JP2891215B2 - Method for producing rare earth-B-Fe based sintered magnet excellent in corrosion resistance and magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth-B-Fe sintered magnet having excellent corrosion resistance and magnetic properties.

[0002]

2. Description of the Related Art In recent years, compared to conventional Sm-Co based magnets, S
An R—B—Fe permanent magnet has been invented, which does not necessarily include m or Co, and at least one of the rare earth elements including Y (hereinafter, referred to as R), and B and Fe as essential components.
While this RB-Fe-based permanent magnet has excellent magnetic properties, it also has the drawback that it is very susceptible to corrosion and the magnetic properties are significantly deteriorated accordingly.

This RB-Fe-based permanent magnet has a predetermined R
The -B-Fe-based alloy powder by compression molding, but are those prepared by sintering, the composition of the R-B-Fe permanent magnets, as shown in FIG. 1, R ₂ Fe ₁₄ B
Phase: a, R-rich phase existing at the grain boundary portion of the R ₂ Fe ₁₄ B phase (it is said to be composed of R ₉₅ Fe ₅ phase, R ₇₅ Fe ₂₅ phase, etc.): b, and RFe B-rich phase consisting of ₄ B ₄ phase: is composed mainly of c, the cause of the corrosion, R-rich phase mainly present in the grain boundary portion: b because it is being susceptible phase corrosion, R-rich phase:
It is said that intergranular corrosion proceeds inside through b.

As a countermeasure against these problems, Japanese Patent Laid-Open Publication No.
In JP-A-910, the surface of an RB-Fe-based permanent magnet is
Method for diffusing and forming a thin film of n.
In Japanese Patent Application Laid-Open No. 8-78, a method of removing a surface layer of an RB-Fe-based permanent magnet and then depositing an Al thin film is disclosed. A method is disclosed in which an oxidation-resistant resin such as a synthetic resin for coating such as an epoxy resin, a thermosetting acrylic resin, an alkyd resin, a melamine resin, and a silicone resin is applied to the surface.

[0005]

However, the RB-Fe-based permanent magnet anticorrosion methods described in the above-mentioned prior art are all provided on the surface of the permanent magnet with Zn, Al, synthetic resin or the like. A protective film with corrosion resistance is applied, and a separate process from the magnet manufacturing process is required, which complicates the process and increases the cost.In addition, since the synthetic resin protective film has a thickness, In particular, the dimensional accuracy of small magnet products is deteriorated. In any case, the anticorrosion method only protects the outside of the permanent magnet against corrosion and the like, and when the protective film is peeled or cracked,
There is a problem that corrosion penetrates into the inside from these places, and that internal corrosion cannot be prevented, and the magnetic properties deteriorate accordingly.

[0006]

Means for Solving the Problems Accordingly, the present inventors have
RBF with excellent corrosion resistance and excellent magnetic properties
As a result of research to produce e-based sintered magnets, RB-
Fe-based alloy powder, Ni, Co, Mn, Cr, Ti,
V, Al, Ga, In, Zr, Hf, Ta, Nb, M
at least one of o, Si, Re and W (hereinafter, referred to as
M) is mixed and mixed to form a mixed powder. The mixed powder is molded to form a compact, and the resulting compact is sintered to obtain an R ₂ Fe ₁₄ B phase (hereinafter referred to as “main phase”). Phase) and an RB-Fe-based sintered magnet having a structure having a grain boundary phase containing 20 to 90 atomic% of M around the main phase, and the RB-Fe-based sintered magnet is obtained. Have been found to exhibit excellent corrosion resistance and magnetic properties.

The present invention has been made on the basis of this finding, and comprises mixing an RB-Fe alloy powder and a hydride powder of M to form a mixed powder, and molding the mixed powder. And a method for producing a rare-earth-B-Fe-based sintered magnet having excellent corrosion resistance and magnetic properties for sintering the obtained molded body.

[0008] Even if the above M is contained in the grain boundary phase in less than 20 atomic%, sufficient corrosion resistance cannot be obtained.
If the content is more than 0 atomic%, the M is diffused and penetrates into the main phase during the production, so that the corrosion resistance is improved, but the magnetic properties are significantly reduced, which is not preferable.

The M-containing grain boundary phase is a phase that is less likely to corrode than the R-rich phase shown in FIG. It is considered that an RB-Fe sintered magnet excellent in both corrosion resistance and magnetic properties due to the action of increasing the density can be obtained.

In the grain boundary phase of the present invention, M: 20 to 90 atomic%
The rare-earth-B-Fe-based sintered magnet containing 0.1% of hydride powder of M is added to an R-B-Fe-based alloy powder having a predetermined composition.
The mixed powder obtained by blending and mixing 0005 to 3% by weight is molded and molded in a non-oxidizing atmosphere at a temperature of 900 to 120.
It is manufactured by sintering at 0 ° C. The above RBF
The powder to be mixed with the e-based alloy powder is M
Is more preferable. While the ultrafine powder of M diffuses into the R ₂ Fe ₁₄ B phase during sintering, the hydride powder of M
_The amount of diffusion into the ₂ Fe ₁₄ B phase is small, and the hydrogen of the hydride of M is released during sintering, and only M remains in the grain boundary phase.

The rare earth-BF thus produced
The e-based sintered magnet may be heat-treated at a temperature of 400 to 700 ° C. in a non-oxidizing atmosphere as necessary.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

Examples 1 to 7 and Conventional Example First, 15% Nd-8% B-residual Fe (% is atomic%)
To obtain an alloy ingot. This alloy ingot was heated in an argon atmosphere at a temperature of 1050.
After performing a heat treatment at a temperature of 20 ° C. for 20 hours, pulverization was performed to prepare an RB-Fe alloy powder having an average particle diameter of 35 μm.

Further, ZrH ₂ powder (average particle size: 1.3 μm) and TaH ₂ powder (average particle size: 1.3 μm) are used as additive powders.
5 μm), TiH ₂ powder (average particle size: 1.3 μm), N
bH ₂ powder (average particle size: 1.3 μm), VH powder (average particle size: 1.5 μm) and HfH ₂ powder (average particle size: 1.
3 μm), and these powders are mixed with the above 15% Nd-8%
B-remaining Fe (however,% is atomic%) is blended with the R-B-Fe-based alloy powder in a predetermined ratio within the range of 0.0005 to 3% by weight, and mixed to form a mixed powder; These mixed powders were molded at a molding pressure of 2 t / cm ² in a magnetic field (14 KOe) to produce a molded body having a length of 20 mm, a width of 20 mm and a height of 15 mm. These compacts are placed in a vacuum (10 ^-5 Torr)
At a heating rate of 10 ° C./min at a temperature of 1080
The mixture was sintered at a temperature of 2 ° C. for 2 hours and cooled at a cooling rate of 100 ° C./min.

The sintered body is heated at a heating rate of 100 ° C./min, and maintained at a temperature of 620 ° C. for 2 hours.
It was cooled at a cooling rate of ° C / min and heat-treated.

Examination of the structure of the heat-treated sintered body revealed that the sintered body was composed of an R ₂ Fe ₁₄ B phase and a grain boundary phase, and had almost the same structure as that shown in FIG. STE
The results are shown in Table 1. Further, the magnetic properties of the sintered body were measured, and the sintered body was heated at a temperature of 60.
After standing in an atmosphere of 90 ° C. and humidity of 90% for 1000 hours to conduct a corrosion resistance test, the magnetic properties were measured again, and the occurrence of rust was visually observed. The results are shown in Table 1.
It was shown to. In Table 1, the measured values of the magnetic properties measured before the corrosion test were shown in the column "Before the corrosion test", and the measured values of the magnetic properties measured after the corrosion test were shown in the column "After the corrosion test".

[0016]

[Table 1]

From the results shown in Table 1, it can be seen that the rare-earth-B-Fe in which the metal element is present in the grain boundary phase of the present invention obtained in the examples.
It can be seen that the sintered magnet based on the conventional example has excellent magnetic properties and excellent corrosion resistance compared to the RB-Fe based sintered magnet having no metal element in the grain boundary phase obtained in the conventional example. .

[0018]

The RB- obtained by the production method of the present invention.
Fe-based sintered magnets do not need to be surface-treated, and the magnetic properties of the sintered magnets are not significantly deteriorated. is there.

[Brief description of the drawings]

FIG. 1 is a structural diagram of an RB-Fe-based sintered magnet.

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Claims (1)

(57) [Claims] 1. An RB—Fe-based alloy powder (R is one or more of rare earth elements including Y), Ni, C
o, Mn, Cr, Ti, V, Al, Ga, In, Zr,
A hydride powder of at least one of Hf, Ta, Nb, Mo, Si, Re and W is blended and mixed to form a mixed powder, and the mixed powder is molded to form a molded body. A method for producing a rare earth-B-Fe sintered magnet having excellent corrosion resistance and magnetic properties, characterized by sintering a body.