JPH0434804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing a permanent magnet. More specifically, the present invention relates to a method of manufacturing a polycrystalline manganese-aluminum-carbon (Mn-Al-C) alloy magnet, and particularly to a method of manufacturing a high-performance Mn-Al-C alloy magnet for multipolar magnetization.

Structure of conventional examples and their problems Mn-Al-C alloy magnets are mainly composed of a face-centered tetragonal (τ phase, L ₁₀ type regular lattice) structure, which is a ferromagnetic phase, and C is an essential constituent element. There are known ternary alloy magnets that contain no additive elements other than impurities, and multi-element alloy magnets that include quaternary or higher alloy magnets that contain small amounts of additive elements, and these are collectively referred to as magnets.

Furthermore, as a manufacturing method for this Mn--Al--C alloy magnet, there are known methods that include a plastic working process such as extrusion in addition to casting and heat treatment.
In particular, the latter method is known as a method for producing anisotropic magnets having excellent properties such as high magnetic properties, mechanical strength, weather resistance, and machinability.

Manufacturing methods for Mn-Al-C alloy magnets for multipolar magnetization include isotropic magnets, compression processing, and uniaxially anisotropic polycrystalline Mn obtained in advance by known methods such as extrusion processing. -Al-C alloy magnets subjected to free compression processing in an anisotropic direction (composite processing method) are known.

Compression processing provides high magnetic properties in the radial direction, but a relatively large processing rate is required, non-uniform deformation may occur, and the presence of undeformed bands is unavoidable. There are problems such as: With the combined processing method, high magnetic properties are obtained in all directions within the plane, including the radial and chordal directions, with small compressive strain. The magnet obtained by the composite processing method has an easy magnetization direction parallel to a specific plane, is magnetically isotropic within the plane, and includes a line perpendicular to the plane and a straight line parallel to the plane. It has a structure that is anisotropic in a plane (hereinafter, such a magnet will be referred to as a plane anisotropic magnet).

On the other hand, the shape of a magnet used in the field of multipolar magnetization is generally an axially symmetrical shape, and an example is a cylindrical shape. FIG. 1 schematically shows the configuration of the magnetic path inside the magnet when the inner circumference of the cylindrical magnet is magnetized with multiple poles. In Figure 1, the broken line indicates the magnetic path,
The chordal direction (θ direction) with respect to one radial direction (r direction) is also shown. The direction perpendicular to the radial direction (r direction) of the cylinder and the axial direction of the cylinder is defined as the chordal direction (θ direction).

As shown in FIG. 1, the magnetic path runs approximately in the radial direction at the inner circumferential portion, along the chord direction at the outer portion, and no magnetic path runs at the outer portion. If the shape of the magnet is cylindrical, the magnet can be divided into three parts as mentioned above.
The first is the part where the magnetic path runs along the radial direction (part A),
The second is the part where the magnetic path is along the chord direction (part B),
The third part is a part (C part) through which no magnetic path passes.

The above-mentioned plane anisotropic magnet is a magnet that has an easy magnetization direction in any direction parallel to the plane including the radial direction and the chordal direction, so when it is magnetized on the inner circumference in this way, it has excellent magnetic properties. However, when it is divided into three parts as described above, each part does not have a desirable anisotropic structure. That is, it is better for the A part to have higher magnetic properties in the radial direction than in the chordal direction, and it is better for the B part to have higher magnetic properties in the chordal direction than in the radial direction. On the other hand, a radially anisotropic magnet (or a magnet with a radial easy magnetization direction,
A magnet whose shape is a hollow body and whose easy magnetization direction is parallel to a straight line passing through an arbitrary point on a plane perpendicular to the axial direction of the hollow body, and in the case of a cylindrical body as shown in Fig. 1, the direction of easy magnetization is the r direction. In a magnet (having an easy magnetization direction in the radial direction), part A has a desirable anisotropic structure, but part B has an undesirable anisotropic structure.

Purpose of the Invention The present invention provides an Mn-Al material suitable for high-performance multipole magnetization.
- It is an object of the present invention to provide a method for manufacturing a C-based alloy magnet.

Structure of the Invention The present invention provides anisotropic polycrystalline material in the hollow part of a hollow billet made of a metal material.
In the presence of a hollow billet made of an Mn-Al-C alloy magnet, the hollow body made of the previously anisotropic polycrystalline Mn-Al-C alloy magnet is heated at a temperature of 530 to 830°C. It is characterized in that the two billets are compressed in the axial direction of the shaped billet until they come into contact with each other or further to be integrated.

With a hollow billet made of a metal material existing on the outside of a hollow billet made of a polycrystalline Mn-Al-C alloy magnet that has been made anisotropic in advance, the billet is heated until the two billets touch or more. By performing compression processing, it is possible to obtain a Mn-Al-C alloy magnet having a radial direction of easy magnetization, and by compression processing a metal material together with a hollow billet. Effectively (refined structure, anisotropy, improved magnetic properties, etc.) is applied to Mn-Al-C alloy magnets.

Furthermore, if the hollow billet made of the metal material is a hollow billet with at least the inner periphery made of a magnetic material, it is possible to obtain a magnet having two structures suitable for inner periphery magnetization as described above. can.

After compression processing, a hollow billet made of a polycrystalline Mn-Al-C alloy magnet that has been made anisotropic in advance becomes a magnet with a structure suitable for part A, and after compression processing, the magnetic body part becomes a magnet with a structure suitable for part B. It becomes a part that has a structure. Moreover, since the two billets are compressed at the same time and brought into contact with each other, it is possible to obtain a magnet having two or more types of structures after the compression process.

Description of Examples Known Mn-Al-C based magnet-like alloys, e.g. 68~
73% by weight (hereinafter simply expressed as %) of Mn and (1/10・
Mn−6.6) to (1/3・Mn−22.2)% of C and the remainder
An anisotropic polycrystalline Mn-Al-C alloy magnet can be obtained by subjecting an alloy made of Al to plastic working such as extrusion in a temperature range of 530 to 830°C. Typical examples of the magnet include a uniaxial anisotropic magnet having an easy magnetization direction in the extrusion direction obtained when the plastic working is performed by extrusion, the above-mentioned planar anisotropic magnet, and radial anisotropic magnet. and so on.

In a state where the hollow billet made of the anisotropic polycrystalline Mn-Al-C alloy magnet is present in the hollow part of the hollow billet made of the metal material, the Mn-Al-C By compressing a hollow billet made of a system alloy magnet in the axial direction until the two billets touch or more, the billet has an easy magnetization direction radially.
Mn-Al-C alloy magnets can be obtained, and since compression processing is performed together with a hollow billet made of metal material, the effects of compression processing (refining of the structure, anisotropy, improvement of magnetic properties, etc.) ) efficiently converts Mn−
Applied to Al-C alloy magnets.

The metal material mentioned above may be any material that can be compressed together with the Mn-Al-C alloy magnet in the temperature range of 530 to 830°C. There is no need to be particular about metal materials in general. In other words, any billet made of a certain material is sufficient. However, in general, materials such as steel, brass, and copper are used, and in some cases, the materials are not limited to bulk materials but may also be powders.

Furthermore, if the hollow billet made of the metal material described above is made of a magnetic material at least in its inner circumference, the inner circumference of the billet after compression processing (before compression processing, the anisotropic Mn -The part corresponding to the hollow billet made of Al-C alloy magnet)
is a portion that has high magnetic properties in the radial direction, and the portion outside of this (corresponding to the magnetic material) is a portion suitable for the magnetic path to follow the string direction when inner circumferential magnetization is applied. As a result, three divided portions A and B are formed when the inner circumferential magnetization described above is applied, and a magnet exhibiting excellent magnetic properties when inner circumference magnetized is obtained.

The above-mentioned magnetic material may be any magnetic material as long as the chord direction does not become the difficult-to-magnetize direction after the above-described compression process. Here, the difficult magnetization direction means the direction in which magnetization is difficult in outer circumferential magnetization, for example, in the [111] direction of single crystal Fe, when H = 500 Oe, the magnetization in the [100] direction of the easy magnetization axis If there is no significant difference in strength from the strength of , it cannot be said that the direction is difficult for magnetization in outer circumferential magnetization. As the magnetic material, Mn-Al-C magnetic alloy (Mn-
Generic term for Al-C magnet alloy and Mn-Al-C alloy magnet), isotropic Mn-Al-C alloy magnet, pure iron,
Examples include high magnetic permeability materials such as electromagnetic soft iron and Fe-Co alloy.

When the hollow body-shaped billet made of the Mn-Al-C alloy magnet is made of a polycrystalline Mn-Al-C alloy magnet (uniaxially anisotropic magnet) having an easy magnetization direction in the axial direction of the hollow body. In order to achieve this, it is necessary to apply a compressive strain of 0.03 or more in the absolute value of logarithmic strain in the axial direction of the hollow billet through the above-mentioned compression process. This is because, as detailed in the examples, the structure is anisotropic in the axial direction before compression processing, and a compressive strain of at least 0.03 is required for the structure to exhibit high magnetic properties in the radial direction. It is.

The hollow billet made of the Mn-Al-C alloy magnet is a polycrystalline Mn-Al-C whose easy magnetization direction is parallel to a plane perpendicular to the axial direction of the hollow body.
In the case of a system alloy magnet (planar anisotropic magnet),
Before compression processing, it already exhibits high magnetic properties in all directions within the plane, including the radial and chordal directions;
By performing the compression process described above, the direction of easy magnetization changes along the radial direction.

The hollow body-shaped billet made of the Mn-Al-C alloy magnet is a polycrystalline Mn-Al- In the case of a C-based alloy magnet (a radially anisotropic magnet or a magnet having an easy direction of magnetization radially), compression processing causes it to exhibit even higher magnetic properties in the radial direction.

The compression process described above does not necessarily have to be continuous compression process, and may be divided into multiple times. Furthermore, the billet which has been subjected to the above-mentioned compression processing may be further subjected to compression processing in the axial direction on a portion (for example, the inner peripheral portion) of the bit.

An example of the above-mentioned compression processing is that two hollow billets are made into cylindrical shapes, and a cylindrical billet made of a metal material is called billet A1, which is made from an Mn-Al-C alloy magnet that has been made anisotropic in advance. It is shown in FIGS. 2 to 6 as a cylindrical billet _B2 . In each figure, (a) shows the state before compression processing, and (b)
schematically shows the state after compression processing. In FIGS. 2 to 6, 1 is billet A and 2 is billet B. 3 is a billet (billet C) made of a metal material other than billet A. 4,5
is a punch that can move freely in the axial direction and can also be fixed at a certain position.
6 is the outer mold.

First, in the example shown in FIG. 2, with the outer periphery of billet A restrained, billet B is placed in contact with billet A as shown in (a), and compression processing is performed. By subjecting both billets A and B to compression processing, billet B has both an outer diameter and an inner diameter smaller after compression processing than before processing. As in the example shown in Fig. 2, compared to the case where both 1 and 2 are one cylindrical bit made of Mn-Al-C alloy magnets, the state in which billet A exists outside billet B described above When both are subjected to compression processing, the compression processing is effectively applied to the Mn-Al-C alloy magnet as described above.

In the example of FIG. 3, unlike the case of FIG. 2, there is a considerable gap between billets A and B. After compression processing, as shown in (b), it is almost the same as the case in FIG. 2.

The example shown in FIG. 4 differs from the case shown in FIG. 2 in that the outer periphery of the billet A is not in contact with the outer mold 6. In other words, the outer periphery of billet A is not constrained before compression processing, and as the compression processing progresses, the diameters of both billets increase, and eventually the outer periphery of billet A comes into contact with the outer mold. After that, the same transformation as in FIG. 2 is performed.

In the example of FIG. 5, billet C3 is present in the center of the case of FIG. 2. Compression processing can be performed until the air in the mold (the space surrounded by the punches 4 and 5 and the outer mold 6) is almost filled with billet. Before compression processing, if the temperature in the area shown in the figure (especially the space where the billet exists and its vicinity) is approximately the same, the inner circumferential surface of the billet will actually be a curved surface, and the central part (height direction, axis Although the inner diameter of the center portion (with respect to the direction) is the smallest, by inserting the billet C and compressing it together, the curvature of the curved surface (change in the inner diameter) can be reduced. Instead of using the billet C illustrated in FIG. 5, a mandrel or the like may be used for the purpose of forming the inner peripheral surface. Further, a mandrel or the like may be used for the purpose of forming the inner circumferential surface not only in FIG. 5 but also in all the examples shown in FIGS. 2 to 6.

In the example of FIG. 6, the billet C in FIG. 5 has a cylindrical shape.

In the above example, the outer periphery of the billet B in FIG. 2 is restrained by the outer mold 6 via the billet A, but the inner periphery can be considered to be in a free state. On the other hand, although the outer periphery of billet B in FIG. 4 is in contact with billet A, the outer periphery of billet A is not in contact with outer mold 6 and can therefore be considered to be in a free state.

Compression processing is performed in a temperature range of 530 to 830°C, so if billets A, B, or C are made of different materials, if they are cooled to room temperature after processing, they may become shrink-fit due to the difference in thermal expansion coefficient. Conversely, gaps may occur between the billets. When using a material other than the Mn-Al-C magnet alloy, it is necessary to consider the magnitude relationship with the coefficient of thermal expansion of the Mn-Al-C magnet alloy.

In the examples shown in FIGS. 2 to 6, there is a portion of the compression process in which at least the outer periphery of billet B is constrained. However, it is not necessarily necessary to have a portion where the compression process is performed while the outer periphery of the billet B is restrained. For example, in the processing shown in FIG. 4, the outer mold 6 may not exist. Even in this case, Mn-Al-C
By processing the billet made of Mn-based alloy magnet with the outside covered with a billet made of metal material, the effect of the compression process mentioned above can be effectively applied to Mn.
-Given to Al-C alloy magnets. However, the effect is greater if the billet B has a portion where the compression process is performed while the outer periphery of the billet B is restrained, and the number of such portions increases.

Further, in the above example, the cylindrical body is made of one of the billets A and B, but this is not necessarily necessary. For example, billet A or billet B in FIG. 2 may be composed of two or more parts forming a cylindrical body. In extreme cases, the portion occupied by billet A in FIG. 2 may be powder.

In the examples of FIGS. 2 to 6, the heights of billets A and B (or even billet C) before compression are approximately equal, but the heights of each billet may be different. For example, in FIG. 3, billet A may be higher than billet B.

In addition, in the above example, the entire billet B (a hollow billet made of an Mn-Al-C alloy magnet that has been made anisotropic) is subjected to compression processing, but compression processing may be performed locally. You may create an area where no processing is performed to preserve the structure before processing. For example, the second
In the figure, there is a method in which the end face of the punch 5 is made into a stepped shape that matches the inner diameter of the billet B2 instead of a flat surface, and a part of the inner circumference is locally restrained to create an area where compression processing is not performed. It is.

Further, as described above, if it is desired to obtain a substantially cylindrical billet after compression processing, a mandrel or the like may be used for the purpose of forming the inner circumferential surface.

Furthermore, if the cylindrical billet (billet A1) made of the metal material described above is a billet whose inner peripheral portion is made of a magnetic material, the billet B can be compressed to radially change the direction of easy magnetization. It becomes a magnet with a magnetic field, and becomes a part suitable for the part A in the above-mentioned inner circumferential magnetization. The magnetic part is B
It is possible to obtain a magnet having two or more types of structures depending on the part suitable for the part. For example, in FIG. 2, billet A1 is made of a high magnetic permeability material and billet B2 is made of a uniaxially anisotropic magnet.

Regarding the possible temperature range of compression processing as mentioned above, it was possible to perform it in the temperature range of 530 to 830℃, but
At temperatures above 780°C, the magnetic properties deteriorated considerably.
A more desirable temperature range was 560 to 760°C.

Next, more specific embodiments of the present invention will be described.

Example 1 Melt and cast a mixture of 69.5% Mn, 29.3% Al, 0.5% C and 0.7% Ni, diameter 80 mm, length
A 50 mm cylindrical billet was made. This billet
Heat treatment was carried out by holding at 1100°C for 2 hours and then allowing it to cool to room temperature. Next, extrusion processing to a diameter of 55 mm was performed at a temperature of 720° C. using a lubricant. Furthermore, extrusion processing up to a diameter of 40 mm was performed at a temperature of 680°C using lubricating oil. This extruded rod was cut to a length of 20 mm and machined to create an outer diameter of 30.6 to 35.3 mm and an inner diameter of 13.2 to 29.1 mm.
Several cylindrical billets (billet B) of various lengths of 20 mm were prepared.

Next, we cut a brass bar material to create a shape with an outer diameter of 40 mm and an inner diameter of 40 mm.
Several cylindrical billets (billet A) of 30.6 to 35.3 mm were prepared.

Using one billet A and one billet B, put billet B into the hollow part of billet A, set it in the state shown in FIG. 2 using a mold as shown in FIG. Compression processing was performed using a lubricant at a temperature of 680°C and varying the compressive strain. Note that the inner diameter of the outer mold 6 of the mold used was 40 mm.

A cubic sample with a side of approximately 4 mm was cut out from the inner periphery of the processed billet (corresponding to billet B before processing) with each side along the radial, chordal, and axial directions, and the magnetic properties were measured.

Residual magnetic flux density (Br) against compressive strain (ε _z )
The change in is shown in FIG. 7 by a solid line.

For comparison, the extruded rod with a diameter of 40 mm was cut and
After cutting, the outer diameter is 40 mm, the inner diameter is 13.2 to 29.1 mm, and the length is
Several 20 mm cylindrical billets of various types were made. Next, this billet was subjected to compression processing under the same conditions as above but with different compression strains.

A cubic sample was cut out from the outer periphery of the processed billet in the same manner as described above, and its magnetic properties were measured. _εz
Figure 7 shows the change in Br as a dotted line.

As shown in FIG. 7, the method according to the present invention
Br in the radial direction with respect to ε _z becomes higher. In other words, high magnetic properties can be obtained with small compressive strain. In the method of the present invention, Br in the radial direction becomes larger than Br in the axial direction when ε _z is 0.03 or more, and as ε _z increases, Br in the radial direction further increases. As can be seen from this figure, the change in the direction of easy magnetization from the axial direction to the radial direction progresses significantly in the range of ε _z up to 0.03.

Example 2 Melt and cast a mixture of 69.5% Mn, 29.3% Al, 0.5% C and 0.7% Ni, diameter 70 mm, length
A 50 mm cylindrical billet was made. This billet
After holding at 1100° C. for 2 hours, heat treatment was performed by allowing it to cool to room temperature. Next, extrusion processing to a diameter of 37 mm was performed at a temperature of 680° C. using a lubricant. This extruded rod was cut to a length of 20 mm and machined to an outer diameter of 35.3 mm.
A cylindrical billet (billet B) with an inner diameter of 29.1 mm and a length of 20 mm was prepared.

Next, a cylindrical billet (billet A) having an outer diameter of 40 mm, an inner diameter of 35.3 mm, and a length of 20 mm was produced by cutting a pure iron bar.

Insert billet B into the hollow part of billet A,
Using the same mold as in Example 1, the billet was set in the state shown in Figure 2, and the billet was heated using lubricant.
Compression processing was performed at a temperature of 680℃. Compression processing was performed until the billet length was 10 mm.

After cutting the processed billet to an outer diameter of 39 mm and an inner diameter of 22 mm, the inner circumference was magnetized with 12 poles. The magnetization is
2000V using 2000μF oil capacitor
It was pulse magnetized. The surface magnetic flux density on the inner circumference was measured using a Hall element. The surface magnetic flux density was 3.0kG, an extremely high value. In this way, when the billet A is made of a magnetic material, a magnet having a structure suitable for extremely high performance inner periphery magnetization can be obtained.

Example 3 The extruded rod with a diameter of 37 mm obtained in Example 2 was cut and machined to form two cylindrical billets with a diameter of 30 mm and a length of 20 mm.
I made one piece. 680 through this billet lubricant
It was freely compressed to a length of 10 mm at a temperature of ℃. After processing, the billet is cut to an outer diameter of 35 mm and an inner diameter of 29 mm.
A cylindrical billet (billet B) with a length of 20 mm was produced by stacking two cylindrical bodies with a length of 10 mm and a length of 20 mm.

Next, a cylindrical billet (billet A) having an outer diameter of 40 mm, an inner diameter of 35 mm, and a length of 20 mm was produced by cutting and machining a bar of electromagnetic soft iron.

Insert billet B into the hollow part of billet A,
Using the same mold as in Example 1, the mold was set in the state shown in FIG. 2, and compression working was carried out at a temperature of 680° C. using a lubricant.

The billet after processing (length: 10 mm) was cut in the same manner as in Example 2, magnetized on the inner circumference, and the surface flux density was measured, and there was no significant difference from that of the magnet obtained in Example 2. .

Example 4 Blend composition: 72% Mn, 27% Al and 1% C
was melted and cast to produce a cylindrical billet with a diameter of 55 mm and a length of 50 mm. This billet is heated to 1150℃ for 2 hours.
After holding for a period of time, cool to 700℃ in about 20 minutes,
Heat treatment was performed at 700°C for 30 minutes. Next, extrusion processing up to a diameter of 35 mm was performed at a temperature of 720°C via a lubricant. Cut this extruded rod into a length of 20 mm,
A cylindrical billet (billet A) with an outer diameter of 34 mm, an inner diameter of 28 mm, and a length of 20 mm was produced by cutting.

The extruded rod with a diameter of 37 mm obtained in Example 2 was cut into a length of 20 mm and machined to produce a cylindrical billet (billet B) with an outer diameter of 28 mm, an inner diameter of 19.6 mm, and a length of 20 mm.

Insert billet B into the hollow part of billet A,
The billet was set in the state shown in FIG. The mold used was the same as in Example 1. It was compressed to a length of 10 mm at a temperature of 680°C using a lubricant. This billet was cut to an outer diameter of 39 mm and an inner diameter of 22 mm, and the inner circumference was magnetized with 8 poles. The surface magnetic flux density on the inner circumference is
It was 2.9kG. Note that the magnetization conditions, measurements, etc. are the same as in Example 2.

Although the above embodiment is a typical example of the examples shown in FIGS. 2 to 6, the lengths of billet A1 and billet B2 before compression processing may be different. Furthermore, instead of compressing the entire billet, a method may be used in which the structure before processing is preserved without deforming a portion of the billet. In some cases, the billet may be formed of two or more billets to form a hollow shape. Furthermore, a mandrel or the like may be used for the purpose of shaping the inner peripheral surface.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a magnet that exhibits excellent magnetic properties in multipolar magnetization. Furthermore, in the method of the present invention, since the Mn--Al--C alloy magnet is compressed together with the billet made of a metal material, the Mn--Al--C alloy magnet is effectively compressed.

[Brief explanation of drawings]

Figure 1 is a diagram schematically showing the formation of a magnetic path inside the magnet when the inner circumference of a cylindrical magnet is subjected to multipolar magnetization, Figures 2, 3, 4, and 5 and FIG. 6 is a cross-sectional view of a part of a mold schematically showing an example of compression processing of the present invention, and FIG. 7 is a diagram showing changes in residual magnetic flux density (Br) with respect to compressive strain in Example 1. be. 1... Billet A, 2... Billet B, 3...
Billet C, 4, 5... Punch, 6... External mold.

Claims (1)

[Scope of Claims] 1. A hollow body-shaped billet made of a polycrystalline manganese-aluminum-carbon alloy magnet that has been made anisotropic in advance, and a hollow body-shaped billet made of a metal material different from that of the alloy magnet. the two billets are compressed in the axial direction of the hollow billet made of the alloy magnet at a temperature of 530 to 830°C until the two billets come into contact with each other or further to be integrated. A method for manufacturing a manganese-aluminum-carbon alloy magnet, characterized by: 2. The method for producing a manganese-aluminum-carbon alloy magnet according to claim 1, wherein the hollow billet made of a metal material has at least an inner peripheral portion made of a magnetic material. 3. A hollow body-shaped billet made of a polycrystalline manganese-aluminum-carbon alloy magnet that has been anisotropically made in advance is made of a polycrystalline manganese-aluminum-carbon alloy magnet having an easy magnetization direction in the axial direction of the hollow body, The method for manufacturing a manganese-aluminum-carbon alloy magnet according to claim 1 or 2, wherein the compressive strain in the axial direction of the compressed hollow body is 0.03 or more in absolute value of logarithmic strain. 4. A hollow billet made of a polycrystalline manganese-aluminum-carbon alloy magnet that has been anisotropically made in advance has an easy magnetization direction parallel to a plane perpendicular to the axial direction of the hollow body, and within said plane Claim 1 comprising a polycrystalline manganese-aluminum-carbon alloy magnet that is magnetically isotropic and anisotropic in a plane that includes the axial direction and a straight line parallel to the plane. 2. A method for producing a manganese-aluminum-carbon alloy magnet according to item 2. 5 A hollow body-shaped billet made of a polycrystalline manganese-aluminum-carbon alloy magnet that has been made anisotropic in advance has an easy magnetization direction parallel to a straight line passing through an arbitrary point on a plane perpendicular to the axial direction of the hollow body. 3. A method for producing a manganese-aluminum-carbon alloy magnet according to claim 1 or 2, which comprises a polycrystalline manganese-aluminum-carbon alloy magnet. 6. The method for producing a manganese-aluminum-carbon alloy magnet according to claim 1 or 2, wherein the hollow body is cylindrical. 7 With the compression process restraining the outer periphery of a hollow billet made of a polycrystalline manganese-aluminum-carbon alloy magnet that has been made anisotropic in advance,
The method for manufacturing a manganese-aluminum-carbon alloy magnet according to claim 1 or 2, wherein the processing is performed with at least a portion of the inner circumference free. 8. After compression processing is performed with at least a portion of the outer periphery and inner periphery of a hollow billet made of an anisotropic polycrystalline manganese-aluminum-carbon alloy magnet made free, the billet is further compressed. 3. The method for producing a manganese-aluminum-carbon alloy magnet according to claim 1 or 2, wherein the processing is carried out with the outer circumference constrained and at least a portion of the inner circumference free.