JP2007250605A - Method for manufacturing r-t-b-based rare-earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an R-T-B-based rare-earth permanent magnet for improving mass-productivity of a high performance R-T-B-besed rare-earth permanent magnet. <P>SOLUTION: The manufacturing method includes the steps of manufacturing an R-T-B alloy that is mainly formed of R<SB>2</SB>T<SB>14</SB>B phase with inclusion of Co, Zr, and Cu, and an R-T alloy that is mainly formed of R and T; obtaining a mixture formed of powder of R-T-B alloy and powder of R-T alloy; producing a mold of the predetermined shape formed of the mixture; and obtaining a sintered material by sintering the mold. In the step of obtaining the mixture, ≥50% Co included in the mixture is supplied from powder of the R-T-B alloy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, R (R is one or more of rare earth elements including Y), T (T is at least one transition metal element in which Fe or Fe and Co are essential) and B (boron). The present invention relates to a method for producing an RTB-based rare earth permanent magnet having excellent magnetic properties as a main component.

  Among the rare earth permanent magnets, RTB rare earth permanent magnets are excellent in magnetic properties, and Nd as a main component is abundant in resources and relatively inexpensive. Yes. Research and development for improving the magnetic properties of RTB-based rare earth permanent magnets has also been vigorously conducted. For example, an RTB-based rare earth permanent magnet has a Cu content of 0.02 to 0.5 at%. There has been a report of improving the magnetic properties and heat treatment conditions by adding (see, for example, Patent Document 1). However, it has been insufficient to obtain the high magnetic properties required for high performance magnets, specifically, high coercive force (HcJ) and residual magnetic flux density (Br).

In order to further improve the performance of the RTB-based rare earth permanent magnet, it is necessary to reduce the amount of oxygen in the alloy. However, when the amount of oxygen in the alloy is reduced, abnormal grain growth is likely to occur in the sintering process, and the squareness ratio is reduced. This is because the oxide formed by oxygen in the alloy suppresses the growth of crystal grains.
Therefore, as means for improving the magnetic characteristics, a fine ZrB compound, NbB compound or HfB compound (hereinafter referred to as M-) is contained in an RTB-based rare earth permanent magnet containing Co, Al, Cu, and Zr, Nb or Hf. It has been reported that by uniformly dispersing and precipitating the (B compound), grain growth in the sintering process is suppressed and magnetic characteristics and sintering temperature range are improved (for example, see Patent Document 2). However, in Example 3-1, disclosed in Patent Document 2, the sintering temperature range is as narrow as about 20 ° C., and it is desirable to further widen the sintering temperature range in order to obtain high magnetic properties in a mass production furnace or the like.
Therefore, according to Patent Document 3, Zr has good dispersibility, and a permanent region obtained by forming a region having a high concentration of Zr together with a specific element (specifically, Cu, Co, Nd). It has been reported that the sintering temperature width at which the magnet squareness ratio (Hk / HcJ) is 90% or more can be 40 ° C. or more.
Further, according to Patent Document 4, in a favorable dispersibility of Zr is an alloy for the main phase formed mainly of R 2 _T 14 _B intermetallic compound, grain boundaries existing between the main phase In the manufacturing method of obtaining a rare earth permanent magnet by mixing with an alloy for phase formation, it is preferable that Zr is contained in the alloy for main phase formation. Further, it is proposed that a method of simultaneously adding one or two of Cu and Al in addition to Zr to the alloy for forming the main phase is good.

JP-A-1-219143 (first page) JP 2002-75717 A (first page) International Publication No. 2004/029995 Pamphlet International Publication No. 2004/029998 Pamphlet

However, the conventional methods as described above have a problem that the magnetic characteristics vary greatly due to the temperature range of the aging heat treatment that has a great influence on the change in coercive force of the obtained RTB-based rare earth permanent magnet.
The magnetic properties of the R-T-B rare earth permanent magnet obtained by sintering depend greatly on the conditions of aging heat treatment after sintering. On an industrial production scale, it is difficult to make the heating temperature uniform throughout the furnace. For this reason, in an R-T-B rare earth permanent magnet, it is required to obtain desired magnetic characteristics even if the heat treatment temperature varies within a temperature distribution range in the furnace.
However, if the appropriate aging temperature range in which good coercive force can be obtained (hereinafter referred to as aging appropriate temperature range) is narrow, it is affected by the temperature distribution in the furnace, and has a good coercive force RT. The rate at which -B rare earth permanent magnets are obtained becomes low, and it becomes difficult to improve productivity.
The present invention has been made on the basis of such a technical problem, and manufacture of an R-T-B rare earth permanent magnet capable of improving the mass productivity of a high-performance R-T-B rare earth permanent magnet. It aims to provide a method.

For this purpose, the method for producing an R-T-B rare earth permanent magnet of the present invention has an R ₂ T ₁₄ B phase (where R is one or more of rare earth elements including Y, and T is Fe. Or an R—T—B-based rare earth comprising a sintered body comprising a main phase composed of one or more transition metal elements essential for Fe and Co) and a grain boundary phase containing more R than the main phase. A method for manufacturing a permanent magnet, comprising a powder composed of an R-T-B alloy mainly composed of an R ₂ T ₁₄ B phase and containing Co, Zr, Cu, and an RT alloy mainly composed of R and T. A step of obtaining a mixture, comprising: a step of obtaining a mixture of powder; a step of producing a molded body of a predetermined shape made of the mixture; and a step of obtaining a sintered body by sintering the molded body. 50% or more of the amount of Co contained in is supplied from powder made of RTB alloy. That.

In such a manufacturing method, the composition of the sintered body is R: 28 to 33 wt%, B: 0.5 to 1.5 wt%, Al: 0.03 to 0.3 wt%, Cu: 0.15 wt% or less ( 0%), Co: 2 wt% or less (not including 0), Zr: 0.05 to 0.25 wt%, and a high-performance R—T—B system rare earth permanent magnet consisting essentially of Fe is manufactured. Suitable for use.
By adopting such a manufacturing method, an RTB-based rare earth permanent magnet in which the amount of oxygen contained in the sintered body is 2000 ppm or less can be manufactured. The amount of carbon contained in the sintered body can be 300 to 2000 ppm.
Further, according to such a manufacturing method, the powder made of the RTB alloy contains Co, Zr, and Cu, and further contains 50% or more of the amount of Co contained in the mixture. The ratio Hk / HcJ (HcJ is the coercive force, Hk is the external magnetic field strength when the ratio of the magnetization to the residual magnetic flux density is 90% in the second quadrant of the magnetic hysteresis loop) is 90% or more. A bonded body, that is, an R-T-B rare earth permanent magnet can be manufactured in a wider heat treatment temperature range.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to extend the heat treatment temperature range which can obtain the RTB system rare earth permanent magnet which has a high squareness ratio, and, thereby, the RTB system rare earth which has the high characteristic. The mass productivity of permanent magnets can be improved.

<Organization>
As is well known, the R-T-B rare earth permanent magnet obtained by the present invention has an R ₂ T ₁₄ B phase (R is one or more of rare earth elements including Y, and T is Fe or It is composed of a sintered body including at least a main phase composed of one or more transition metal elements including Fe and Co) and a grain boundary phase containing more R than the main phase.

<Chemical composition>
Next, the desirable chemical composition of the RTB-based rare earth permanent magnet according to the present invention will be described. The chemical composition here refers to the chemical composition after sintering.
The RTB-based rare earth permanent magnet of the present invention contains 25 to 35 wt% of a rare earth element (R).
Here, the rare earth element is one or more of Y-containing rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu). If the amount of the rare earth element is less than 25 wt%, the R ₂ T ₁₄ B phase that is the main phase of the R—T—B system rare earth permanent magnet is not sufficiently generated, and α-Fe having soft magnetism is precipitated, The coercive force is significantly reduced. On the other hand, if the rare earth element exceeds 35 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, the rare earth element reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for generating the coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of rare earth elements is 25 to 35 wt%. A desirable rare earth element amount is 28 to 33 wt%, and a more desirable rare earth element amount is 29 to 32 wt%.

Since Nd is abundant in resources and relatively inexpensive, it is preferable to use Nd as the main component as a rare earth element. The inclusion of Dy is effective in improving the anisotropic magnetic field of the R ₂ T ₁₄ B phase and improving the coercive force. Therefore, it is desirable that Nd and Dy are selected as the rare earth elements, and the total of Nd and Dy is 25 to 33 wt%. In this range, the amount of Dy is preferably 0.1 to 12 wt%. It is desirable to determine the amount of Dy 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, the Dy amount is preferably 0.1 to 3.5 wt%, and when a high coercive force is desired, the Dy amount is desirably 3.5 to 12 wt%.

  The RTB-based rare earth permanent magnet of the present invention contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.

  The RTB-based rare earth permanent magnet of the present invention can contain one or two of Al and Cu in the range of 0.02 to 0.5 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the obtained permanent magnet. In the case of adding Al, a desirable amount of Al is 0.03 to 0.3 wt%, and a more desirable amount of Al is 0.05 to 0.25 wt%. In addition, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.08 wt%.

  The RTB-based rare earth permanent magnet of the present invention desirably contains Zr in the range of 0.03 to 0.25 wt%. Zr exhibits the effect of suppressing the abnormal growth of crystal grains during the sintering process when reducing the oxygen content in order to improve the magnetic properties of the R-T-B rare earth permanent magnet, and the structure of the sintered body To make it uniform and fine. Therefore, Zr has a remarkable effect when the amount of oxygen is low. A desirable amount of Zr is 0.1 to 0.23 wt%, and a more desirable amount is 0.15 to 0.2 wt%.

  The RTB-based rare earth permanent magnet of the present invention has an oxygen content of 2000 ppm or less. If the amount of oxygen is large, the rare-earth oxide phase, which is a non-magnetic component, increases and the magnetic properties are degraded. Therefore, in the present invention, the amount of oxygen contained in the sintered body is set to 2000 ppm or less, desirably 1500 ppm or less, and more desirably 1000 ppm or less.

  In the R-T-B rare earth permanent magnet of the present invention, Co is 4.0 wt% or less (not including 0), preferably 0.1 to 2.0 wt%, more preferably 0.3 to 0.7 wt%. contains. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

<Manufacturing method>
Next, the suitable manufacturing method of the RTB system rare earth permanent magnet by this invention is demonstrated.
In the present embodiment, a method for producing a rare earth permanent magnet according to the present invention using an alloy for a main phase mainly composed of R ₂ T ₁₄ B phase and an alloy for a grain boundary phase mainly composed of R and T Show about.

First, the main phase alloy and the grain boundary phase alloy are obtained by strip casting in a vacuum or an inert gas, preferably in an Ar atmosphere.
In addition to the rare earth elements, Fe, Co, Zr, Cu and B, the main phase alloy can contain Al. In addition to the rare earth elements, Fe and Co, the grain boundary phase alloy can also be contained. Cu and Al can be contained.
Here, it is preferable to add 50% or more of the Co content in the final composition to Co in the main phase alloy constituting the main phase. By increasing the amount of Co added to the main phase alloy, the squareness ratio of the R-T-B rare earth permanent magnet finally obtained can be increased. Here, a preferable range of the amount of Co added to the main phase alloy constituting the main phase is 60% or more of the Co content in the final composition, and a more preferable range is 80% or more.
Furthermore, it is preferable that Co, Zr, and Cu are essential additions to the main phase alloy. This makes it possible to widen the appropriate temperature range in heat treatment, particularly aging treatment.

After the main phase alloy and the grain boundary phase alloy are made, these raw material alloys are ground separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the raw material alloys are coarsely pulverized until each 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.
After the coarse pulverization process, the process proceeds to the fine pulverization process. In the fine pulverization, a jet mill is mainly used, and a coarsely pulverized powder having a particle size of about several hundreds of μm is pulverized until the average particle size becomes 3 to 5 μm. The jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates the coarsely pulverized powder. Or it is the method of generating and colliding with a container wall.

When the main phase alloy and the grain boundary phase alloy are separately pulverized in the fine pulverization step, the finely pulverized main phase alloy powder and the grain boundary phase alloy powder are mixed in a nitrogen atmosphere. The mixing ratio of the main phase alloy powder and the grain boundary phase alloy powder may be about 80:20 to 97: 3 by weight. The same applies to the mixing ratio when the main phase alloy and the grain boundary phase alloy are pulverized together. By adding about 0.01 to 0.3 wt% of a lubricant such as fatty acid amide, fatty acid or metal soap during fine pulverization, fine powder with high orientation can be obtained during molding.
Next, a mixed powder composed of the main phase alloy powder and the grain boundary phase alloy powder is filled in a mold held by an electromagnet and molded in a magnetic field with its crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be performed in a magnetic field of 12 to 17 kOe (960 to 1360 kA / m) at a pressure of about 0.7 to 1.5 ton / cm ² (about 70 to 150 MPa).

After molding in a magnetic field, the compact 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 difference of a particle size and a particle size distribution, what is necessary is just to sinter at 1000-1100 degreeC for about 1 to 5 hours.
After sintering, the obtained sintered body can be subjected to an aging treatment. This process 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.

  Next, the present invention will be described in more detail with specific examples.

1) Raw material alloys As shown in Tables 1 and 2, raw material alloys (main phase alloy and grain boundary phase alloy) having different compositions of Co, Cu, and Zr were produced by strip casting. In Table 1 and Table 2, the content of Dy in the raw material alloy is different.

2) Hydrogen pulverization step After the hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed in an Ar atmosphere at 600 ° C for 1 hour.
In this embodiment, in order to obtain high magnetic properties, the atmosphere in each step from hydrogen pulverization (recovery after pulverization) to sintering (put into the sintering furnace) is suppressed to an oxygen concentration of less than 100 ppm.

3) Mixing / Pulverizing Step Usually, two-stage pulverization by coarse pulverization and fine pulverization is performed, but in this example, the coarse pulverization step is omitted.
Before pulverization, 0.1 wt% of oleic amide was added as a grinding aid, and the main phase alloy and the grain boundary phase alloy were mixed for 30 minutes with a Nauta mixer in the combinations shown in Tables 3 and 4. . The mixing ratio of the alloy a which is the main phase alloy and the alloy b which is the grain boundary phase alloy is 95: 5.
Thereafter, fine pulverization was performed with a jet mill until the average particle size became 4 μm.

4) Molding step The obtained fine powder was molded at a pressure of 1.2 ton / cm ² (120 MPa) in an orientation magnetic field of 15 kOe (1200 kA / m) to obtain a molded body.
5) Sintering and aging process This compact was sintered in a vacuum at the sintering temperatures shown in Tables 3 and 4 for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 850 ° C. × 1 hour and 570 ° C. × 1 hour (both in an Ar atmosphere).

  The chemical composition of the obtained permanent magnet is 21.8 wt% Nd-8.4 wt% Dy-0.2 wt% Al-0.1 wt% Cu- in the case of the RTB-based rare earth permanent magnet shown in Table 3. 1.0 wt% B-0.2 wt% Zr-0.5 wt% Co-bal. In the case of the R-T-B rare earth permanent magnet shown in Table 4, it is 25.0 wt% Nd-5.0 wt% Dy-0.2 wt% Al-0.1 wt% Cu-1.0 wt% B -0.2 wt% Zr-0.5 wt% Co-bal. Fe. In addition, although the oxygen amount and nitrogen amount of each magnet are shown in Tables 3 and 4, the oxygen amount is as low as 0.08 wt% or less and the nitrogen amount is as low as 0.03 wt% or less.

  Magnetic properties of the obtained permanent magnet were measured with a BH tracer. The results are shown in Tables 3 and 4. In Tables 3 and 4, Br represents the residual magnetic flux density, and HcJ represents the coercive force. Further, 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 ratio of magnetization to the residual magnetic flux density is 90% in the second quadrant of the magnetic hysteresis loop.

In Tables 3 and 4, when the coercive force (HcJ) is compared, in the blending types C, D, E, H, I, J, and K in which the supply ratio of Co to the main phase alloy is 50% or more, Co Compared with the blending types A, B, F, and G in which the supply ratio to the main phase alloy is less than 50%, a high coercive force (HcJ) can be maintained in a wider sintering temperature range, and a high squareness ratio is achieved. Can be secured.
In particular, in the case of the composition shown in Table 3, regardless of the sintering temperature, in the combination types C, D, and E in which the supply ratio of Co to the main phase alloy is 50% or more, The absolute value of the squareness ratio itself is improved as compared with the blending types A and B in which the supply ratio is less than 50%.
Further, in the case of the composition shown in Table 4, in the combination type H in which the supply ratio of Co to the main phase alloy is 50%, the squareness ratio is decreased when the sintering temperature is 1130 ° C. It can be seen that the supply ratio to the main phase alloy is 60% or more. Furthermore, in the blending type I in which the supply ratio of Co to the main phase alloy is 70%, since the squareness ratio is slightly reduced at the sintering temperature of 1130 ° C., more preferable supply of Co to the main phase alloy is achieved. It turns out that a ratio is 80% or more.
Thus, when the supply ratio of Co to the main phase alloy is 50% or more, a high squareness ratio can be maintained in a wider sintering temperature range, which is practical in industrial production. Can be.

Subsequently, alloy a, which is the main phase alloy obtained in the same manner as described above, and alloy b, which is the grain boundary phase alloy, are blended according to blending types F to K shown in Table 4 and finely pulverized. The obtained fine powder was molded at a pressure of 1.2 ton / cm ² (120 MPa) in an orientation magnetic field of 15 kOe (1200 kA / m) to obtain a molded body.
Thereafter, the compact was sintered in a vacuum at a sintering temperature of 1090 ° C. for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment under the conditions shown in Table 5. At this time, the temperature holding time for the first and second stages was 1 hour each.

Magnetic properties of the obtained permanent magnet were measured with a BH tracer. The results are shown in Table 5.
In Table 5, when the coercive force (HcJ) is compared, the temperature range in which a high coercive force (HcJ) can be secured in the second stage aging treatment is a blending type in which the supply ratio of Co to the main phase alloy is 50% or more. It can be seen that H, I, and K can secure a range of about 60 ° C., whereas the blending type G in which the supply ratio of Co to the main phase alloy is less than 50% is about 40 ° C.
As described above, when the supply ratio of Co to the main phase alloy is 50% or more, a high squareness ratio can be maintained in a wider heat treatment temperature range, thereby improving productivity and industrial production. It can be made practical.

Subsequently, alloy a, which is the main phase alloy obtained in the same manner as described above, and alloy b, which is the grain boundary phase alloy, are blended according to the blending types L to O shown in Table 6 and finely pulverized. The obtained fine powder was molded at a pressure of 1.2 ton / cm ² (120 MPa) in an orientation magnetic field of 15 kOe (1200 kA / m) to obtain a molded body. Here, as shown in Table 2, the blending types L and M did not contain Zr in the main phase alloy, and the blending types N and O did not contain Cu in the main phase alloy.
Thereafter, the compact was sintered in a vacuum at a sintering temperature of 1090 ° C. for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment under the conditions shown in Table 5. At this time, the temperature holding time for the first and second stages was 1 hour each.

Magnetic properties of the obtained permanent magnet were measured with a BH tracer. The results are shown in Table 6.
In Tables 5 and 6, when the coercive force (HcJ) is compared, formulation types L to O that do not contain Zr or Cu in the main phase alloy with respect to formulation types I and K that contain Zr and Cu in the main phase alloy. It can be seen that the temperature range in which a high coercive force (HcJ) can be secured in the second aging treatment is as narrow as about 40 ° C.
In this way, not only Co but also the addition of Zr, Cu to the main phase alloy is essential, and by making the supply ratio of Co to the main phase alloy 50% or more, a high squareness ratio is obtained. It can be seen that it can be maintained over a wider heat treatment temperature range, thereby increasing productivity and making it practical in industrial production.

Claims (5)

R ₂ T ₁₄ B phase (where R is one or more of rare earth elements including Y, T is one or more transition metal elements essential for Fe, Fe and Co) And an R-T-B rare earth permanent magnet manufacturing method comprising a sintered body including a grain boundary phase containing more R than the main phase,
Obtaining a mixture of a powder composed mainly of an R ₂ T ₁₄ B phase and composed of an R—T—B alloy containing Co, Zr, and Cu, and a powder composed of an R—T alloy mainly composed of R and T;
Producing a molded body having a predetermined shape made of the mixture;
And sintering the molded body to obtain a sintered body,
In the step of obtaining the mixture, 50% or more of the amount of Co contained in the mixture is supplied from the powder made of the R-T-B alloy, and a method for producing an R-T-B rare earth permanent magnet .   The composition of the sintered body was R: 28 to 33 wt%, B: 0.5 to 1.5 wt%, Al: 0.03 to 0.3 wt%, Cu: 0.15 wt% or less (excluding 0) R—T—B-based rare earth permanent according to claim 1, wherein Co: 2 wt% or less (excluding 0), Zr: 0.03 to 0.25 wt%, and the balance being substantially Fe. Magnet manufacturing method.   The method for producing an RTB-based rare earth permanent magnet according to claim 1 or 2, wherein the amount of oxygen contained in the sintered body is 2000 ppm or less.   4. The method for producing an RTB-based rare earth permanent magnet according to claim 1, wherein the amount of carbon contained in the sintered body is 300 to 2000 ppm.   The sintered body has a squareness ratio Hk / HcJ (HcJ is the coercive force, Hk is the external magnetic field strength when the magnetization is 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop). It is the above, The manufacturing method of the RTB system rare earth permanent magnet in any one of Claim 1 to 4 characterized by the above-mentioned.