JPH056831A - Manufacture of rare-earth cobalt magnet with excellent heat-resistant property - Google Patents

Abstract

PURPOSE:To obtain an intermetallic compound permanent magnet composed of rare-earth elements and cobalt, especially a Cu- -s ubstitution type permanent magnet whose heat-resistant property is excellent by a method wherein, after an alloy by a specific composition has been changed to a molten metal, a specific temperature range is cooled at a specific speed. CONSTITUTION:An alloy by a composition expressed by the general formula of R (Co1-a-b-cFeaCubZre)z (where R represents a combination of one kind or two or more kinds of rare-earth elements including Sm and Ce as central elements, 0.24<=a<=0.26, 0.058<=b<=0.064, 0.018<=c<=0.024 and 7.2<=z<=7.8) is changed to a molten metal. The alloy is changed to the molten metal; after that, a temperature range of 800 deg.C or higher is cooled at a peed of 2 to 25 deg.C/sec; the molten metal is crushed; fine powders which have been obtained are compressed and molded in a magnetic field; after that, the moldered powders are sintered, changed to a solution; an aging treatment is executed. Thereby, it is possible to obtain a rare-earth cobalt magnet whose maximum energy product is at 27MGOe or higher in a temperature range from room temperature to 150 deg.C and whose heat-resistant property is excellent.

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 an intermetallic compound permanent magnet composed of rare earth and Co, particularly a Cu-substitution type R ₂ Co ₁₇ system permanent magnet having excellent heat resistance.

[0002]

2. Description of the Related Art Rare earth magnets are being used in a wide range of fields as materials for various electric appliances and electronic devices. However, they have been made of materials having high performance and high heat resistance in order to meet the recent demand for miniaturization and high efficiency. Development is desired. In the case of rare earth magnets, the recently developed R-Fe-B magnets are advantageous in terms of high performance at room temperature, but this magnet material has the drawback of having a large temperature coefficient of magnetic characteristics. Therefore, the residual magnetic flux density Br and the coercive force iHc decrease sharply as the temperature rises, which poses a serious problem in practical use. In particular, the rapid decrease in iHc greatly limits the operating temperature range. This is because the coercive force generation mechanism is a nucleation growth type. On the other hand, R ₂ C having a two-phase separation type coercive force generation mechanism
Since the o ₁₇ magnet has a smaller temperature coefficient of magnetic characteristics and a higher Curie temperature than the R-Fe-B magnet, it has been conventionally used as a rare earth magnet suitable for use at high temperatures.

[0003]

However, when the content of Fe is increased in the composition of the R ₂ Co ₁₇ system magnet, the coercive force Hc and the squareness of the hysteresis curve decrease, and
If the content of is reduced, the residual magnetic flux density Br decreases.
On the other hand, if the Cu content is increased, the residual magnetic flux density Br decreases,
If the Cu content is reduced, the coercive force Hc decreases. Also,
Increasing the Zr content decreases the residual magnetic flux density Br,
If the content of is reduced, the coercive force Hc and the squareness of the hysteresis curve are reduced. Therefore, the composition dependence of magnetic properties tends to conflict with each other among the constituent elements. That is, in order to obtain high magnetic properties in the R ₂ Co ₁₇ system magnet, it is necessary to increase the Br, and it is essential to increase the Fe content or decrease the Cu and Zr. In this composition region, the coercive force Hc and the squareness are lowered, so that it was impossible with the conventional technique to simultaneously achieve high magnetic properties and high heat resistance. The purpose of this study is to improve the shortcomings of the prior art and to provide R ₂ with high performance and excellent heat resistance.
(EN) It is intended to provide a Co _17- based magnet, particularly a rare earth cobalt magnet having a maximum energy product of 27 MGOe or more in a temperature range from room temperature to 150 ° C, and a method for producing the same.

[0004]

According to the present invention, the general formula R (Co _1-abc Fe _a Cu _b Zr _c ) _z (where R: S
One or a combination of two or more rare earth elements centering on m and Ce, 0.24 ≦ a ≦ 0.26, 0.058 ≦ b ≦ 0.064, 0.018
≦ c ≦ 0.024, 7.2 ≦ z ≦ 7.8),
And the maximum energy product is 27M in the temperature range from room temperature to 150 ℃.
Provided is a rare earth cobalt magnet having excellent heat resistance that is equal to or higher than GOe. The characteristic of the method for producing this magnet is that the alloy having the above composition is crushed, and the obtained fine powder is compression-molded in a magnetic field, followed by sintering, solutionizing, and aging treatment. The alloy having the composition is to cool the temperature range of 800 ° C. or higher after casting the molten metal at a rate of 2 to 25 ° C./sec.

The present invention will be described in detail. Two-phase separation type R ₂ Co ₁₇
The crystallographic characteristic of the system magnet is that it has a more stable 1/7 structure (TbCu ₇ structure) in the high temperature region. This 1/7 phase is
By subjecting it to appropriate aging annealing, it decomposes into two phases, a 1/5 phase and a 2/17 phase with a cellular structure. The domain wall is trapped at the phase boundary and becomes difficult to move, resulting in high coercive force. Further, the squareness of the hysteresis curve also shows a change largely dependent on the cell-like structure in which the two phases are separated. The present invention is intended to homogenize the two-phase separated cellular structure. That is, the present inventors have diligently studied to reduce the coercive force and the squareness of the hysteresis curve caused by the increase in the Fe content or the decrease in the Cu and Zr contents according to the prior art.
As a result of discussion, it was found that the cause was due to the non-uniform crystal structure distribution of the alloy immediately after melting, that is, the ingot. FIG. 1 shows the crystal structure of an alloy of Sm (Co _0.67 Fe _0.25 Cu _0.06 Zr _0.02 ) _7.5 produced by arc melting and the analysis results by SEM / EDX of each existing phase. According to a general idea, the existing phases are compared with the atomic ratio of (Sm, Zr) _A (Co, Fe, Cu) _B. 1,
2), phase close to 1/5 phase with B / A = 5.4-6.3 (analysis points 3, 4)
And 4 kinds of stoichiometric compositions close to 2/7 phase, which are Cu rich (analysis points 5 and 6) or Zr rich (analysis points 7 and 8), can be confirmed. Table 1 shows the analytical values.

[0006]

[Table 1] Atomic ratio B / A: (Sm, Zr) _A (Co, Fe, Cu) _B FIG. 2 shows the crystal structure and the analysis results of each phase when the above alloy is a sintered body. It can be seen that the inside of the frame is B / A = 6.9 to 7.0, which is almost a 1/7 phase. Table 2 shows the analytical values.

[0007]

[Table 2] Atomic ratio B / A: (Sm, Zr) _A (Co, Fe, Cu) _B

However, a composition similar to that of the analysis points 7 and 8 in FIG. That is, the presence of the analysis point 4 in FIG. 2 means that there is an undiffused portion inside the sintered body even by performing pulverization, molding, sintering, solution treatment, and heat treatment. Since analysis point 4 in FIG. 2 is a Zr-rich 2/7 phase, it means that a Zr-poor region is inevitably present in the frame. In such a case, a uniform cellular structure cannot be obtained, and as a result, the domain wall movement becomes irregular, and in particular, the squareness of the hysteresis curve is deteriorated. In some cases, the coercive force iHc also decreases. The present inventor has made the aforementioned R ₂ Co ₁₇
It was thought that the key to achieving high performance of magnets was the modification of the interior of the alloy. Further, the improvement of the squareness of the hysteresis curve is extremely important when it is used at high temperature at the same time as the performance is improved. From such a viewpoint, as a result of diligent study, as a result of cooling the alloy in a temperature range of 800 ° C. or higher at a rate of 2 to 25 ° C./sec after casting the alloy, the analysis points 3 and 4 shown in FIG. / 5 We found that the number of phases close to phase 5 increased relatively. Figure 10
The crystal structure when cooled at a speed of / sec is shown.
A relative increase of 1/5 phase can be confirmed. The improvement of the magnetic properties by the relative increase of the 1/5 phase is that the 1/5 phase acts as a sintering aid during sintering and diffuses the Zr rich 2/7 phase, Cu rich 2/7 phase and 2/17 phase. It is believed that this is due to the promotion of the above and a homogeneous sintered body. Table 3 shows the analysis values at each analysis point in FIG.

[Table 3] Atomic ratio B / A: (Sm, Zr) _A (Co, Fe, Cu) _B
The present invention, after casting the alloy of limited composition, 2-25 ℃ / s
It was completed by crushing, molding, sintering, solutionizing and heat treatment after cooling at the rate of ec. When the alloy is cooled at a rate exceeding 25 ° C / sec after casting, the cooling rate is too high, and a relative increase in 1/5 phase cannot be achieved. If the cooling rate after the molten metal is less than 2 ° C / sec, the relative increase of 1/5 phase can be achieved, but it is not industrially preferable.

Next, the reasons for limiting the composition will be described. If a is less than 0.24, the residual magnetic flux density Br is greatly reduced and the temperature is 150 ° C
It is difficult to obtain maximum energy product over 27MGOe in the temperature range of. When a exceeds 0.26, the squareness of the hysteresis curve is greatly reduced and cannot be improved by homogenizing the alloy.
When b is less than 0.058, the coercive force is largely reduced, and a magnet with high heat resistance cannot be obtained. When b exceeds 0.064, the residual magnetic flux density Br is remarkably reduced, and the maximum energy product of 27 MGOe or more cannot be maintained in the temperature range from room temperature to 150 ° C. c is
If it is less than 0.018, high coercive force and good squareness of the hysteresis curve cannot be obtained even by homogenizing the alloy. c
When the value exceeds 0.024, the residual magnetic flux density Br is remarkably reduced, and the maximum energy product is 27MGOe in the temperature range from room temperature to 150 ℃.
The above cannot be maintained. When z is less than 7.2, the residual magnetic flux density Br and the coercive force decrease. When z exceeds 7.8, the coercive force is significantly reduced. In addition to the above basic components, impurities that are unavoidable in the manufacturing process may be contained. The present invention will be described below with reference to examples.

[0010]

EXAMPLES Example 1 Sm (Co _0.67 Fe _0.25 Cu
An alloy having a composition of _0.06 Zr _0.02 ) _7.4 was prepared by high frequency melting. At this time, the ingot uses a book-type mold and 45 mm
And the thickness. Cooling rate after casting is about 6 ℃ / se up to 800 ℃
It was c. The obtained ingot was roughly pulverized by a stamp mill and a disc mill and then pulverized by a jet mill. At this time, N ₂ gas was used as the grinding medium, and the grinding particle size was 3.5 μm (FSSS). 15 kO of the obtained fine powder
Transverse magnetic field molding was performed in the magnetic field of e. The molding pressure was ² ton / cm ² . The compact was sintered under vacuum at 1200 ° C. for 1 hour, and then solution-treated at 1160 ° C. for 1 hour in an Ar stream. After holding this sintered body at 850 ° C. for 5 hours, it was cooled to room temperature at a rate of 1 ° C./min. The magnetic properties obtained are shown in Table 4 in comparison with Comparative Example 1. (Comparative Example 1) Sm (Co _0.67 Fe _0.25 Cu _0.06 Z
An alloy having a composition of r _0.02 ) _7.4 was prepared by high frequency melting.
At this time, the mold used was a water-cooled book type. The thickness of the produced ingot was 15 mm, and the cooling rate after casting was 80
It was 35 ° C / sec up to 0 ° C. The obtained ingot was made into a sintered body by the same method as in Example 1, and subjected to solution heat treatment and heat treatment. The magnetic properties obtained are shown in Table 4 in comparison with Example 1. It can be seen from Table 4 that the energy product at a high temperature of 150 ° C. shows a remarkably high value by cooling the ingot within the scope of the claims of the present invention. The results in Table 4 show the improvement of the squareness of the history curve, namely H
This is due to the improvement of k.

[0011]

[Table 4] (Example 2) Sm (Co _0.662 Fe _0.26 Cu _0.058 Zr
An alloy having a composition of _0.020 ) _7.4 was prepared by high frequency melting. At this time, the ingot used a book-type mold and had a thickness of 25 mm. The cooling rate in this case is 11 ℃ / sec up to 800 ℃ after casting
Met. The magnetic characteristics of the obtained ingot were evaluated in the same manner as in Example 1. The results are shown in Table 5 in comparison with Comparative Example 2. (Comparative Example 2) Sm (Co _0.662 Fe _0.26 Cu _0.058 Zr
An alloy having a composition of _0.020 ) _7.4 was prepared by high frequency melting. In this case, the same method as in Comparative Example 1 was used to evaluate the ingot production conditions and magnetic properties. The magnetic properties obtained are shown in Table 5 in comparison with Example 2.

[0012]

[Table 5] Example 3 Sm (Co _0.662 Fe _0.25 Cu _0.064 Zr
An alloy having a composition of _0.024 ) _7.5 was prepared by high frequency melting. At this time, the mold was heated to a mold temperature of about 500 ° C., and molten metal was poured into the heated mold. The thickness of the ingot in this case is 25m
The cooling rate up to 800 ° C after casting was 3 ° C / sec. The mold heating was terminated after confirming that the ingot temperature after casting was 800 ° C or lower. After cooling to room temperature, the ingot was evaluated for magnetic characteristics by the same method as in Example 1. The results are shown in Table 6 in comparison with Comparative Example 3. (Comparative Example 3) Sm (Co _0.662 Fe _0.25 Cu _0.064 Zr
An alloy having a composition of _0.024 ) _7.5 was prepared by high frequency melting. In this case, the same method as in Comparative Example 1 was used to evaluate the ingot production conditions and magnetic properties. The obtained magnetic characteristics are shown in Table 6 in comparison with Example 3. As is clear from Table 4, Table 5 and Table 6, the remarkable improvement of the magnetic properties according to the present invention is the improvement of the squareness of the hysteresis curve, and this improvement effect is particularly remarkable in the high temperature region near 150 ° C. Recognize.

[0013]

[Table 6]

[0014]

As described above, according to the manufacturing method of the present invention, it is possible to manufacture a rare earth cobalt magnet having high performance and excellent heat resistance, which was difficult with the prior art.

[Brief description of drawings]

FIG. 1 is a photograph showing a metallographic structure of an alloy produced by arc melting according to the present invention.

FIG. 2 is a photograph showing a metallographic structure of a sintered body according to the present invention.

FIG. 3 is a photograph showing the metallographic structure of the alloy according to the present invention when it is cooled at a rate of 10 ° C./sec after casting.

Claims (1)

Claims: 1. A compound of the general formula R (Co _{1 -abc} Fe _a Cu _b Z
r _c ) _z (where R: Sm, Ce, one or a combination of two or more rare earth elements, 0.24 ≦ a ≦ 0.26, 0.05
8 ≤ b ≤ 0.064, 0.018 ≤ c ≤ 0.024, 7.2 ≤ z ≤ 7.8) is cast into a molten alloy to obtain a massive alloy, which is then crushed and the fine powder obtained is subjected to a magnetic field. After compression molding, sintering,
In the method for producing a rare earth cobalt magnet to be subjected to solution treatment and aging treatment, the alloy is cast and then cooled in a temperature range of 800 ° C. or higher at a rate of 2 to 25 ° C./sec, which is excellent in heat resistance. Manufacturing method of rare earth cobalt magnet.