RTB-type permanent magnet alloy, method for manufacturing RTB-type permanent magnet alloy, and method for manufacturing RTB-type permanent magnet.

Abstract

This invention provides an alloy for RTB-type permanent magnets that can produce RTB-type permanent magnets with high magnetic properties and low cracking, as well as a method for manufacturing the same. [Solution] An RTB-type permanent magnet alloy containing rare earth elements, Fe and / or Co, boron, and M. M is one or more selected from Ga, Al, Cu, Zn, In, P, Sb, Si, Ge, Sn, and Bi. The RTB-type permanent magnet alloy contains a main phase and an R-rich phase, and the area ratio of the 6-13-1 phase, which is a type of R-rich phase, in the cross-section of the RTB-type permanent magnet alloy is 7.0% or less.

Description

Technical Field

[0001] The present disclosure relates to an alloy for an R-T-B permanent magnet, a method for manufacturing the alloy for an R-T-B permanent magnet, and a method for manufacturing an R-T-B permanent magnet.

Background Art

[0002] Patent Document 1 describes an invention related to a raw material alloy for an R-T-B magnet. In particular, the crystal structure of the raw material alloy for an R-T-B magnet is a crystal structure in which an amorphous phase and a crystal phase coexist in an R-rich phase, and the Ga content of the amorphous phase is higher than the Ga content of the crystal phase. Due to this feature, the magnetic saturation of the main phase of the finally obtained sintered magnet is improved, the energy product of the sintered magnet is improved, and the coercive force is improved and stabilized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide an alloy for an R-T-B permanent magnet that can produce an R-T-B permanent magnet having high magnetic properties and being less likely to crack.

Means for Solving the Problems

[0005] To achieve the above object, an alloy for an R-T-B permanent magnet according to the present disclosure is an alloy for an R-T-B permanent magnet containing a rare earth element, Fe and / or Co, boron, and M, where M is one or more selected from Ga, Al, Cu, Zn, In, P, Sb, Si, Ge, Sn, and Bi the alloy for an R-T-B permanent magnet contains a main phase and an R-rich phase, In the cross-section of the RTB-type permanent magnet alloy, the area ratio of the 6-13-1 phase, which is a type of R-rich phase, is 7.0% or less.

[0006] The area ratio of the 6-13-1 phase may be 1.0% or more and 6.5% or less.

[0007] In the cross-section of the RTB-type permanent magnet alloy, the area ratio of the 2-17 phase may be 2.0% or less.

[0008] The boron content may be 0.78% by mass or more and 0.95% by mass or less.

[0009] The boron content may be 0.80% by mass or more and 0.95% by mass or less.

[0010] The boron content may be 0.83% by mass or more and 0.90% by mass or less.

[0011] The boron content may be 0.75% by mass or more and 0.95% by mass or less, and the carbon content may be 0.05% by mass or more and 0.25% by mass or less.

[0012] The sum of the boron content and the carbon content may be 0.80% by mass or more and 1.20% by mass or less, and the value obtained by dividing the carbon content by the boron content may be 0.05 or more and 0.33 or less.

[0013] The Ga content may be 0.10% by mass or more and 0.70% by mass or less.

[0014] The total content of rare earth elements may be 30.0% by mass or more and 33.0% by mass or less.

[0015] The total content of rare earth elements may be 30.0% by mass or more and 33.0% by mass or less, the content of Al may be 0.1% by mass or more and 0.4% by mass or less, the content of Co may be 0.4% by mass or more and 1.1% by mass or less, the content of Cu may be 0.05% by mass or more and 0.2% by mass or less, the content of Zr may be 0.15% by mass or more and 0.7% by mass or less, and the content of Ga may be 0.10% by mass or more and 0.70% by mass or less.

[0016] The method for producing an alloy for an R-T-B permanent magnet according to the present disclosure is a step of solidifying a molten alloy to obtain a cast alloy ribbon, a step of crushing the cast alloy ribbon to obtain a cast alloy flake, and a step of cooling the cast alloy flake, and the cooling rate from 600 °C to 400 °C in the step of cooling the cast alloy flake is 0.7 °C / second or more.

[0017] The method for producing an R-T-B permanent magnet according to the present disclosure is characterized by having a step of hydrogen crushing the above alloy for an R-T-B permanent magnet, and the dehydrogenation temperature in the step of hydrogen crushing is 530 °C or more and 650 °C or less.

Brief Description of the Drawings

[0018] [Figure 1] It is a backscattered electron image of the coarsely crushed powder of the alloy for an R-T-B permanent magnet. [Figure 2] It is a backscattered electron image of the coarsely crushed powder of the alloy for an R-T-B permanent magnet. [Figure 3] It is a backscattered electron image of the coarsely crushed powder of the alloy for an R-T-B permanent magnet. [Figure 4] It is a backscattered electron image of the coarsely crushed powder of the alloy for an R-T-B permanent magnet. [Figure 5] It is a backscattered electron image of the alloy for an R-T-B permanent magnet. [Figure 6] It is an image obtained by binarizing FIG. 5. [Figure 7] It is a schematic diagram showing a method for measuring the R-rich phase interval of the alloy for an R-T-B permanent magnet.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the present disclosure will be described based on the embodiments shown in the drawings.

[0020] <Microstructure of the Alloy for R-T-B System Permanent Magnet> The alloy for the R-T-B system permanent magnet according to the present embodiment contains a rare earth element, Fe and / or Co, boron, and M. M is one or more selected from Ga, Al, Cu, Zn, In, P, Sb, Si, Ge, Sn, and Bi.

[0021] Generally, the alloy for the R-T-B system permanent magnet contains a main phase having a R2T 14 B-type crystal structure and a R-rich phase having a higher R content than the main phase.

[0022] Generally, when observing the cross-section of the alloy for the R-T-B system permanent magnet with a reflection electron image, the portion with a larger average atomic number appears brighter (whiter). And the R-rich phase has a larger average atomic number compared to the main phase.

[0023] And when appropriately adjusting the luminance histogram of the reflection electron image, the R-rich phase included in the reflection electron image can be divided into a plurality of types according to the brightness of the R-rich phase.

[0024] Specifically, the R-rich phase can be classified into the brightest white phase and the 6-13-1 phase (intermediate phase) which is the brightness between the white phase and the main phase. And the alloy for the R-T-B system permanent magnet according to the present embodiment has an area ratio of the 6-13-1 phase in the cross-section of 7.0% or less (including 0%). It may be 1.0% or more and 6.5% or less, or may be 1.0% or more and 6.0% or less.

[0025] In other words, the RTB-type permanent magnet alloy according to this embodiment has a smaller area ratio of the 6-13-1 phase compared to conventional RTB-type permanent magnet alloys. By using an RTB-type permanent magnet alloy with a smaller area ratio of the 6-13-1 phase to manufacture an RTB-type permanent magnet, it becomes easier to improve the magnetic properties of the resulting RTB-type permanent magnet. The reasons why it becomes easier to improve the magnetic properties of RTB-type permanent magnets will be explained below.

[0026] The main phase may have a ratio of 6.0 to 7.0 on an atomic basis, obtained by dividing the total ratio of Fe and Co by the total ratio of rare earth elements. In contrast, the 6-13-1 phase may have a ratio of greater than 1.0 and 3.0 or less on an atomic basis, obtained by dividing the total ratio of Fe and Co by the total ratio of rare earth elements. The white phase may have a ratio of 0 to 1.0 on an atomic basis, obtained by dividing the total ratio of Fe and Co by the total ratio of rare earth elements. The 6-13-1 phase is a phase containing relatively large amounts of Fe and Co within the R-rich phase, while the white phase is a phase containing relatively small amounts of Fe and Co within the R-rich phase. There are no particular restrictions on the type of 6-13-1 phase, but for example, La6Co 11 R6T with a Ga3-type crystal structure 13 M compound is an example.

[0027] Figures 1 to 4 show backscattered electron images of cross-sections of coarsely ground powder obtained by performing hydrogenation treatment on the same RTB-type permanent magnet alloy at varying dehydrogenation temperatures. Specifically, the cross-sections observed are those obtained by embedding the coarsely ground powder after hydrogenation treatment in resin and polishing it.

[0028] Figure 1 shows the results of hydrogenation treatment at a dehydrogenation temperature of 400°C, Figure 2 shows the results at a dehydrogenation temperature of 500°C, Figure 3 shows the results at a dehydrogenation temperature of 600°C, and Figure 4 shows the results at a dehydrogenation temperature of 640°C. The observation magnification is 10,000x.

[0029] Figures 1 and 2, which show the results when the dehydrogenation temperature is relatively low, clearly show the white phase 11, the 6-13-1 phase 13, and the main phase 15.

[0030] In contrast, Figures 3 and 4, which show the results when the dehydrogenation temperature is relatively high, show a significant decrease in the 6-13-1 phase 13, and instead, a black, spot-like phase 17 is formed. On the other hand, the vicinity of the black, spot-like phase 17 tends to be whiter than the 6-13-1 phase 13. The black, spot-like phase 17 is thought to mainly consist of fine particles made of Fe and / or Co. That is, the ratio of the total ratio of Fe and Co to the total ratio of rare earth elements is very large in the black, spot-like phase 17. It is thought that when the dehydrogenation temperature is high, the 6-13-1 phase 13 decomposes to produce the spot-like phase 17.

[0031] When RTB-type permanent magnets are fabricated using alloy powders containing a large amount of fine particles of Fe and / or Co, the magnetic properties, particularly the square aspect ratio Hk / HcJ, tend to decrease.

[0032] Lowering the dehydrogenation temperature makes it less likely for fine particles composed of Fe and / or Co to be generated in the alloy powder. However, lowering the dehydrogenation temperature also increases the amount of hydrogen remaining in the alloy powder. As a result, cracks are more likely to occur during the molding and sintering processes due to the release of hydrogen.

[0033] Therefore, by reducing the area ratio of the 6-13-1 phase 13 in the cross-section of the RTB-type permanent magnet alloy, specifically to 7.0% or less, the amount of point phase 17 generated is reduced even when dehydrogenation is performed at a relatively high temperature. In other words, when dehydrogenation is performed at a high temperature sufficient to suppress crack generation, reducing the area ratio of the 6-13-1 phase 13 makes it easier to maintain the magnetic properties of the final RTB-type permanent magnet in a suitable manner.

[0034] The area ratio of the 6-13-1 phase 13 may be between 1.0% and 6.5%. If the area ratio of the 6-13-1 phase 13 is less than 1.0%, the average spacing of the R-rich phase, described later, is unlikely to be between 2.0 μm and 4.0 μm. When the area ratio of the 6-13-1 phase 13 is between 1.0% and 6.5%, the Hk / HcJ ratio is particularly likely to improve compared to when the area ratio of the 6-13-1 phase 13 is greater than 6.5%.

[0035] There are no particular restrictions on the average spacing of the R-rich phases in the cross-section of the RTB-type permanent magnet alloy according to this embodiment, but the magnetic properties tend to improve when the spacing is between 2.0 μm and 4.0 μm.

[0036] Cross-section of the RTB-type permanent magnet alloy according to this embodiment, phases 2-17 (R2T 17 The area ratio of the 2-17 phase is preferably small. Furthermore, it is preferable that the 2-17 phase is not observed in the backscattered electron image of the cross-section of the RTB-type permanent magnet alloy. The larger the area ratio of the 2-17 phase, the more likely the magnetic properties are to deteriorate. There is no particular upper limit on the area ratio of the 2-17 phase, but it is preferable that the area ratio of the 2-17 phase is 2.0% or less.

[0037] In this embodiment, it is preferable that the area ratio of the point phase 17 in the cross-section of the RTB-type permanent magnet alloy is small. Furthermore, it is preferable that the point phase 17 is not observed in the backscattered electron image of the cross-section of the RTB-type permanent magnet alloy.

[0038] <Method for calculating the area ratio of each phase> In this embodiment, when calculating the area ratio of each phase in the cross-section of the RTB-type permanent magnet alloy, backscattered electron images obtained using a SEM or the like are used. Alternatively, the area ratio of each phase in the cross-section of the RTB-type permanent magnet alloy may be considered as the volume ratio of each phase in the RTB-type permanent magnet alloy.

[0039] First, adjust the brightness and contrast of the backscattered electron image. Specifically, create a luminance histogram for the obtained backscattered electron image. Then, when the luminance of the darkest part is set to 0 and the luminance of the brightest part is set to 255, adjust the brightness and contrast of the backscattered electron image so that the luminance of the main phase is about 70 and the luminance of the white phase is about 240. By adjusting the image quality of the backscattered electron image in this way, the luminance of the 6-13-1 phase becomes about 140. After that, perform binarization on the backscattered electron image by the well-known K-means method and classify it into three types of phases: the main phase, the 6-13-1 phase, and the white phase. When adjusting the luminance of the backscattered electron image, make sure that the whole backscattered electron image is the cross-section of the R-T-B-based permanent magnet alloy.

[0040] Next, for the binarized backscattered electron image, count the number of pixels of the white phase and the number of pixels of the 6-13-1 phase by image analysis. Then, calculate the area ratio of each phase by calculating the ratio of the number to the total number of pixels in the whole backscattered electron image. For the area ratio of the main phase, the number of pixels of the main phase may be analyzed, or it may be calculated by 1 - (area ratio of the white phase + area ratio of the 6-13-1 phase).

[0041] The presence and area ratio of the 2-17 phase can be confirmed using the backscattered electron image. EDS may be used in combination as needed. The presence and area ratio of the dot-like phase can be confirmed using the backscattered electron image.

[0042] Figure 5 is an example of a backscattered electron image of the cross-section of the R-T-B-based permanent magnet alloy according to this embodiment. Figure 6 is a backscattered electron image after binarization of Figure 5 by the K-means method.

[0043] <Measurement method for the average spacing of the R-rich phase> The measurement method for the average spacing of the R-rich phase will be described. First, for the obtained backscattered electron image, adjust the luminance so that the main phase becomes gray and the 6-13-1 phase and the white phase become white. That is, adjust the luminance so that the main phase becomes gray and the R-rich phase becomes white.

[0044] Next, in the reflected electron image, measurement lines perpendicular to the thickness direction of the R-T-B-based permanent magnet alloy are set at equal intervals (for example, intervals of 5 μm to 50 μm). The lengths of all the measurement lines are made the same.

[0045] Hereinafter, a method for calculating the average interval of the R-rich phase in a certain measurement line will be described. First, count the number of R-rich phases that have contacted the measurement line. Then, by dividing the length of the measurement line by the number of R-rich phases that have contacted the measurement line, the average interval of the R-rich phase in the measurement line can be obtained.

[0046] A schematic diagram showing the relationship between the measurement line and each phase is shown in FIG. 7. In FIG. 7, the average interval of the R-rich phase in the measurement line 21 is the value obtained by dividing the length of the measurement line 21 by the number of R-rich phases 101 that contact the measurement line 21. Since the number of R-rich phases 101 that contact the measurement line 21 is 4, the value obtained by dividing the length of the measurement line 21 by 4 is the average interval of the R-rich phase in the measurement line 21.

[0047] Then, by dividing the sum of the average intervals of the R-rich phases in all the measurement lines by the number of measurement lines, the average interval of the R-rich phase in the R-T-B-based permanent magnet alloy can be obtained.

[0048] There is no particular limitation on the number of measurement lines, but it should be at least 10 or more. There is no particular limitation on the length of the measurement line, but it should be at least 100 μm or more. Furthermore, the length of the measurement line should be such that all the measurement lines contact at least one R-rich phase.

[0049] <Composition of the R-T-B-based permanent magnet alloy> Regarding the composition of the alloy for RTB permanent magnets, there are no particular restrictions other than the fact that it contains rare earth elements (R), Fe and / or Co, boron, and M, as described above. Rare earth elements refer to Sc, Y, and lanthanide elements belonging to Group 3 of the long-period periodic table. Lanthanide elements include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. Rare earth elements are classified into light rare earth elements and heavy rare earth elements. Heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, while light rare earth elements are rare earth elements other than heavy rare earth elements. In this embodiment, from the viewpoint of suitably controlling manufacturing costs and magnetic properties, Nd and / or Pr may be included as R. Furthermore, both light and heavy rare earth elements may be included, particularly from the viewpoint of improving HcJ. There are no particular restrictions on the content of heavy rare earth elements, and it is not required to contain heavy rare earth elements. The content of heavy rare earth elements is, for example, 5% by mass or less (including 0% by mass). M is one or more selected from Ga, Al, Cu, Zn, In, P, Sb, Si, Ge, Sn, and Bi.

[0050] The R content may be 30.0% by mass or more and 33.0% by mass or less, or 30.0% by mass or more and 31.5% by mass or less.

[0051] The content of B may be 0.78% by mass or more and 1.00% by mass or less, or 0.80% by mass or more and 1.00% by mass or less. The content of B may be 0.78% by mass or more and 0.95% by mass or less, or 0.80% by mass or more and 0.95% by mass or less. The content of B may be 0.83% by mass or more and 0.90% by mass or less, or 0.86% by mass or more and 0.90% by mass or less. The smaller the content of B, the larger the area ratio of the 6-13-1 phase tends to be. The larger the content of B, the smaller the area ratio of the 6-13-1 phase tends to be. Also, if the content of B is too small, the 2-17 phase tends to precipitate easily.

[0052] The carbon content may be between 0.000% by mass and 0.25% by mass, or between 0.002% by mass and 0.20% by mass. When the carbon content is within the above range, the magnetic properties tend to improve.

[0053] The content of C may be 0.05% by mass or more and 0.25% by mass or less, and the content of B may be 0.75% by mass or more and 1.00% by mass or less. The content of C may be 0.05% by mass or more and 0.25% by mass or less, and the content of B may be 0.78% by mass or more and 0.95% by mass or less.

[0054] When the content of B and the content of C are within the above ranges, the sum of the content of B and C may be 0.80% by mass or more and 1.20% by mass or less, or 0.80% by mass or more and 1.10% by mass or less. Furthermore, the value obtained by dividing the content of C by the content of B may be 0.05 or more and 0.33 or less, or 0.06 or more and 0.30 or less. When the content of B, the content of C, the sum of the content of B and C, and the value obtained by dividing the content of C by the content of B are all within the above ranges, the area ratio of the 6-13-1 phase becomes smaller, and the magnetic properties tend to improve.

[0055] When the B content is relatively low, such as 0.75% by mass or more and 0.80% by mass or 0.75% by mass or more and 0.77% by mass, it is difficult to reduce the area ratio of the 6-13-1 phase. Even in such cases, reducing the C content to 0.05% by mass or more and 0.25% by mass makes it easier to reduce the area ratio of the 6-13-1 phase.

[0056] The Co content may be between 0.4% and 3.0% by mass, between 0.4% and 2.0% by mass, or between 0.4% and 1.1% by mass. The lower the Co content, the more likely the corrosion resistance is to decrease. The higher the Co content, the more likely the coercivity and angular ratio are to decrease. Also, the higher the Co content, the more expensive the RTB-type permanent magnet alloy tends to be.

[0057] There are no particular restrictions on the total content of M. It may be between 0.4% by mass and 2.0% by mass. M may substantially consist of only one or more elements selected from Ga, Al, and Cu. That is, the content of elements other than Ga, Al, and Cu in M ​​may be 0.1% by mass or less each.

[0058] There are no particular restrictions on the amount of Cu (carbon dioxide) contained. For example, it may be between 0.0% and 0.5% by mass, between 0.05% and 0.3% by mass, or between 0.05% and 0.2% by mass. Having a Cu content within a predetermined range tends to improve magnetic properties.

[0059] There are no particular restrictions on the Ga content. For example, it may be between 0.1% by mass and 1.5% by mass, between 0.1% by mass and 1.0% by mass, or between 0.1% by mass and 0.7% by mass. Having a Ga content within a specified range tends to improve magnetic properties. Furthermore, the lower the Ga content, the less likely the 6-13-1 phase is to precipitate.

[0060] There are no particular restrictions on the amount of Al (aluminum) contained. For example, it may be between 0.1% by mass and 0.5% by mass, or between 0.1% by mass and 0.4% by mass. Having an Al content within a specified range tends to improve magnetic properties.

[0061] Furthermore, the RTB-type permanent magnet alloy according to this embodiment may contain Zr in addition to rare earth elements, Fe, Co, B, and M. There are no particular restrictions on the Zr content. For example, it may be 0.0% by mass or more and 0.7% by mass or less, 0.15% by mass or more and 0.7% by mass or less, or 0.3% by mass or more and 0.5% by mass or less. If the Zr content is too high, the magnetic properties, especially Br and Hk / HcJ, tend to deteriorate.

[0062] The content of Fe is the substantial remainder among the components of the alloy for R-T-B permanent magnets. That the content of Fe is the substantial remainder means the case where the total content of elements other than R, Fe, Co, B, M, and Zr is 0.2 mass% or less.

[0063] The R-T-B permanent magnet manufactured using the alloy for R-T-B permanent magnets according to this embodiment is processed into an arbitrary shape and used. The shape of the R-T-B permanent magnet is not particularly limited, and for example, it can be in an arbitrary shape such as a rectangular parallelepiped, hexahedron, flat plate shape, columnar shape such as a quadrangular prism, and a cylindrical shape with a C-shaped cross section of the R-T-B permanent magnet.

[0064] Also, the R-T-B permanent magnet includes both a magnet product magnetized with the magnet and a magnet product not magnetized with the magnet.

[0065] <Manufacturing method of alloy for R-T-B permanent magnet> As an example of a method for manufacturing an alloy for R-T-B permanent magnets, a method of manufacturing by the strip casting method will be described.

[0066] The casting device may have components well-known as components of a general casting device, such as a refractory crucible, tundish, cooling roll, and recovery container. There is no particular limitation on the type of refractory crucible. For example, an alumina crucible, mullite crucible, zirconia crucible, etc. can be mentioned. There is no particular limitation on the material of the cooling roll. For example, copper, copper alloy, those with plating or thermal spraying on the surface of copper, those with plating or thermal spraying on the surface of copper alloy, etc. can be mentioned.

[0067] First, raw materials are weighed and mixed so as to have the alloy composition of the target alloy for R-T-B permanent magnets to obtain a raw material mixture.

[0068] Next, the obtained raw material mixture is loaded into a refractory crucible, and the loaded raw material mixture is melted to obtain a molten alloy. There are no particular restrictions on the method of melting the raw material mixture. For example, one method is to place the refractory crucible loaded with the raw material mixture in a high-frequency vacuum induction furnace and heat it.

[0069] The resulting molten alloy is then cast to obtain a cast alloy strip (RTB-type permanent magnet alloy). Specifically, the molten alloy is supplied via a tundish to a cooling roll whose interior is water-cooled. The molten alloy supplied onto the cooling roll is cooled and detaches from the cooling roll on the opposite side of the tundish, becoming a cast alloy strip.

[0070] The cast alloy strip is crushed by a crusher placed between the cooling roll and the recovery container, resulting in flake-shaped cast alloy flakes. These flake-shaped cast alloy flakes then accumulate as sediment within the recovery container.

[0071] In a cast alloy strip, the surface in contact with the cooling roll is the roll surface, and the surface opposite the roll surface is the free surface. Distinguishing between the roll surface and the free surface is also possible in flake-shaped RTB-type permanent magnet alloys.

[0072] There are no particular restrictions on the temperature of the molten alloy. For example, 1300-1600°C. There are no particular restrictions on the peripheral speed of the cooling roll. For example, 0.5-2.5 m / s. There are no particular restrictions on the supply rate of the molten alloy to the cooling roll. For example, 0.5-2.5 kg / (min·cm).

[0073] A thin strip of cast alloy is crushed to obtain flake-shaped cast alloy flakes. Then, the flake-shaped cast alloy flakes are cooled in a recovery container.

[0074] Generally, the cooling of the cast alloy using cooling rolls is sometimes called primary cooling, and the cooling of the cast alloy in a recovery container is sometimes called secondary cooling. In this embodiment, the area ratio of the 6-13-1 phase can be reduced by adjusting the cooling rate during secondary cooling.

[0075] Among the secondary cooling processes, particularly by increasing the cooling rate between 600°C and 400°C, the area ratio of the 6-13-1 phase can be reduced. Specifically, the average cooling rate between 600°C and 400°C is set to 0.7°C / second or more. Although there is no particular upper limit for the average cooling rate between 600°C and 400°C, for example, it is 10°C / second or less. The faster the average cooling rate between 600°C and 400°C, the less likely the R-rich phase interval is to increase.

[0076] When the casting alloy has already reached 600°C or less when it enters the recovery container, the above-mentioned 600°C is read as the temperature at the time when the casting alloy enters the recovery container (hereinafter, may be referred to as the maximum temperature).

[0077] Conventionally, mainly by controlling the cooling rate in primary cooling, it has been widely practiced to control the cooling rate in a relatively high temperature range from the melting point to 600°C. In contrast, in this embodiment, by controlling the cooling rate in secondary cooling and making the cooling rate particularly high in the temperature range of 600°C or less, the area ratio of the 6-13-1 phase is reduced. And by reducing the area ratio of the 6-13-1 phase, even if the dehydrogenation temperature in hydrogen storage crushing is increased, no punctate phase occurs, and finally the magnetic properties of the obtained magnet can be improved.

[0078] In order to make the cooling rate high in the temperature range of 600°C or less, first, a crusher is installed between the cooling roll and the recovery container to crush the cast alloy ribbon after primary cooling to obtain flaky cast alloy flakes. Then, a cooling device is installed in the recovery container to cool the cast alloy flakes. There is no particular limitation on the type of the cooling device, and examples include cooling plates such as Cu plates and Fe plates. There is also a method of flowing an inert gas as a cooling gas into the recovery container.

[0079] If an attempt is made to increase the cooling rate in secondary cooling by strengthening the capacity of the cooling device, the manufacturing cost increases. In this embodiment, the capacity of the cooling device is deliberately strengthened to increase the cooling rate in secondary cooling.

[0080] <Method for manufacturing R-T-B-based permanent magnet> There are no particular restrictions on the method for manufacturing RTB-type permanent magnets using the flake-shaped RTB-type permanent magnet alloy manufactured by the method described above. For example, a method having the following steps can be cited. (a) Grinding process for grinding RTB-type permanent magnet alloys (b) Molding process for forming the obtained alloy powder (c) Sintering process to obtain an RTB-type permanent magnet by sintering the molded body. (d) Aging process for RTB permanent magnets (e) Cooling process for cooling RTB permanent magnets (f) Processing steps for RTB-type permanent magnets (g) Grain boundary diffusion process for diffusing heavy rare earth elements into the grain boundaries of RTB permanent magnets (h) Surface treatment process for RTB permanent magnets

[0081] [Grinding process] The flake-shaped RTB-type permanent magnet alloy is crushed (crushing process). The crushing process consists of a coarse crushing process, in which the material is crushed until the particle size is several hundred micrometers to several millimeters, and a fine crushing process, in which the material is crushed until the particle size is several micrometers.

[0082] (Coarse grinding process) The RTB-type permanent magnet alloy is coarsely ground until the particle size is several hundred micrometers to several millimeters (coarse grinding process). This yields coarsely ground powder of the RTB-type permanent magnet alloy. Coarse grinding can be achieved, for example, by adsorbing hydrogen into the RTB-type permanent magnet alloy, then releasing hydrogen based on the difference in hydrogen storage amounts between different phases, thereby causing self-destructive grinding. This type of grinding is called hydrogen decomposition.

[0083] Furthermore, the oxygen concentration in each manufacturing process is adjusted by controlling the atmosphere, etc. From the viewpoint of obtaining high magnetic properties, the oxygen content of the final RTB-type permanent magnet may be reduced. To this end, the oxygen concentration in each process from the pulverization process to the sintering process described later may be set to 100 ppm or less.

[0084] When crushing an RTB-type permanent magnet alloy with a small area ratio of phase 6-13-1 according to this embodiment, it becomes easier to maintain the magnetic properties, especially the square aspect ratio, favorably even when the dehydrogenation temperature is high. The dehydrogenation temperature is preferably 530°C to 650°C. If the dehydrogenation temperature is too low, cracks are likely to occur in the RTB-type permanent magnet after molding and sintering. If the dehydrogenation temperature is too high, point-like phases 17 are likely to occur in the coarsely crushed powder of the RTB-type permanent magnet alloy after dehydrogenation.

[0085] (Fine grinding process) After coarsely grinding the RTB-type permanent magnet alloy, the resulting coarsely ground powder of the RTB-type permanent magnet alloy is finely ground until the average particle size is about a few micrometers (fine grinding step). This yields finely ground powder of the RTB-type permanent magnet alloy. By further fine grinding the coarsely ground powder, it is possible to obtain finely ground powder having particles of, for example, 1 μm to 10 μm or 3 μm to 5 μm.

[0086] Fine grinding is carried out by further grinding the coarsely ground powder using a fine grinding machine such as a jet mill, ball mill, vibratory mill, or wet attritor, while appropriately adjusting conditions such as grinding time. A jet mill is a method of grinding by releasing a high-pressure inert gas (for example, N2 gas) from a narrow nozzle to generate a high-speed gas flow, which accelerates the coarsely ground raw alloy powder, causing collisions between the coarsely ground raw alloy powders themselves or with a target or container wall.

[0087] When finely grinding the coarse powder of the raw alloy, adding grinding aids such as zinc stearate, urea, stearamide, and oleamide makes it possible to obtain a finely ground powder with high orientation during molding.

[0088] [Molding process] The finely ground powder is molded into the desired shape (molding process). In the molding process, the finely ground powder is filled into a mold held by an electromagnet and pressurized to mold it into the desired shape. This is done while applying a magnetic field, which causes the finely ground powder to have a predetermined orientation, and the molding is performed in the magnetic field with the crystal axes oriented. This yields a molded body. Since the resulting molded body is oriented in a specific direction, an RTB-type permanent magnet with stronger anisotropy is obtained.

[0089] The pressure applied during molding may be 30 MPa to 300 MPa. The applied magnetic field may be 950 kA / m to 1600 kA / m. The applied magnetic field is not limited to a static magnetic field; a pulsed magnetic field can also be used. Furthermore, a combination of a static magnetic field and a pulsed magnetic field can be used.

[0090] In addition to dry molding, which involves molding the finely ground powder as described above, wet molding can also be applied, which involves molding a slurry in which the finely ground powder is dispersed in a solvent such as oil.

[0091] The shape of the molded body obtained by molding the finely ground powder is not particularly limited and can be any shape depending on the desired shape of the RTB-type permanent magnet, such as a rectangular parallelepiped, flat plate, columnar shape, or ring shape.

[0092] [Sintering process] The molded body, formed in a magnetic field to obtain the desired shape, is sintered in a vacuum or inert gas atmosphere to obtain an RTB-type permanent magnet (sintering process). The sintering temperature needs to be adjusted depending on various conditions such as composition, grinding method, particle size and particle size distribution. The molded body is sintered by heating, for example, in a vacuum or in the presence of an inert gas at a temperature of 1000°C to 1200°C for 1 to 48 hours. This causes liquid-phase sintering of the finely ground powder, resulting in an RTB-type permanent magnet (sintered body of an RTB-type magnet) with an improved volume ratio of main phase particles. After sintering the molded body to obtain the sintered body, the sintered body may be rapidly cooled to improve production efficiency.

[0093] In particular, when the boron content in RTB-type permanent magnet alloys is low, magnets with desirable properties can be easily obtained by performing sintering at relatively low temperatures and for relatively long periods of time. Furthermore, even with a low boron content in RTB-type permanent magnet alloys, magnets with desirable properties can be easily obtained by ensuring a sufficiently high carbon content.

[0094] [Statute of Limitations Treatment Process] After sintering the molded body, the RTB-type permanent magnet is subjected to aging treatment (aging treatment step). After sintering, the obtained RTB-type permanent magnet is subjected to aging treatment by holding it at a lower temperature than that used during sintering. The aging treatment can be performed in two stages, such as heating at a temperature of 700°C to 1000°C for 10 minutes to 6 hours, and then at a temperature of 500°C to 700°C for 10 minutes to 6 hours, or in one stage, such as heating at a temperature of around 600°C for 10 minutes to 6 hours. The treatment conditions are adjusted as appropriate depending on the number of times the aging treatment is performed. Such aging treatment can improve the magnetic properties of the RTB-type permanent magnet. The aging treatment step may also be performed after the processing step described later.

[0095] [Cooling process] After aging treatment is performed on the RTB-type permanent magnet, the RTB-type permanent magnet is rapidly cooled in an Ar gas atmosphere (cooling step). This allows the RTB-type permanent magnet according to this embodiment to be obtained. The cooling rate is not particularly limited and may be 30°C / min or higher.

[0096] [Processing process] The resulting RTB-type permanent magnets may be processed into the desired shape as needed (processing step). Processing methods include, for example, shaping such as cutting and grinding, and chamfering such as barrel polishing.

[0097] [Grain boundary diffusion process] Further diffusion of heavy rare earth elements into the grain boundaries of the processed RTB-based permanent magnet is possible (grain boundary diffusion process). There are no particular restrictions on the method of grain boundary diffusion. For example, it may be carried out by applying a compound containing heavy rare earth elements to the surface of the RTB-based permanent magnet by coating or vapor deposition, followed by heat treatment. Alternatively, it may be carried out by heat treatment of the RTB-based permanent magnet in an atmosphere containing heavy rare earth element vapor. Grain boundary diffusion can further improve the HcJ of the RTB-based permanent magnet.

[0098] [Surface treatment process] The RTB-type permanent magnets obtained through the above process may be subjected to surface treatments such as plating, resin coating, oxidation treatment, or chemical conversion treatment (surface treatment process).

[0099] In this embodiment, processing steps, grain boundary diffusion steps, and surface treatment steps are performed, but these steps are not necessarily required.

[0100] The above describes the case where a magnet is fabricated using a single alloy method, in which a magnet is fabricated from one type of alloy having a composition close to that of the final magnet. The method for fabricating the magnet according to this embodiment is not limited to the single alloy method. For example, a two-alloy method may be used, in which a magnet is fabricated from two types of alloys: a main phase alloy that mainly constitutes the main phase and a grain boundary phase alloy that mainly constitutes the grain boundary phase. At least the main phase alloy is the RTB-type permanent magnet alloy according to this embodiment. In addition to the main phase alloy, the grain boundary phase alloy may also be the RTB-type permanent magnet alloy according to this embodiment.

[0101] When using the two-alloy method, the composition of the main phase alloy, the composition of the grain boundary phase alloy, and the mixing ratio of the main phase alloy and the grain boundary phase alloy are determined according to the composition of the target RTB-type permanent magnet. Other points are the same as when using the one-alloy method.

[0102] When the main phase alloy and grain boundary phase alloy are mixed such that the proportion of the main phase alloy to the total amount of the main phase alloy and grain boundary phase alloy is 85% by mass or more, the characteristics of the main phase alloy become dominant in the final RTB-type permanent magnet. In other words, the properties of the final RTB-type permanent magnet can be suitably controlled by controlling the area ratio of the 6-13-1 phase in the cross-section of the main phase alloy.

[0103] In particular, when the main phase alloy and grain boundary phase alloy are mixed in a mixing ratio of main phase alloy:grain boundary phase alloy = 85:15 to 95:5 (by mass), and the area ratio of the 6-13-1 phase in the cross-section of the main phase alloy is 7.0% or less, cracks are less likely to occur in the final RTB-type permanent magnet, and the magnetic properties of the final RTB-type permanent magnet are improved.

[0104] The method for preparing the main phase alloy is the same as the method for preparing RTB-type permanent magnet alloys when using the single-alloy method.

[0105] There are no particular restrictions on the area ratio of the 6-13-1 phase in the grain boundary alloy. The area ratio of the 6-13-1 phase in the grain boundary alloy may be 50% or less, or 30% or less. The area ratio of the α-Fe phase in the grain boundary alloy may be 10% or less, or 5% or less.

[0106] There are no particular restrictions on the method for producing the grain boundary phase alloy. The method may be the same as that used for producing RTB-type permanent magnet alloys when using the single-alloy method. In particular, by setting the average cooling rate at 600°C to 400°C to 0.7°C / second or higher, it is easier to obtain a grain boundary phase alloy in which the area ratio of the 6-13-1 phase and the area ratio of the α-Fe phase are within the above range.

[0107] The RTB-based permanent magnet obtained according to this embodiment has good magnetic properties and a wide sintering temperature range. As a result, the RTB-based permanent magnet according to this embodiment is a magnet that can be produced stably.

[0108] The RTB-type permanent magnet obtained in this manner according to this embodiment is suitably used as a magnet in, for example, a surface permanent magnet (SPM) rotating machine with magnets attached to the rotor surface, an interior permanent magnet (IPM) rotating machine such as an inner rotor type brushless motor, and a PRM (Permanent magnet Reluctance Motor). Specifically, the RTB-type permanent magnet according to this embodiment is suitably used in applications such as spindle motors and voice coil motors for hard disk rotation drive in hard disk drives, motors for electric vehicles and hybrid cars, motors for electric power steering in automobiles, servo motors for machine tools, motors for vibrators in mobile phones, motors for printers, and motors for generators.

[0109] This disclosure is not limited to the embodiments described above, and can be modified in various ways within the scope of this disclosure. [Examples]

[0110] The invention will be described in more detail below with reference to examples, but this disclosure is not limited to these examples.

[0111] (Experimental Example 1) (Fabrication of alloys for RTB-type permanent magnets) Nd metal (purity 99% by mass or higher), Nd-Pr alloy (didymium, purity 99% by mass or higher), ferroboron (Fe content 80% by mass, B content 20% by mass), Fe metal (purity 99% by mass or higher), Co metal (purity 99% by mass or higher), Zr metal (purity 99% by mass or higher), Cu metal (purity 99% by mass or higher), Al metal (purity 99% by mass or higher), and / or Ga metal (purity 99% by mass or higher) were weighed and mixed to obtain the raw material mixtures shown in Table 1 below. In Table 1, "TRE" represents the total content (by mass) of rare earth elements (Nd and Pr). The carbon content in all RTB permanent magnet alloys is between 0 and 0.03% by mass. "bal." represents the remainder. The reason for indicating the Fe content as "bal." is to show that the Fe content is the remainder when the total RTB permanent magnet alloy containing elements other than those listed in Table 1 is considered as 100% by mass.

[0112] The obtained raw material mixture was loaded into an alumina crucible, which is a refractory crucible. The alumina crucible loaded with the raw material mixture was placed in a high-frequency vacuum induction furnace, and the inside of the high-frequency vacuum induction furnace was replaced with Ar. Then, by heating the inside of the high-frequency vacuum induction furnace, the raw material mixture loaded into the alumina crucible was melted to obtain molten alloy. The molten alloy obtained by the strip casting method was cast to obtain a cast alloy strip (RTB-type permanent magnet alloy). The casting was carried out in an Ar atmosphere. Furthermore, the cast alloy strip was crushed using a crusher placed between the cooling roll and the recovery container, and the resulting flake-like cast alloy flakes were deposited as sediment in the recovery container.

[0113] The temperature of the molten alloy (casting temperature) was set to 1300-1550°C. The material of the cooling roll was a copper alloy. The peripheral speed of the cooling roll was set to 1 m / s. The supply rate of molten metal to the cooling roll (supply rate per unit contact width between the molten metal and the cooling roll) was set to 1.2 kg / (min·cm).

[0114] The average cooling rate within the recovery container was controlled by appropriately installing a cooling device inside the container. The temperature of the sediment was measured by pre-positioning the tip of a sheathed thermocouple near the center of the sediment. The average cooling rate of the sediment was then calculated from the temperature change of the sediment. The RTB-type permanent magnet alloy was obtained by cooling the sediment.

[0115] In Experimental Example 1, the average cooling rate of the sediment in the collection container was set to 1.8°C / second between 600°C and 400°C. In Experimental Example 1, the maximum temperature of the sediment was between 400°C and 600°C in all examples and comparative examples. When the maximum temperature was between 400°C and 600°C, the average cooling rate from the maximum temperature to 400°C was considered to be the average cooling rate between 600°C and 400°C.

[0116] (Measurement of the area ratio of each phase) The area ratio of each phase in the RTB-type permanent magnet alloy was measured using an electron microscope.

[0117] First, evaluation samples were collected. Specifically, in the process of supplying one manufacturing lot of RTB-type permanent magnet alloy by the strip casting method described above, flake-shaped RTB-type permanent magnet alloy (hereinafter, flake-shaped RTB-type permanent magnet alloy may be simply referred to as alloy pieces) supplied at regular time intervals was sampled. Specifically, 30 alloy pieces were randomly selected and each alloy piece was used as an evaluation sample.

[0118] Next, the thickness of the collected evaluation samples was measured. Of the 30 evaluation samples, the 2nd, 3rd, and 4th thickest samples were selected as thickened samples, the 14th, 15th, and 16th thickest samples were selected as near-average samples, and the 27th, 28th, and 29th thickest samples were selected as thinned samples.

[0119] Next, the nine selected evaluation samples were glued together with super glue, and processed so that a cross-section parallel to the thickness direction could be observed. When gluing the evaluation samples together, they were arranged in a way that made it clear which samples were thicker, near-average, or thin.

[0120] Next, the nine evaluation samples, which had been glued together with instant adhesive, were combined and embedded in resin to form a single embedded resin sample. Then, the cross-section parallel to the thickness direction was polished to a mirror finish to create the observation surface.

[0121] Next, the imaging mode was set to backscattered electron imaging, with a magnification of 2500x and a resolution of 1280 x 960 pixels, and the observation range was defined. The entire surface from the roll surface to the free surface was observed by scanning from the roll surface to the free surface. Specifically, images were continuously captured from the roll surface to the free surface. The number of images for each observation range was set to between 7 and 10. Nine observation ranges were then set and observed. One observation range was set for each evaluation sample. In addition, the observation range was selected from the observation surface of each evaluation sample to represent the average condition.

[0122] Next, the area ratio of each phase within the observation range was calculated by analysis. Then, the area ratio of each phase in the cross-section of each evaluation sample was averaged to calculate the area ratio of each phase in the cross-section of one manufacturing lot of RTB-type permanent magnet alloy. The results are shown in the tables.

[0123] The presence or absence and area ratio of phases 2-17 were confirmed by backscattered electron imaging. Furthermore, in all examples, the absence of a point phase before the hydrogen storage described later was confirmed by backscattered electron imaging.

[0124] (Measurement of average R-rich phase interval) The brightness of the backscattered electron image was adjusted for the observation range described above. Next, measurement lines perpendicular to the thickness direction of the alloy piece were set at 10 μm intervals. The length of each measurement line was set to 189 μm. The average R-rich phase spacing was then calculated by dividing the sum of the R-rich phase spacings for each measurement line by the number of measurement lines.

[0125] (Fabrication of RTB-type permanent magnets) In this example, an alloy for RTB-type permanent magnets was subjected to hydrogen absorption at room temperature, followed by dehydrogenation in an Ar atmosphere at 600°C for 2 hours to obtain alloy powder (coarsely ground powder). In this example, each step from the hydrogen absorption treatment to sintering (fine grinding and molding) was carried out in a low-oxygen atmosphere with an oxygen concentration of less than 50 ppm.

[0126] Next, zinc stearate and stearamide were added to the alloy powder as grinding aids and mixed using a Nauta mixer. The amount of zinc stearate added was 0.05 parts by mass per 100 parts by mass of coarsely ground powder. The amount of stearamide added was also 0.05 parts by mass per 100 parts by mass of coarsely ground powder. After that, the powder was finely ground using a jet mill to obtain a finely ground powder with an average particle size of approximately 3.2 μm.

[0127] The obtained finely ground powder was filled into a mold placed in an electromagnet, and a molded body was obtained by magnetic field molding, which was performed by applying a magnetic field of 1200 kA / m and a pressure of 120 MPa.

[0128] Subsequently, the obtained molded body was sintered by holding it in a vacuum at 1050°C for 4 hours, and then rapidly cooled to obtain a sintered body having the magnet composition shown in Table 1. The obtained sintered body was then subjected to a two-stage aging treatment at 900°C for 1 hour and at 500°C for 1 hour (both under an Ar atmosphere) to obtain an RTB-type permanent magnet (RTB-type sintered magnet).

[0129] [Magnetic properties] The Br, HcJ, and Hk / HcJ values ​​of RTB permanent magnets were measured at room temperature using a BH tracer. The presence or absence of cracks in the RTB magnets was confirmed visually. The results are shown in Table 1.

[0130] For the overall evaluation, an A rating was given if the Hk / HcJ ratio was 90% or higher, the HcJ ratio was 1600kA / m or higher, the Br ratio was 1225mT or higher, and no cracks were observed. A B rating was given if the Hk / HcJ ratio was 85% or higher, the HcJ ratio was 1200kA / m or higher, the Br ratio was 1100mT or higher, and it did not receive an A rating. A C rating was given if it did not receive either an A or a B rating. An A or B rating was considered good, and an A rating was considered particularly good.

[0131] [Table 1]

[0132] Table 1 shows that RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with a 6-13-1 phase area ratio of 7.0% or less exhibited good properties. In contrast, sample number 2, which had a low B content, and sample number 12, which had a high Zr content, had an excessively large 6-13-1 phase area ratio. Furthermore, RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with an excessively large 6-13-1 phase area ratio did not exhibit good properties.

[0133] (Experimental Example 2) Samples 19-22 were conducted under the same conditions as sample 1 in Experimental Example 1, except that the average cooling rate was changed.

[0134] Sample No. 19 was prepared so that the maximum temperature of the sediment exceeded 600°C, and the average cooling rate between 800°C and 600°C was 0.3°C / second, and the average cooling rate between 600°C and 400°C was 0.2°C / second. If the maximum temperature was above 600°C but below 800°C, the average cooling rate from the maximum temperature to 600°C was considered to be the average cooling rate between 800°C and 600°C.

[0135] Samples 20-22 were prepared so that the average cooling rate of the sediment between 600°C and 400°C was as shown in Table 2. For samples 20-22, the maximum temperature of the sediment was between 400°C and 600°C.

[0136] Samples 23 and 24 were conducted under the same conditions as sample 1 in Experimental Example 1, except that the sediment was kept warm in the collection container. Specifically, the sediment was kept warm for the warming time and temperature shown in Table 2. After that, it was cooled to room temperature. The average cooling rate from the warming temperature to 400°C was set to 2.5°C / second.

[0137] For sample number 25, the RTB-type permanent magnet alloy was prepared under the same conditions as for sample number 1. The only difference was that the dehydrogenation temperature for the RTB-type permanent magnet was set to 500°C.

[0138] [Table 2]

[0139] Table 2 shows that RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with a 6-13-1 phase area ratio of 7.0% or less exhibited good properties. In contrast, sample number 19, which had a low average cooling rate, and sample number 23, which was kept at 580°C for 1 hour, had an excessively large area of ​​the 6-13-1 phase. RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with an excessively large area of ​​the 6-13-1 phase did not exhibit good properties.

[0140] (Experimental Example 3) The experiment was conducted under the same conditions as in Experiment 1, except that the composition of the RTB-type permanent magnet alloy was changed. The results are shown in Table 3.

[0141] [Table 3]

[0142] Table 3 shows that RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with a 6-13-1 phase area ratio of 7.0% or less exhibited good properties. In contrast, sample number 32, which had a low B content, and sample number 40, which had a high Zr content, had excessively large 6-13-1 phase areas. Furthermore, RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with excessively large 6-13-1 phase areas did not exhibit good properties.

[0143] (Experimental Example 4) Samples 41 and 42 were conducted under the same conditions as sample 31 in Experimental Example 3, except that the average cooling rate was changed.

[0144] Sample No. 41 was prepared so that the maximum temperature of the sediment exceeded 600°C, and the average cooling rate between 800°C and 600°C was 0.3°C / second, and the average cooling rate between 600°C and 400°C was 0.2°C / second. If the maximum temperature was above 600°C but below 800°C, the average cooling rate from the maximum temperature to 600°C was considered to be the average cooling rate between 800°C and 600°C.

[0145] Sample No. 42 was prepared so that the average cooling rate of the sediment between 600°C and 400°C was 10.0°C / second. The maximum temperature of the sediment in Sample No. 42 was between 400°C and 600°C.

[0146] Samples 43 and 44 were conducted under the same conditions as sample 31 in Experimental Example 3, except that the sediment was kept warm in the collection container. Specifically, the sediment was kept warm for the warming time and temperature shown in Table 4. After that, it was cooled to room temperature. The average cooling rate from the warming temperature to 400°C was set to 2.5°C / second.

[0147] For sample number 45, the RTB-type permanent magnet alloy was prepared under the same conditions as for sample number 31. The only difference was that the dehydrogenation temperature for the RTB-type permanent magnet was set to 500°C.

[0148] [Table 4]

[0149] Table 4 shows that RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with a 6-13-1 phase area ratio of 7.0% or less exhibited good properties. In contrast, sample number 41, which had a low average cooling rate, and sample number 43, which was kept warm at 580°C for 1 hour, had an excessively large 6-13-1 phase area ratio. RTB-type permanent magnets fabricated using RTB-type permanent magnet alloys with an excessively large 6-13-1 phase area ratio did not exhibit good properties.

[0150] (Experimental Example 5) Sample No. 32a was prepared under the same conditions as Sample No. 32 in Experimental Example 3, except that the sintering temperature was 1000°C and the sintering time was 48 hours. Sample No. 46 was prepared under the same conditions as Sample No. 32 in Experimental Example 3, except that the content of B was varied and the sintering temperature was 1000°C and the sintering time was 48 hours. Sample No. 46a was prepared under the same conditions as Sample No. 32 in Experimental Example 3, except that the content of B was varied. The results are shown in Table 5.

[0151] [Table 5]

[0152] Table 5 shows that even when the B content was lower than that of the examples shown in Tables 1 to 4, an RTB-based permanent magnet alloy was obtained in which the area ratio of the 6-13-1 phase was 7.0% or less. Furthermore, RTB-based permanent magnets made using this RTB-based permanent magnet alloy and sintered at relatively low temperatures and for relatively long periods of time exhibited good properties.

[0153] In contrast, when using an RTB-type permanent magnet alloy in which the area ratio of the 6-13-1 phase is too large due to a low B content, RTB-type permanent magnets with good properties could not be obtained even when sintering was performed at relatively low temperatures and for relatively long periods of time.

[0154] (Experimental Example 6) Samples 47 and 48 were prepared using the two-alloy method. The composition and microstructure of the main phase alloy are shown in Table 6. The composition of the grain boundary phase alloy is shown in Table 7. It was confirmed that the area ratio of the 6-13-1 phase in the grain boundary phase alloy was 4.0%, and that the grain boundary phase alloy did not contain the α-Fe phase.

[0155] For the preparation conditions of main phase alloys 1 and 2, the maximum temperature of the deposit was set to exceed 400°C. Furthermore, the average cooling rate between 600°C and 400°C was set to 2.2°C / second. No heat retention measures were taken for the deposit within the recovery container.

[0156] For the preparation conditions of grain boundary phase alloy No. 1, the maximum temperature of the deposit was set to exceed 600°C. Furthermore, the average cooling rate from 800°C to 600°C was set to 3.5°C / second, and the average cooling rate from 600°C to 400°C was set to 3.0°C / second. No heat retention measures were taken for the heat-resistant material within the recovery container.

[0157] In sample number 47, the main phase alloy of main phase alloy number 1 and the grain boundary phase alloy of grain boundary phase alloy number 1 were mixed in a ratio of 93:7. In sample number 48, the main phase alloy of main phase alloy number 2 and the grain boundary phase alloy of grain boundary phase alloy number 1 were mixed in a ratio of 90:10. For all other aspects, the magnets were fabricated under the same conditions as sample number 32 in Experimental Example 3. The composition and properties of the obtained magnets are shown in Table 8.

[0158] [Table 6]

[0159] [Table 7]

[0160] [Table 8]

[0161] Tables 6 to 8 show that even when the B content in the main phase alloy was 0.75% by mass or 0.78% by mass, increasing the C content in the main phase alloy compared to other examples and comparative examples tended to lower the area ratio of the 6-13-1 phase in the main phase alloy. As a result, a main phase alloy with an area ratio of 7.0% or less of the 6-13-1 phase was obtained. RTB-type permanent magnets fabricated using the two-alloy method with such a main phase alloy exhibited good properties.

[0162] Trinarization was performed on the backscattered electron images obtained by observing all alloys shown in Tables 1 to 5, and all main phase alloys shown in Table 6, using the K-meaning method. Trinarization confirmed that the backscattered electron images contained a white phase with a brightness of 201 to 255, a main phase with a brightness of 0 to 119, and an intermediate phase with a brightness of 120 to 200. It was then confirmed that the intermediate phase was the 6-13-1 phase. Specifically, it was confirmed that the value obtained by dividing the total ratio of Fe and Co in the intermediate phase by the total ratio of rare earth elements was greater than 1.0 and less than or equal to 3.0 on an atomic basis. [Explanation of Symbols]

[0163] 11…White phase (R-rich phase) 13…6-13-1 phase (R-rich phase) 15…Main phase 17...Point-like phase 21... Measurement line 101…R-Rich Phase

Claims

1. An R-T-B system permanent magnet alloy comprising rare earth elements, Fe and / or Co, boron, and M, M is one or more selected from Ga, Al, Cu, Zn, In, P, Sb, Si, Ge, Sn, and Bi. The aforementioned R-T-B permanent magnet alloy comprises a main phase and an R-rich phase. An R-T-B permanent magnet alloy in which the area ratio of the 6-13-1 phase, which is a type of R-rich phase, in the cross-section of the R-T-B permanent magnet alloy is 7.0% or less.

2. The R-T-B alloy for permanent magnets according to claim 1, wherein the area ratio of the 6-13-1 phase is 1.0% or more and 6.5% or less.

3. The R-T-B permanent magnet alloy according to claim 1 or 2, wherein the area ratio of the 2-17 phase in the cross-section of the R-T-B permanent magnet alloy is 2.0% or less.

4. The R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the boron content is 0.78% by mass or more and 0.95% by mass or less.

5. The R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the boron content is 0.80% by mass or more and 0.95% by mass or less.

6. The R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the boron content is 0.83% by mass or more and 0.90% by mass or less.

7. An R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the boron content is 0.75% by mass or more and 0.95% by mass or less, and the carbon content is 0.05% by mass or more and 0.25% by mass or less.

8. The R-T-B permanent magnet alloy according to claim 7, wherein the sum of the boron content and the carbon content is 0.80% by mass or more and 1.20% by mass or less, and the value obtained by dividing the carbon content by the boron content is 0.05 or more and 0.33 or less.

9. The R-T-B permanent magnet alloy according to claim 1 or 2, wherein the Ga content is 0.10% by mass or more and 0.70% by mass or less.

10. The R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the total content of rare earth elements is 30.0% by mass or more and 33.0% by mass or less.

11. The R-T-B alloy for permanent magnets according to claim 1 or 2, wherein the total content of rare earth elements is 30.0% by mass or more and 33.0% by mass or less, the content of Al is 0.1% by mass or more and 0.4% by mass or less, the content of Co is 0.4% by mass or more and 1.1% by mass or less, the content of Cu is 0.05% by mass or more and 0.2% by mass or less, the content of Zr is 0.15% by mass or more and 0.7% by mass or less, and the content of Ga is 0.10% by mass or more and 0.70% by mass or less.

12. The process of solidifying molten alloy to obtain a cast alloy strip, A step of crushing the aforementioned cast alloy strip to obtain a cast alloy flake, The process includes a step of cooling the cast alloy thin sheet, A method for manufacturing an R-T-B type permanent magnet alloy, wherein the cooling rate from 600°C to 400°C in the step of cooling the cast alloy thin sheet is 0.7°C / second or more.

13. The process comprises a step of hydrogenating the R-T-B permanent magnet alloy described in claim 1 or 2, A method for manufacturing an R-T-B permanent magnet, wherein the dehydrogenation temperature in the hydrogen decomposition step is 530°C or higher and 650°C or lower.

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