JP3032385B2 - Fe-BR bonded magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fe-BR based bonded magnet which is most suitable for motors and actuators, and has a specific composition of Fe-Co-B- (R, Dy) based alloy having a small content of rare earth elements. Most of the molten metal (where R is one or two of Pr or Nd) is made to have an amorphous structure by the rapid quenching method, and body-centered tetragonal Fe ₃ B
Iron-based boride phase with crystal structure and Nd ₂ Fe
₁₄ Fe-BR bonded magnets with a residual magnetic flux density Br of 5 kG or more, which were not obtained with hard ferrite magnets, by combining an alloy powder consisting of fine crystal aggregates with constituent phases of B-type crystal structure with resin About.

[0002]

2. Description of the Related Art Permanent magnets used in motors and actuators for electrical components are mainly limited to hard ferrite magnets. However, low-temperature demagnetization due to a decrease in iHc at low temperatures and mechanical strength due to ceramic materials. However, there are problems that cracks and chips are apt to occur due to the low shape, and that it is difficult to obtain a complicated shape.

[0003] Today, there is a strong demand for automobiles to improve fuel efficiency by reducing the weight of the vehicles in order to save resources, and it is required to further reduce the size and weight of electrical components for automobiles. Also,
Designs to maximize the performance-to-weight ratio are also being considered for applications such as motors for home appliances other than automotive electrical components, and the current motor structure is optimal for magnet materials with a Br material of about 5 to 7 kG. It has been. That is,
When Br of the magnet material to be used is 8 kG or more, the current motor structure needs to increase the cross-sectional area of the iron plate of the rotor or the stator which becomes the magnetic path, which leads to an increase in weight. If so, the performance to weight ratio can be maximized.

Accordingly, a magnetic material for a small motor is required to have a residual magnetic flux density Br of at least 5 kG in terms of magnetic properties, but cannot be obtained with a conventional hard ferrite magnet. For example, an Nd—Fe—B-based bonded magnet satisfies such magnetic properties, but Nd or the like, which requires a large number of steps and large-scale facilities for metal separation and purification or reduction reaction, is required.
Since it contains １５15 at%, it is significantly more expensive than a hard ferrite magnet, and at present, a magnet material having Br of about 5 to 7 kG that can be mass-produced and can be provided at low cost has not been found.

[0005]

On the other hand, Nd-Fe-B
In recent years, a magnet material having a main phase of Fe ₃ B type compound in the vicinity of Nd ₄ Fe ₇₇ B ₁₉ (at%) has been proposed as a system magnet (R. Cohoenor et al., J. de Phys., C.
8, 1988, 669-670). This magnet material is obtained by heat-treating an amorphous ribbon to obtain Fe.
Metastable structure having ₃ B and Nd ₂ Fe ₁₄ B crystalline texture but, iHc is low as 2～3KOe, also the heat treatment conditions for obtaining the iHc is narrowly limited, not industrial production on a practical .

Researches have been published to improve the performance by adding an additional element to the magnetic material having the Fe ₃ B-type compound as a main phase to make it multi-component. One of them is to improve iHc by using Dy and Tb in addition to Nd as a rare earth element. In addition to the problem of adding an expensive element, the added rare earth element has a magnetic moment of Nd or Fe. There is a problem that magnetization decreases due to coupling in anti-parallel to the moment (R. Coehorn, J. Magn, Magn, M
at. , 83 (1990) 228-230).

[0007] Other studies (Shen Bao-gen et al.,
J. See Magn, Magn, Mat. , 89 (1991)
335-340), a part of Fe is replaced with Co to raise the Curie temperature to improve the temperature coefficient of iHc, but there is a problem that Br is reduced with the addition of Co.

In any case, the Fe ₃ B-based Nd-Fe-B magnet can be made into a hard magnet material by heat treatment after being made amorphous by a super-quenching method. However, since the iHc is low and the heat treatment conditions are narrow, the addition of If the element is made to have high iHc, stable industrial production cannot be performed, such as a decrease in magnetic energy product, and it cannot be provided at a low cost as a substitute for a hard ferrite magnet.

Further, in order to make the Nd-Fe-B-based alloy amorphous, it is necessary to remarkably increase the roll peripheral speed at the time of ultra-quenching, and there is a problem that the product recovery rate and the yield are reduced. Since it is a base alloy, there is a problem that corrosion at the time of storage is apt to progress, and the magnetic properties at the initial stage cannot be maintained due to long-term storage, resulting in deterioration.

The present invention focuses on Fe ₃ B-based Fe-BR magnets (R is a rare earth element), improves iHc and (BH) max, has a residual magnetic flux density Br of 5 kG or more, and has a stable industrial production. Fe ₃ B system that can be provided at low cost as an alternative to hard ferrite magnets
Intended for Fe-BR bonded magnets.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a Fe ₃ B-based Fe-B
As a result of various investigations for the purpose of improving the iHc and (BH) max of the -R magnet and achieving stable industrial production, the following findings were obtained and completed. Rare earth element R (R: Pr, Nd 1
Nd ₂ Fe by substituting one part of
_While improving the anisotropic magnetic field of the ₁₄ B phase to achieve high coercive force, a small amount of Co is added, and a part of Fe in the Fe ₃ B phase is replaced by Co, resulting in a completely amorphous phase. Even without it, the same crystal structure as Fe ₃ B, that is, a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure,
After addition quenching, by suitable heat treatment, a compound phase of the boride phase and Nd ₂ Fe ₁₄ B crystal structure coexist in the same powder particles, yet when the average crystal grain size in the range of 5 nm to 100 nm, Demonstrate a specific coercive force of 2 kOe or more necessary for practical use,
By molding and solidifying the alloy powder into a required shape with a resin, a metastable crystal structure phase can be provided in a form usable as a permanent magnet without being decomposed at around room temperature.

According to the invention, the composition formula of the alloy powder is Fe
_{100-xyz Co x B y (} R 1-a Dy a) z ( where R is Pr or one or two of Nd) represents the symbol limiting the composition range x, y, z, a
Satisfies the following values, a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure and a constituent phase of Nd ₂ Fe ₁₄ B type crystal structure coexist in the same powder particles, The average crystal grain size of the constituent phases is in the range of 5 nm to 100 nm, and the average grain size is 3 μm to 500 μm
Fe-BR characterized in that the powder is bonded with a resin
It is a bonded magnet. 0.05 ≦ x ≦ 15at% 16 ≦ y ≦ 22at% 3 ≦ z ≦ 5.5at% 0.02 ≦ a ≦ 0.7

In order to obtain the Fe-BR bond magnet according to the present invention, the following manufacturing method is used. (1) the composition formula _{Fe 100-xyz Co x B y} (R 1-a Dy a) z
(Where R represents one or two of Pr or Nd), and the symbols x, y, z, and a defining the composition range substantially satisfy 90% of the molten alloy by the ultra-quenching method. The above is regarded as an amorphous structure. (2) In the heat treatment, the temperature is raised from 500 ° C. at a rate of 1 to 15 ° C./min to 5
Heat treatment at 50 to 700 ° C. for 5 minutes to 6 hours,
(3) having a ferromagnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure with an Fe ₃ B type compound as a main phase, and having an average crystal grain size of 5 nm
After obtaining a fine crystal aggregate having a size of about 100 nm, (4) a powder having an average particle diameter of 3 to 500 μm obtained by pulverizing the aggregate is molded and solidified into a required shape with a resin.

Reasons for Limiting Constituent Phase of Powder The alloy powder constituting the bonded magnet according to the present invention is a boride phase containing iron as a main component and having a body-centered tetragonal Fe ₃ B crystal structure having a high saturation magnetization of 1.6 T. Is the main phase. This boride is Fe ₃ B or a compound in which a part of Fe is substituted with Co, and the boride phase is Fe ₃ B or
A part of Fe is replaced by Co. This boride phase can metastable in a specific range and coexist with the Nd _{2 (} Fe, Co) ₁₄ B ferromagnetic phase having the Nd ₂ Fe ₁₄ B type crystal structure of the space group P ₄ / nmn. The coexistence of these boride phase and ferromagnetic phase is essential for obtaining a high magnetic flux density and sufficient iHc, and even if they have the same composition, for example, in a casting method or the like, C1
When the Fe ₂ B phase having a 6-type crystal structure and the body-centered cubic α-Fe phase become the main phases, high magnetization is obtained, but iHc is deteriorated to 1 kOe or less, which is not preferable because it cannot be used as a magnet. .

Reasons for Limiting Composition The rare earth element R can provide high magnetic properties only when it contains Dy in addition to one or two kinds of specific amounts of Pr or Nd, and rare earth elements R such as Ce and La iHc is 2k
Characteristics higher than Oe cannot be obtained, and medium rare earth elements and heavy rare earth elements after Sm are not preferable because they cause deterioration of magnetic characteristics and increase the cost of the magnet. R is 3at%
If it is less than 2, iHc of 2 kOe or more cannot be obtained, and 5.5
If it exceeds at%, the Fe ₃ B phase is not formed, and the metastable phase R ₂ Fe ₂₃ B ₃ phase which does not show hard magnetism is deposited. Range. The reason why the amount of Dy in R is limited to 0.02 to 0.7 is that if less than 0.02, iHc of 4 kOe or more cannot be obtained, and if it exceeds 0.7, the reduction of Br is not preferable. .

If B is less than 16 at% or more than 22 at%, iHc of 2 kOe or more cannot be obtained.
２２22 at%.

Co is effective for improving and improving the squareness of the iHc and demagnetization curve. However, if the content is less than 0.05 at%, such an effect cannot be obtained. If the content exceeds 15 at%, iHc is remarkably reduced and 2 kOe or more. Since iHc cannot be obtained, 0.
The range is from 0.5 to 15 at%.

Fe accounts for the residual content of the above-mentioned elements.

Reasons for limiting crystal grain size and powder grain size Body-centered tetragonal coexisting in the alloy powder constituting the bonded magnet of the present invention
Iron-based boride phase with Fe ₃ B crystal structure and Nd
_{The 2} Fe ₁₄ B-type crystal phases are all ferromagnetic phases, but the former phase is magnetically soft by itself, and the coexistence of the latter phase is essential for the expression of iHc. However, simply coexisting both phases is not enough, and if the average crystal grain size of both is not in the range of 5 nm to 100 nm, the squareness of the second quadrant of the demagnetization curve deteriorates, and as a permanent magnet, Since sufficient magnetic flux cannot be extracted at the operating point, the average crystal grain size is
Limited to 5-100 nm. Making use of the characteristics of bonded magnets that can produce magnets with complex shapes and thin shapes, high-precision molding requires that the powder particle size be sufficiently small. It is necessary to use a large amount of resin as a binder as the surface area increases, and the packing density decreases, which is not preferable.
Limited to 500 μm.

The bonded magnet according to the present invention is an isotropic magnet, and has the following compression molding, injection molding, extrusion molding,
Any known production method such as rolling molding and resin impregnation may be used. In the case of compression molding, it is obtained by adding and kneading a thermosetting resin, a coupling agent, a lubricant and the like to the magnetic powder, and then compressing and heating to cure the resin. In the case of injection molding, extrusion molding, or rolling molding, a thermoplastic resin, a coupling agent, a lubricant, etc. are added and kneaded to the magnetic powder, and then molded by any of injection molding, extrusion molding, and rolling molding. Can be In the resin impregnation method, after magnetic powder is compression-molded, heat-treated if necessary, then impregnated with a thermosetting resin, and heated to cure the resin. Further, the magnetic powder is obtained by compression molding, heat-treating as necessary, and then impregnating with a thermoplastic resin.

In the present invention, the filling rate of the magnetic powder in the bonded magnet varies depending on the above-mentioned manufacturing method.
5 wt%, and the remaining 0.5 to 30 wt% is resin and others. In the case of compression molding, the filling ratio of the magnetic powder is 95 to 9
9.5 wt%, in the case of injection molding, the filling rate of the magnetic powder is 9
In the case of the resin impregnation method, the filling rate of the magnetic powder is preferably 96 to 99.5 wt%.

As the synthetic resin used as the binder, those having both thermosetting properties and thermoplastic properties can be used, but thermally stable resins are preferable. For example, polyamides, polyimides, phenol resins, fluorine resins, silicon resins, and the like can be used. A basic resin, an epoxy resin, or the like can be appropriately selected.

[0023]

According to the present invention, by replacing a part of the rare earth element R (R is one or two of Pr and Nd) with Dy, a specific composition F
Space group I ₄
When forming a metastable mixed structure of a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure and a Nd ₂ Fe ₁₄ B type crystal phase, since a specific amount of Co is contained, Space group that is stable phase
The boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure of I ₄ is stabilized, and the boride phase of the space group I ₄ is used as the main phase without completely forming an amorphous structure. The average crystal grain size becomes a fine crystal aggregate of 5 nm to 100 nm, and in addition to a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure of the main phase, an Nd ₂ Fe ₁₄ B type crystal structure Thus, an alloy powder for a bonded magnet having a ferromagnetic phase is obtained, and a bonded magnet having magnetic characteristics of iHc ≧ 4 kOe, Br ≧ 5 kG, and (BH) max ≧ 3MGOe can be obtained by bonding with a resin.

[0024]

【Example】

Example No. 1 in Table 1 99.5 purity so as to have a composition of 1-5
% Or more of metals of Fe, Co, B, Nd, Pr, and Dy, weighed so that the total amount becomes 30 gr, and put into a quartz crucible having an orifice with a diameter of 0.8 mm at the bottom. After melting by high frequency heating in an Ar atmosphere and setting the melting temperature to 1400 ° C.,
A molten metal is jetted from a height of 0.7 mm onto the outer peripheral surface of a Cu roll which is pressurized with a gas and rotates at a high speed at a roll peripheral speed of 20 m / sec at room temperature to have a width of 2-3 mm and a thickness of 30-4.
A 0 μm ultra-quenched ribbon was produced. The obtained ultra-quenched ribbon was characterized by the characteristic X-ray of CuKα and the SEM photograph of the cross section of the ribbon.
It was confirmed that most (about 90 vol% or more) were amorphous.

After the ultra-quenched ribbon was rapidly heated to 500 ° C. in Ar gas, the temperature was raised to 500 ° C. or more at the temperature rising rate shown in Table 1, and kept at the heat treatment temperature shown in Table 1 for 10 minutes. After cooling to room temperature, the ribbon was removed. The structure of the sample was such that the tetragonal Fe ₃ B phase was the main phase, and the Nd ₂ Fe ₁₄ B phase and α
-Fe phase was mixed, and the average crystal grain size was 0.1 µm or less in each case. Note that Co replaces part of Fe in each of these phases.

The ribbon is pulverized to a particle size of 5 to 120 μm.
After obtaining a powder having an average particle size of 60 μm distributed over m, an epoxy resin was mixed at a ratio of 2 wt% with respect to 98 wt% of the powder, compression molded at a pressure of 6 ton / cm ² , and cured at 150 ° C. To obtain a bonded magnet. The density of this bonded magnet was 5.6 gr / cm ³ , and the magnet properties are shown in Table 2.

Comparative Example A super-quenched ribbon was prepared under the same conditions as in Example 1 using Fe, Co, B, and Nd having a purity of 99.5% or more so as to have the compositions of Nos. 6 and 7 in Table 1. . A
After rapidly heating to 500 ° C. in r gas, the temperature was raised to 500 ° C. or more at the temperature increasing rate shown in Table 1, and heat treatment was performed at the heat treatment temperature shown in Table 1 for 10 minutes. Samples were taken under the conditions and the magnetic properties were measured. Table 2 shows the measurement results.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

According to the present invention, R (R is Nd, Pr)
Fe-C of a specific composition in which one part of
The super-quenched oB- (R, Dy) alloy melt is heat-treated to form a boride phase mainly composed of iron having a body-centered tetragonal Fe ₃ B crystal structure, even if it is not completely amorphous. An average crystal grain size of 5 nm to 100 nm becomes a fine crystal aggregate, in addition to the boride phase, an alloy powder for a bonded magnet in which a ferromagnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure is obtained, and a resin is obtained. By bonding, a bonded magnet having magnetic characteristics of iHc ≧ 4 kOe, Br ≧ 5 kG, and (BH) max ≧ 3MGOe can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01F 1/08 C22C 38/00 303 H01F 1/053

Claims (1)

(57) [Claims] 1. The composition formula of an alloy powder is represented by Fe _100-xyz Co _{x By (} R
_1-a Dy _a ) _z (where R is one or two of Pr or Nd), and the symbols x, y, z, a that limit the composition range satisfy the following values, and the body-centered tetragonal Fe ₃ and construction phases of boride phase and Nd ₂ Fe ₁₄ B crystal structure coexist in the same powder particles containing iron as a main component having a B crystal structure, an average grain diameter of each component phase is 5nm~100nm
Wherein the powder having an average particle size of 3 μm to 500 μm is bonded with a resin. 0.05 ≦ x ≦ 15at% 16 ≦ y ≦ 22at% 3 ≦ z ≦ 5.5at% 0.02 ≦ a ≦ 0.7