JP2005159054A - Method of manufacturing r-t-b-based permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an R-T-B based permanent magnet at a low cost that has a comprehensively favorable magnetic characteristic by obtaining a high magnetism holding force and a squareness ratio by suppressing abnormal grain growth, in the R-T-B based permanent magnet reduced in an O-content for obtaining high remanent density. <P>SOLUTION: The method of manufacturing the R-T-B-based permanent magnet includes a step of obtaining a molded body constituted of the mixed powder of main raw material powder containing 27.5-32 wt.% R, 0.9-1.2 wt.% B, 0.05-0.3 wt.% Al, ≤3.0 wt.% Co (excluding 0 wt.%), 0.02-1.2 wt.% Cu, 300-1,500 ppm O, 200-1,300 ppm C, 200-1,500 ppm N, and substantially Fe in the remnant and hard ferrite powder added to the main raw material powder at a rate of 0.05-0.5 wt.%. The method also includes a sintering step of sintering the molded body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is an R-T-B excellent in magnetic properties mainly composed of at least one transition metal element (T) and boron (B), each of which contains rare earth elements (R), Fe or Fe and Co as essential components. The present invention relates to a method for manufacturing a permanent magnet.

  Among the rare earth magnets, the R-T-B permanent magnet has excellent magnetic properties and has a feature that Nd as a main component is abundant in resources and relatively inexpensive. In order to improve the magnetic properties of the RTB-based permanent magnet, particularly the residual magnetic flux density, it is effective to reduce the oxygen (O) content in the alloy. However, if the O content in the alloy is extremely reduced, abnormal grain growth occurs in the sintering process, the coercive force and the squareness ratio are lowered, and the overall magnetic properties are never high.

With respect to this problem, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-75717), abnormal grain growth is suppressed by dispersing a ZrB compound, an NbB compound, or an HfB compound in an RTB-based permanent magnet. Proposals have been made.
In Patent Document 2 (Japanese Patent Publication No. 4-26525), Patent Document 3 (Japanese Patent Laid-Open No. 61-289605) and Patent Document 4 (Japanese Patent Laid-Open No. 62-134907), the coercive force is improved or the grain growth is increased. Proposals have been made to add rare earth oxides for suppression.

JP 2002-75717 A Japanese Patent Publication No. 4-26525 JP 61-289605 A Japanese Patent Laid-Open No. 62-134907

However, Zr, Nb, and Hf for precipitating the ZrB compound, NbB compound, or HfB compound proposed in Patent Document 1 are expensive, which is not preferable from the viewpoint of reducing the cost of electronic parts and devices. Moreover, since the proposal of patent document 1 presupposes that a ZrB compound, a NbB compound, or a HfB compound precipitates during sintering, it is necessary to make Zr, Nb, or Hf suitable for it contain in a raw material alloy. This means that a raw material alloy having a new composition must be prepared in place of the raw material alloy having the existing composition, and Zr, Nb and Hf are manufactured in combination with the fact that they are expensive in the first place. This increases the cost of the magnet.
Although the addition of rare earth oxides proposed in Patent Documents 2 to 4 does not have the cost problem as in Patent Document 1, application to R-T-B permanent magnets having a low O content has not been studied. Met.
The present invention has been made on the basis of such a technical problem. In an R-T-B permanent magnet having a reduced O content in order to obtain a high residual magnetic flux density, the abnormal grain growth is suppressed and is high. An object of the present invention is to provide an R-T-B type permanent magnet that can provide a comprehensively good magnetic property by obtaining a coercive force and a squareness ratio at a lower cost.

For this purpose, as a result of diligent investigation of additives, when a predetermined amount of hard ferrite powder is added, abnormal grain growth during sintering is suppressed, and high squareness and good coercive force are obtained. It has been found that an RTB-based permanent magnet having comprehensively good magnetic properties can be manufactured at low cost.
The present invention is based on the above findings, R: 27.5 to 32 wt% (R is one or more rare earth elements, where the rare earth element is a concept including Y), B: 0.9 -1.2 wt%, Al: 0.05-0.3 wt%, Co: 3.0 wt% or less (excluding 0), Cu: 0.02-1.2 wt%, O: 300-1500 ppm, C: 200-1300 ppm, N: 200-1500 ppm, the main raw material powder having the balance substantially Fe, and a hard ferrite powder added in a range of 0.05-0.5 wt% with respect to the main raw material powder, It is a manufacturing method of the RTB type | system | group permanent magnet characterized by including the process of obtaining the molded object comprised from this mixed powder, and the sintering process which sinters this molded object.
In the present invention, the hard ferrite powder is preferably M-type Ba ferrite powder and / or Sr ferrite powder.
In the present invention, the main raw material powder is a mixture comprising a first alloy powder mainly composed of an R ₂ T ₁₄ B compound and a second alloy powder mainly composed of R and T and having a larger R content than the first alloy powder. It is desirable to obtain higher magnetic characteristics.

  According to the present invention, in an R-T-B system permanent magnet having a reduced O content in order to obtain a high residual magnetic flux density, an abnormal grain growth is suppressed to obtain a high coercive force and a squareness ratio. An RTB-based permanent magnet having good magnetic properties can be obtained. The elements used in the present invention are less expensive than Zr, Nb and Hf disclosed in Patent Document 1. In addition, since the present invention employs a technique of adding hard ferrite powder, it is not necessary to produce a raw material alloy having a new composition, and the hard ferrite powder itself is inexpensive. Therefore, according to the present invention, it is possible to obtain an R-T-B system permanent magnet having low-cost and comprehensively good magnetic properties.

Hereinafter, the RTB-based permanent magnet according to the present invention will be described in detail.
<Chemical composition>
The RTB-based permanent magnet of the present invention contains 27.5 to 32 wt% of rare earth element (R).
Here, R in the present invention has a concept including Y, and one or two of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. More than a seed. When the R content is less than 27.5 wt%, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. Moreover, if it is less than 27.5 wt%, the sinterability is inferior. On the other hand, when the R content exceeds 32 wt%, the volume ratio of the R ₂ T ₁₄ B crystal grains as the main phase decreases, and the residual magnetic flux density decreases. Therefore, the R content is 27.5 to 32 wt%. A desirable R content is 28 to 31.5 wt%, and a more desirable R content is 29 to 31 wt%.

  Among R, Nd and Pr have the best balance of magnetic characteristics, and are abundant in resources and relatively inexpensive, so that the main component as R is preferably Nd or Pr. Further, the inclusion of Dy is effective in improving the coercive force in order to increase the anisotropic magnetic field. Therefore, it is desirable to select Nd, Pr and Dy as R. The content of Dy is preferably determined within the above range depending on which of the residual magnetic flux density and the coercive force is important. That is, when it is desired to obtain a high residual magnetic flux density, it is desirable to set Dy to 0.1 to 4 wt%, and to obtain a high coercive force, it is desirable to set Dy to 4 to 12 wt%.

  The RTB-based permanent magnet of the present invention contains 0.9 to 1.2 wt% of boron (B). When the B content is less than 0.9 wt%, a high coercive force cannot be obtained. However, when the B content exceeds 1.2 wt%, the residual magnetic flux density decreases. Therefore, the upper limit is set to 1.2 wt%. A desirable B content is 0.9 to 1.15 wt%, and a more desirable B content is 0.95 to 1.1 wt%.

  The RTB-based permanent magnet of the present invention contains 0.05 to 0.3 wt% of Al. Al has an effect of improving the coercive force and expanding the temperature range of the aging treatment capable of obtaining a high coercive force. However, excessive addition of Al leads to a decrease in residual magnetic flux density, so 0.05 to 0.3 wt%. Desirable Al content is 0.15-0.3 wt%, and more desirable Al content is 0.1-0.25 wt%.

  The RTB-based permanent magnet of the present invention contains 3.0 wt% or less (excluding 0) of Co. Co is effective in improving the Curie temperature and the corrosion resistance. Moreover, it has the effect that the aging treatment temperature range from which a high coercive force is obtained is expanded by adding together with Cu. However, excessive addition causes a decrease in coercive force and increases the cost, so that it is 3.0 wt% or less. The desirable Co content is 0.2 to 3.0 wt%, and the more desirable Co content is 0.2 to 1.5 wt%.

  The RTB-based permanent magnet of the present invention contains 0.02 to 1.2 wt% of Cu. Cu is effective in improving the coercive force like Al. Cu is effective in improving the coercive force in a smaller amount than Al, but excessive addition causes a decrease in residual magnetic flux density, so 0.02 to 1.2 wt%. A desirable Cu content is 0.02 to 0.5 wt%, and a more desirable Cu content is 0.02 to 0.2 wt%.

  O content of the main raw material powder used for this invention shall be 300-1500 ppm. It is difficult to make the O content less than 300 ppm on an industrial production scale. On the other hand, when the O content exceeds 1500 ppm, the amount of R forming the oxide is increased, the magnetically effective R is decreased, and the coercive force is decreased. The O content is preferably 500 to 1300 ppm, more preferably 700 to 1000 ppm.

  In addition, the carbon (C) content of the main raw material powder used in the present invention is set to 200 to 1300 ppm. It is difficult to make the C content less than 300 ppm on an industrial production scale. On the other hand, when the C content exceeds 1300 ppm, the amount of R forming the carbide increases, the magnetically effective R decreases, and the coercive force decreases. The C content is preferably 300 to 1000 ppm, more preferably 500 to 900 ppm.

  The nitrogen (N) content of the main raw material powder used in the present invention is 200 to 1500 ppm. When the N content in the sintered body is less than 200 ppm, the corrosion resistance is poor. On the other hand, if it exceeds 1500 ppm, the amount of R that forms nitride increases, so that the magnetically effective R decreases and the coercive force decreases. By setting it as the said range, the outstanding corrosion resistance and the high magnetic characteristic can be made to make compatible. The N content is preferably 200 to 1000 ppm, more preferably 400 to 800 ppm.

Next, the suitable manufacturing method of the RTB type | system | group permanent magnet by this invention is demonstrated.
In the present embodiment, an R-T-B permanent magnet according to the present invention is manufactured using a low R alloy mainly composed of an R ₂ T ₁₄ B compound and a high R alloy containing more R than the low R alloy. How to do. The use of two or more kinds of alloys having different compositions is called a mixing method. The mixing method is effective in obtaining high magnetic properties because an ideal structure can be obtained for an R-T-B system permanent magnet. However, it goes without saying that the RTB-based permanent magnet according to the present invention is not limited to those manufactured by the mixing method.

First, a low R alloy and a high R alloy are obtained by strip casting of a raw metal in a vacuum or an inert gas, preferably an Ar atmosphere, and other known methods. As the raw material metal, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used.
In addition to R, Fe and B, the low R alloy can contain Cu and Al. At this time, the low R alloy constitutes an R-Cu-Al-Fe-B alloy. In addition to R, Fe, and B, the high R alloy can contain Cu, Co, and Al. At this time, the high R alloy constitutes an R-Cu-Co-Al-Fe-Co-B alloy.

After making the low R and high R alloys, each of these master alloys is ground separately or together. The pulverization is generally composed of coarse pulverization and fine pulverization. First, the ingot of each mother alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen. Further, after hydrogen storage, hydrogen can be released and further coarse pulverization can be performed.
After coarse pulverization, move to fine pulverization. A jet mill is mainly used for pulverization. In the coarse pulverization, a coarsely pulverized powder having a particle size of about several hundreds of μm is pulverized to an average particle size of 1 to 10 μm, desirably 3 to 7 μm. The N content of the main raw material powder can be controlled by changing the type of atmospheric gas for performing the jet mill, the O concentration in the atmosphere, and the pulverized gas pressure.

When the low R alloy and the high R alloy are pulverized separately in the fine pulverization, the finely pulverized low R alloy powder and high R alloy powder are mixed in, for example, a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same. By adding about 0.01 to 0.3 wt% of a grinding aid such as oleic acid amide or zinc stearate at the time of fine grinding, a fine powder with high orientation can be obtained at the time of molding.
Next, the mixed fine powder is pressure-molded in a state where the crystal axis is oriented by applying a magnetic field. The forming in the magnetic field may be performed at a pressure of about 0.7 to 1.5 t / cm ² in a magnetic field of about 12 to 17 kOe.

  In the present invention, hard ferrite powder is added and mixed before coarse pulverization, before fine pulverization, or before molding in a magnetic field. As a result, the mixed powder subjected to molding in a magnetic field and the resulting molded body are composed of a low R alloy powder, a high R alloy powder, and a hard ferrite powder.

  In the present invention, hard ferrite powder is an important composition for obtaining high coercive force and squareness ratio by suppressing abnormal grain growth during sintering. This effect due to the addition of the hard ferrite powder becomes remarkable when the O content and the N content in the main raw material powder are within the scope of the present invention. That is, when the O content in the main raw material powder exceeds 1500 ppm or the N content exceeds 700 ppm, it is difficult to enjoy the effect. If the amount of hard ferrite powder added is less than 0.01 wt%, this effect cannot be sufficiently obtained. On the other hand, when the addition amount of the hard ferrite powder exceeds 0.5 wt%, the sinterability is lowered and it is difficult to obtain a high coercive force. A desirable addition amount of hard ferrite powder is 0.01 to 0.3 wt%, and a more desirable addition amount of hard ferrite powder is 0.02 to 0.25 wt%. In addition, since hard ferrite powder is added, the O content increases at least by an amount resulting from the addition of hard ferrite powder after sintering.

As the hard ferrite, conventionally known M type and W type hard ferrites can be widely applied. The use of one or two of the most popular M type (Magnet Plumbite type) Ba ferrite (BaFe ₁₂ O ₁₉ ) and Sr ferrite (SrFe ₁₂ O ₁₉ ) is desirable from the standpoint of characteristics and cost. As the hard ferrite powder, various forms such as a powder prepared for a bonded magnet and a powder obtained by pulverizing a sintered magnet can be used.
Further, the particle diameter of the hard ferrite powder to be added may be equal to or smaller than that of the finely pulverized main raw material powder. When the hard ferrite powder is mixed with the main raw material powder before pulverization, the particle size can be equal to or smaller than that of the main raw material powder during pulverization. When the hard ferrite powder is added after finely pulverizing the main raw material powder, the particle diameter of the hard ferrite powder is adjusted to the same particle size as that of the finely pulverized main raw material powder.

After molding in a magnetic field, a compact made of a mixed powder of low R alloy powder, high R alloy powder and M oxide powder is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a particle size, and a particle size distribution difference, what is necessary is just to hold | maintain about 1 to 10 hours in 1000-1100 degreeC. In this sintering process, the added hard ferrite powder suppresses abnormal grain growth.
After sintering, the obtained sintered body can be subjected to an aging treatment. This aging treatment is an important process for controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by the heat treatment at around 600 ° C., the aging treatment at around 600 ° C. is preferably performed when the aging treatment is performed in one stage.

  In order to set the O content of the main raw material powder to 300 to 1500 ppm, it is necessary to control the O content in the atmosphere of the process from melting of the raw material alloy to mixing with the hard ferrite powder to be low, for example, about 300 ppm. . Moreover, in order to make the N content of the main raw material powder 200 to 700 ppm, it is necessary to control the process conditions from the melting of the raw material alloy to the mixing with the hard ferrite powder. When fine pulverization is performed, the N content can be controlled by changing the type of atmospheric gas, the O concentration in the atmosphere, and the pulverization gas pressure. Thus, the O and N contents can be controlled within the scope of the present invention by controlling the atmosphere of the production process and other conditions.

  Two types of alloy a (low R alloy) and alloy b (high R alloy) shown in Table 1 were produced by the strip casting method. Then, alloy a and alloy b were weighed and mixed at 90:10 (weight ratio). The mixture was occluded with hydrogen at room temperature, and then subjected to hydrogen pulverization (coarse pulverization) in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere. In order to suppress the O content of the sintered body to 1500 ppm or less, the atmosphere in each step from hydrogen pulverization (recovery after pulverization) to sintering (put into the sintering furnace) is an oxygen concentration of less than 100 ppm. It is suppressed to. Hereinafter, this manufacturing process in a low oxygen atmosphere is referred to as an oxygen-free process.

A grinding aid was mixed with the coarsely pulverized powder before fine pulverization. The grinding aid is not particularly limited, but 0.1 wt% of oleic amide was added in this example. For example, a Nauta mixer can be used for mixing the grinding aid.
Thereafter, fine pulverization was performed using a jet mill. As a result of measuring the finely pulverized powder that passed through the jet mill using a laser diffraction particle size distribution measuring device, the average particle diameter D50 (particle diameter of particles with a cumulative volume of 50%) was 5.24 μm.
Next, 0.05 wt% of hard ferrite powder (FA700 manufactured by Toda Kogyo Co., Ltd.) was added to and mixed with this finely pulverized powder. The addition and mixing were performed using a Nauta mixer.
The obtained mixed powder was molded in a magnetic field. Specifically, molding was performed at a pressure of 1.2 t / cm ^{2 in} a magnetic field of 15 kOe.
The molded body was sintered in vacuum at 1030 ° C. for 4 hours and 1050 ° C. for 4 hours, and then rapidly cooled. The obtained sintered body was subjected to a two-stage aging treatment in which the sintered body was held at 800 ° C. for 1 hour and further at 550 ° C. for 2.5 hours (both in an Ar atmosphere) to produce an RTB-based permanent magnet.

  About the obtained RTB-based permanent magnet, residual magnetic flux density (Br), coercive force (HcJ), and squareness ratio (Hk / HcJ) were measured with a BH tracer. Note that the squareness ratio (Hk / HcJ) is an index of magnet performance and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop. Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. The results are shown in Table 2. Sample No. Sample No. 1 except that no hard ferrite powder was added. 2 to 6, when an R-T-B permanent magnet was produced, the sample No. 7 and no. No. 8 was prepared without applying the oxygen-free process. 9 and no. 10 shows the result when changing the pulverization conditions during jet milling to produce an RTB-based permanent magnet with a high N content. Note that sample no. 7 and no. In No. 8, the oxygen concentration in the atmosphere during molding in a magnetic field was about 1000 ppm.

  From Table 2, it can be seen that by adding hard ferrite powder within the range of the present invention, abnormal grain growth during sintering can be suppressed and coercive force (HcJ) and squareness ratio (Hk / HcJ) can be improved. However, Sample No. As can be seen by referring to 7 to 10, if the O content or the N content exceeds the range defined in the present invention, the effect of adding the hard ferrite powder cannot be enjoyed. Moreover, the residual magnetic flux density (Br) remains at a low value.

  An RTB-based permanent magnet was produced in the same manner as in Example 1 except that the sintering temperature was two types of 1030 ° C. (4 hours) and 1050 ° C. (4 hours). The magnetic properties (residual magnetic flux density (Br), coercive force (HcJ) and squareness ratio (Hk / HcJ)) were measured. The results are shown in Table 3.

  As shown in Table 3, it can be seen that the coercive force (HcJ) and the squareness ratio (Hk / HcJ) can be improved at any sintering temperature of 1030 ° C. and 1050 ° C. by adding hard ferrite powder.

Claims (3)

R: 27.5 to 32 wt% (R is one or more rare earth elements, where the rare earth element is a concept including Y), B: 0.9 to 1.2 wt%, Al: 0.05 to 0.3 wt%, Co: 3.0 wt% or less (excluding 0), Cu: 0.02 to 1.2 wt%, O: 300 to 1500 ppm, C: 200 to 1300 ppm, N: 200 to 1500 ppm, A step of obtaining a molded body composed of a mixed powder of the main raw material powder substantially having the composition of Fe and the hard ferrite powder added in the range of 0.05 to 0.5 wt% with respect to the main raw material powder. When,
A sintering step of sintering the molded body;
The manufacturing method of the RTB type | system | group permanent magnet characterized by including.   The method for producing an R-T-B system permanent magnet according to claim 1, wherein the hard ferrite powder is M-type Ba ferrite powder and / or Sr ferrite powder. The main raw material powder is a mixture comprising a first alloy powder mainly composed of an R ₂ T ₁₄ B compound and a second alloy powder mainly composed of R and T and having a larger R amount than the first alloy powder. The manufacturing method of the RTB type | system | group permanent magnet of Claim 1 or 2 characterized by the above-mentioned.