JP7052201B2 - Manufacturing method of RFeB-based sintered magnet - Google Patents

Description

The present invention relates to a method for producing an RFeB-based sintered magnet containing R (rare earth element), Fe (iron) and B (boron), and in particular, RFeB to which Ga (gallium) is added in order to increase the coercive force. The present invention relates to a method for manufacturing a system sintered magnet.

The RFeB-based sintered magnet was discovered by Masato Sagawa et al. In 1982, and has the feature that many magnetic characteristics such as residual magnetic flux density are much higher than those of conventional permanent magnets. Therefore, RFeB-based sintered magnets are various, such as motors for driving hybrid vehicles and electric vehicles, motors for electrically assisted bicycles, industrial motors, voice coil motors such as hard disks, speakers, headphones, and permanent magnet type magnetic resonance diagnostic devices. Used in various products.

Early RFeB-based sintered magnets had the drawback of having a relatively low coercive force among various magnetic properties. The coercive force represents the force that withstands the reversal of magnetization when a magnetic field opposite to the direction of magnetization is applied to the magnet, and the higher the coercive force, the more suitable the magnet for applications such as motors. I can say. Therefore, various methods for increasing the coercive force of RFeB-based sintered magnets have been proposed conventionally.

As one of the methods, Patent Document 1 describes an RFeB-based sintered magnet to which Ga is added. In the RFeB-based sintered magnet to which Ga is added, the composition formula is represented by R ₂ Fe ₁₄ B, and the composition formula has a La ₆ Co ₁₁ Ga ₃ type crystal structure between the crystal grains having ferromagnetism. A layer containing a substance having magnetism different from ferromagnetism (hereinafter referred to as "grain boundary layer"), which is represented by R ₆ Fe ₁₃ Ga, is formed. As a result, even if the magnetic interaction between adjacent crystal grains is divided at the grain boundary layer and the magnetization is reversed within one crystal grain, the effect of this is to reverse the magnetization at the crystal grains adjacent to the crystal grain. Is less likely to occur. Therefore, the RFeB-based sintered magnet to which Ga is added has a higher coercive force than the case where Ga is not added.

Japanese Unexamined Patent Publication No. 2014-209546 Japanese Unexamined Patent Publication No. 2006-019521

In Patent Document 1, a raw material alloy plate having the same composition as the final product is produced by a strip casting method, and the raw material alloy plate is crushed to produce a raw material alloy powder. However, in the RFeB-based sintered magnet manufactured by using the raw material alloy powder produced by this method, there are many places where the thickness of the grain boundary layer is small. Where the thickness of the grain boundary layer is small, even if the grain boundary layer contains R ₆ Fe ₁₃ Ga, which has a magnetism different from that of ferromagnetism, the magnetic interaction between adjacent crystal grains is sufficiently disrupted. Can't. Therefore, the RFeB-based sintered magnet manufactured by this method cannot have a sufficiently high coercive force.

The problem to be solved by the present invention is to manufacture an RFeB-based sintered magnet having a grain boundary layer containing R ₆ Fe ₁₃ Ga, which can have a higher coercive force than the conventional one. Is to provide a way to do it.

The method for manufacturing an RFeB-based sintered magnet according to the present invention, which has been made to solve the above problems, is
Rare earth element R (excluding heavy rare earth elements Dy, Tb, Gd and Ho) , first raw material powder composed of alloy containing Fe, B and Ga, and containing R, Fe and B and containing Ga. The second raw material powder, which is a powder made of a non-alloy, has a mass ratio of 45:55 to 50:50 between the first raw material powder and the second raw material powder, and has an R content of 30.0 to 33.0% by mass. A mixed raw material powder preparation step for producing a mixed raw material powder in which the Fe content is 65.0 to 68.0% by mass, the B content is 0.8 to 0.9% by mass, and the Ga content is 0.2 to 0.6% by mass. ,
The alignment step of orienting the mixed raw material powder in a magnetic field and
It is characterized by having a sintering step of sintering the mixed raw material powder subjected to the alignment step.

The mixed raw material powder may contain elements other than the above R, Fe, B and Ga. Therefore, the total content of these R, Fe, B and Ga may be less than 100% by mass.

According to the method for producing an RFeB-based sintered magnet according to the present invention, a mixed raw material powder obtained by mixing a first raw material powder made of a metal containing Ga and a second raw material powder made of an alloy containing R, Fe and B. By manufacturing an RFeB-based sintered magnet by the so-called two-alloy method using Alloy method) Higher coercive force than RFeB-based sintered magnets. Although the reason is not clear, when manufactured by the two-alloy method rather than the one-alloy method, Ga became R ₆ Fe ₁₃ Ga without being incorporated into the crystal grains and was surrounded by three crystal grains. It is more likely to exist at the grain boundary triple point, which is the grain boundary, so that the thickness of the two-grain grain boundary, which is an R-rich layer with a higher R content than R ₂ Fe ₁₄ B, is applied to the entire RFeB-based sintered magnet. It is presumed that this is due to the fact that the magnetic interaction becomes large enough to be sufficiently disrupted.

In the present invention, the content of Ga in the mixed raw material powder is set to 0.2% by mass or more in order to exert the effect of increasing the coercive force of the RFeB-based sintered magnet. On the other hand, when the content of Ga in the mixed raw material powder exceeds 0.6% by mass, the coercive force is not improved and other magnetic properties are deteriorated as compared with the case of 0.6% by mass or less. Therefore, the content of Ga in the mixed raw material powder is 0.2 to 0.6% by mass. Further, the content of B in R ₂ Fe ₁₄ B containing no Ga is about 1.0% by mass, but in the present invention, R ₆ Fe ₁₃ Ga containing R and Fe and not containing B is formed at the grain boundary. Therefore, the content of B in the mixed raw material powder in the present invention is 0.8 to 0.9% by mass, which is lower than the value in R ₂ Fe ₁₄ B.

The above B and Ga contents are both defined with significant figures as one digit, and if the content is within the above range by rounding to the second digit, it is included in the present invention. For example, when the significant figure is two digits, the Ga content is in the range of 0.15 to 0.64% by mass, and when rounded to the second digit, it is in the range of 0.2 to 0.6% by mass. include. The content of R and Fe is defined as 3 significant figures, and if the content is within the above range by rounding to the 4th digit, it is included in the present invention.

The content of each element in the mixed raw material powder can be adjusted by the content of each element in the first raw material powder and the second raw material powder, and the mixing ratio of the first raw material powder and the second raw material powder.

In the present invention, the mixed raw material powder obtained by mixing the first raw material powder and the second raw material powder is the first raw material powder and the second raw material powder by separately pulverizing the metal containing Ga and the alloy containing R, Fe and B. The raw material powder may be prepared separately and then mixed with the first raw material powder and the second raw material powder, or the metal containing Ga and the alloy containing R, Fe and B are crushed together. It may be produced by this.

The first raw material powder may contain an element other than Ga, and the second raw material powder may contain an element other than R, Fe and B. For example, the first raw material powder may contain R, Fe and / or B, which are the main constituent elements of the RFeB-based sintered magnet, in addition to Ga.

It is desirable that the mixed raw material powder contains 0.05 to 0.3% by mass of Cu and / or 0.1 to 0.4% by mass of Al. By containing these Cu and Al, the coercive force of the RFeB-based sintered magnet can be further increased. Cu and / or Al may be contained in either the first raw material powder or the second raw material powder, or may be contained in both the first raw material powder and the second raw material powder. Alternatively, a powder containing Cu and / or Al, which is different from the first raw material powder and the second raw material powder, is prepared, and the mixed raw material powder is prepared by mixing the powder with the first raw material powder and the second raw material powder. You may. In addition, the content rates of B and Ga are both specified with significant figures as one digit, and if the content rate is within the above range by rounding to the second digit, the above requirements are satisfied.

In the present invention, the strength of the magnetic field when the mixed raw material powder is oriented in the magnetic field and the temperature when the mixed raw material powder is sintered may be the same as in the case of manufacturing a conventional RFeB sintered magnet. For example, the strength of the magnetic field may be 2 to 5 T, and the temperature at the time of sintering may be 800 to 1100 ° C.

In the present invention, compression molding may be performed by applying pressure to the mixed raw material powder during the alignment step (press method), but the alignment step and the subsequent sintering step without applying pressure to the mixed raw material powder. (Press-less process: PLP method) is desirable. Thereby, the coercive force can be further increased (see Patent Document 2).

According to the RFeB-based sintered magnet method according to the present invention, the coercive force of the RFeB-based sintered magnet on which the grain boundary layer containing R ₆ Fe ₁₃ Ga is formed can be made higher than before.

The schematic diagram which shows the process of one Embodiment of the manufacturing method of RFeB-based sintered magnet which concerns on this invention. The schematic diagram which shows a part of the process about the modification of the manufacturing method of the RFeB-based sintered magnet of this embodiment. The graph which shows the magnetization curve of the RFeB-based sintered magnet obtained by the method of this embodiment and the RFeB-based sintered magnet obtained by the comparative example at a temperature of 180 ° C.

An embodiment of the method for manufacturing an RFeB-based sintered magnet according to the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows an outline of the process of the RFeB-based sintered magnet of the present embodiment. First, the first raw material powder 111 and the second raw material powder 112 are prepared as follows (a).

The first raw material powder 111 is produced by pulverizing a metal containing Ga. Metals containing Ga include elemental Ga, Cu and / or alloys of Al and Ga, R, Fe and / or alloys of B and Ga, Ga and Cu and / or Al and R, Fe and / or B. Ga alloys and the like can be used. These metals can be suitably produced by the strip casting method. When pulverizing a metal containing Ga, first, the metal is occluded by occluding hydrogen to make the metal embrittlement, and then coarsely pulverized, and then finely pulverized using a jet mill. can do. The average particle size of the first raw material powder 111 is preferably 0.5 to 5.0 μm as measured by the laser method.

The second raw material powder 112 is produced by pulverizing an alloy containing R, Fe and B and not containing Ga. As this alloy, an alloy containing only R, Fe and B, an alloy containing Cu and / or Al in addition to these three elements, and the like can be used. These metals can also be suitably produced by the strip casting method as in the case of the first raw material powder 111. Further, the same method as in the case of the first raw material powder 111 can be used for pulverizing the alloy. The average particle size of the second raw material powder 112 is preferably 0.5 to 5.0 μm as measured by the laser method.

Next, the mixed raw material powder 11 is produced by mixing the first raw material powder 111 and the second raw material powder 112 (b). At that time, depending on the element content of the first raw material powder 111 and the second raw material powder 112, the R content after mixing is 30.0 to 33.0% by mass, the Fe content is 65.0 to 68.0% by mass, and B The mixing ratio of the first raw material powder 111 and the second raw material powder 112 is adjusted so that the content is 0.8 to 0.9% by mass and the Ga content is 0.2 to 0.6% by mass.

Up to this point, the case where the first raw material powder 111 and the second raw material powder 112 are separately prepared and then mixed has been described, but as shown in FIG. 2, Ga which is the raw material of the first raw material powder 111 is contained. The mixed raw material powder 11 may be produced by pulverizing the Ga-containing metal 101 and the RFeB-containing alloy 102 containing R, Fe and B, which are the raw materials of the second raw material powder 112, and not containing Ga. .. The mixed raw material powder 11 produced by such a method also satisfies the requirements of the mixed raw material powder in the present invention because the first raw material powder 111 and the second raw material powder 112 are in a mixed state.

Next, the obtained mixed raw material powder 11 is filled in the cavity 121 of the container 12 (c). The cavity 121 of the container 12 has a shape corresponding to the shape of the RFeB-based sintered magnet to be manufactured. The container 12 is made of a material having heat resistance at the sintering temperature (1100 ° C.) described later. As this material, for example, a carbon material such as graphite can be preferably used. In this embodiment, the filling density of the mixed raw material powder 11 when filling the cavity 121 is equal to or slightly higher than the density when naturally filled, but the mixed raw material powder 11 is not compression-molded. After filling the cavity 121 with the mixed raw material powder 11, the opening of the cavity 121 is covered with a lid 122.

Next, by applying a magnetic field of 2 to 5 T to the mixed raw material powder 11 filled in the cavity 121 of the container 12, the particles of Nd ₂ Fe ₁₄ B, which are the particles having ferromagnetism in the mixed raw material powder 11, are oriented. Let (d). At that time, no mechanical pressure is applied to the mixed raw material powder 11.

Then, the mixed raw material powder 11 is sintered by heating the mixed raw material powder 11 to 800 to 1100 ° C. while being filled in the cavity 121 of the container 12 (e). Even at that time, no mechanical pressure is applied to the mixed raw material powder 11. By the operations up to this point, the RFeB-based sintered magnet M can be obtained (f).

Up to this point, the case of the PLP method in which the mixed raw material powder 11 is not compression-molded in each step has been described, but in the present invention, the press method may be used.

[Example]
Next, an example in which an RFeB-based sintered magnet is manufactured by the method of this embodiment (PLP method) will be described. In this example, the alloy 1 having the composition shown in Table 1 and prepared by strip casting (Ga-containing metal 101 in FIG. 2) and the alloy 2 having the composition shown in the same table and prepared by strip casting (the same RFeB). The mixed raw material powder 11 produced by pulverizing the contained alloy 102) together was used. The average particle size of the mixed raw material powder 11 was 1.34 μm (measured by the laser method). The mixing ratio of alloy 1 and alloy 2 was 1: 1 by weight. The strength of the magnetic field at the time of orientation was 4T, and the heating temperature at the time of sintering was 880 ° C. As a comparative example, RFeB was produced by a one-alloy method using only raw material powder having the composition shown in Table 1 and having an average particle size of 1.29 μm (measured by the laser method) produced by pulverizing the alloy 3 produced by strip casting. A system sintered magnet was produced. The strength of the magnetic field at the time of orientation and the heating temperature at the time of sintering in the comparative example were the same as in the case of the example. By mixing the alloy 1 and the alloy 2 at a weight ratio of 1: 1 as described above, the composition of the mixed raw material powder 11 of the example becomes substantially the same as the composition of the raw material powder of the comparative example.

The residual magnetic flux density and coercive force were measured for the RFeB-based sintered magnets produced in the examples and comparative examples. The measurements were performed at room temperature and at 180 ° C, which is the heat resistant temperature required for the drive motor of an automobile. The measurement results are shown in Table 2. In addition, the magnetization curve at 180 ° C. is shown in FIG.

From these measurement results, it can be seen that although the composition of the raw material powder is almost the same, the coercive force of the example is higher than that of the comparative example at both room temperature and 180 ° C. The residual magnetic flux density in the examples is slightly smaller than that in the comparative example, but there is no problem in practical use.

In the above embodiment, the mixing ratio of the alloy 1 and the alloy 2 was 45:55 instead of 1: 1 (50:50), so that the content of Ga and Cu was smaller than that of the raw material powder of the comparative example. A mixed raw material powder 11 was produced, and an RFeB-based sintered magnet was produced using the mixed raw material powder 11 by the same method as described above. The residual magnetic flux density of the obtained RFeB-based sintered magnet was 13.8 kG at room temperature and 10.8 kG at 180 ° C. The coercive force of this RFeB-based sintered magnet was 21.4 kOe at room temperature and 5.5 kOe at 180 ° C. As described above, this RFeB-based sintered magnet has a higher coercive force at 180 ° C. than that of the comparative example even though the content of Ga and Cu is lower than that of the comparative example. It can be seen that is effective in improving the coercive force using Ga.

It goes without saying that the embodiments described so far are examples of the present invention and various modifications can be made.

11 ... Mixed raw material powder 111 ... First raw material powder 112 ... Second raw material powder 12 ... Container 121 ... Cavity 122 ... Lid M ... RFeB-based sintered magnet

Claims (4)

Rare earth element R (excluding heavy rare earth elements Dy, Tb, Gd and Ho) , first raw material powder composed of alloy containing Fe , B and Ga, and containing R, Fe and B and containing Ga. The second raw material powder, which is a powder made of a non-alloy, has a mass ratio of 45:55 to 50:50 between the first raw material powder and the second raw material powder, and has an R content of 30.0 to 33.0% by mass. A mixed raw material powder preparation step for producing a mixed raw material powder in which the Fe content is 65.0 to 68.0% by mass, the B content is 0.8 to 0.9% by mass, and the Ga content is 0.2 to 0.6% by mass. ,
The alignment step of orienting the mixed raw material powder in a magnetic field and
A method for producing an RFeB-based sintered magnet, which comprises a sintering step of sintering the mixed raw material powder subjected to the alignment step. The method for producing an RFeB-based sintered magnet according to claim 1, wherein the mixed raw material powder contains 0.05 to 0.3% by mass of Cu. The method for producing an RFeB-based sintered magnet according to claim 1 or 2, wherein the mixed raw material powder contains 0.1 to 0.4% by mass of Al. The method for producing an RFeB-based sintered magnet according to any one of claims 1 to 3, wherein the alignment step and the sintering step are performed without applying pressure to the mixed raw material powder.

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