JP4556727B2 - Manufacturing method of rare earth sintered magnet - Google Patents

Description

  The present invention relates to a method for reusing a rare earth sintered magnet having defects such as cracks and chips as a raw material for a sintered magnet.

Among the rare earth sintered magnets, the RTB-based sintered magnet has excellent magnetic properties, and the main component Nd is relatively abundant compared to conventional Sm-Co-based sintered magnets. Since it is inexpensive, it is used for various purposes.
Although the RTB-based sintered magnet is rich in resources compared to the conventional Sm-Co-based sintered magnet, Nd, which is the main component, is limited in resources, and RTB Considering the current usage of sintered magnets, there is a concern about resource depletion. For this reason, in recent years, there has been an increasing interest in reusing R-T-B based sintered magnets.
For example, in Patent Document 1, an alloy powder in which M (M is Al, Cu, Zn, etc.) is added to the above alloy with respect to 99 to 70 wt% of the scraped R ₂ T ₁₄ B sintered magnet alloy powder. 1 to 30 wt% is mixed, this mixed alloy powder is pressed in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere, and further subjected to an aging heat treatment at a temperature lower than the sintering temperature. A method for producing a rare earth sintered permanent magnet is proposed.

JP-A-6-340902

  Patent Document 1 proposes an approach of adding an alloy that supplements the oxidized content of a sintered magnet alloy to be reused, but the present invention reuses defective materials by an approach different from Patent Document 1. Another object of the present invention is to provide a rare earth sintered magnet having excellent magnetic properties.

In order to increase the main phase ratio of the RTB-based sintered magnet and achieve high performance, it is necessary to reduce the amount of oxygen in the alloy. However, the defective material used for reuse is usually a sintered magnet containing about 3000 to 5000 ppm of oxygen. Even if such a sintered magnet is reused as a magnet raw material, the amount of oxygen is reduced. Remains high and a sintered magnet with high magnetic properties cannot be obtained. Such a sintered magnet may be reused after being subjected to a reduction treatment, but this increases the cost.
The present inventors have studied to obtain a sintered magnet that exhibits high magnetic properties even when a defective material is used without incurring high costs. As a result, it was confirmed that a low-magnetism sintered magnet having an oxygen content of 2000 ppm or less does not require a reduction step and can be pulverized with hydrogen, so that a sintered magnet having high magnetic properties can be obtained. Here, the hydrogen pulverization is a method of expanding and pulverizing the alloy by occluding hydrogen in the alloy, and is an effective method as a pulverization method for preventing an increase in oxygen in the pulverized powder. A sintered magnet containing about 3000 to 5000 ppm of oxygen does not occlude hydrogen and cannot be subjected to hydrogen pulverization even when exposed to a hydrogen atmosphere. If mechanical pulverization is performed on the sintered magnet instead of hydrogen pulverization, the amount of oxygen in the pulverized powder increases, and a rare-earth sintered magnet with high magnetic properties cannot be obtained. However, if a low oxygen sintered magnet having an oxygen content of 2000 ppm or less can be subjected to hydrogen pulverization, a sintered magnet having high magnetic properties can be obtained.

That is, the present invention includes a step (1) of hydrogen-sintering a sintered magnet having an oxygen content of 2000 ppm or less, a step (2) of producing a molded body using hydrogen-pulverized powder, and sintering the molded body. and a step (3), the oxygen content of the rare earth sintered magnet finally obtained to suppress the 2000ppm or less, the above steps (1), (2), the atmosphere in (3), of less than 300ppm oxygen It is a manufacturing method of the rare earth sintered magnet characterized by controlling to a concentration .
In the present invention, a rare earth sintered magnet is newly produced using only a low oxygen sintered magnet, and a low oxygen sintered magnet to be reused and a new cast alloy material (hereinafter referred to as a new material). A rare earth sintered magnet is also included. In this case, A powder obtained by hydrogen pulverizing a new material having an oxygen amount of 1000 ppm or less and a sintered magnet (hereinafter sometimes referred to as a recycled material) having an oxygen amount of 2000 ppm or less are hydrogen crushed. What is necessary is just to produce a molded object using the obtained B powder. The ratio of the A powder to the B powder is preferably 99 wt%: 1 wt% to 70 wt%: 30 wt%.

  As a sintered magnet to be subjected to hydrogen pulverization, a magnet having an average crystal grain size of 1 to 30 μm and a crystal grain orientation degree of 88% or more can be used.

[Production method]
First, with reference to FIG. 1, the outline | summary of the manufacturing method of the RTB type | system | group sintered magnet by this invention is demonstrated. In the present invention, an A-material (new material) made of a cast alloy and a B-material (recycled material) made of a sintered magnet are used as magnet raw materials to produce an RTB-based sintered magnet.
The A material is obtained by strip casting the raw metal in a vacuum or an inert gas, preferably in an Ar atmosphere. In addition, you may use not only a strip casting method but another casting method.
As the raw material metal, rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. The obtained raw material 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 1300 ° C. in a vacuum or Ar atmosphere.

  B material which is a reuse material is a sintered magnet. This sintered magnet is obtained in a coarse pulverization process in which the raw material alloy obtained by strip casting is pulverized with hydrogen, a fine pulverization process in which the coarse powder obtained in the coarse pulverization process is further finely pulverized, and the fine pulverization process. The obtained fine powder is obtained by a molding process for molding the fine powder into a predetermined shape and a sintering process for sintering the molded body obtained in the molding process. For example, sintered magnets that have not been shipped as products due to problems of dimensional accuracy, cracks, chipping, and the like are targeted. Details of the coarse pulverization step, fine pulverization step, molding step, and sintering step will be described later.

In the present invention, a low oxygen sintered magnet having an oxygen content of 2000 ppm or less is used as the B material. When the amount of oxygen exceeds 2000 ppm, coarse pulverization by hydrogen pulverization becomes difficult. If a powder that has not been sufficiently coarsely pulverized is subjected to a fine pulverization step, fine pulverization becomes difficult, or the fine pulverization time becomes long, leading to high costs.
Coarse pulverization is not limited to hydrogen pulverization but can be performed using mechanical means such as a stamp mill, a jaw crusher, and a brown mill. However, coarse pulverization by mechanical means is not preferable because the amount of oxygen in the powder after pulverization increases, and it becomes difficult to finally obtain a sintered magnet having a small amount of oxygen and high magnetic properties. In the present invention, the desirable oxygen content of the low oxygen sintered magnet is 1500 ppm or less, more desirably 1000 ppm or less.

The crystal grain size of the B material is 1 to 30 μm as an average crystal grain size. When crystal grains of less than 1 μm are present, there is a tendency that many phases different from the R ₂ T ₁₄ B phase constituting the main phase are present, which causes a decrease in magnetic properties. On the other hand, if there are crystal grains exceeding 50 μm, rough pulverization by hydrogen pulverization becomes difficult. Therefore, in the present invention, a low oxygen sintered magnet having an average crystal grain size of 1 to 30 μm is used. The preferred average crystal grain size of the low oxygen sintered magnet is 1 to 20 μm, and the more preferred average crystal grain size is 2 to 15 μm. In addition, the average crystal grain diameter in this invention is a number average particle diameter, The measuring method was as follows. After taking an SEM (scanning electron microscope) photograph and recognizing each crystal grain, the maximum diameter passing through the center of gravity of each crystal grain was determined by image analysis, and this was taken as the crystal grain size. The average crystal grain size was measured for about 100 crystal grains per magnet, and the average value of the crystal grain sizes of all the measured particles was defined as the average crystal grain size.

  The B material has a crystal orientation degree of 88% or more. Usually, it is used as a raw material alloy for sintered magnets. The crystal orientation of the cast alloy is about 60%, and the crystal orientation of the strip cast alloy is about 70%. The B material used in the present invention has a degree of crystal orientation of 90% or more when it is high. The degree of crystal orientation can be calculated, for example, by measuring the residual magnetization in the orientation direction and the residual magnetization in the direction orthogonal to the orientation direction using a BH tracer and determining the ratio between the two.

The so-called new material A and the recycled material B are pulverized separately or together. Here, the grinding step will be described with reference to FIG.
The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the A material and the B material are coarsely pulverized until the particle diameter is about several hundred μm. The coarse pulverization is performed by so-called hydrogen pulverization in which the alloy is pulverized by storing hydrogen. It is desirable to dehydrogenate after hydrogen storage. This is because hydrogen is an impurity for the RTB-based sintered magnet.
Note that the A material may be mechanically pulverized. According to mechanical pulverization, the oxygen content of the powder obtained after pulverization increases, but the oxygen content of the new material A is about 50 to 500 ppm, which is less than that of the B material. This is because it is not as problematic as wood.

After the coarse pulverization step, the coarse powder of the A material and the coarse powder of the B material are mixed in a non-oxidizing gas atmosphere. The mixing ratio of the A material and the B material is desirably 99 wt%: 1 wt% to 70 wt%: 30 wt%. If the mixing ratio of the B material is less than 1 wt%, the reuse rate of the defective material is low, and the cost cannot be reduced by mixing the defective material. On the other hand, when the mixing ratio of the B material exceeds 30 wt%, it becomes difficult to obtain characteristics equivalent to those of the rare earth sintered magnet obtained from only the new material. Moreover, the A material which is a new material and the B material which is a reuse material have different shrinkage ratios during sintering, and the B material which has been sintered once has a smaller shrinkage ratio. For this reason, when the mixing ratio of the B material exceeds 30 wt%, it is difficult to obtain a rare earth sintered magnet having the same size as the magnet obtained using only the A material even if the same mold is used.
A preferable mixing ratio of the B material is 3 to 20 wt%, more preferably 3 to 15 wt%.
However, in the present invention, it is not excluded that the mixing ratio of the B material exceeds 30 wt%. This is because, depending on the use of the rare earth sintered magnet, there is a case where it is desired to place importance on the cost rather than the characteristics. The present invention includes a form in which the B material is mixed in excess of 30 wt%, and further a form in which the rare earth sintered magnet is produced only from the B material.

  In the subsequent 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 non-oxidizing gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder by this high-speed gas flow, This is a method of crushing by generating a collision with a target or a container wall. By adding about 0.01 to 0.3 wt% of an additive such as zinc stearate at the time of fine pulverization, a fine powder having high orientation during molding can be obtained.

  Next, the mixed powder composed of the A material powder and the B material 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 70 to 150 MPa in a magnetic field of 940 to 1400 kA / m.

  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 magnet can be subjected to an aging treatment. The aging treatment is important for controlling the coercive force. When the aging treatment is performed in two stages, it is effective to hold for a predetermined time at around 800 ° C. and around 500 ° C. 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 500 ° C., when the aging treatment is performed in one stage, the aging treatment at around 500 ° C. is preferably performed.

  According to the present invention, which uses a low-oxygen sintered magnet having an oxygen content of 2000 ppm or less as a magnet raw material, it is possible to reuse a defective material without increasing the cost, and to improve the yield of the material. Also contributes. Further, as shown in the examples described later, according to the present invention, a rare earth sintered magnet having a residual magnetic flux density (Br) of 1400 mT or more and a coercive force (HcJ) of 1200 kA / m or more can be obtained.

  In FIG. 1, the form in which the A material and the B material are roughly pulverized and the coarse powder of the A material and the coarse powder of the B material are mixed is shown, but other forms may be adopted. For example, as shown in FIG. 2, the A material and the B material may be coarsely pulverized and finely pulverized together. In this case, the mixing process shown in FIG. 1 is unnecessary. Alternatively, as shown in FIG. 3, the A material and the B material may be coarsely pulverized and finely pulverized, respectively, and then both may be mixed.

  Further, for example, the A material is coarsely pulverized and finely pulverized, while the B material is only coarsely pulverized and the fine pulverization is omitted. A compact may be prepared by mixing the fine powder of the A material and the coarse powder of the B material. If the molding is performed with the coarse powder interposed in the fine powder, the filling property into the mold can be improved, and finally a high-density molded product can be obtained. And a sintered magnet with a high residual magnetic flux density (Br) can be obtained by sintering a high-density molded object. However, in the case where fine pulverization is omitted for the B material, the average particle size of the B material after coarse pulverization is 1 to 30 μm. The material B is once subjected to molding and sintering in a magnetic field, and when it is newly sintered together with the material A, it is difficult for the grains to grow. When used for sintering, the sintered magnet body cannot be finally densified, the residual magnetic flux density (Br) becomes low, and the RTB-based sintering has a high coercive force (HcJ). This is because it becomes difficult to obtain a magnet.

[Chemical composition]
Next, the chemical composition will be described.
First, the composition of the finally obtained RTB-based sintered magnet will be described.
The composition of the RTB-based sintered magnet to which the present invention is applied may be appropriately set according to the purpose, but in order to obtain a magnet having excellent magnetic properties, R: It is desirable that the composition be 20 to 40 wt%, B: 0.5 to 4.5 wt%, and T: the balance. Here, R in the present invention has a concept including Y, and one or two of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y Selected from more than species. If the amount of R is less than 20 wt%, the R ₂ Fe ₁₄ B phase, which is the main phase of the R-TM-B sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 40 wt%, the volume ratio of the R ₂ Fe ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, 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, so the amount of R is set to 20 to 40 wt%. . Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as the rare earth element R is Nd.

  Moreover, when boron B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when boron 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 boron B is 0.5 to 1.5 wt%.

The RTB-based sintered magnet of the present invention has a Co content of 2.0 wt% or less (excluding 0), preferably 0.1 to 1.0 wt%, more preferably 0.3 to 0.7 wt%. % Can be contained. 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.
Moreover, the RTB system sintered magnet of this invention can contain 1 type or 2 types of Al and Cu in 0.02-0.5 wt%. By containing one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained sintered magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.3 wt%, and the more desirable amount of Al is 0.05 to 0.25 wt%. Further, 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 0.12 wt%.

The RTB-based sintered magnet of the present invention allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is desirable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is desirably 2000 ppm or less, further 1500 ppm or less, and more preferably 1000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.
However, if the amount of oxygen in the RTB-based sintered magnet is reduced in order to obtain high magnetic properties, 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. In order to suppress such grain growth in the sintering process, it is desirable that the RTB-based sintered magnet of the present invention contains at least one of Zr, Nb and Ta. When reducing the oxygen content in order to improve the magnetic properties of the sintered magnet, Zr, Nb and Ta all exert the effect of suppressing abnormal growth of crystal grains during the sintering process, Make the tissue uniform and fine.
In the RTB-based sintered magnet, the Zr content is 0.05 to 0.3 wt%, the Nb content is 0.05 to 0.3 wt%, and the Ta content is 0.1 to 2.0 wt%. % Is preferred. A more preferable Zr content is 0.1 to 0.25 wt%, and a more preferable Zr content is 0.1 to 0.2 wt%. A more preferable Nb content is 0.1 to 0.25 wt%, and a still more preferable Nb content is 0.1 to 0.2 wt%. A more preferable Ta content is 0.2 to 1.7 wt%, and a more preferable Ta content is 0.3 to 1.5 wt%.

What is necessary is just to determine the composition of A material according to the composition of the RTB system sintered magnet to obtain finally, and the composition of B material.
Specifically, when a B material having a composition equivalent to the composition of the RTB-based sintered magnet to be finally obtained is used, the composition of the A material is also an RTB-based sintered magnet. The composition is equivalent to
On the other hand, when using the B material having a composition different from the composition of the R-T-B system sintered magnet to be finally obtained, the ratio of the A material to the B material, the desired R-T-B system The composition of the A material may be determined in consideration of the composition of the sintered magnet and the composition of the B material to be used.

  The composition of the B material is preferably equivalent to the composition of the RTB-based sintered magnet to be finally obtained, but such a B material cannot always be prepared. Therefore, when using the B material having a composition different from the composition of the RTB-based sintered magnet to be finally obtained, the composition of the A material and the ratio of the A material and the B material as described above. Can be adjusted.

Further, a high R alloy having a larger amount of rare earth elements than materials A and B may be further prepared, and these three types may be combined to obtain a sintered magnet. The use of the high R alloy is effective when the oxygen content of the B material is within a range of 2000 ppm or less but the oxygen content is relatively large. When the amount of oxygen in the B material is relatively large, it is assumed that the R-rich phase in the grain boundary phase is insufficient due to oxidation and the magnetic properties are deteriorated, but the rare earth element that supplements the oxidation content of the grain boundary phase. By supplementing, it is possible to suppress the deterioration of the magnetic characteristics.
The addition amount of the high R alloy can be 0.5 to 10 wt% with respect to the total amount of the A material and the B material. By adding the high R alloy in this range, the coercive force (HcJ) and / or the residual magnetic flux density (Br) can be improved. However, if the addition amount exceeds 10 wt%, the amount of rare earth elements in the entire sintered magnet increases, and the residual magnetic flux density (Br) decreases.

Next, the present invention will be described in more detail with specific examples.
In this example, a rare earth sintered magnet was manufactured according to the manufacturing process shown in FIG. In order to obtain high magnetic properties, in this experiment, in order to suppress the oxygen content of the rare earth sintered magnet finally obtained to 2000 ppm or less, from hydrogen treatment (recovery after pulverization treatment) to sintering (to a sintering furnace). The atmosphere of each step until (input) was suppressed to an oxygen concentration of less than 300 ppm.
First, as the A material (alloy), 29.6 wt% Nd-1.0 wt% Dy-0.5 wt% Co-0.05 wt% Cu-0.1 wt% Zr-0.2 wt% Al-- 1.1 wt% B-bal. An alloy having a composition of Fe was produced. The amount of oxygen in the A material was 320 ppm. As B material (reuse material), 29.4 wt% Nd-1.0 wt% Dy-0.5 wt% Co-0.05 wt% Cu-0.1 wt% Zr-0.2 wt% Al-1.1 wt% B -Bal. A sintered magnet having a composition of Fe (wt%) was prepared. The amount of oxygen in the B material was 950 ppm. Moreover, it was 4.1 micrometers when the average crystal grain diameter of B material was calculated | required by the above-mentioned method.
Subsequently, hydrogen was occluded in the A material and the B material at room temperature, and then hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere. This hydrogen pulverization treatment was performed for each of the A material and the B material.
The obtained coarse powder of the A material and the coarse powder of the B material were mixed at a ratio shown in Table 1 using a V mixer, and thereafter, the A material powder and the B material powder each had an average particle size of 4. Fine grinding was performed until the thickness became about 0 μm. The obtained fine powder was molded at a pressure of 120 MPa in a magnetic field of 1200 kA / m to obtain a molded body. Fine grinding, mixing of A material and B material and molding are also performed by a low oxygen process.
The molded body was sintered in a vacuum at 1050 ° C. for 4 hours and then rapidly cooled. Next, the obtained sintered magnet was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 540 ° C. × 1 hour (both in an Ar atmosphere).

  About the obtained RTB-based sintered magnet, the residual magnetic flux density (Br) and the coercive force (HcJ) were measured with a BH tracer. The results are also shown in Table 1 and FIGS.

As shown in Table 1, even when 5 to 20 wt% of the B alloy as a reusable material was added, a residual magnetic flux density (Br) of 1400 mT or more and a coercive force (HcJ) of 1250 kA / m or more could be obtained. .
However, as shown in FIG. 4 and FIG. 5, the coercive force (HcJ) and the residual magnetic flux density (Br) are gradually reduced as the amount of addition of the B alloy as the reuse material increases. In order to obtain the same characteristics as in the case of not performing (Sample No. 1), it is desirable that the amount of the recycled material added is 1 to 30 wt%.

<Comparative example>
As the B material (recycled material), a material having the same composition as in the above example but having an oxygen content of 3500 ppm was prepared. The B material was subjected to hydrogen storage and dehydrogenation treatment in the same manner as in the example, but the B material could not be pulverized with hydrogen.

It is a flowchart which shows the manufacturing process of the rare earth sintered magnet in this embodiment. It is a flowchart which shows the other manufacturing process of the rare earth sintered magnet in this embodiment. It is a flowchart which shows the other manufacturing process of the rare earth sintered magnet in this embodiment. It is a graph which shows the relationship between the reuse material addition amount in an Example, and a residual magnetic flux density (Br). It is a graph which shows the relationship between the reuse material addition amount in an Example, and a coercive force (HcJ).

Claims (5)

A step (1) of hydrogen-pulverizing a sintered magnet having an oxygen amount of 2000 ppm or less;
A step (2) of producing a molded body using hydrogen-pulverized powder;
And (3) a step of sintering the molded body ,
In order to suppress the oxygen content of the finally obtained rare earth sintered magnet to 2000 ppm or less, the atmosphere in the step (1), the step (2), and the step (3) is controlled to an oxygen concentration of less than 300 ppm. A method for producing a rare earth sintered magnet.   The compact is produced using A powder obtained by hydrogen pulverizing a cast alloy having an oxygen content of 1000 ppm or less and B powder obtained by hydrogen pulverizing the sintered magnet having an oxygen content of 2000 ppm or less. The method for producing a rare earth sintered magnet according to claim 1.   The method for producing a rare earth sintered magnet according to claim 2, wherein a ratio of the A powder and the B powder is 99 wt%: 1 wt% to 70 wt%: 30 wt%. The method for producing a rare earth sintered magnet according to any one of claims 1 to 3, wherein the sintered magnet subjected to the hydrogen pulverization has an average crystal grain size of 1 to 30 µm. The method for producing a rare earth sintered magnet according to any one of claims 1 to 4, wherein the sintered magnet subjected to the hydrogen pulverization has an orientation degree of crystal grains of 88% or more.

Images