JPH05234789A - Molding method and manufacture of sintered magnet - Google Patents

Abstract

PURPOSE:To improve the degree of orientation of a molded body in manufacturing a rare-earth sintered magnet by applying a pulse magnetic field to a green compact of magnetic powder when the green compact is in a predetermined density range. CONSTITUTION:Magnetic powder containing R (at least one type of rare-earth elements which include Y) and transition elements is subjected to a dry molding. In this event, when a relative density of a green compact of the magnetic powder is in a range of 25-55%, a pulse magnetic field is applied to the compact at least three times. Thereby, a molded body having a considerably high degree of orientation is obtained, and hence it is possible to obtain a sintered magnet of good magnetization having a considerably high residual magnetic flux density. Moreover, it is possible to improve a mechanical strength of the molded body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method and a method for manufacturing a rare earth sintered magnet using a molded body manufactured by this method.

[0002]

2. Description of the Related Art As a rare earth magnet having high performance, an Sm-Co type magnet manufactured by powder metallurgy has an energy product of 32M.
GOe's are in mass production. In recent years, Nd-Fe
R-T-B magnets (T is Fe, or Fe and Co) such as -B magnets and Nd-Fe-Co-B magnets have been developed,
Japanese Patent Application Laid-Open No. 59-46008 discloses a sintered magnet. For the magnet by the sintering method, the conventional Sm-Co powder metallurgical process (melting → casting → coarse grinding of ingot → fine grinding → molding → sintering → magnet) can be applied, and it is easy to obtain high magnetic characteristics. Is.

When manufacturing an anisotropic sintered magnet, molding is performed in a magnetic field. In order to improve the residual magnetic flux density of the anisotropic sintered magnet, it is important to improve the degree of orientation during molding in a magnetic field. If the degree of orientation is high, the squareness is improved, a high residual magnetic flux density is obtained, and the magnetization rate is also improved. In addition, the mechanical strength of the molded body is also improved.

Although the wet molding method can obtain a higher degree of orientation than the dry molding method, rare earth magnets, particularly R-T-B magnets are easily oxidized and an organic solvent is used during the wet molding, so that sintering is performed. The amount of carbon in the magnet increases, and high magnetic properties cannot be obtained.

Therefore, when manufacturing a rare earth magnet,
Generally, a dry molding method is used, and a method of increasing the applied magnetic field strength to improve the degree of orientation is adopted. However, it is difficult to apply an extremely large magnetic field because the heat generation of the magnetic field generating coil becomes large. Therefore, a method of applying a strong magnetic field by utilizing a pulsed magnetic field having a short magnetic field application time has been proposed (Japanese Patent Laid-Open No. 61-208809).

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the degree of orientation of a compact when manufacturing a rare earth sintered magnet.

[0007]

[Means for Solving the Problems]
It is achieved by the present invention of (1) to (6). (1) R (R is at least 1 of rare earth elements including Y)
It is a seed. ) And a magnetic powder containing a transition element are dry-molded, and when the relative density of the green compact of the magnetic powder is in the range of 25 to 55%, the pulse magnetic field is applied at least three times to the green compact. A molding method comprising applying to a body.

(2) The intensity of the pulsed magnetic field is 20 kOe
The molding method according to the above (1).

(3) The duration of the pulsed magnetic field is 10
The molding method according to (1) or (2) above, wherein the time is from μs to 0.5 sec.

(4) The molding method according to any one of (1) to (3) above, wherein the green compact does not contain a lubricant release agent.

(5) The magnet powder is an RTB-based magnet powder (T is Fe or Fe and Co) or an R-Co magnet powder. ) To (4).

(6) A method for producing a sintered magnet, which comprises a sintering step of sintering a compact produced by the method according to any one of the above (1) to (5).

[0013]

In the present invention, the pulse magnetic field is applied at least three times when the green compact of the magnetic powder is in the predetermined density range. As a result, a molded product having an extremely high degree of orientation is obtained, and a sintered magnet having an extremely high residual magnetic flux density is realized. In addition, the mechanical strength of the molded body is also improved.

Conventionally, a fatty acid compound or the like has been added as a lubricant release agent in order to improve the lubricity between the magnet particles in the green compact, but in the present invention, such a lubricant release agent is not used. Also provides a sufficient degree of orientation.

Japanese Patent Laid-Open No. 61-208809 discloses that magnesium stearate is added to the magnet powder during the production of the R-T-B system sintered magnet for molding. The publication discloses that it is preferable to use a pulsed magnetic field at the time of forming, and "a single application is sufficient before the lowering of the upper punch is started, but a multiple application may result in an orientation degree. Will be further improved. ” However, as described above, a significant improvement in the degree of orientation cannot be expected unless a pulsed magnetic field is applied when the density reaches a predetermined value after the start of compacting.In addition, an organic lubricant release agent such as magnesium stearate has a magnetic property. Lower.

Further, Japanese Patent Application Laid-Open No. 1-245503 discloses a method of intermittently applying an orientation magnetic field during application of a molding pressure in manufacturing an RTB based sintered magnet. The publication does not describe the density of the green compact when applying the orientation magnetic field, nor the strength of the orientation magnetic field. It is difficult to apply a high-strength magnetic field because the orientation magnetic field in the publication is long in application time and is not a pulse magnetic field.

[0017]

[Specific Structure] The specific structure of the present invention will be described in detail below. INDUSTRIAL APPLICABILITY The present invention is applied to a method of dry-molding a magnet powder containing R (R is at least one kind of rare earth element including Y) and a transition element.

<Magnet Powder> The composition of the magnet powder is not particularly limited and is not particularly limited as long as it contains a rare earth element and a transition element. However, the present invention is not limited to the RTB sintered magnet (T). Is Fe, or Fe and Co.) or R
-Suitable for manufacturing Co-based sintered magnets.

In the R-T-B type magnet powder, R is usually 2
7-38 wt%, T 51-72 wt%, B 0.5-
It is preferable to contain 4.5% by weight. If the R content is too small, a phase rich in iron precipitates and high coercive force cannot be obtained, and if the R content is too large, high residual magnetic flux density cannot be obtained. If the B content is too small, a high coercive force cannot be obtained, and if the B content is too large, a high residual magnetic flux density cannot be obtained. The amount of Co in T is preferably 30% by weight or less. Further, in order to improve the coercive force, Al,
Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W,
Elements such as V, Zr, Ti and Mo may be added,
If the amount added exceeds 6% by weight, the residual magnetic flux density will decrease.

In addition to these elements, the magnet powder may contain unavoidable impurities or trace additives such as carbon and oxygen.

The magnet powder having such a composition has a main phase having a substantially tetragonal crystal structure. Further, it usually contains a non-magnetic phase of about 0.5 to 10% by volume.

The method for producing the magnet powder is not particularly limited, but it is usually produced by casting a mother alloy ingot and crushing it, or by crushing the alloy powder obtained by the reduction diffusion method. The average particle size of the magnet powder is usually 1 to
It is about 10 μm.

The R-Co type magnet powder is composed of R, Fe, and N.
at least one metal selected from i, Mn and Cr, and C
contains o and. In this case, preferably, in addition to the above, Cu or Nb, Zr, Ta, Hf, Ti and V
Containing at least one metal selected from among the above, particularly preferably Cu, Nb, Zr, Ta, Hf, and T in addition to the above.
and one or more metals selected from i and V.
Among these, it is particularly preferable that the main phase is an intermetallic compound of Sm and Co, preferably the Sm ₂ Co ₁₇ intermetallic compound, and the main phase has a substantially rhombohedral crystal structure. In this case, the grain boundary has a subphase mainly composed of SmCo ₅ system. The specific composition may be appropriately selected according to the manufacturing method, required magnetic properties, etc., but the following compositions are preferable, for example.

R: 20 to 30% by weight, particularly about 22 to 28% by weight, one or more of Fe, Ni, Mn and Cr: 1
~ 35 wt%, one or more of Nb, Zr, Ta, Hf, Ti and V: 0-6 wt%, especially 0.5-4 wt%
%, Cu: 0 to 10% by weight, particularly about 1 to 10% by weight, Co: balance.

Specific examples of the rare earth element include, for example, Y, La, Ce, Pr, Nb, Sm, Eu, Gd,
Examples thereof include Tb, Dy, Ho, Er, Tm, Yb and Lu, and it is particularly preferable that Sm and / or Ce are contained.

Further, as one or more kinds of Fe, Ni, Mn and Cr, Fe is preferable, and particularly, it is preferable to contain Fe and, if necessary, one or more kinds of Ni, Mn and Cr.

Further, Zr is preferable as one or more of Nb, Zr, Ta, Hf, Ti and V. Particularly, Zr is contained and, if necessary, one or more of Nb, Ta, Hf, Ti and V is contained. Is preferred.

In addition to the above elements, Si,
One or more of other elements such as Mo, Ca, O, and C are included in the total 3
You may add about less than weight%. Note that these may be contained as impurities in an amount of about 3% by weight or less of the whole.

The method for producing the R-Co magnet powder is not particularly limited.

<Molding Step> In the present invention, at least three times of the dry compacting are carried out when the relative density of the green compact of the magnetic powder is in the range of 25 to 55%, preferably 30 to 45%. A pulsed magnetic field is applied to the green compact. In this specification, the relative density is a percentage of a value obtained by dividing the measured density by the theoretical density. The measured density is calculated from the weight of the magnet powder filled in the molding space of the molding device and the internal volume of the molding space.

The pulsed magnetic field applied when the relative density of the green compact is outside the above range has a low contribution to the improvement of the orientation degree of the magnet powder. Therefore, even if the pulse magnetic field is applied three times or more, a sufficient degree of orientation cannot be obtained unless the pulse magnetic field is applied at least three times when the green compact relative density is within the above range.

The strength of the pulsed magnetic field is preferably 20 kOe
As described above, more preferably 30 kOe or more, and it is preferable that the intensity of all pulse magnetic fields is within this range. When the intensity of the pulse magnetic field is less than the above range, the orientation of the magnet powder tends to be insufficient. Although there is no particular upper limit to the strength of the pulsed magnetic field, the size of the magnetic field generator becomes large and 50 kO
Even if the strength exceeds e, the degree of orientation is hardly improved. Therefore, the strength is usually set to 50 kOe or less.

The duration of the pulsed magnetic field is usually 10 μs
It is preferably about 0.5 sec. If the duration is less than the above range, the orientation tends to be insufficient, and if it exceeds the above range, the heat generation of the magnetic field applying coil tends to be too large. In this specification, the duration is the time from the start to the end of the magnetic field application.

The interval for applying the pulse magnetic field is not particularly limited.

Further, the pulse magnetic field may be applied at least three times while increasing the density of the green compact, or the pulse magnetic field may be applied at least three times while keeping the density of the green compact substantially constant. ..

The molding pressure may be constant from the start to the end of compacting, may be gradually increased or decreased, and may be irregularly changed. There is no particular limitation on the molding pressure. The lower the molding pressure is, the better the orientation is. However, when the molding pressure is too low, the strength of the molded product is insufficient, which causes a problem in handling. Therefore, it is usually preferable that the pressure is about 1 ton / cm ² .

In the present invention, the magnetic field may be applied even when the relative density of the green compact is outside the above range. That is, a pulse magnetic field, a steady magnetic field, an intermittent magnetic field, etc. may be applied before and / or after applying the pulse magnetic field in the density range.

The final relative density of the green compact, that is, the relative density of the molded body is usually about 50 to 60%.

The present invention can be applied to a so-called transverse magnetic field forming method in which the pressure applying direction and the magnetic field applying direction are substantially orthogonal to each other, and to a so-called longitudinal magnetic field forming method in which the pressure applying direction and the magnetic field applying direction substantially coincide with each other. it can. Although a magnet having high anisotropy can be obtained by the transverse magnetic field molding method, applicable shape of the molded body is limited and the molding apparatus becomes complicated.
The effect of improving the degree of orientation according to the present invention is particularly high in the longitudinal magnetic field molding method.

The molding apparatus used in the present invention may be any apparatus having a pulse magnetic field generating means, and other configurations are not particularly limited. When applying a high-strength magnetic field that saturates the punches and dies of the forming apparatus, it is preferable to use an air-core coil type magnetic field forming apparatus in which the punches and dies are made of a non-magnetic material.

<Sintering Step> The molded body obtained as described above is sintered and magnetized.

There are no particular restrictions on the various conditions during sintering, but for example, at 1000 to 1200 ° C. for 0.5 to 12 hours, especially 1
It is preferable to sinter for about 5 hours and then quench. The sintering atmosphere is preferably vacuum or a non-oxidizing gas atmosphere such as Ar gas.

After sintering, an aging treatment, a magnetizing treatment and the like are carried out if necessary.

[0044]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

[Example 1] The composition was 31.5 Nd-1.5.
Dy-1B-bal. An alloy ingot of Fe (wt%) was made by casting. The alloy ingot was roughly crushed to-# 32 by a jaw crusher and a brown mill, and then finely crushed by a jet mill to obtain a magnetic powder having an average particle diameter of 4 µm.

This magnet powder was molded in a magnetic field by a vertical magnetic field molding method, and the obtained molded body was heated at 1100 ° C. in an Ar atmosphere.
After sintering for 3 hours, the mixture was rapidly cooled, and further subjected to an aging treatment at 600 ° C. for 3 hours in an Ar atmosphere to obtain a sintered magnet shown in Table 1 below.

In the magnetic field molding, while applying a pressure of 1 ton / cm ² , a pulse magnetic field of 35 kOe (duration 0.5 mse) was applied.
c) was applied and the pressurization was continued until the relative density of the green compact of the magnetic powder reached 59%. The internal volume of the forming space required to obtain the measured density was calculated from the moving amount of the upper punch of the forming apparatus. The theoretical density was calculated as 7.62 g / cm ³ . The pulsed magnetic field was applied when the density was marked with O or X in Table 1. X represents the pulsed magnetic field applied when the relative density of the green compact was other than 25 to 55%.

For comparison, a sintered magnet was manufactured in the same manner as above except that the molding was performed while applying a DC magnetic field of 15 kOe.

With respect to these sintered magnets, the residual magnetic flux density (Br) in the direction in which a magnetic field was applied during molding was measured. The results are shown in Table 1.

[0050]

[Table 1]

[Example 2] Table 2 below shows the strength of the pulse magnetic field.
Other than that, the sintered magnet of Example 1 was changed.
Sintered magnets were manufactured in the same manner as in manufacturing No. 1-4. Table 2 shows the residual magnetic flux density (Br) of these sintered magnets.

[0052]

[Table 2]

From the results shown in Table 2, it is understood that a particularly high residual magnetic flux density can be obtained when the intensity of the pulse magnetic field is 20 kOe or more.

Example 3 An R-Co magnet powder having the following composition and an average particle diameter of 4 μm was produced.

Sm: 25.5% by weight, Co: 50.9% by weight, Fe: 14.0% by weight, Zr: 2.6% by weight, C
u: 7.0 wt% This magnet powder was molded under the same conditions as the sintered magnet No. 1-4 of Example 1, sintered at 1150 ° C. for 3 hours, and then 800
Aging treatment was performed at ℃ for 3 hours to produce a sintered magnet No. 3-1.

For comparison, the molding conditions were set as in Example 1.
Sintered magnet No. 1-11 and other sintered magnets
Sintered magnet No. 3-2 was manufactured in the same manner as No. 3-1.

The residual magnetic flux density (Br) of these sintered magnets was measured. The results were as follows. Sintered magnet No. 3-1: 11.0kG Sintered magnet No. 3-2: 10.4kG From the results of the above examples, the present invention improves the orientation degree and has a high residual magnetic flux density. It is clear that

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01F 1/08 B 7371-5E

Claims (6)

[Claims] 1. A method for dry-molding magnet powder containing R (R is at least one kind of rare earth element including Y) and a transition element, wherein the relative density of the green compact of the magnet powder is A molding method, wherein a pulsed magnetic field is applied to the green compact at least three times when it is in the range of 25 to 55%. 2. The molding method according to claim 1, wherein the intensity of the pulsed magnetic field is 20 kOe or more. 3. The duration of the pulsed magnetic field is 10 μs
The molding method according to claim 1 or 2, wherein the molding time is 0.5 sec. 4. The molding method according to claim 1, wherein the green compact does not contain a lubricant release agent. 5. The magnet powder is an RTB-based magnet powder (T is Fe or Fe and Co) or an R—Co magnet powder. The molding method according to any one of 4 above. 6. A method for manufacturing a sintered magnet, comprising a sintering step of sintering a molded body manufactured by the method according to claim 1.