Manufacturing method of rare-earth magnet

Abstract

To provide a manufacturing method of a rare-earth magnet, capable of improving a magnetic characteristic of a magnet.SOLUTION: A manufacturing method of a rare-earth magnet of the present invention, comprises: a step of preparing a base powder containing a magnetic powder containing Sm, Fe, and N; a step of adjusting packing density of the base powder to 4.0 g / cm3 to 5.5 g / cm3 by compressing the base powder; a step of distributing the magnetic powder contained in the base powder by applying a magnetic field to the base powder after the adjustment of the packing density; and a step of obtaining a sinter body by performing a compression sinter of the base powder after the distribution of the magnetic powder.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing an SmFeN rare earth magnet containing Sm, Fe, and N. [Background technology]

[0002] Conventionally, a method for manufacturing SmFeN-based rare earth magnets has been adopted in which magnetic powder is pressure-sintered to manufacture magnets. As a method for manufacturing such rare earth magnets, a method for imparting magnetic anisotropy to a sintered body to improve magnetic properties is known. For example, a method is known in which a magnetic field molding method is used, which includes sandwiching raw powder containing magnetic powder between a pair of first members, further sandwiching the raw powder and the pair of first members between a pair of second members to obtain a laminate, and compressing the raw powder in the laminate by applying pressure to the laminate in the stacking direction, in which at least a part of the first member is a rare earth magnet and at least a part of the second member is a permendur-based alloy, and then pressure-sintering the magnetic field molding to obtain a magnetic field molding (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-141121 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for a method for producing SmFeN rare earth magnets that further improves the magnetic properties of the magnets. The present invention has been made in view of these circumstances, and an object of the present invention is to provide a method for producing rare earth magnets that can improve the magnetic properties of the magnets. [Means for solving the problem]

[0005] In order to solve the above problems, the method of the present invention for producing a rare earth magnet includes the steps of preparing a raw material powder containing a magnetic powder containing Sm, Fe, and N, and compressing the raw material powder to a bulk density of 4.0 g / cm. 3 ~5.5g / cm 3 a step of adjusting the bulk density of the raw material powder to a desired value, a step of applying a magnetic field to the raw material powder after adjusting the bulk density to orient the magnetic powder contained in the raw material powder, and a step of pressure sintering the raw material powder after orienting the magnetic powder to obtain a sintered body. Effect of the Invention

[0006] According to the present invention, the magnetic properties of the magnet can be improved. [Brief description of the drawings]

[0007] [Figure 1] 1A is a schematic perspective view of a die of a powder molding die according to one embodiment, and FIG. 1B is a schematic top view and schematic cross-sectional view of the die, upper punch, and lower punch of the powder molding die according to one embodiment. [Diagram 2] 1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Diagram 3] 1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Figure 4] 1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Diagram 5] FIG. 2 is a schematic diagram showing a mold according to an embodiment. [Figure 6] Graphs (a) to (c) show the bulk density [g / cm3] of the sintered body versus the bulk density [g / cm3] of the mixed powder (raw material powder) for the examples and comparative examples, the degree of orientation of the sintered body versus the bulk density of the mixed powder, and the residual magnetization [T] of the magnet versus the bulk density of the mixed powder, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] First, the method for manufacturing a rare earth magnet according to the embodiment will be described by exemplifying the method for manufacturing an SmFeN rare earth magnet according to one embodiment. FIG. 1(a) is a schematic perspective view of a die of a powder molding die according to one embodiment. FIG. 1(b) is a schematic top view and schematic cross-sectional view of the die, upper punch, and lower punch of a powder molding die according to one embodiment. FIGS. 2(a) to 4(c) are schematic process diagrams of a manufacturing method according to one embodiment. In these figures, the depth direction of the molding hole of the die of the die is the Z direction, one direction perpendicular to the Z direction is the X direction (width direction), and the direction perpendicular to the Z direction and the X direction is the Y direction (opposing direction). Each top view shown in FIG. 1(b) is a plan view from the Z direction, and each cross-sectional view shown in FIG. 1(b) is a view showing a cross section perpendicular to the Y direction passing through the center in the Y direction. The cross sections of the die shown in FIG. 2(c) to FIG. 4(b) are cross sections perpendicular to the X direction passing through the center in the X direction of the die, and the upper punch and the lower punch.

[0009] In a manufacturing method of a magnet according to one embodiment, a powder molding die 10 according to one embodiment shown in Fig. 1 and Fig. 2 is prepared in advance (die preparation step). The powder molding die 10 is a die used for molding raw powder containing magnetic powder, and includes a die 20, an upper punch 80, and a lower punch 90. The die 20 has a right cylindrical shape having an upper surface 20t and a lower surface (bottom surface) 20b parallel to the XY plane, and includes a frame portion 22 (plate portion) and an insert portion 30. The frame portion 22 and the insert portion 30 are made of a non-magnetic cemented carbide. The frame portion 22 is provided with a fitting hole 24 that penetrates in the Z direction from a central portion of the upper surface 22t to the lower surface 22b. The insert portion 30 is fitted into the fitting hole 24 of the frame portion 22. The upper opening 24t of the fitting hole 24 and the upper surface 30t of the insert part 30 are generally rectangular with short sides parallel to the X direction and long sides parallel to the Y direction with rounded corners. The lower opening 24b of the fitting hole 24 and the lower surface 30b of the insert part 30 are rectangular with short sides parallel to the X direction and long sides parallel to the Y direction. The side surfaces 24x on both sides in the X direction of the fitting hole 24 and the side surfaces 30x on both sides in the X direction of the insert part 30 have a tapered shape that inclines toward the center of the fitting hole 24 and the insert part 30 in the X direction (the center of the die in the X direction) as it moves from the upper end to the lower end along the Z direction. The side surfaces 30x on both sides in the X direction of the insert part 30 abut against the side surfaces 24x on both sides in the X direction of the fitting hole 24, respectively, so that the insert part 30 does not fall off the frame part 22. On the other hand, side surfaces 24y on both sides in the Y direction of the fitting hole 24 and side surfaces 30y on both sides in the Y direction of the insert portion 30 are provided parallel to the ZX plane. The side surfaces 30y on both sides in the Y direction of the insert portion 30 are in contact with the side surfaces 24y on both sides in the Y direction of the fitting hole 24, respectively.

[0010] The insert part 30 is provided with a molding hole 32 that penetrates in the Z direction from the center of the upper surface 30t to the lower surface 30b. The cross section of the molding hole 32 perpendicular to the Z direction is a square with two sides parallel to the X direction and two sides parallel to the Y direction. The insert part 30 is provided with a first magnet hole 34 and a second magnet hole 36 that penetrate in the Z direction from the upper surface 30t to the lower surface 30b on both sides of the molding hole 32 in the Y direction and communicate with the molding hole 32 from the upper end to the lower end along the Z direction. The first magnet hole 34 and the second magnet hole 36 have the same shape and size. The upper opening 34t of the first magnet hole 34 and the upper opening 36t of the second magnet hole 36, and the lower opening 34b of the first magnet hole 34 and the lower opening 36b of the second magnet hole 36 are approximately rectangular with long sides parallel to the X direction and short sides parallel to the Y direction and rounded corners. The side surfaces 34x on both sides in the X direction of the first magnet hole 34 and the side surfaces 36x on both sides in the X direction of the second magnet hole 36 have a tapered shape that inclines toward the center of each magnet hole in the X direction (the center of the die in the X direction) from the upper end to the lower end along the Z direction. Meanwhile, the side surfaces 34yf, 34yr on both sides in the Y direction of the first magnet hole 34 and the side surfaces 36yf, 36yr on both sides in the Y direction of the second magnet hole 36 are provided parallel to the ZX plane. The long sides of the upper opening 34t of the first magnet hole 34 and the upper opening 36t of the second magnet hole 36, and the long sides of the lower opening 34b of the first magnet hole 34 and the lower opening 36b of the second magnet hole 36 (the widths of the parts adjacent to the communication openings of the first and second magnet holes with the molding hole) are longer than the two sides parallel to the X direction of the cross section perpendicular to the Z direction of the molding hole 32 (the widths of the parts adjacent to the communication openings of the molding hole equal to the widths of the communication openings).

[0011] The mold 10 further includes a first magnet 40, a first magnetic plate 50, a second magnet 60, and a second magnetic plate 70. The first and second magnets have the same shape and dimensions, and are generally rectangular prisms with the Z direction as the height direction. The first and second magnets are SmCo magnets (samarium-cobalt magnets). Before the mold 10 is used in the manufacturing method according to one embodiment, the first and second magnets are not magnetized. The first and second magnetic plates are rectangular flat plates separated from the insert portion 30. The first and second magnetic plates have the same shape and dimensions, and are plate-shaped parallel to the ZX plane. The material of the first and second magnetic plates is SKD61.

[0012] The first magnet 40 and the second magnet 60 are embedded in the first magnet hole 34 and the second magnet hole 36 of the insert part 30, respectively, with a gap between them and the molding hole 32. The upper surface 40t of the first magnet 40 and the upper surface 60t of the second magnet 60 are flush with the upper surface 30t of the insert part 30. The lower surface 40b of the first magnet 40 and the lower surface 60b of the second magnet 60 are flush with the lower surface 30b of the insert part 30. The upper surface 40t and the lower surface 40b of the first magnet 40 and the upper surface 60t and the lower surface 60b of the second magnet 60 are approximately rectangular with long sides parallel to the X direction and short sides parallel to the Y direction, and with rounded corners. The side surface 40yr of the first magnet 40 opposite the molding hole 32 side in the Y direction abuts against the side surface 34yr of the first magnet hole 34 opposite the molding hole 32 side in the Y direction. Similarly, a side surface 60yr of the second magnet 60 opposite the molding hole 32 in the Y direction abuts a side surface 36yr of the second magnet hole 36 opposite the molding hole 32 in the Y direction. The first magnetic plate 50 is embedded in the gap on the molding hole 32 side of the first magnet hole 34 of the insert part 30 from the first magnet 40 so as to close the communication opening 35 with the molding hole 32, so that the thickness direction is the Y direction. Similarly, the second magnetic plate 70 is embedded in the gap on the molding hole 32 side of the second magnet hole 36 of the insert part 30 from the second magnet 60 so as to close the communication opening 37 with the molding hole 32, so that the thickness direction is the Y direction.

[0013] The side faces 50x on both sides in the X direction of the first magnetic plate 50 and the side faces 70x on both sides in the X direction of the second magnetic plate 70 have a tapered shape that inclines toward the center of each magnetic plate in the X direction (the center of the die in the X direction) from the upper end to the lower end along the Z direction. The side faces 50x on both sides in the X direction of the first magnetic plate 50 and the side faces 70x on both sides in the X direction of the second magnetic plate 70 are in contact with the side faces 34x on both sides in the X direction of the first magnet hole 34 and the side faces 36x on both sides in the X direction of the second magnet hole 36, respectively, so that the first magnetic plate 50 and the second magnetic plate 70 are fixed so as not to move downward relative to the insert part 30. Furthermore, the first magnet 40 and the second magnet 60 are fixed to the first magnetic plate 50 and the second magnetic plate 70 by magnetic force, respectively, so that they do not fall from the insert part 30. On the other hand, the surface 50yf of the first magnetic plate 50 on the molding hole 32 side in the Y direction and the surface 70yf of the second magnetic plate 70 on the molding hole 32 side in the Y direction are in contact with the side surfaces 34yf located on both sides of the communication opening of the first magnet hole 34 on the molding hole 32 side in the Y direction and the side surfaces 36yf located on both sides of the communication opening of the second magnet hole 36 on the molding hole 32 side in the Y direction, respectively, blocking the communication opening 35 of the first magnet hole 34 with the molding hole 32 and the communication opening 37 of the second magnet hole 36 with the molding hole 32. The surface 50yr of the first magnetic plate 50 opposite the molding hole 32 side in the Y direction and the surface 70yr of the second magnetic plate 70 opposite the molding hole 32 side in the Y direction are in contact with the side surface 40yf of the first magnet 40 on the molding hole 32 side in the Y direction and the side surface 60yf of the second magnet 60 on the molding hole 32 side in the Y direction, respectively.

[0014] The upper punch 80 has a spacer 82 (plate portion) having a right circular cylindrical shape, and a punch portion 84 extending downward along the Z direction from the center of the lower surface 82b of the spacer 82. The lower punch 90 has a spacer 92 (plate portion) having a right circular cylindrical shape, and a punch portion 94 extending upward along the Z direction from the center of the upper surface 92t of the spacer 92. The punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 have substantially the same dimensions and shapes of the cross section perpendicular to the Z direction as the forming hole 32 so that they can be fitted into the forming hole 32 from the upper end and the lower end, respectively, and can slide against the inner surface 32s of the forming hole 32. The material of the upper punch 80 and the lower punch 90 is a non-magnetic cemented carbide.

[0015] Next, in a manufacturing method of a magnet according to one embodiment, as shown in Fig. 2(a), an SmFeN magnetic powder 4 including magnetic particles 2 containing Sm, Fe, and N, and a metal zinc powder 8 (modifier powder) including metal zinc particles 6 are prepared, and then, as shown in Fig. 2(b), the magnetic powder 4 and the metal zinc powder 8 are mixed to obtain a mixed powder 1A and prepared as a raw material powder (powder preparation step). Next, as shown in Fig. 2(c), the punch portion 94 of the lower punch 90 is fitted from the lower end into the molding hole 32 of the insert portion 30 of the die 20 until the upper surface 92t of the spacer 92 of the lower punch 90 abuts against the lower surface 30b of the insert portion 30 of the die 20. Then, in the air or inert gas atmosphere (e.g., an argon gas atmosphere, a nitrogen gas atmosphere, etc.) at room temperature, the mixed powder 1A (raw material powder) is filled into the cavity C surrounded by the inner surface 32s (shown in Figure 1 (b)) of the forming hole 32 of the insert portion 30 of the die 20, the surface 50yf of the first magnetic plate 50 facing the forming hole 32, the surface 70yf of the second magnetic plate 70 facing the forming hole 32, and the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 (powder filling process).

[0016] Next, as shown in Fig. 3(a), in the air or inert gas atmosphere at room temperature, the punch portion 84 of the upper punch 80 is fitted into the molding hole 32 of the insert portion 30 of the die 20 from the upper end and moved downward along the Z direction to press the mixed powder 1A filled in the cavity C with the punch portion 84 of the upper punch 80. As a result, the mixed powder 1A filled in the cavity C is compressed by the inner side surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 on the molding hole 32 side and the surface 70yf of the second magnetic plate 70 on the molding hole 32 side, as well as the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90. In this way, the filled mixed powder 1A is compressed to a bulk density of 4.0 g / cm3. 3 ~5.5g / cm 3 (powder density adjustment process).

[0017] Next, as shown in FIG. 3(b), in the air or inert gas atmosphere at room temperature, a pulsed magnetic field is applied along the Y direction to both the filled mixed powder 1A and the first magnet 40 and the second magnet 60 by electromagnetic coils (not shown) arranged on both sides of the die 20 in the Y direction (magnetic field application step). In this way, the magnetic aggregation of the magnetic powder 4 contained in the mixed powder 1A is alleviated by the pulsed magnetic field, and the magnetic powder 4 is oriented. At the same time, the first magnet 40 and the second magnet 60 are magnetized by the pulsed magnetic field, so that the magnetic powder 4 is oriented by applying a magnetic field to the mixed powder 1A by the first magnet 40 and the second magnet 60 from before the pressure sintering, and the application of the magnetic field to the mixed powder 1A is continued until the pressure sintering is completed (at least halfway through the pressure sintering).

[0018] Next, as shown in FIG. 3(c), in an inert gas atmosphere, the filled mixed powder 1A is heated by a heater (not shown) equipped with a high-frequency induction coil arranged around the die 20 in a direction perpendicular to the Z direction. In this way, the mixed powder 1A is heated to the temperature of pressure sintering (heating process). As a result, the α-Fe phase on the surface of the magnetic particles of the magnetic powder 4 contained in the mixed powder 1A reacts with the zinc component of the metal zinc powder 8 on the surface of the magnetic particles to form an Fe-Zn phase (modified phase). Even during this process, the first magnet 40 and the second magnet 60 continue to apply a magnetic field to the mixed powder 1A, and the orientation of the magnetic powder 4 progresses.

[0019] Next, as shown in FIG. 4(a), in an inert gas atmosphere, the filled mixed powder 1A is continuously heated by the heater (not shown) while the punch portion 84 of the upper punch 80 is further moved downward along the Z direction to further press the mixed powder 1A with the punch portion 84 of the upper punch 80. As a result, the mixed powder 1A is pressurized with the inner surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 facing the molding hole 32 and the surface 70yf of the second magnetic plate 70 facing the molding hole 32, as well as the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 while being continuously heated. In this manner, the mixed powder 1A is pressure-sintered to obtain a sintered body 1C (pressure-sintering process). In the pressure-sintering, an Fe-Zn phase (modified phase) is formed in which the α-Fe phase of the surface portion of the magnetic particles of the magnetic powder 4 reacts with the zinc component of the metal zinc powder 8. Even during the pressure sintering process, the first magnet 40 and the second magnet 60 continue to apply a magnetic field to the mixed powder 1A, and the orientation of the magnetic powder 4 progresses.

[0020] Next, as shown in Fig. 4(b), in an inert gas atmosphere, the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 are moved downward along the Z direction, so that the sintered body 1C is moved downward in the molding hole 32 of the insert portion 30 of the die 20 while sliding against the inner side surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 facing the molding hole 32, and the surface 70yf of the second magnetic plate 70 facing the molding hole 32, and is ejected from the lower end of the molding hole 32 (ejection process). Next, as shown in Fig. 4(c), the sintered body 1C is heat-treated in a heating furnace 100 (heat treatment process). In this way, a SmFeN-based rare earth magnet 1 including the sintered body 1C is manufactured.

[0021] In the method for producing an SmFeN rare earth magnet according to the above embodiment, the bulk density of the packed mixed powder is set to 4.0 g / cm 3 ~5.5g / cm 3After adjusting the bulk density of the mixed powder, a pulsed magnetic field is applied to the filled mixed powder to orient the magnetic powder contained in the mixed powder. After the orientation of the magnetic powder, the mixed powder is pressure-sintered to obtain a sintered body. This allows the magnetic powder contained in the mixed powder to be oriented after the density of the mixed powder is adjusted to a density that allows easy flow by a magnetic field and high density of the sintered body, and the mixed powder can be pressure-sintered. Therefore, a magnet can be manufactured that has a sintered body with a high degree of orientation, sufficient magnetic anisotropy, and high density, and the residual magnetization of the magnet can be improved. Furthermore, after adjusting the bulk density of the mixed powder, a magnetic field is applied to the mixed powder by the first and second magnets before pressure-sintering to orient the magnetic powder contained in the mixed powder, and the application of the magnetic field to the mixed powder is continued until the completion of pressure-sintering (at least halfway through pressure-sintering). This allows the density of the mixed powder to be adjusted to a density that allows easy flow by a magnetic field, and the magnetic powder can be oriented by the magnetic field of the magnet until the mutual bonding of the magnetic particles of the magnetic powder contained in the mixed powder occurs. Therefore, the degree of orientation of the sintered body can be further increased. Furthermore, while the magnetic field is being applied by the first and second magnets, the mixed powder is heated to the pressure sintering temperature before pressure sintering, and an Fe-Zn phase is formed on the surface of the magnetic particles of the magnetic powder, thereby improving the fluidity of the mixed powder. This allows the orientation of the magnetic powder by the magnetic field of the magnet to proceed effectively. Therefore, the method for producing a rare earth magnet according to the embodiment can improve the magnetic properties of the magnet. Next, the method for producing a rare earth magnet according to the embodiment will be described in detail.

[0022] 1. Powder preparation process In the powder preparation step, raw material powder containing magnetic powder containing Sm, Fe, and N (hereinafter sometimes abbreviated as "SmFeN magnetic powder" or "magnetic powder") is prepared. The raw material powder is not particularly limited and may be a general one, but a mixed powder containing SmFeN magnetic powder and modifier powder containing a zinc component is preferable. This is because the magnetic powder can be bonded when the raw material powder is heated or sintered under pressure, and the surface of the magnetic powder can be modified with an Fe-Zn phase (modifier phase).

[0023] The SmFeN magnetic powder contains Sm (samarium), Fe (iron), and N (nitrogen), and at least a portion of the powder is Th2Zn. 17 Type and Th2Ni 17 There are no particular limitations on the magnetic powder, so long as it has a magnetic phase with at least one of the crystal structures of the types (Th: thorium, Zn: zinc, Ni: nickel), and any general magnetic powder may be used, but examples include powders in which the magnetic phase further has a crystal structure of the TbCu7 type (Tb: terbium, Cu: copper). Rare earth magnets exhibit magnetization due to the magnetic phase. SmFeN magnetic powders, for example, have the composition formula 1: (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The magnetic phase may have a magnetic phase represented by the formula (1). In the formula (1), R is one or more selected from rare earth elements other than Sm and Zr (zirconium), Co is cobalt, and i, j, and h are molar ratios. The magnetic phase may contain R in a range that does not impair the magnetic properties. In the formula (1), i is, for example, 0 to 0.50, preferably 0.10 to 0.40, and more preferably 0.20 to 0.30. The magnetic phase may contain Co in a range that does not impair the magnetic properties. In the formula (1), j is, for example, 0 to 0.50, preferably 0.10 to 0.40, and more preferably 0.20 to 0.30. In the formula (1), h is, for example, 1.8 to 4.2, preferably 2.0 to 4.0, and more preferably 2.5 to 3.5. The content of the magnetic phase in the SmFeN magnetic powder is, for example, from the viewpoint of ensuring the magnetic properties, 80% by mass or more and 97% by mass or less, preferably 85% by mass or more and 95% by mass or less, and more preferably 90% by mass or more and 93% by mass or less. The remainder of the SmFeN magnetic powder other than the magnetic phase contains, for example, oxygen and unavoidable impurity elements to the extent that the magnetic properties are not substantially impaired. Some of these elements may be present in the magnetic phase in an interstitial and / or substitutional form. The cumulative 50% particle diameter D in the volume-based particle size distribution of the magnetic powder 50The (median diameter) is not particularly limited and may be a general one, but from the viewpoint of obtaining a desired bulk density of the raw material powder, it is preferable that the diameter is 2 μm or more and 5 μm or less. 50 can be determined, for example, by measurement using a laser diffraction particle size distribution measuring device.

[0024] The modifier powder is not particularly limited and may be a general one, for example, at least one of a metal zinc powder containing metal zinc particles and a zinc alloy powder containing zinc alloy particles. 50 is not particularly limited and may be a general one, but is preferably 0.1 μm or more and 4 μm or less, from the viewpoint of obtaining a desired bulk density of the raw material powder. The content of the modifier powder in the mixed powder is not particularly limited and may be a general amount, but is preferably 1 mass % or more and 20 mass % or less, preferably 3 mass % or more and 10 mass % or less, and more preferably 5 mass % or more and 8 mass % or less, from the viewpoint of residual magnetization. The method of mixing the magnetic powder and the modifier powder is not particularly limited and may be a general method, but is preferably a mortar or the like.

[0025] The raw powder is, for example, a mixed powder containing SmFeN magnetic powder and metal zinc powder (modifier powder), the content of the metal zinc powder in the mixed powder is 3% by mass or more and 10% by mass or less, and the D of the magnetic powder is 50 is 2μm or more and 5μm or less, and the D of the modifier powder 50 It is preferable that the particle size is 0.1 μm or more and 4 μm or less, because the magnetic properties of the magnet can be suitably improved by adjusting the bulk density of the raw material powder in the powder density adjustment step.

[0026] 2. Powder density adjustment process In the powder density adjustment step, the raw material powder is compressed to adjust the bulk density of the raw material powder to 4.0 g / cm 3 ~5.5g / cm 3The raw powder is adjusted to the desired density. When the raw powder has a low bulk density, the orientation of the magnetic powder is easily promoted due to the improved fluidity, while the bulk density of the sintered body is reduced, and the orientation disorder during compression of the raw powder may become large. Furthermore, the generation of Fe-Zn phases on the surface of the magnetic powder may be reduced. When the raw powder has a high bulk density, the bulk density of the sintered body is increased, and the orientation disorder during compression of the raw powder can be suppressed, while the generation of Fe-Zn phases on the surface of the magnetic powder increases, and the orientation of the magnetic powder may become difficult to proceed due to the reduced fluidity. Examples of methods for compressing the raw powder include a method in which the raw powder is filled into a forming hole of a die of a metal mold and the filled raw powder is pressed with a punch. The atmosphere in which the powder density is adjusted may be a general one.

[0027] 3.Magnetic field application process In the magnetic field application step, after adjusting the bulk density, a magnetic field is applied to the raw powder to orient the magnetic powder contained in the raw powder. As a method for applying a magnetic field, for example, a method of applying a pulse magnetic field or a static magnetic field to the raw powder filled in the molding hole by an electromagnetic coil or the like is preferable, and among them, a method of applying a pulse magnetic field is preferable. This is because the magnetic aggregation of the magnetic powder can be alleviated. The conditions of the pulse magnetic field are not particularly limited and may be general. The magnitude of the pulse magnetic field is not particularly limited, but for example, 500 kA / m or more and 20000 kA / m or less is preferable. The number of times the pulse magnetic field is applied is preferable because the magnetic aggregation of the magnetic powder can be effectively alleviated as the number of times is increased. The atmosphere in which the magnetic field is applied may be general.

[0028] The magnetic field application step is preferably a step of applying a magnetic field to the raw material powder before the pressure sintering to orient the magnetic powder, and continuing the application of the magnetic field to the raw material powder until at least halfway through the pressure sintering. This is because the mutual bonding of the magnetic powder occurs as early as halfway through the pressure sintering of the raw material powder, and by continuing the application of the magnetic field until at least halfway through the pressure sintering, the sintered body can be sufficiently given magnetic anisotropy. Among these steps, a step of applying a magnetic field to both the raw material powder filled in the molding hole and the first and second magnets of the mold along the facing direction of the first and second magnets before the pressure sintering to orient the magnetic powder contained in the raw material powder and magnetize the first and second magnets at the same time is preferable. This is because the application of the magnetic field to the raw material powder can be continued by the first and second magnets after the application of the magnetic field to the raw material powder.

[0029] 4. Pressure sintering process In the pressure sintering step, the magnetic powder is oriented in the magnetic field application step, and then the raw material powder is pressure sintered to obtain a sintered body. Examples of the pressure sintering method include a method in which the raw material powder filled in the molding hole is pressed with a punch while being heated.

[0030] The temperature of the pressure sintering is not particularly limited and may be a general one, but from the viewpoint of mutual bonding of the magnetic powder and avoidance of decomposition of the magnetic phase, for example, 310°C to 500°C or less is preferable, and among them, 350°C to 450°C or less is preferable. Furthermore, from the viewpoint of avoiding excessive reaction of the magnetic powder and the modifier powder, the temperature of the pressure sintering is, for example, 430°C or less, and among them, 390°C or less is preferable. The pressure of the pressure sintering is not particularly limited and may be a general one, but from the viewpoint of increasing the density of the sintered body and suppressing distortion of the magnetic phase, for example, 100MPa to 2000MPa or less is preferable, and among them, 300MPa to 1200MPa or less, and particularly 400MPa to 600MPa or less is preferable. The time of the pressure sintering is not particularly limited and may be a general one, but from the viewpoint of increasing the density of the sintered body and suppressing distortion of the magnetic phase, for example, 1 minute to 60 minutes or less is preferable, and among them, 10 minutes to 50 minutes or less, and particularly 20 minutes to 40 minutes or less is preferable. The atmosphere in which the pressure sintering is performed may be a general one, but for example, an inert gas atmosphere is preferable.

[0031] 5. Manufacturing method of rare earth magnets The method for manufacturing a rare earth magnet is not particularly limited as long as it includes the above steps, but for example, as in one embodiment, a method including a step of heating the filled raw material powder to the pressure sintering temperature (heating step) after starting the application of a magnetic field to the raw material powder and before pressure sintering is preferable. The atmosphere during the temperature rise may be a general one, but for example, an inert gas atmosphere is preferable. In the method for manufacturing a rare earth magnet, a mold including a die with a molding hole and a punch that is inserted into the molding hole of the die can be used. As the mold, for example, a mold including a first and second magnet holes respectively provided on both sides of the molding hole of the die and a first and second magnet embedded in the first and second magnet holes respectively is preferable. Among them, a mold including a first magnetic plate embedded in the first magnet hole on the molding hole side of the first magnet so as to close the communication opening with the molding hole, and a second magnetic plate embedded in the second magnet hole on the molding hole side of the second magnet so as to close the communication opening with the molding hole is preferable, in which the first and second magnet holes communicate with the molding hole. This is because cracking of the first and second magnets can be prevented. The die and punch are preferably made of a non-magnetic material. The first and second magnets are, for example, permanent magnets such as rare earth magnets (for example, SmCo magnets). EXAMPLES

[0032] The method for producing a rare earth magnet according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0033] [Example 1] An example of a method for manufacturing an SmFeN rare earth magnet according to one embodiment was carried out. First, a powder molding die shown in Fig. 1 and Fig. 2 was prepared having dimensions [mm] and a tapered inclination angle as shown in Fig. 5 (die preparation step). The thickness of the first and second magnetic plates of the die was 1.45 mm. Next, SmFeN magnetic powder (D 50 A mixed powder (content of metal zinc powder: 5.0 mass%) containing SmFeN magnetic powder (zinc powder: 3.08 μm) and metal zinc powder (modifier powder) was prepared (powder preparation step). The SmFeN magnetic powder was a commercially available product (Z12 manufactured by Nichia Corporation). 17It has a magnetic phase represented by N3. Next, the mixed powder (raw material powder) was filled into a cavity in a molding hole of an insert part of a die (powder filling step).

[0034] Next, the packed mixed powder was compressed to a bulk density of 4.0 g / cm 3 (powder density adjustment step). Next, a pulse magnetic field was applied along the Y direction to both the filled mixed powder and the first and second magnets (magnetic field application step). At this time, the magnitude of the pulse magnetic field was set to 4775 kA / m, the number of times the magnetic field was applied back and forth in the Y direction was set to one round trip, and the number of times the pulse magnetic field was applied was set to 10 round trips.

[0035] Next, the filled mixed powder was heated in an argon gas atmosphere to raise the temperature of the mixed powder to 380°C (heating step). Next, in an argon gas atmosphere, the mixed powder was pressure sintered at a temperature of 380°C and a pressure of 500 MPa for 30 minutes to obtain a sintered body (pressure sintering step). Next, the sintered body was extracted from the bottom end of the molding hole (extraction step). Next, the sintered body was heat treated in a vacuum at a temperature of 390°C for 24 hours (heat treatment step). In this way, a SmFeN-based rare earth magnet comprising a sintered body was manufactured.

[0036] [Examples 2 and 3 and Comparative Examples 1 and 2] A method for producing an SmFeN rare earth magnet was carried out similarly to Example 1, except that in the powder density adjusting step, the density of the mixed powder (raw material powder) was adjusted to the value shown in Table 1 below.

[0037] [evaluation] The bulk density [g / cm 3 ] of the sintered bodies of the SmFeN rare earth magnets produced in Examples 1 to 3 and Comparative Examples 1 and 2 was 3The degree of orientation was calculated and the magnetic properties were evaluated. In calculating the degree of orientation, the magnetization when the magnetic field was 0T in the magnetization-magnetic field curve was taken as M(0T) and the magnetization when the magnetic field was 8T was taken as M(8T), and the degree of orientation was calculated from M(0T) / M(8T). In evaluating the magnetic properties, the rare earth magnets of each example were pulse magnetized at room temperature in a magnetizing magnetic field of 4775 kA / m, and the residual magnetization [T] was measured using a direct current magnetization fluxmeter (TRF). The results are shown in Table 1 below. Figures 6(a) to (c) show the bulk density [g / cm3] of the mixed powders (raw material powders) of the examples and comparative examples. 3 ] versus bulk density of sintered body [g / cm 3 ], the degree of orientation of the sintered body versus the bulk density of the mixed powder, and the remanence magnetization [T] of the magnet versus the bulk density of the mixed powder.

[0038] [Table 1]

[0039] [Consideration] As shown in Table 1 and Figs. 6(a) to 6(c), the bulk density of the mixed powder (raw material powder) was 4.0 g / cm 3 ~5.5g / cm 3 When the bulk density of the mixed powder was 4.0 g / cm, the residual magnetization was significantly higher than in the other cases, and the residual magnetization was highest when the bulk density of the mixed powder was 5.0 g / cm. On the other hand, when the bulk density of the mixed powder was too high, the bulk density of the sintered body increased, but the degree of orientation of the sintered body tended to decrease. From these results, it was found that when the bulk density of the mixed powder was 4.0 g / cm, the residual magnetization was significantly higher than in the other cases, and the residual magnetization was highest when the bulk density of the mixed powder was 5.0 g / cm. On the other hand, when the bulk density of the mixed powder was too high, the bulk density of the sintered body increased, but the degree of orientation of the sintered body tended to decrease. 3 ~5.5g / cm 3 In this case, it is believed that the bulk density of the sintered body can be increased and the decrease in the degree of orientation of the sintered body that would otherwise occur due to a decrease in the fluidity of the mixed powder can be prevented, thereby improving the magnetic properties of the magnet.

[0040] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as described in the claims. [Explanation of symbols]

[0041] 1: rare earth magnet, 1A: mixed powder (raw powder), 1C: sintered body, 10: mold, 20: die, 30: insert portion, 32: molding hole, 34: first magnet hole, 36: second magnet hole, 40: first magnet, 50: first magnetic plate, 60: second magnet, 70: second magnetic plate, 80: upper punch, 90: lower punch

Claims

[Claim 1] A step of preparing a raw material powder including a magnetic powder containing Sm, Fe, and N; The raw material powder is compressed to a bulk density of 4.0 g / cm ３ ~5.5g / cm ３ and adjusting the a step of orienting the magnetic powder contained in the raw material powder by applying a magnetic field to the raw material powder after adjusting the bulk density; and after orienting the magnetic powder, pressure sintering the raw material powder to obtain a sintered body.

Images