JPH066770B2 - Rare earth magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a motor, an actuator, various electric appliances,
The present invention relates to a method for manufacturing a rare earth magnet, which is widely used in the field of mechatronics such as computer peripherals and watches.

[Outline of Invention]

In general, RFeB magnets have excellent magnetic characteristics and R
As Y or La, Ce, Nd, Pr, Sm, D
one or more rare earth elements such as y and Tb, and B,
There is also one composed of Fe and a part of Fe replaced with a transition metal element such as Co.

The excellent characteristics of this RFeB magnet are the R contained in it.
_This is due to the fact that the compound ₂ Fe ₁₄ B has large uniaxial anisotropy and magnetic moment. However, R ₂ Fe ₁₄
It is known that a large coercive force cannot be obtained in the compound single phase of B, and a method containing a large amount of Nd and B exhibits high magnet characteristics as compared with this compound composition. The aging treatment causes Nd-ric to be formed in the grain boundaries of the main phase R ₂ Fe ₁₄ B.
This is because the h phase and the B-rich phase are generated as the grain boundary phase and cause the nucleation difference.

In the present invention, an RFeB-based magnet and an Nd _X Fe _1-X (x = 0.65 to 0.85) eutectic alloy centered on Nd _0.75 Fe _0.25 are mixed in a powder state, and this Nd _X Fe _1-X is mixed. Melting point of 64
By the heat treatment in the range of 0 to 800 ° C., the sintering effect and the aging effect could be simultaneously activated. Furthermore, it was possible to suppress the deformation after sintering due to the anisotropy of thermal contraction due to the magnetic field orientation. In addition, since the B-rich phase, which is the main point of rust generation, can be minimized, a rust prevention effect is also expected.

[Conventional technology]

At present, permanent magnet materials are
It is an important functional material used in a wide range of fields from various electric products to medical devices, and in recent years, there has been a demand for higher performance permanent magnets due to the demands for device miniaturization and high efficiency. R
FeB-based magnets have high magnetic characteristics as compared with SmCo-based magnets, and are mainly characterized in that light rare earth elements such as Nd and Pr, which are abundant in resources, are mainly used, and that Co is not always required. is there. As described in JP-A-59-46008, a method for producing this magnet is as follows. A cast ingot having a predetermined composition is ground to an average of 3 to 5 μm, an organic binder is added and kneaded, and then pressed in a magnetic field. The compact obtained by molding is sintered in Ar gas at 900 to 1200 ° C. for about 1 hour and then rapidly cooled to room temperature. When the aging treatment is performed at a temperature of around 600 ° C. after sintering, the coercive force is improved.

[Problems to be Solved by the Invention]

The RFeB-based magnet is composed of tetragonal Nd ₂ Fe ₁₄ B having high crystal magnetic anisotropy energy as a main phase and Nd-ric.
It is composed of a grain boundary phase including an h phase and a B-rich phase. Particularly, a magnet exhibiting a high coercive force has a very smooth vicinity of the crystal grain boundary, and it is possible that no lattice distortion or defects are observed. It is a feature. In order to achieve the perfection of the crystal in the vicinity of the grain boundary, the heat treatment at about 600 ° C. after the sintering effectively acts and the high coercive force is generated. (M.Sagawa et al; J.AP
PL.Phys.55 (1984) p.2083) On the other hand, some problems have been pointed out. One is SmC
Unlike the case of the o-based magnet, the RFeB-based magnet causes about 10% anisotropy in the magnetic field orientation direction and the direction perpendicular to the heat shrinkage during sintering. In the case of magnets oriented in the radial direction, concentric molds may be used in the SmCo system and the like, whereas expensive elliptical molds must be used in consideration of the anisotropy of heat shrinkage. Next, the problem of rust prevention is also large, and the rust generation of this magnet is due to the low contact resistance of the B-rich phase in comparison with the main phase and the Nd-rich phase. (Reference: Katsuhisa Sugimoto et al. The Institute of Metals, Japan 1
The 01st Autumn Meeting 604) As a rust preventive method, most of them are dealt with by forming a protective film such as epoxy coating, Ni plating, or Al ion plating on the surface. These treatments also increase the number of steps and cause a high cost.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, in the magnet manufacturing method of the present invention, RFeB-based magnet alloy powder and Nd _X Fe are used.
_1-X (0.65 ≦ χ ≦ 0.85) alloy powder is mixed,
After magnetic field molding, the melting point of the Nd _X Fe _1-X alloy or more, 9
A means for sintering in a temperature range of 00 ° C. or lower was adopted.

[Action]

The Nd _X Fe _1-X alloy to be added has a low melting point,
The RFeB-based magnet powder particles can be surrounded in a liquid phase by heat treatment at 900 ° C., and liquid phase sintering is performed at a low temperature. Therefore, it is effective against the anisotropic heat shrinkage at the time of sintering, which has been a problem in the past, and enables the use of conventional dies. Furthermore, in a magnet with a nucleation type coercive force mechanism such as the present magnet, even though the coercive force decreases due to the coarsening of the crystal grain size caused by oversintering, liquid phase sintering at low temperature The present invention according to is an effective means.

Further, Nd _X Fe _1-X plays a role of an Nd-rich phase and can form a grain boundary phase required for a coercive force generating mechanism.

Nd _X Fe _1-X synthetic composition is χ <0.65, or χ
In the range of> 0.85, the melting point of the alloy becomes 900 ° C. or higher, the sintering temperature becomes the optimum aging treatment temperature of RFeB or higher, and the obtained magnet characteristics are extremely deteriorated. It is limited to the range of 0.85. Further, χ = 0.75 has the lowest melting point (640 ° C.) and is the optimum composition.

_If the amount of Nd _X Fe _1-X added to RFeB is 10% or less, the molding strength after sintering will be weak, and if it is 35% or more, the magnetic properties obtained from the dilution effect will be below the practical range. From the viewpoint of sintering strength and magnetic properties, 10 to 3
5% is suitable.

The heat treatment temperature is 90 ° C or higher than the melting point of Nd _X Fe _1-X since liquid phase sintering and RFeB aging treatment are performed.
A range of 0 ° C or lower is suitable. Furthermore, the heat treatment atmosphere is
If the vacuum is higher than 1 × 10 ⁻³ Torr, there is no particular problem.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples.
As starting materials, electrolytic iron having a purity of 99.9%, ferroboron, and Nd having a purity of 99.7% or more were used. In the case of a nucleation type NdFeB magnet, as described above, the Nd ₂ Fe ₁₄ B main phase and the Nd-rich grain boundary phase are important, and therefore, Nd is generally larger than the composition of the main phase. It is necessary to mix them, but in this production method, only the composition of the main phase may be used.

Example 1 (1) Nd 11.8 at%, Fe 82.3 at%, B
The raw material is 5.9 at% as a main component. Of course, it is possible to substitute other rare earth elements such as Pr and Dy in place of Nd, or other transition metals such as Co in place of Fe. The composition of the Nd _X Fe _1-X alloy is 0.65.
≦ χ ≦ 0.85, but χ = 0.75 has the lowest melting point and is preferable. Also, χ <0.65 or χ> 0.8
In the range of 5, the melting point is 900 ° C. or higher, which is higher than the optimum aging temperature of the NdFeB magnet raw material, and the magnet characteristics are extremely deteriorated. Therefore, Nd _X Fe _{1-X to be} added is Nd
_{A 0.75} Fe _0.25 alloy is used.

(2) For melting, an arc furnace in an Ar atmosphere was used. Grinding was done with a stamp mill to 80 mesh or less, finely crushed with a jet mill, and Nd ₂ Fe ₁₄ magnet powder was about 10 μm.
m, Nd _0.75 Fe _0.25 alloy powder was about 3 μm.
These are thoroughly stirred and mixed using a ball mill. The mixing ratio is shown in Table 1. Here, if the mixing ratio of the NdFe raw material is too small, for example, 10% or less, the molding strength after sintering is weak, and if it is too large, for example, if 35% or more, the magnetic properties are below the practical range due to the dilution effect. Became.

(3) These mixed powders were filled in a concentric ring mold, oriented with a magnetic field of about 20 kOe, and then pressed to obtain a molded product.

(4) The heat treatment was performed in a vacuum of 1 × 10 ^-2 Torr or more. After degassing at 450 ° C. for 0.5 hour, heat treatment was performed at 700 ° C. for 10 hours, which was used for both sintering and aging treatment.
The magnetic properties obtained are also shown in Table 1.

[Example 2] Nd _0.75 Fe _0.25 alloy powder was added in a weight ratio of 15 wt% to various RFeB-based magnet raw materials, and a magnet was manufactured in the same manner as in Example 1, and the characteristics thereof are shown in Table 2. .

To Example 3 composition of the various _{Nd X Fe 1-X -y B} y, Nd 0.75 F
e _0.25 alloy powder was added in an amount of 15 wt% by weight, and Example 1 was added.
A magnet was manufactured in the same manner as in, and its characteristics are shown in Table 3.

[Advantages of the Invention] As described above, the RFeB magnet raw material powder of the present invention and Nd
The heat treatment after mixing the alloy powder of Fe is about 400 ° C. lower than the normal sintering temperature (about 1100 ° C.), and Nd
Since the sintering with the Fe alloy and the aging treatment for the RFeB magnet proceed at the same time, the heat treatment step can be reduced by one step. Further, the magnet manufactured for the low temperature heat treatment does not show the anisotropy of the heat shrinkage, so that a special mold is not required and industrially great effects can be obtained.

Originally, the excellent magnetic characteristics of RFeB magnets are
This is due to the uniaxial anisotropy and magnetic moment of the R ₂ Fe ₁₄ B compound, and the added Nd _X Fe _1-X is
The particles of RFeB are enclosed in a liquid phase state to achieve the crystal perfection in the vicinity of the grain boundaries and further improve the magnetic characteristics. Therefore, NdFeB, PrFeB, DyFeB
It is clear that the present invention is also an effective method for other RFeB-based magnets.

Claims (2)

[Claims] 1. Y, La, Ce, Nd, Pr, Sm, D
A method for producing a rare earth magnet by powder metallurgy from an RFeB magnet alloy powder containing B and Fe as main components, and one or more rare earth elements (R) such as y and Tb. Magnet alloy powder and Nd _X Fe _1-X
(0.65 ≦ χ ≦ 0.85) After being mixed with an alloy powder and subjected to magnetic field molding, the melting point of the Nd _X Fe _1-X alloy or more is 900
A method for producing a rare earth magnet, which comprises sintering in a temperature range of ℃ or less. 2. Nd is added to the RFeB-based magnet alloy powder.
_The method for producing a rare earth magnet according to claim 1, wherein 10 wt% to 35 wt% of _X Fe _1-X alloy powder is mixed.