JP2000026901A - RAW MATERIAL ALLOY POWDER FOR R-Fe-B SERIES SINTERED MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the crystal structure of alloy powder to exhibit high magnetic properties and to reduce load in a pulverizing stage in magnet production by allowing almost particles to have almost spherical shapes. SOLUTION: In alloy powder, almost particles have almost spherical shapes, preferably, of 20 to 500 μm diameter. As for the sintered magnet structure capable of exhibiting high magnetic properties, preferably, R2Fe14B phases (main phases) of about 5 to 10 μm particle size are coated with R-rich phase and B-rich phase liq. phase components, and the ratio of the main phases occupied in a magnet is made high as much as possible. Thus, as the raw material alloy powder, preferably, R-rich phases and B-rich phases are dispersed to stick to the vicinities of the main phase particles of single crystals of about 1 to 5 μm as to pulverized powder before sintering. The preferable compsn. of the alloy is composed of, by weight, 30 to 35% R, 0.9 to 1.2% B, and the balance Fe as the main components, where R denotes at least one kind among rare earth elements including Y, and a part of Fe may be substituted by one or two kinds of Co and Ni.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to R (where R is at least one of the rare earth elements including Y), Fe, and
Regarding the raw material alloy powder for an R-Fe-B based sintered magnet containing B as a main component, in particular, an R-Fe-B based sintered magnet having excellent magnetic properties can be obtained, The present invention relates to a raw material alloy powder for an R-Fe-B-based sintered magnet with a small load.

[0002]

BACKGROUND OF THE INVENTION R-Fe-B based sintered magnet, R ₂ Fe ₁₄
It is an excellent permanent magnet that can achieve a maximum energy product (BH) max of 50 MGOe or more by sintering an alloy powder having a structure composed of a B phase, an R rich phase, and a B rich phase after pressure molding. Various compositions have been proposed for this magnet to achieve desired magnetic properties.

[0003] As a method for producing an alloy powder which is a raw material of the magnet, a "melting casting method" and a "strip casting method" are known.

[0004] The "melting casting method" is a method in which a constituent metal or a mother alloy is blended in accordance with a target composition, and is melt-cast to obtain an ingot, which is pulverized. This method has a low oxygen content at the time of ingot, and the sedimentation of the rare earth metal phase which is easily oxidized is largely segregated, so that oxidation in the ingot crushing step can be relatively easily suppressed, and alloy powder having relatively low oxygen content Can be obtained.

However, primary crystals such as α-Fe segregate during casting, resulting in poor uniformity of the alloy structure and unavoidable coarsening of R ₂ Fe ₁₄ B phase crystal grains. Disadvantages are that a large amount of energy is required for the pulverization process.

[0006] The "strip casting method" is an improvement of the "melting casting method", and is a method in which a molten alloy is formed into a cast piece having a thickness of 0.1 to 10 mm by a roll method, and this is crushed. In this method, by controlling the cooling rate of the molten metal by the roll, there is no crystallization of α-Fe, and 0.1 to 50 μm in the short axis direction and 5 to 200 μm in the long axis direction.
And a raw alloy having a crystal structure occupied by a columnar R ₂ Fe ₁₄ B phase, an R-rich phase finely dispersed between the R ₂ Fe ₁₄ B phase, and the B-rich phase, A magnet with high magnetic properties can be obtained. Since the cast pieces obtained are smaller than in the "melting casting method", there is also an advantage that the cost required for the pulverizing step in the magnet manufacturing step is small (Japanese Patent Laid-Open No. 7-1995).
197182).

[0007]

However, even in the "strip casting method", it is necessary to coarsely pulverize a cast piece to a particle size that can be put into a fine pulverizer.

Therefore, the present invention has a crystal structure capable of exhibiting high magnetic properties and has a small load on a pulverizing step in a magnet manufacturing step. It is an object of the present invention to provide a possible R-Fe-B based sintered magnet raw material alloy powder.

[0009]

The raw material alloy powder for an R-Fe-B based sintered magnet according to the present invention for solving the above-mentioned object, comprises:
Most of the particles are substantially spherical with a diameter of 20 to 500 μm.

[0010] Desirably, the crystal structure in the particle has a short axis direction of 1 to 10 µm and a long axis direction of 5 to 100 µm.
μm columnar crystal R ₂ Fe ₁₄ B phase and its R ₂ Fe ₁₄ B phase
It is characterized by being composed of an R-rich phase and a B-rich phase finely dispersed in phase gaps.

The composition of the alloy powder is as follows: R: 30 to 35% by weight, B: 0.9 to 1.2% by weight, balance Fe (Fe
Can be replaced by one or two of Co and Ni) and inevitable impurities, or the composition is R: 2
6 to 35% by weight, B: 0.9 to 1.2% by weight, balance Fe
(However, a part of Fe can be replaced by one or two of Co and Ni) and an alloy powder that is an unavoidable impurity may be further mixed with an alloy powder for adjusting the composition.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention, that is, the function of each technical element (constituent article) and the reasons for limiting the numerical values will be described below.

In order to increase the remanent magnetization (Br), which is one of the magnetic characteristics of the R—Fe—B sintered magnet, the R ₂ Fe ₁₄ B phase in the magnet (hereinafter referred to as “main phase”). ) And the degree of orientation of the main phase needs to be increased. If the magnet composition is close to the main phase composition, the proportion of the main phase in the magnet can be increased.However, if the magnet composition is extremely close to the main phase composition, a liquid phase shortage in liquid phase sintering will occur, and the magnet Since the coercive force is reduced, there is a limit in approaching the composition.

Therefore, the main point of the current high magnetic properties is to increase the degree of orientation of the main phase rather than to make the magnet composition close to the main phase. In order to increase the degree of orientation of the main phase, it is necessary that the particles of the finely pulverized powder before the sintering step in magnet production are close to a single magnetic domain particle diameter. The maximum diameter of a single magnetic domain that can exist stably is about 5 to 10 μm.

On the other hand, the coercive force of the R—Fe—B sintered magnet is expressed by the fact that the surface of the main phase, which is a ferromagnetic phase, is covered with a low melting point phase (R-rich phase and B-rich phase), The nucleation mechanism eliminates the reverse magnetic domain generation site. Therefore, at the time of liquid phase sintering, a sufficient liquid phase component needs to be present around the main phase particles.

From the above, as a sintered magnet structure capable of exhibiting high magnetic properties, a main phase having a crystal grain size of about 5 to 10 μm is covered with an R-rich phase and a B-rich phase liquid phase component. In addition, it is desirable that the proportion of the main phase in the magnet is as large as possible. Therefore, as the raw material alloy powder, it is desirable that the R-rich phase and the B-rich phase are dispersed and attached around the single crystal main phase particles of about 1 to 5 μm in the finely pulverized powder before sintering.

As one of the crystal structures of the raw alloy powder before pulverization to obtain such a finely pulverized powder, the main phase is a columnar crystal having a length of 1 to 10 μm in the short axis direction and 5 to 500 μm in the long axis direction. The gaps between the columnar crystals include a crystal structure in which a finely dispersed R-rich phase and a B-rich phase are present. When the alloy powder having such a crystal structure is finely pulverized, crushing proceeds from the R-rich phase and the B-rich phase between the main phase columnar crystals, and the pulverization proceeds in such a manner that the columnar crystals dissociate. Further, the dissociated main phase columnar crystal particles are pulverized by collision with other particles, and finally the R-rich phase and the B-rich phase are dispersed and attached around the single crystal main phase particles of about 1 to 5 μm. Become particles.

As described above, the finely pulverized powder from the cast piece by the strip casting method also becomes particles in which the R-rich phase and the B-rich phase are dispersed and attached around the single crystal main phase particles of about 1 to 5 μm. However, the cast pieces obtained by the strip casting method need to be coarsely pulverized into particles of several mm or less before being put into a fine pulverizing apparatus. It is desirable to have spherical particles of 20 to 500 μm in diameter. The reason for setting the particle diameter to 20 to 500 μm is that the particles having a particle diameter of 500 μm or more exert a large load on a fine pulverizing device such as a jet mill, and the particles having a diameter of 20 μm or less cannot sufficiently grow the above-described crystal structure in the particles.

As a desirable composition of the alloy used in the present invention, R (where R is at least one of rare earth elements including Y): 30 to 35% by weight, B: 0.9 to 1.2% by weight,
The remainder: Fe (however, part of Fe can be replaced by one or two of Co and Ni) is the main reason for the following reasons.

The reason why the R grade is 30 to 35% by weight is that R
If the grade is 30% by weight or less, a sufficient coercive force cannot be obtained because a sufficient liquid phase is not supplied during liquid phase sintering in the magnetizing process.
If the R grade exceeds 35% by weight, the ratio of the main phase in the alloy decreases, the residual magnetic flux density decreases, and the magnetic properties deteriorate. Therefore, the R grade is desirably 30 to 35% by weight.

[0021] B grade from a 0.9 to 1.2% by weight, in the quality is less than 0.9 wt% of B to stabilize the main phase generating unnecessary to magnetic properties expression of R ₂ Fe ₁₇ phase etc. This is because when a phase is generated and exceeds 1.2% by weight, the generation ratio of the B-rich phase increases, the main phase ratio in the alloy powder decreases, the residual magnetic flux density decreases, and the magnetic properties deteriorate. Therefore, the B grade is desirably 0.9 to 1.2% by weight.

[0022] Co is effective to substitute for Fe because it raises the Curie temperature of the R-Fe-B based sintered magnet and improves the heat resistance of the magnet. It is not preferable because it lowers.

Further, R having the above-mentioned crystal structure (however, R
Is at least one of the rare earth elements containing Y): 26 to
35% by weight, B: 0.9 to 1.2% by weight, and the balance of raw material alloy powder containing Fe as a main component (however, part of Fe can be replaced by one or two of Co and Ni), especially Adding alloy powder for component composition adjustment to alloy powder with high phase ratio and supplementing the liquid phase component during liquid phase sintering to obtain magnet raw material alloy powder is an effective method for developing magnetic properties. is there.

The alloy powder for composition adjustment includes the required R-Fe
"Melting and pulverizing method" in which a B-based alloy is melted and pulverized after casting,
"Direct reduction diffusion method" to obtain powder directly by Ca reduction, "Quenched alloy method" in which required R-Fe-B-based alloy powder is crushed and annealed as a ribbon foil by a melt jet caster, required R-Fe- "Gas atomizing method" for dissolving B-based alloy and pulverizing by gas atomization, "Mechanical alloying method" for pulverizing required raw metal, pulverizing it by mechanical alloying and heat-treating, R-Fe-B required
"H" which is heated and decomposed and recrystallized in hydrogen
Isotropic or anisotropic R-Fe-B-based alloy powder obtained by various known manufacturing methods such as "DDR method", or R-Fe manufactured by "molten salt electrolysis method" or "melting casting method" -B eutectic composition alloy pulverized powder and the like can be used.

The raw material alloy powder for the R—Fe—B sintered magnet of the present invention can be, for example, an atomizing method, particularly a gas atomizing method. The reason is described below.

In order to cool the molten metal having the desired composition to obtain the above crystal structure, it is necessary to control the cooling rate of the molten metal. If the cooling rate is too high, the alloy becomes amorphous, and if the cooling rate is too low, coarse crystals grow and the desired crystal structure cannot be obtained.

In the strip casting method, the temperature can be controlled by the temperature of the molten metal, the temperature of the roll, the linear velocity of the roll relative to the molten metal, the plate thickness, and the like. However, in the strip casting method, it is necessary to grind the cast pieces to obtain powder.
On the other hand, in the atomization method, it is easy to directly obtain an alloy powder having a target particle size, and particles are controlled by controlling production conditions such as a spray medium, a melt temperature, a spray pressure, a spray nozzle diameter, and a spray nozzle shape. It can be obtained with the desired particle size. Further, control of the crystal structure, that is, 1 to 10 μm in the short axis direction
m, a columnar crystal of the main phase grown to 5 to 100 μm in the major axis direction, and an R-rich phase finely dispersed between the main-phase columnar crystals, and a structure in which the B-rich phase occupies,
It can be easily obtained by optimizing the manufacturing conditions in the atomizing method.

The R-Fe-B alloy powder according to the present invention,
In particular, in the production of an Nd-Fe-B-based alloy powder in which Nd is selected as R by an atomizing method, an inert gas is desirably used as a spray medium. This is because the Nd—Fe—B-based alloy powder has a high activity in the atomization method using air and water, so that low-oxygen alloy powder cannot be obtained.

The melting point of the Nd ₂ Fe ₁₄ B phase is 1150
° C, the temperature of the molten metal is 1300-1600
C is desirable. If the molten metal temperature is too high, the sprayed molten liquid droplets will have an irregular particle shape when solidified in the chamber, and if the molten metal temperature is too low, the crystal structure tends to be amorphous and the resulting alloy powder becomes coarse. Because it is easy. As for the other manufacturing conditions, the optimum conditions are different for each atomizing apparatus, but the target particles can be obtained by controlling the manufacturing conditions.

[0030]

EXAMPLES Example 1 Nd: 84.0% by weight,
The balance: 1890 g of Nd-Fe alloy lump by commercial melting electrolysis of Fe, Dy: 86.3% by weight, balance: 73 g of Dy-Fe alloy lump by commercial fusion electrolysis of Fe, B: 2
0.1 wt%, Al: 2.9 wt%, balance: 249 g of commercial FeB alloy of Fe, metal Co lump 40 having a purity of 99 wt%
g, 99% pure metal Cu granules 10g, 99% pure by weight
Was inserted into an alumina crucible in a crucible-type high-frequency induction furnace of an Ar gas atomizing powder manufacturing apparatus and melted under a vacuum atmosphere. Melt temperature is 1500
° C, and after confirming that the molten metal is uniform, let the molten metal flow out from the nozzle below the alumina crucible,
Ar gas was atomized at an ejection pressure of / cm ² . The alloy powder was recovered after being left to cool to around room temperature in a chamber in an Ar atmosphere.

The recovered alloy powder weighed 4520 g. As a result of component analysis, Nd: 30.9% by weight, Dy: 1.24% by weight, B: 1.01% by weight, Co: 0.81% by weight, A:
l: 0.28% by weight, Cu: 0.21% by weight, Ca: <
0.01% by weight, O: 0.22% by weight, C: 0.026
It was an alloy powder having a substantially spherical particle shape composed of wt%, balance: Fe.

The recovered alloy powder is passed through a JIS sieve (70, 100,
140, 235, 390 mesh) and classified using an automatic tap sieving machine. As a result, 8.5 weight% of 70 mesh or more, 4.3 weight% of 70 to 100 mesh, 100 to 100 mesh
9.5% by weight of 140 mesh, 19.6% by weight of 140 to 235 mesh, and 49.95% of 235 to 390 mesh.
8.7% by weight was 4% by weight and 390 mesh or less.

The polarization of the alloy powder of each particle size was observed with an optical microscope and the phase was identified by EPMA. As a result, alloy powder having a mesh size of 100 mesh or more was found to be flat and partially amorphous, and 390 mesh or less. The alloy powder was found to be entirely amorphous. The alloy powder of 100 to 390 mesh is spherical, and most of the inside is N grown to 3 to 10 μm in the short axis direction and 10 to 50 μm in the long axis direction.
It was a d ₂ Fe ₁₄ B phase columnar crystal, and had a crystal structure occupied by an R-rich phase and a B-rich phase finely dispersed between the main phase columnar crystals.

A 100-390 mesh portion of the above alloy powder (1000 g) was pulverized by a jet mill to obtain an average particle size of 2.7 μm.
m of finely pulverized powder was obtained. The obtained finely pulverized powder is subjected to a magnetic field of 12 kO.
e, after molding in a magnetic field with a molding pressure of 1.3 ton / cm ² , Ar
After sintering at 1050 ° C for 3 hours in gas, 1
Aging treatment was performed for a time to obtain an Nd-Fe-B based sintered magnet. The magnetic properties of the obtained magnet were Br = 14.1 k
G, iHc = 14.0 kOe, (BH) max = 42.
1MGOe showed excellent magnetic properties.

Example 2 Nd: 84.0% by weight, balance: 1560 g of Nd-Fe alloy ingot by commercial melt electrolysis of Fe, Dy: 86.3% by weight, balance: commercial melt electrolysis of Fe 73 g of Dy-Fe alloy ingot by the method, B:
20.1% by weight, Al: 2.9% by weight, balance: 249 g of commercial FeB alloy of Fe, metal Co lump 4 having a purity of 99% by weight
0 g, 10 g of metal Cu granules having a purity of 99%, and 3068 g of metal Fe lump having a purity of 99 wt% were subjected to Ar gas atomization in the same manner as in Example 1 to obtain an alloy powder.

The collected alloy powder weighed 4500 g. As a result of component analysis, Nd: 26.21% by weight, Dy: 1.24% by weight, B: 1.00% by weight, Co: 0.79% by weight, A
l: 0.26% by weight, Cu: 0.21% by weight, Ca: <
0.01% by weight, O: 0.15% by weight, C: 0.025
It was an alloy powder having a substantially spherical particle shape composed of wt%, balance: Fe.

The recovered alloy powder is passed through a JIS sieve (70, 100,
140, 235, and 390 mesh) and classified using an automatic tap sieving machine. As a result, 9.5% by weight of 70 mesh or more, 3.2% by weight of 70 to 100 mesh, and 100 to 100%.
6.8% by weight of 140 mesh, 18.3% by weight of 140-235 mesh, 51.51% of 235-390 mesh.
6% by weight, 390 mesh or less was 10.6% by weight.

The polarization of the alloy powder of each particle size was observed with an optical microscope and the phase was identified by EPMA. As a result, alloy powder having a mesh size of 100 mesh or more was found to be flat and partially amorphous, and 390 mesh or less. The alloy powder was found to be entirely amorphous. The alloy powder of 100 to 390 mesh is spherical, and most of the inside is Nd ₂ Fe ₁₄ B phase columnar crystal grown to 5 to 10 μm in the short axis direction and 10 to 100 μm in the long axis direction. The R-rich phase and the B-rich phase finely dispersed in between were smaller than those in Example 1.

Nd-Fe eutectic alloy (Nd: 85.5% by weight, O: 0.01% by weight or less, balance: Fe) by commercially available molten salt electrolysis was applied to 930 g of the above alloy powder 100 to 390 mesh portion. After hydrogen pulverization, 70 g of alloy powder pulverized to 35 mesh or less by a disk mill was added and then jet mill pulverized to obtain a finely pulverized powder having an average particle size of 2.7 μm. The obtained finely pulverized powder is subjected to a magnetic field of 12 kOe and a molding pressure of 1.3.
After molding in a magnetic field of ton / cm ² ,
After sintering at 0 ° C. for 3 hours, aging treatment was performed at 590 ° C. for 1 hour to obtain an Nd—Fe—B based sintered magnet. The magnetic properties of the obtained magnet were Br = 14.0 kG, iHc = 14.0.
At 3 kOe and (BH) max = 42.2 MGOe, excellent magnetic properties were exhibited.

Comparative Example 1 An alloy material similar to that used in Example 1 was melted in a high-frequency induction furnace, and was quenched by a molten metal quenching method using a twin-roll type sheet manufacturing apparatus provided with two copper rolls having a diameter of 250 mm. A thin plate cast material having a thickness of 1.0 mm was obtained.
All tests were performed in an Ar atmosphere. This slab was roughly pulverized to 35 mesh or less. Example 1
Observation with an optical microscope and EPMA in the same manner as in the above, a columnar crystal structure of Nd ₂ Fe ₁₄ B phase grown in the plate thickness direction was found inside the slab. The columnar crystals were Nd ₂ Fe ₁₄ B phase columnar crystals which grew to 5 to 20 μm in the short axis direction and 50 to 300 μm in the long axis direction. In addition, as a result of component analysis, Nd: 31.
1% by weight, Dy: 1.22% by weight, B: 1.00% by weight, Co: 0.82% by weight, Al: 0.26% by weight, C
u: 0.22% by weight, Ca: <0.01% by weight, O:
The alloy powder was composed of 0.13% by weight, C: 0.024% by weight, and the balance: Fe.

A finely pulverized powder having an average particle size of 2.8 μm was obtained by jet milling 1000 g of the above alloy powder. An Nd—Fe—B-based sintered magnet was obtained from the obtained finely pulverized powder in the same manner as in Example 1. The magnetic properties of the obtained magnet are Br = 1
4.3 kG, iHc = 13.9 kOe, (BH) max
= 42.2 MGOe, showing excellent magnetic properties.

As described above, a raw material alloy powder capable of exhibiting the same magnetic properties as the present invention can be obtained by the strip casting method, but in the strip casting method, it is necessary to roughly pulverize the cast piece before the fine pulverizing step. According to the present invention, there is an advantage that the obtained alloy powder can be directly used in the fine pulverization step.

[0043]

According to the present invention, it has a crystal structure capable of exhibiting high magnetic properties and has a small load on the pulverizing step in the magnet manufacturing process. An R-Fe-B-based sintered magnet raw material alloy powder that can be charged is obtained.

Claims (7)

[Claims] 1. A raw material alloy powder for an R—Fe—B based sintered magnet, wherein most of the particles are substantially spherical. 2. Most of the particles have a diameter of 20 to 500 μm.
A raw alloy powder for an R-Fe-B-based sintered magnet, which is substantially spherical. 3. The crystal structure in a particle is a columnar crystal of R ₂ Fe.
And ₁₄ B phase, the R ₂ Fe ₁₄ B phase gap finely dispersed R-rich phase, and, R-Fe-B based sintered magnet according to claim 1 or claim 2 comprising a B-rich phase Raw material alloy powder. 4. The crystal structure in a particle has a minor axis direction of 1 to 1.
0 μm, R ₂ of a columnar crystal having a major axis direction of 5 to 100 μm
And Fe ₁₄ B phase, the R ₂ Fe ₁₄ B phase R-rich phase which is finely dispersed in the gap, and consists of a B-rich phase, according to any claims 1 to 3 R-Fe-B Raw material alloy powder for sintered magnets. 5. A composition comprising R: 30 to 35% by weight, B:
5. The method according to claim 1, wherein the content is 0.9 to 1.2% by weight, the balance being Fe (however, part of Fe can be replaced with one or two of Co and Ni) and inevitable impurities. 6. R-F
Raw material alloy powder for e-B based sintered magnets. 6. A raw material for a spherical R—Fe—B-based sintered magnet according to claim 1, which is obtained by a gas atomization method using an R—Fe—B-based alloy having a required composition as a raw material. Alloy powder. 7. A composition comprising R: 26 to 35% by weight, B:
7. The method according to claim 1, wherein 0.9 to 1.2% by weight, the balance is Fe (however, part of Fe can be replaced by one or two of Co and Ni) and inevitable impurities. R-F
A raw alloy powder for an R-Fe-B sintered magnet obtained by adding and blending a composition adjusting alloy powder to the raw alloy powder for an eB sintered magnet.