JPH0219604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to permanent magnets, and more particularly to improvements in polycrystalline manganese-aluminum-carbon (Mn--Al--C) alloy magnets.

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 contain C as an essential constituent element. Multi-component alloy magnets, including ternary alloy magnets containing no additive elements and quaternary or higher alloy magnets containing small amounts of additive elements, are known. Depending on the alignment of the [001] axis of the face-centered tetragonal crystal, this Mn-Al-C alloy magnet can be classified into isotropic magnets and anisotropic magnets with easy magnetization in a specific direction. is already known.

Generally, anisotropic magnets have high magnetic properties in a specific direction, and exhibit their advantages in the field of unidirectional magnetization, that is, bipolar magnetization. Examples include speaker magnets, two-pole rotor magnets for motors, etc.
On the other hand, there are significant restrictions on the direction of magnetization, and for example, in the field of multipolar magnetization, many isotropic magnets are used. Anisotropic magnets used in the field of multipolar magnetization are known to have easy magnetization directions in all radial directions radially from the center, but as described later, the magnetic properties in the string direction are Due to its low temperature, it is not necessarily suitable for multi-pole magnetization, and in particular,
This is disadvantageous for high-density multi-pole magnetization with a larger number of poles.
A permanent magnet for multi-pole magnetization, particularly for high-density multi-pole magnetization, has been desired to have high magnetic properties in all directions within a plane, including the radial direction and the chord direction.

In view of the above-mentioned background, the present invention provides a new permanent magnet that has a plane-like easy magnetization direction and exhibits excellent magnetic properties within that plane. The permanent magnet of the present invention is an anisotropic magnet in a broad sense, but it is a permanent magnet with a novel anisotropic structure that cannot be easily assumed from the conventional general concept of anisotropic magnets.

That is, general anisotropic magnets are uniaxially anisotropic, regardless of whether they are crystal anisotropic materials such as ferrite magnets or shape anisotropic materials such as alnico magnets. High magnetic properties are obtained at the expense of magnetic properties in orthogonal planes. Even if the magnet has the above-mentioned radial easy magnetization direction, if you look at a part of the magnet, it will have high magnetic properties only in the radial direction, and only low magnetic properties in the plane orthogonal thereto, including the chordal direction.

On the other hand, in the permanent magnet of the present invention, high magnetic properties in a two-dimensional plane perpendicular to the one-sided magnetic property are obtained at the expense of one-sided magnetic properties. Although it is magnetically anisotropic in three dimensions, it is anisotropic in the two-dimensional plane, and can be used in the same way as an isotropic magnet, except that the magnetic properties have been greatly improved. . Furthermore, as an additional feature, there is also the advantage that there is little magnetic leakage in the direction perpendicular to the two-dimensional plane.

The present invention produces a permanent magnet with a novel anisotropic structure having a planar easy magnetization direction as described above.
This is provided by improving C-based alloy magnets. The permanent magnet of the present invention is not different from known Mn-Al-C alloy magnets in terms of alloy composition and crystal structure of individual microcrystals.
Due to the difference in the statistical distribution of the [001] axis, the polycrystalline material exhibits novel magnetic anisotropy. Specifically, individual τ phase microcrystals within a polycrystalline magnet preferentially orient their [001] axis in any direction parallel to a particular plane within the magnet compared to a direction perpendicular to that plane. It is arranged in the form of

Generally, the preferential orientation state of crystal orientation in a polycrystalline body is expressed by polar density P. Since the τ phase is a tetragonal system, the orientation of the [001] axis can be understood as a (001) polar density distribution. The (001) polar density in a certain orientation of a polycrystal is measured as the ratio of the integrated intensity of (00n) plane diffraction when the X-ray diffraction normal is placed in that orientation to that of an isotropic material. In an isotropic magnet, the polar density is 1 for all three-dimensional orientations. In other words, the permanent magnet of the present invention has P>1 in any direction parallel to a specific plane within the magnet,
And within that plane, there is no big difference in each direction,
At the same time, P<1 in the vertical direction of the plane. Regarding the permanent magnets of the present invention prototyped by the inventors, the difference in (001) polar density between both directions was more than three times as large for all samples. In addition, the change in the (001) polar density in the direction parallel to the plane was about 10% or less, which was at the level of a typical accuracy in X-ray diffraction intensity measurement.

A multipolar magnetized magnetic article, which is a main application example of the magnet of the present invention, generally has an axially symmetrical shape, such as a permanent magnet rotor. FIG. 1 illustrates an example of an axially symmetrical magnetic article according to the present invention. Z is the axis of symmetry, and the hatching represents a plane perpendicular to Z that includes any point P in the magnetic article. In the case of the axially symmetrical magnetic article shown in FIG. 1, the specific plane referred to in the present invention refers to a plane perpendicular to the axis of symmetry, and includes the radial direction (r in the figure) and chordal direction (u in the figure). It is. At point P, z is in the axial direction and parallel to Z. The internal hole may be unnecessary depending on the purpose.

FIG. 2 schematically shows the formation of a magnetic path inside the magnet when the outer periphery of such a magnetic article is subjected to eight-pole magnetization. In the above plane, radially near the magnetic pole,
A curved magnetic path along the string direction is formed at the intermediate position, taking advantage of the features of the magnetic article of the present invention, which has high characteristics in all directions within the plane.

Furthermore, a feature of the permanent magnet of the present invention is that the microstructure consisting of the τ phase is the same regardless of the macroscopic position within the article. For example, there is no coarse crystalline region at the center edge due to the undeformed zone. This means that not only the magnetic properties but also the mechanical strength and machinability are uniform and high at all locations within the article. As shown in FIG. 1, the center hole can also be easily machined by drilling.

One of the axially symmetrical permanent magnet articles of the present invention was cut along a plane including the axis of symmetry, then polished and etched, and the macrometallic structure was observed. Figure 3 is a photograph of its macrometallic structure, with a magnification of 4x. It can be seen from FIG. 3 that this magnetic article has a homogeneous macrometallic structure, and there are no coarse crystal regions due to undeformed zones. Figure 4 shows this microstructure.
This is a metal micrograph at 650x magnification. Microstructures similar to those in FIG. 4 are observed at all positions in FIG. 3. As can be seen from FIG. 4, this microstructure is mainly composed of fine τ phase crystals of approximately 1 μm or less.

The effect of the permanent magnet of the present invention having an anisotropic structure having a planar easy magnetization direction in magnetic applications compared to a general radially anisotropic structure will be specifically described.

As an example of a permanent magnet with a radially anisotropic structure,
A radially anisotropic strontium ferrite magnet manufactured by a known method was used. Its magnetic properties are
In the radial direction, Br=3.6kG, Hc=2.6kOe, (BH)
max=2.8MG・Oe in string direction, Br=1.4kG, Hc
= 1.2kOe, (BH)max = 0.5MG・Oe.
The shape used for magnetization is outer diameter 24 mm, inner diameter 12 mm, and length.
It is 15mm. The outer periphery of this cylindrical magnetic article was magnetized with 20 poles. For magnetization, a 2000μF oil capacitor was used, and pulse magnetization was performed at 1500V. When the surface magnetic flux density at the outer periphery was measured using a Hall element, the peak value at each magnetic pole was 1.3 to 1.4 kG.

Next, from among the permanent magnets of the present invention, one that can be considered to have almost the same magnetic properties in the radial direction as the above-mentioned magnet is selected, processed into the same cylindrical shape as above, and magnetized with a multi-pole outer circumference under the same magnetization conditions. was applied. Although the shape of the demagnetization curve of this magnet is somewhat different from that of the above-mentioned strontium ferrite, it is thought that the magnetic flux density near the operating point on the demagnetization curve is not significantly different. That is, Br=4.2kG, Hc=1.9kOe, (BH)
max=2.9MG·Oe, and this magnetic property is uniform in each direction in the plane perpendicular to the axis of symmetry. When the surface magnetic flux density of the outer peripheral portion was similarly measured, the peak value at each magnetic pole was 2.1 to 2.2 kG, indicating that the anisotropic structure of the present invention is highly effective. The difference in the (001) pole density mentioned above was measured by X-ray diffraction method for the permanent magnet used here, and it was found that the difference in the (001) pole density was approximately
It was 3.5 times as hot.

The permanent magnet of the present invention is made of a known Mn-Al-C alloy for magnets, for example, 68 to 73% by weight of Mn and (1/10
An alloy consisting of Mn-6.6) to (1/3Mn-22.2)% by weight of C and the balance Al is processed into a uniaxial, homogeneous, fine powder by a known method such as warm extrusion in a temperature range of 530℃ to 830℃. It can be obtained by forming a [001] fiber structure and then subjecting it to warm compression in the axial direction. In other words, after applying macroscopically positive plastic strain, negative plastic strain is applied. In this compression process, it is necessary that the absolute value of logarithmic strain (hereinafter simply referred to as logarithmic strain) of at least 0.1 is free compression. 0.1
In the above processing, mold upsetting may be performed depending on the purpose. For example, axisymmetric magnetic articles such as rotor magnets can also be shaped by molding.

Next, an example will be described.

In the blended composition, 69.5% by weight of Mn, 29.3% by weight of Al,
A cylindrical billet with a diameter of 40 mm and a length of 40 mm was prepared by melting and casting 0.5% by weight of C and 0.7% by weight of Ni in the atmosphere. This billet was held at 1100°C for 2 hours, then air cooled to 500°C and heat treated at 600°C for 20 minutes. Next, warm extrusion processing to a diameter of 15 mm was performed at a temperature of 720°C using a lubricant.
The extrusion ratio is 7.1 and the logarithmic strain is 0.2. extruded rod length
It was cut into 30 mm pieces, and warm free compression processing was performed at 700°C to a height of 7.5 mm with lubricant applied to both ends. The logarithmic distortion is 1.4. A 6 mm x 6 mm x 6 mm sample for measuring magnetic properties was cut from a portion near the outer periphery of this magnet with a diameter of approximately 30 mm. Magnetic properties are radial and chordal, Br=4.7kG, Hc=2.9kOe, (BH)max=
It was 4.3MG・Oe. On the other hand, in the axial direction, Br=
2.6kG, Hc=2.0kOe, (BH)max=1.4MG・Oe
It was hot. When the difference in the above-mentioned (001) polar density was measured from the remaining sample by X-ray diffraction, it was found to be about 9 times as large.

Further, the magnet produced under the same conditions as above was machined into a cylindrical shape with an outer diameter of 24 mm, an inner diameter of 12 mm, and a length of 7 mm, and the outer periphery was magnetized with 20 poles under the above conditions. The surface magnetic flux density peak value at each magnetic pole on the outer periphery was 2.6 to 2.7 kG, and it was an extremely excellent permanent magnet article for multipolar magnetization.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of an axially symmetrical magnetic article according to the present invention, and Fig. 2 schematically shows the formation of a magnetic path inside the magnet when shifting magnetization is applied to the outer periphery of the magnetic article. FIG. 3 is a photograph macroscopically showing the metal structure in a plane including the axis of symmetry, and FIG. 4 is a photomicrograph showing the microscopic structure.

Claims (1)

[Scope of Claims] 1. In a polycrystalline manganese-aluminum-carbon alloy magnet mainly composed of a face-centered tetragonal structure, the [001] axis of the face-centered tetragonal structure may be in any direction parallel to a specific plane. is arranged preferentially in the direction of the perpendicular line to the plane, has an easy magnetization direction in the plane, is magnetically isotropic within the plane, and is magnetic within any plane including the perpendicular line. is anisotropic, exhibits a (001) polar density in any direction parallel to the plane that is three times or more as compared to the perpendicular direction, and has a (001) density in any direction parallel to the plane. ) A permanent magnet characterized by a change in polar density of 10% or less.