured Was Idashi. The fine particles were analyzed by a high-resolution electron microscope equipped with an energy dispersive X-ray analyzer, and as a result, it was confirmed that they were a rare earth element oxide.

Here, when the temperature of the molten metal is lower than 50 ° C., the alloy structure in which fine rare earth oxides having a diameter of 1 μm or less are dispersed and precipitated in crystal grains in the alloy is hardly formed, so that the pulverization ability is reduced. Is not preferable because it does not improve,
If the temperature exceeds 200 ° C, the temperature of the molten metal is so high that the evaporation phenomenon is so severe that the composition of the finally obtained alloy is significantly different from the composition at the time of weighing, and it is difficult to control the composition. , Preferably in the range of 100 ° C to 150 ° C. By manufacturing the Nd-based magnet as described above, the pulverizing ability at the time of fine pulverization was remarkably improved, and as a result, the productivity of the Nd-based magnet was significantly improved and was very effective.

First, raw metal is weighed so as to have the above composition. Next, using a crucible made of an oxide such as alumina, in a vacuum or in an inert atmosphere, in a high-frequency melting furnace, the temperature of the molten metal is set to be 50 ° C to 200 ° C higher than the melting temperature of the composition. Is melted and then cast to form an alloy having an alloy structure in which fine rare-earth element oxides having a diameter of 1 μm or less are dispersed and precipitated in the crystal grains in the alloy.

Next, the prepared alloy is subjected to a jaw crusher,
After grinding with a brown mill etc., the supersonic gas flow
And pulverizing with a jet mill. The thus-obtained fine powder having an average grain size of 20 μm is molded in a magnetic field of about 15 kOe at a pressure of 0.2 to ² Ton / cm ² to obtain a molded body having a density of 3 to 5 g / cc. . The molded body obtained as described above is sintered in a vacuum at 1000 ° C. to 1150 ° C. or in an inert gas at atmospheric pressure or lower for 0.1 to 10 hours, cooled, and then cooled to 400 ° C. Aging treatment is performed at 1000 ° C. for 0.1 to 10 hours to obtain an Nd-based magnet.

[0019]

The problem to be solved by the present invention is to improve the fine grinding ability of the Nd-based magnet and to improve the productivity accompanying the improvement. The study focused on the pulverization ability and the metal microstructure of the alloy for Nd-based magnets manufactured through the melting process. As a result, the conditions in the melting process were optimized, and the alloy after melting was placed inside the crystal grains. It has been discovered that when fine rare earth oxides having a diameter of 1 μm or less are dispersed and precipitated, the pulverizing ability is significantly improved.
When fine rare-earth oxides of less than μm are dispersed and precipitated, it is predicted that the fine oxides will become stress-concentrated sites when grinding energy is applied to the alloy during grinding. It is considered that the concentrated portion easily becomes a crack generation site. Therefore, it is considered that the energy required for grinding is smaller than that of an alloy in which fine oxides are dispersed and not precipitated, and as a result, when the same grinding energy is applied, the grinding ability is improved.

[0020]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 An alloy having a composition formula of Nd _13.7 Dy _0.9 Fe _76.9 Co ₂ B ₆ Al _0.5 was mixed with a raw material having a purity of 99.9 wt% or more. Also 100 ℃
The alloy was controlled and melted at a high temperature of 1340 ° C., and then cast to obtain an alloy having the above composition. This alloy is coarsely pulverized in an Ar atmosphere using a jaw crusher and a brown mill, and the supply conditions of the coarse powder are adjusted by a jet mill using nitrogen gas so that the fine powder has an average particle diameter of 5 μm. Grinding was performed. In order to align the fine powder in a magnetic field of about 15 kOe, about 0.9 kO in a direction perpendicular to the magnetic field.
Press molding was performed at a pressure of Ton / cm ² to obtain a molded body. The molded body was sintered at 1060 ° C. for 90 minutes in a vacuum, and then cooled to obtain a sintered body. The sintered body thus obtained was subjected to a heat treatment at 600 ° C. for 120 minutes in an inert gas atmosphere to obtain Example 1.

Comparative Example 1 and Comparative Example 2 The same procedure as in Example 1 was carried out except that the temperature of the molten metal was controlled to be 1280 ° C., which is 40 ° C. higher than the melting temperature. The sample obtained was used as Comparative Example 1. A sample prepared and produced in the same manner as in Example 1 was used as Comparative Example 2 except that the temperature of the molten metal was controlled to be 1470 ° C. which was 230 ° C. higher than the melting temperature.

Example 2 and Comparative Example 3 Example 1 was repeated except that the alloy having the composition formula Nd _12.4 Pr _1.2 Dyo _0.4 Fe _73.2 Co ₆ B ₆ Al _0.4 Ti _0.4 was heated to 1360 ° C., which was 100 ° C. higher than the melting temperature. A sample obtained by the same method as in Example 2 was used as Example 2, and the temperature of the molten metal was 1300 ° C. higher than the melting temperature by 1300.
A sample prepared and produced in the same manner as in Example 1 except that the temperature was changed to ° C. was used as Comparative Example 3.

The photograph in FIG. 1 is the result of observing the alloy of Example 1 after melting by an electron microscope. The result of similarly observing the alloy of Comparative Example 1 is shown in the photograph of FIG. In the photograph of FIG. 1, precipitation of fine rare earth element oxides of 1 μm or less is observed, but from the photograph in FIG. 2, it can be seen that no precipitate is observed.

The residual magnetic flux density (Br) and coercive force (H
c) and the maximum energy product (BHmax) was calculated. Table 1
As shown in FIG.

[0025]

[Table 1]

As is apparent from Table 1, according to the method of the present invention, when fine rare-earth element oxides of 1 μm or less are present in the alloy, the pulverizing ability is improved and Nd having good magnetic properties is obtained. The production of the system magnet became possible.

[0027]

According to the manufacturing method of the present invention, a high performance rare earth sintered magnet can be provided under high productivity, and the effect is extremely high in industry.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (magnification: 10,000) showing the crystal structure of an alloy according to the method of the present invention.

FIG. 2 is an electron micrograph (magnification: 10,000) showing the crystal structure of an alloy according to a conventional method.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01F 1/053 C22C 33/02 H01F 1/08 H01F 41/02

Claims (3)

(57) [Claims] 1. The formula R _x (Fe _{1 -a} Co _a ) _y B _z T _b (wherein R is at least one of the rare earth elements containing Y, and T is Fe, Co
And x represents 11 to 16% by weight percentage and y represents
Is 70 to 85%, z is 4 to 9%, b is 0 to 4%, and a is 0 ≦ a ≦ 0.2) in a rare earth magnet manufacturing method. An alloy in which a raw metal is melted in a crucible at a high temperature of not less than 200 ° C and not more than 200 ° C, and a fine rare earth element oxide having a diameter of 1 µm or less is contained in crystal grains in the alloy after casting . The supersonic gas flow
And pulverizing it with a jet mill using the above method and sintering it. 2. A jet mill according to claim 1,
A method for producing a rare earth magnet, wherein the average particle diameter is 1 to 20 μm . 3. Use of a crucible made of alumina.
3. The method for producing a rare earth magnet according to 1 or 2.