JP2006100434A - Method of manufacturing r-t-b based rare earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize addition modes of M element and Tb which suppress grain growth in sintering process when manufacturing R-T-B based rare earth permanent magnet of which oxygen content is reduced by a mixing method. <P>SOLUTION: The R-T-B based rare earth permanent magnet consists of a sintered body of which R<SB>2</SB>T<SB>14</SB>B<SB>1</SB>compound (R always contains Tb, R includes Y, T requires Fe or Fe and Co) is magnetic phase, with M element (M is one or more kinds of Zr, Nb, and Hf) contained in it. The manufacturing method includes a process for producing a molding containing particles consisting of main phase forming alloy containing R<SB>2</SB>T<SB>14</SB>B<SB>1</SB>compound and the particles consisting of grain boundary phase forming alloy whose main component is R and T, and a process for sintering the molding. Tb and M elements are supplied in a mode other than such mode as supplied from the main phase forming alloy containing Tb and M elements. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to R (R is one or more of rare earth elements, where the rare earth element is a concept including Y), T (T is at least one or more transition metals essentially comprising Fe or Fe and Co) The present invention relates to a method for producing an RTB-based rare earth permanent magnet mainly composed of (element) and B (boron).

Among rare earth permanent magnets, RTB rare earth permanent magnets have excellent magnetic properties, and Nd, which is a main component, is abundant in resources and relatively inexpensive, so that the demand is increasing year by year. .
In order to improve the magnetic properties of the R-T-B rare earth permanent magnet, it is effective to reduce the amount of oxygen in the alloy. However, if 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 amount of oxygen is reduced while the oxide formed by oxygen in the alloy suppresses the growth of crystal grains.

Japanese Patent Laid-Open No. 2002-75717 (Patent Document 1) includes R containing Co, Al, Cu, and one or more of Zr, Nb, and Hf (hereinafter sometimes collectively referred to as M element). -By uniformly dispersing and precipitating fine ZrB compounds, NbB compounds or HfB compounds (hereinafter referred to as MB compounds) in TB rare earth permanent magnets, grain growth in the sintering process is suppressed, and magnetic Reports have been made to improve the properties and sintering temperature range.
Here, the magnetic properties of the R-T-B rare earth permanent magnet obtained by sintering depend on the sintering temperature. On the other hand, on an industrial production scale, it is difficult to make the heating temperature uniform throughout the sintering furnace. Therefore, the R-T-B rare earth permanent magnet is required to obtain desired magnetic characteristics even if the sintering temperature varies. The temperature range in which the desired magnetic properties can be obtained is called the sintering temperature range.

In Patent Document 1, a mixing method is used to obtain an RTB-based rare earth permanent magnet having high magnetic properties. In this mixing method, typically, an alloy for forming a main phase containing an R ₂ T ₁₄ B ₁ compound and an alloy for forming a grain boundary phase for forming a grain boundary phase existing between the main phases are mixed.

  On the other hand, in order to improve the coercive force of the R-T-B rare earth permanent magnet, in addition to light rare earth elements Nd and Pr, heavy rare earth elements Dy, Tb, Gd, Ho, Er, The addition of one or more of Tm and Y is proposed in, for example, Japanese Patent Publication No. 5-10806 (Patent Document 2).

In order to improve the coercive force, a predetermined amount of heavy rare earth element may be added as R as described above, but the effect of improving the coercive force varies depending on the type of heavy rare earth element. This is because the anisotropic magnetic field of the R ₂ T ₁₄ B ₁ compound differs depending on the element. Since the Tb ₂ T ₁₄ B ₁ compound is 220 kOe and the Dy ₂ T ₁₄ B ₁ compound is 150 kOe and exhibits a high anisotropic magnetic field (Ha), Tb or Dy may be used as a heavy rare earth element to improve the coercive force. In particular, it is effective to use Tb.

JP 2002-75717 A Japanese Patent Publication No. 5-10806

  In view of the above prior art, when manufacturing an RTB-based rare earth permanent magnet with a reduced oxygen content by a mixing method, an M element capable of suppressing grain growth in the sintering process, and further a heavy rare earth It is an object to provide a technique for optimizing the form of addition of Tb as an element.

  On the premise that an R-T-B rare earth permanent magnet having a reduced oxygen content is manufactured by a mixing method, an addition form of Tb capable of obtaining the highest anisotropic magnetic field was examined. At this time, the addition form of M element for controlling grain growth in the sintering process by reducing the oxygen content was also examined. As a result, depending on whether the Tb and M elements are added to the main phase forming alloy or the grain boundary phase forming alloy used in the mixing method, the magnetic properties of the R-T-B rare earth permanent magnet obtained can be improved. It was confirmed that there was a difference as follows. That is, when Tb and M element coexist in the main phase forming alloy, the residual magnetic flux density and the squareness are lowered. Therefore, the Tb and M elements are allowed to coexist in the grain boundary phase forming alloy, or may be contained in different alloys among the main phase forming alloy and the grain boundary phase forming alloy. It is important in suppressing the decline in sex.

That is, the present invention is an R ₂ T ₁₄ B ₁ compound (R is one or more rare earth elements and includes Tb, rare earth elements include Y, and T is essential for Fe, Fe and Co) At least one transition metal element) having a magnetic phase, and the sintered body contains M element (M: one or more of Zr, Nb, and Hf). A method for producing a TB-based rare earth permanent magnet, comprising particles made of an alloy for forming a main phase containing an R ₂ T ₁₄ B ₁ compound, particles made of an alloy for forming a grain boundary phase mainly composed of R and T, And a step of sintering the green body, and the Tb and M elements are supplied in a form excluding the form supplied from the main phase forming alloy containing the Tb and M elements. This is a method for producing an RTB-based rare earth permanent magnet.

As a form supplied from the main phase forming alloy containing Tb and M elements, Tb and M elements can be supplied from the grain boundary phase forming alloy. The Tb and M elements can be supplied from different alloys among the main phase forming alloy and the grain boundary phase forming alloy.
Sintered body: R: 22 to 33 wt% (Tb: 6% or less), B: 0.5 to 1.5 wt%, Al: 0.03 to 0.30 wt%, Cu: 0.15 wt% or less (0 Zr: 0.05 to 0.30 wt%, Co: 2 wt% or less (not including 0), and the balance being substantially composed of Fe.

  According to the present invention, since the RTB-based rare earth permanent magnet is manufactured by the mixing method, high magnetic characteristics can be obtained. In addition, since the M element is added in the present invention, even if the amount of oxygen is reduced, abnormal growth of crystal grains can be suppressed and the sintering temperature range can be widened. And the effect by addition of Tb and M element can fully be enjoyed by supplying in the form except the form supplied from the main phase formation alloy containing Tb and M element.

Hereinafter, the present invention will be described in detail.
<Manufacturing method>
First, the desirable form of the manufacturing method of the RTB system rare earth permanent magnet by this invention is demonstrated.
The present invention uses an alloy mainly composed of R ₂ T ₁₄ B ₁ compound (main phase forming alloy) and an alloy mainly composed of R and T (alloy for forming grain boundary phase) to produce R-T-B. Manganese rare earth permanent magnets are manufactured.
The main phase forming alloy and the grain boundary phase forming alloy can be obtained by strip casting the raw metal in a vacuum or an inert gas, preferably in an Ar atmosphere. As the raw material metal, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. The obtained mother alloy is subjected to a solution treatment as necessary when there is solidification segregation. The conditions may be maintained for 1 hour or more in a region of 700 to 1500 ° C. under vacuum or Ar atmosphere.

The main phase forming alloy contains an R ₂ T ₁₄ B ₁ compound. Further, the grain boundary phase forming alloy typically contains more R than the main phase forming alloy and also contains the T element. Here, there are several forms in which the Tb and M elements, which are essential elements of the RTB rare earth permanent magnet according to the present invention, are added to the main phase forming alloy and the grain boundary phase forming alloy. It is shown in Table 1. In Table 1, “◯” indicates that the element is added, and “−” indicates that the element is not added. For example, “Form” 1 in Table 1 indicates that both the Tb and M elements are added to the main phase forming alloy, and the Tb and M elements are not added to the grain boundary phase forming alloy. “Form” 2 in Table 1 shows that Tb is added to the main phase forming alloy but M element is not added, and M element is added to the grain boundary phase forming alloy. Tb is not added.

  As shown in Table 1, although there are several forms of adding Tb and M elements to the main phase forming alloy and the grain boundary phase forming alloy, the present invention adds Tb and M elements to the main phase forming alloy. Except for the forms that are used. That is, if it says in Table 1, this invention applies "form" 2, 4, 7, 8, and 9 instead of "form" 1, 3, 5, and 6 and applies R-T-B system rare earth permanent. A magnet is manufactured.

  In the method for producing an R-T-B rare earth permanent magnet according to the present invention, the main phase forming alloy and the grain boundary phase forming alloy need not be one type, and may be composed of two or more types. . That is, the present invention provides, for example, different compositions in addition to the case where one type of main phase forming alloy and one type of grain boundary phase forming alloy are used when producing an R-T-B type rare earth permanent magnet. Two types (or more) of the main phase forming alloy and one type of grain boundary phase forming alloy, or two types (or more) of grain boundary phases having different compositions from one type of main phase forming alloy A forming alloy can be used. Also, two (or more) grain boundary phase forming alloys having different compositions from two (or more) main phase forming alloys having different compositions may be used. When two types of main phase forming alloys are used and one of the main phase forming alloys contains both Tb and M elements, it is outside the scope of the present invention.

  In addition to R, T, and B, the main phase forming alloy can contain Cu, Al, Co, and further M element. In addition to R and T, the grain boundary phase forming alloy may contain B, Cu, Al, Co, and further M element.

  After the main phase forming alloy and the grain boundary phase forming alloy are produced, each of these master alloys is ground separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, 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. Moreover, after hydrogen occlusion, hydrogen can be released and further coarse pulverization can be performed. In order to obtain high magnetic properties, it is desirable to suppress the atmosphere in each step from pulverization (recovery after pulverization) to sintering (put into a sintering furnace) to an oxygen concentration of less than 100 ppm. By doing so, the amount of oxygen contained in the sintered body can be controlled to 2000 ppm or less.

  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 diameter of about several hundreds of micrometers is pulverized until the average particle diameter 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 forming alloy and the grain boundary phase forming alloy are separately pulverized in the pulverization step, the finely pulverized main phase forming alloy powder and the grain boundary phase forming alloy powder are mixed in a nitrogen atmosphere. To do. The mixing ratio of the alloy powder for forming the main phase and the alloy powder for forming the grain boundary phase may be about 80:20 to 97: 3 by weight. Similarly, the mixing ratio when the main phase forming alloy and the grain boundary phase forming alloy are pulverized together may be about 80:20 to 97: 3 by weight. By adding about 0.01 to 0.3 wt% of additives such as zinc stearate at the time of fine pulverization, fine powder having high orientation can be obtained at the time of molding.

Next, a mixed powder composed of the main phase forming alloy powder and the grain boundary phase forming alloy powder is molded in a magnetic field with its crystal axis 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 12.0 to 17.0 kOe.
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. The aging treatment is important 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.

<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 according to the present invention contains 22 to 33 wt% of R.
Here, R is one or more selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y. The invention contains Tb as an essential element. When the amount of R is less than 22 wt%, the production of the R ₂ T ₁₄ B ₁ compound that becomes the main phase of the R-T-B rare earth permanent magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. On the other hand, when the amount of R exceeds 33 wt%, the volume ratio of the R ₂ T ₁₄ B ₁ compound as the main phase decreases, and the residual magnetic flux density decreases. On the other hand, when R exceeds 33 wt%, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases and the coercive force decreases. Therefore, the amount of R is 22 to 33 wt%. A desirable amount of R is 28 to 33 wt%, and a more desirable amount of R is 29 to 32 wt%.

  Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as R is Nd. Further, the inclusion of Tb is effective in improving the coercive force in order to increase the anisotropic magnetic field. Therefore, it is desirable for the present invention that Nd and Tb are selected as R and the total of Nd and Tb is 25 to 33 wt%. In this range, the amount of Tb is desirably 6 wt% or less (excluding 0). It is desirable to determine the amount of Tb 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 amount of Tb is desirably 2.0 to 4.0 wt%, and when it is desirable to obtain a high coercive force, the amount of Tb is desirably 4.0 to 6.0 wt%. . The cost can be reduced by replacing a part of Tb with Dy.

  The RTB-based rare earth permanent magnet according to the present invention contains 0.5 to 1.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 1.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 1.5 wt%. A desirable amount of B is 0.7 to 1.3 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.

  The RTB-based rare earth permanent magnet according to the present invention can contain 0.03 to 0.30 wt% Al and 0.15 wt% (not including 0) Cu. By containing Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the resulting RTB-based rare earth permanent magnet. In the case of adding Al, a desirable amount of Al is 0.05 to 0.25 wt%, and a more desirable amount of Al is 0.07 to 0.22 wt%. In addition, when adding Cu, the amount of Cu is preferably 0.02 to 0.12 wt%, and more preferably 0.03 to 0.08 wt%.

  The RTB-based rare earth permanent magnet according to the present invention preferably contains 0.05 to 0.30 wt% of M element. When the oxygen content is reduced in order to improve the magnetic properties of the R-T-B rare earth permanent magnet, the M element exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process. To make the structure uniform and fine. Therefore, the effect of M element becomes remarkable when the amount of oxygen is low. A desirable amount of M element is 0.10 to 0.25 wt%, and a more desirable amount is 0.15 to 0.25 wt%.

  The RTB rare earth permanent magnet according to the present invention preferably has an oxygen content of 2000 ppm or less. This is because if the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated. 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. However, when the oxygen amount is simply reduced, the oxide phase having the effect of suppressing grain growth decreases, and grain growth easily occurs in the process of obtaining a sufficient density increase during sintering. Therefore, in the present invention, a predetermined amount of M element that exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process is contained in the R-T-B system rare earth permanent magnet.

  The R-T-B rare earth permanent magnet according to the present invention contains 2 wt% or less of Co (not including 0), preferably 0.1 to 2 wt%, and more preferably 0.3 to 1 wt%. 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.

Next, the present invention will be described in more detail with specific examples.
1) Raw material alloys Six types of alloys shown in Table 2 were produced by a strip casting method.

2) Hydrogen pulverization step After each hydrogen alloy was occluded with hydrogen at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
In order to obtain high magnetic properties, in this experiment, the atmosphere of each process from hydrogen treatment (recovery after pulverization) to sintering (put into the sintering furnace) to suppress the amount of oxygen in the sintered body to 2000 ppm or less Is suppressed to an oxygen concentration of less than 100 ppm. Hereinafter, it is referred to as an oxygen-free process.

3) Pulverization process Usually, two-stage pulverization by coarse pulverization and fine pulverization is performed, but since the coarse pulverization process could not be performed by an oxygen-free process, the coarse pulverization process is omitted in this embodiment.
Additives are mixed before milling. The type of the additive is not particularly limited, and any additive that contributes to improvement in grindability and orientation during molding may be appropriately selected. In this example, zinc stearate is added in an amount of 0.03 to 0. 1% mixed. The additive may be mixed for about 5 to 30 minutes using, for example, a Nauter mixer.
Thereafter, fine grinding was performed using a jet mill until the alloy powder had an average particle size of about 3 to 6 μm. In this experiment, two types of pulverized powders having an average particle diameter of 4 μm and 5 μm were prepared.
Naturally, both the additive mixing step and the fine pulverization step are performed in an oxygen-free process.

4) Blending Step The raw material alloys shown in Table 2 were blended in the combinations shown in Table 3 and mixed. The final composition is as shown in Table 3. In this case, the mixing may be performed for about 5 to 30 minutes using, for example, a Nauter mixer. It is desirable to carry out the blending process by an oxygen-free process.
In Table 3, compounding types B and C supply Tb and Zr from the main phase forming alloy. In addition, the blending types D and E supply Tb and Zr from the alloy for forming the grain boundary phase.

5) Molding step The obtained mixed powder is molded in a magnetic field. Specifically, the fine powder is filled in a mold held by an electromagnet, and is molded in a magnetic field with its crystal axis 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 12.0 to 17.0 kOe. In this experiment, molding was performed at a pressure of 1.2 t / cm ² in a magnetic field of 15 kOe to obtain a molded body. This step was also performed by an oxygen-free process.
6) Sintering and aging process This molded body was sintered in a vacuum at 1010 to 1090 ° C for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 550 ° C. × 2.5 hours (both in an Ar atmosphere).

  About the obtained RTB-based rare earth permanent magnet, residual magnetic flux density (Br), coercive force (HcJ), and squareness ratio (Hk / HcJ) were measured with a BH tracer. 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 4 and FIGS.

  As shown in Table 3 and FIGS. 1 to 3, the RTB-based rare earth permanent magnet according to blending type A not containing Zr has a residual magnetic flux density (Br) of 13.3 kG or more and a coercive force (HcJ) of 22 kOe. As described above, the sintering temperature width at which the squareness ratio (Hk / HcJ) can obtain a characteristic of 96% or more is 20 ° C. (1030 to 1050 ° C.). Similarly, the RTB-based rare earth permanent magnet according to the blending type B and the RTB-based rare earth permanent magnet according to the blending type C, which contain Zr but Zr and Tb coexist in the main phase forming alloy, are 96 Since the squareness ratio (Hk / HcJ) of not more than% can be obtained, the sintering temperature width is 0 ° C. In contrast, the grain boundary phase-forming alloy contains Tb and Zr, but the main phase-forming alloy contains Tb but does not contain Zr. The RTB-based rare earth permanent magnet can obtain characteristics such as a residual magnetic flux density (Br) of 13.3 kG or more, a coercive force (HcJ) of 22 kOe or more, and a squareness ratio (Hk / HcJ) of 96% or more. The sintering temperature range which can be performed is 40 degreeC (1030-1070 degreeC) or more.

  Table 5 shows a comparison of the magnetic properties of the R-T-B rare earth permanent magnet having a sintering temperature of 1030 ° C. Sample No. containing Tb and Zr in the main phase forming alloy Samples Nos. 5 and 8 are sample Nos. It can be seen that it has a low residual magnetic flux density (Br) and a low squareness ratio (Hk / HcJ) as compared with 2 (no Zr added). On the other hand, although the grain boundary phase forming alloy contains Tb and Zr, the main phase forming alloy contains Tb but does not contain Zr. 11 and 14 are sample Nos. It can be seen that the residual magnetic flux density (Br) and the squareness ratio (Hk / HcJ) are improved as compared with 5 and 8.

  As described above, according to the present invention, a sintering temperature range of 40 ° C. or more can be obtained. Furthermore, according to the present invention, it is possible to enjoy the effect of improving the coercive force (HcJ) by adding Tb without lowering the residual magnetic flux density (Br) and the squareness ratio (Hk / HcJ).

It is a graph which shows the relationship between the sintering temperature and residual magnetic flux density (Br) in this Embodiment. It is a graph which shows the relationship between the sintering temperature and coercive force (HcJ) in this Embodiment. It is a graph which shows the relationship between the sintering temperature and squareness ratio (Hk / HcJ) in this Embodiment.

Claims (4)

R ₂ T ₁₄ B ₁ compound (R is one or more rare earth elements and must contain Tb, rare earth elements include Y, and T is at least one element that essentially contains Fe or Fe and Co) R-T-B type rare earth comprising a sintered body having the above transition metal element) as a magnetic phase and containing M element (M: one or more of Zr, Nb and Hf) in the sintered body A method for producing a permanent magnet, comprising:
Producing a molded body comprising particles made of a main phase forming alloy containing an R ₂ T ₁₄ B ₁ compound and particles made of a grain boundary phase forming alloy mainly composed of R and T;
A step of sintering the molded body, wherein the Tb and M elements are supplied in a form excluding the form supplied from the main phase forming alloy containing the Tb and M elements. A method for producing a rare earth permanent magnet.   The method for producing an R-T-B rare earth permanent magnet according to claim 1, wherein the Tb and M elements are supplied from the grain boundary phase forming alloy.   The method for producing an R-T-B rare earth permanent magnet according to claim 1, wherein the Tb and M elements are supplied from different alloys of the main phase forming alloy and the grain boundary phase forming alloy. .   The sintered body has R: 22 to 33 wt% (Tb: 6% or less), B: 0.5 to 1.5 wt%, Al: 0.03 to 0.30 wt%, Cu: 0.15 wt% or less ( 0 to 3), Zr: 0.05 to 0.30 wt%, Co: 2 wt% or less (not including 0), and the balance substantially consisting of Fe The manufacturing method of the RTB system rare earth permanent magnet in any one.

Images