JP2966168B2 - Rare earth magnet, alloy powder for rare earth magnet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth sintered magnet or a bonded magnet which is most suitable for a motor or an actuator, and more particularly to a Fe--Co having a specific composition containing a small amount of a rare earth element.
A bonded magnet having a residual magnetic flux density Br of 5 kG or more, which cannot be obtained with a hard ferrite magnet, by forming an amorphous structure of a molten BR alloy by an ultra-quenching method and obtaining a fine crystal aggregate by a specific heat treatment. The present invention relates to a production method for obtaining an alloy powder for a rare earth magnet which is most suitable for the present invention.

[0002]

2. Description of the Related Art Permanent magnets used for motors and actuators for electrical components are mainly limited to hard ferrite magnets. 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. Cohoorn et al., J. dePhys., C.
8, 1988, 669-670). This magnet material is obtained by heat-treating an amorphous ribbon to obtain Fe.
₃ is a metastable structure with a crystal texture of B and Nd ₂ Fe ₁₄ B but, iHc is not high as about 2～3KOe, also the heat treatment conditions for obtaining the iHc is narrowly restricted, industrial production practical Not.

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. Magn, Magn, Mat, 89 (1991)
(Pp. 335-340) is to increase the Curie temperature by replacing a part of Fe with Co to improve the temperature coefficient of iHc, but there is a problem that iHc is reduced with the addition of Co.

In any case, Fe ₃ B type Nd-Fe-B
The system magnet can be made into a hard magnet material by heat treatment after being made amorphous by a super quenching method. However, the iHc is low, and the heat treatment conditions are severe. As a result, stable industrial production cannot be performed, 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 type Fe—BR based magnets (R is a rare earth element) and focuses on iHc and (BH) m
a. Manufacturing method that enables stable industrial production by improving ax and Fe ₃ B that has a residual magnetic flux density Br of 5 kG or more and can be provided at low cost as a substitute for hard ferrite magnets
It is intended for a type Nd-Fe-B based magnet.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been studied variously for the purpose of improving the iHc and (BH) max of a Fe ₃ B type Fe—BR magnet and enabling a stable industrial production. As a result, it was found that when a molten alloy having a specific composition with a low content of rare earth elements is formed into an amorphous structure by the ultra-quenching method, the addition of a small amount of Co enhances the ability of the alloy to form an amorphous phase. The present inventors have found that by obtaining a fine crystal aggregate by heat treatment, it is possible to obtain a rare earth magnet alloy powder that is optimal for a bonded magnet having a residual magnetic flux density Br of 5 kG or more, which was not obtained with a hard ferrite magnet. completed.

According to the present invention, the composition formula is represented by Fe _100-xyz Co _x
B _y R _z (where R is Pr or one or two of Nd)
The symbols x, y, and z that limit the composition range satisfy the following values, have a Fe ₃ B-type compound as a main phase, have a ferromagnetic phase having an Nd ₂ Fe ₁₄ B-type crystal structure, and have an average crystal. Particle size is 0.
A rare earth magnet comprising a fine crystal aggregate having a diameter of from 0.1 to 0.1 μm. 0.05 ≦ x ≦ 15 at% 16 ≦ y ≦ 22 at% 3 ≦ z ≦ 6 at%

Further, according to the present invention, the composition formula is Fe
_{100-xyz Co x B y R} z ( where R is 1 Pr or Nd
Or two kinds), and a symbol x for limiting the composition range,
y and z satisfy the above-mentioned values, have a ferromagnetic phase having a Fe ₃ B-type compound as a main phase and an Nd ₂ Fe ₁₄ B-type crystal structure, and an average crystal grain size of 0.01 to 0.1 μm. Having an average particle diameter of 3 to 500 μm, magnetic properties of iHc ≧ 2 kOe, Br ≧ 7 kG, and (BH) max ≧ 6.
It is an alloy powder for rare earth magnets, which is MGOe.

The present invention also provides (1) a composition formula of Fe
_{100-xyz Co x B y R} z ( where R is 1 Rr or Nd
Or two kinds), and a symbol x for limiting the composition range,
An alloy structure in which y and z satisfy the above-mentioned values substantially has an amorphous structure of 90% or more by the ultra-quenching method. (2) Further, the rate of temperature rise from 500 ° C. to 1 ° C. to 10 ° C. in heat treatment
/ 3 minutes and heat treatment at 550 to 700 ° C. for 5 minutes to 6 hours. (3) Fe ₃ B type compound as main phase,
After obtaining a fine crystal aggregate having a ferromagnetic phase having an Nd ₂ Fe ₁₄ B-type crystal structure and an average crystal grain size of 0.01 to 0.1 μm, (4) pulverizing the aggregate to obtain an alloy for magnets A method for producing an alloy powder for a rare earth magnet, characterized by obtaining a powder.

[0015]

According to the present invention, when a molten alloy of Fe-Co-BR-based alloy having a specific composition with a small content of rare earth elements has an amorphous structure of substantially 90% or more by a super-quenching method, a specific amount of Co is reduced. , The recovery rate of the amorphous ribbon is significantly improved, and the obtained flakes and ribbons are heated at a rate of 1 to 10 ° C./min.
By performing a heat treatment at a temperature of about 700 ° C. for 5 minutes to 6 hours, a fine crystal aggregate having an average crystal grain size of 0.01 to 0.1 μm is formed, and in addition to the main phase Fe ₃ B-type compound phase, Nd ₂
By increasing the ratio of the ferromagnetic phase having the Fe ₁₄ B-type crystal structure phase and decreasing the α-Fe phase, a permanent magnet ribbon is formed. iHc ≧ 2 kOe, Br ≧ 7 kG, (BH)
A magnetic property of max ≧ 6 MGOe is obtained, and Fe—C optimal for a bonded magnet having a residual magnetic flux density Br of 5 kG or more
An alloy powder for an o-B-R magnet can be obtained, and by forming a sintered magnet, magnetic properties equal to or higher than those of a conventional alnico magnet can be obtained.

Reasons for Restriction of Composition High magnetic properties can be obtained only when the rare earth element R contains one or two kinds of Pr or Nd in a specific amount.
For example, in Ce and La, iHc characteristics of 2 kOe or more cannot be obtained, and middle rare earth elements and heavy rare earth elements after Sm cause deterioration of magnetic characteristics and make the magnet expensive, which is not preferable. If R is less than 3 at%, iHc of 2 kOe or more cannot be obtained, and if it exceeds 6 at%, Fe ₃
Since the B phase is not generated and the α-Fe phase becomes the main phase and iHc is remarkably lowered, it is not preferable. Therefore, the range is 3 to 6 at%.

When 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. Is not obtained, so that
The range is from 0.5 to 15 at%.

Fe occupies the residual content of the above-mentioned elements.

Reasons for Limiting Manufacturing Conditions In the present invention, the molten alloy having the specific composition described above is made amorphous by a rapid quenching method,
After raising the temperature at a rate of 50 ° C./min,
By performing a heat treatment of holding for minutes to 6 hours, the ferromagnetic phase having a Fe ₃ B type compound and a Nd ₂ Fe ₁₄ B type crystal structure which are thermodynamically metastable, and having an average crystal grain size of 0.
It is most important to obtain a fine crystal aggregate having a diameter of from 0.1 to 0.1 μm. For the ultra-quenching treatment of the molten alloy, a known ultra-quenching method using a rotating roll can be employed. The above must be made amorphous. For example, when a Cu roll is used, the roll surface peripheral speed is preferably in the range of 10 to 50 m / sec because a suitable structure can be obtained. In other words, if the peripheral speed is less than 10 m / sec, it does not become amorphous and the precipitation amount of the α-Fe phase increases, which is not preferable. If the roll surface peripheral speed exceeds 50 m / sec, a quenched alloy is formed as a continuous ribbon. However, the alloy pieces are scattered, and the recovery rate and recovery efficiency when recovering the alloy from the apparatus are undesirably reduced. However, even if a trace amount of the α-Fe phase is present in the quenched ribbon, the characteristics are not remarkably deteriorated but are acceptable.

In the present invention, after the molten alloy having the above specific composition is made to be substantially 90% or more amorphous by the ultra-quenching method, the heat treatment for maximizing the magnetic properties depends on the composition. If the temperature is lower than 550 ° C., iHc of 2 kOe or more cannot be obtained while maintaining the amorphous phase.
If the temperature exceeds ℃, an α-Fe phase which is a thermal equilibrium phase and a Fe ₂ B or Nd _1.1 Fe ₄ B ₄ phase are formed and iHc is not generated, so the heat treatment temperature is limited to 550 to 700 ° C. The heat treatment atmosphere is preferably an inert gas atmosphere such as Ar gas.

The heat treatment time may be short, but if it is less than 5 minutes, a sufficient microstructure is not formed, iHc and the squareness of the demagnetization curve are degraded, and if it exceeds 6 hours, it is 2 kOe.
Since the above iHc cannot be obtained, the heat treatment holding time is limited to 5 minutes to 6 hours.

An important feature of the present invention is that the rate of temperature rise during heat treatment from 500 ° C. or higher is 1 ° C. /
At a heating rate of less than 10 minutes, the Nd ₂ Fe ₁₄ B phase and F
The crystal grain size of the e ₃ B phase grows too large to deteriorate iHc, and iHc of 2 kOe or more cannot be obtained. 10 ° C
If the temperature rise rate exceeds 500 ° C./min, the precipitation of the Nd ₂ Fe ₁₄ B phase formed after passing through 500 ° C. is not sufficiently performed, and α-
The precipitation amount of the Fe phase increases, and Br in the second quadrant of the magnetization curve.
A demagnetization curve with a decrease in magnetization near the point is obtained, and (BH) m
This is not preferable because ax deteriorates. However, a small amount of α-
The presence of the Fe phase is acceptable. In addition, 50
Up to a temperature of less than 0 ° C., the heating rate such as rapid heating is arbitrary.

Crystal Structure The crystal phase of the rare earth magnet and the alloy powder for the rare earth magnet according to the present invention is mainly composed of Fe ₃ B type compound, and Nd ₂ Fe ₁₄
It has a ferromagnetic phase having a B-type crystal structure, and is characterized by comprising a fine crystal aggregate having an average crystal grain size of 0.01 to 0.1 μm.

In the present invention, if the average crystal grain size of the magnet alloy exceeds 0.1 μm, the squareness of the demagnetization curve is remarkably deteriorated, and the magnetic properties of Br ≧ 8 kG and (BH) max ≧ 7MGOe are obtained. Can not. Although the average crystal grain size is preferably as small as possible, it is difficult to obtain an average crystal grain size of less than 0.01 μm in industrial production.
01 μm.

Magnetization Method A melt of an alloy having a specific composition is made amorphous by a rapid quenching method, and the temperature is raised from 500 ° C. or more at a rate of 1 to 10 ° C./min. By performing the heat treatment for 6 hours, the average crystal grain size becomes 0.01 to 0.1.
In order to magnetize using the alloy powder for a rare earth magnet according to the present invention obtained as a 1 μm fine crystal aggregate, any of a known method of forming a sintered magnet and a method of forming a bonded magnet that can be solidified and consolidated at 700 ° C. or lower. In particular, after pulverizing the alloy into an alloy powder having an average particle diameter of 3 to 500 μm, and then mixing the alloy with a known binder to form a required bonded magnet, a residual magnetic flux density Br of 5 kG or more can be obtained. A bonded magnet having the same can be obtained.

[0027]

Example 1 Example 1 of Table 1 99.5 purity so as to have a composition of 1-5
% Or more of metals of Fe, Co, B, Nd, and Pr,
The weight is weighed so that the total amount becomes 30 gr.
into a quartz crucible having a 2.5 mm orifice, melted by high-frequency heating in an Ar atmosphere at a pressure of 56 cmHg, set the melting temperature to 1400 ° C., pressurized the molten metal surface with Ar gas, and rolled at room temperature a roll peripheral speed of 20 m. The molten metal is ejected from the height of 0.7 mm onto the outer peripheral surface of the Cu roll rotating at a high speed at a rate of 2 to 3 mm in width and 30 to 40 μm in thickness.
A super quenched ribbon was prepared. The obtained super-quenched ribbon is CuK
It was confirmed by the characteristic X-ray of α that the film was amorphous.

After the ultra-quenched ribbon was rapidly heated to 500 ° C. in Ar gas, the temperature was raised to 500 ° C. or higher 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, take out the ribbon, width 2-3mm,
A sample having a thickness of 30 to 40 μm and a length of 3 to 5 mm is prepared,
Magnetic properties were measured using VSM. Table 2 shows the measurement results. The measurement results of the sample show that the main phase is a Fe ₃ B phase in which tetragonal and orthorhombic are mixed, and a multiphase structure in which Nd ₂ Fe ₁₄ B and α-Fe are mixed. Was 0.1 μm or less. Note that Co replaces part of Fe in each of these phases.

Comparative Example Composition No. 1 of Example 1 obtained under the same conditions as Example 1 5 was rapidly heated to 500 ° C. in Ar gas, and the temperature was raised from 500 ° C. or higher at 11 ° C./min.
A heat treatment for 5 minutes was performed, and after cooling, a sample was prepared under the same conditions as in Example 1 (Comparative Example No. 6), and the magnetic characteristics were measured using a VSM. Table 2 shows the measurement results.

The composition No. of Example 1 obtained under the same conditions as in Example 1 After rapidly heating the ultra-quenched ribbon of Example 2 to 500 ° C. in Ar gas, Comparative Example No. 2 was heated. No. 7 was heat-treated at 500 ° C. for 10 minutes. 8 was subjected to a heat treatment at 500 ° C. or higher at 4 ° C./min and held at 750 ° C. for 10 minutes.
Was used to measure magnetic properties. Table 2 shows the measurement results.
Comparative Example No. 7 is an amorphous structure; 8 is Fe
₂ B phase and alpha-Fe phase was multi-phase morphology of mixed.

Example 2 The composition No. in Table 1 obtained in Example 1 was used. After the heat treatment shown in Table 1, the ultra-quenched ribbon 2 was pulverized to an average particle diameter of 100 μm or less, and a binder made of an epoxy resin was mixed at a ratio of 3 wt% to prepare a bonded magnet having a size of 12 mm × 12 mm × 8 mm. . The magnetic properties of the obtained bonded magnet were as follows: density 5.4 g / cm ³ , iHc = 3.9 kOe, B
r = 5.25 kG, (BH) max = 4.6 MGOe.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

According to the present invention, Fe-Co-B having a specific composition
-R-based alloy melt is formed into an amorphous structure by a rapid quenching method, and is subjected to heat treatment under specific conditions to form a fine crystal aggregate having an average crystal grain size of 0.01 to 0.1 μm, and the main phase Fe ₍₃₎ in addition to B type compound phase, Nd ₂ ratio of Fe ₁₄ B type crystal structure phase is increased by alpha-Fe phase decreases, becomes permanent magnet ribbon, alloy powder for a magnet was further pulverized into By the conversion, iHc ≧ 2 kOe,
Magnetic characteristics of Br ≧ 7 kG and (BH) max ≧ 6 MGOe are obtained, and an alloy powder for a Fe—Co—BR based magnet optimal for a bonded magnet having a residual magnetic flux density Br of 5 kG or more can be obtained. By using a sintered magnet, magnetic properties equal to or higher than those of a conventional alnico magnet can be obtained. Further, the present invention has a low rare earth element content,
Since the manufacturing method is simple and suitable for mass production, it has a residual magnetic flux density Br of 5 kG or more, has magnetic performance exceeding that of hard ferrite magnets, and adopts integral molding of magnetic parts and magnet bodies. Process can be shortened,
It is possible to provide a bonded magnet capable of realizing a performance-to-cost ratio exceeding that of sintered hard ferrite.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01F 1/06 C22C 38/00 303 H01F 1/053

Claims (3)

(57) [Claims] The method according to claim 1] composition formula _{Fe 100-xyz Co x B y} R z
(Where R is one or two of Pr or Nd)
Symbols x, y and z for limiting the composition range satisfy the following values,
Fe ₃ B type compound as main phase, having ferromagnetic phase having Nd ₂ Fe ₁₄ B type crystal structure, average grain size of 0.01 to
A rare earth magnet comprising a fine crystal aggregate of 0.1 μm. 0.05 ≦ x ≦ 15 at% 16 ≦ y ≦ 22 at% 3 ≦ z ≦ 6 at% 2. A method composition formula _{Fe 100-xyz Co x B y} R z
(Where R is one or two of Pr or Nd)
Symbols x, y and z for limiting the composition range satisfy the following values,
Fe ₃ B type compound as main phase, having ferromagnetic phase having Nd ₂ Fe ₁₄ B type crystal structure, average grain size of 0.01 to
It is composed of a fine crystal aggregate of 0.1 μm and has an average particle size of 3 to
500 μm, magnetic properties iHc ≧ 2 kOe, Br ≧ 7 k
G, (BH) max ≧ 6MGOe, an alloy powder for rare earth magnets. 0.05 ≦ x ≦ 15 at% 16 ≦ y ≦ 22 at% 3 ≦ z ≦ 6 at% The 3. A composition formula _{Fe 100-xyz Co x B y} R z
(Where R is one or two of Rr or Nd)
The alloy melt in which the symbols x, y, and z satisfying the following values that limit the composition range have substantially 90% or more of an amorphous structure by a rapid quenching method. A heat treatment is performed by raising the temperature at 10 ° C./min and maintaining the temperature at 550 to 700 ° C. for 5 minutes to 6 hours, and has a ferromagnetic phase having an Fe ₃ B type compound as a main phase and having an Nd ₂ Fe ₁₄ B type crystal structure. And obtaining a fine crystal aggregate having an average crystal grain size of 0.01 to 0.1 μm, and then pulverizing the fine crystal aggregate to obtain an alloy powder for a magnet. 0.05 ≦ x ≦ 15 at% 16 ≦ y ≦ 22 at% 3 ≦ z ≦ 6 at%