JP2844269B2 - Corrosion resistant permanent 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 Fe-BR permanent magnet having high magnetic properties and excellent corrosion resistance, which is subjected to heat treatment after grinding to make the surface of the magnet stable against moisture. To the Fe-
The present invention relates to a BR permanent magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art Today, F is a typical high-performance permanent magnet.
e-B-R Permanent Magnet (JP-A-59-46008)
Exhibits high magnet properties in a structure having a main phase of a ternary tetragonal compound and an R-rich phase, iHc of 25 kOe or more,
(BH) max is not less than 45 MGOe, exhibiting a remarkably high performance even when compared with conventional high performance rare earth cobalt magnets. Further, Fe-BR-based permanent magnets of various compositions have been proposed so as to exhibit various magnet properties selected according to applications.

[0003] However, the Fe-BR-based permanent magnet having the excellent magnetic properties described above is mainly composed of a rare earth element and iron, which are easily oxidized or hydroxylated in the air to produce oxides or hydroxides gradually. Fe-
Oxide or hydroxide generated on the magnet surface when a BR permanent magnet is incorporated into a magnetic circuit causes a reduction in the output of the magnetic circuit and a variation in magnetism between the magnetic circuits, and also causes the generation on the surface. There is a problem of contamination of peripheral devices due to the dropout of the oxides.

Therefore, in order to improve the corrosion resistance of the above-mentioned Fe-BR permanent magnet, the surface of the magnet body is coated with a corrosion-resistant metal plating layer by an electroless plating method or an electrolytic plating method, or a corrosion-resistant resin is immersed. Coating by a coating method, forming a corrosion resistant metal or alloy film such as Al by a vapor phase film forming method, forming a resin layer containing a corrosion resistant metal flake, or laminating different kinds of corrosion resistant films. A technique for providing a corrosion-resistant coating such as the above has been proposed.

[0005]

In the electroless plating method or the electrolytic plating method, the treatment is carried out in an acidic or alkaline solution, so that the magnet surface is not only corroded to cause deterioration and variation in magnetic characteristics, but also a pin is formed on the plating film. Due to the presence of holes, sufficient corrosion resistance cannot be obtained for severe tests such as a salt spray test.

On the other hand, when a corrosion resistant resin is coated by a dipping method, a coating method, or an electrodeposition method, no pinholes exist, but sufficient corrosion resistance cannot be obtained because the water permeability of the resin film is larger than that of a metal film. There was a problem.

SUMMARY OF THE INVENTION The present invention aims at improving the corrosion resistance of Fe-BR based permanent magnets,
It is an object of the present invention to provide a corrosion-resistant Fe-BR-based permanent magnet capable of not only improving the corrosion resistance of a -R permanent magnet but also reducing the surface treatment time by reducing the thickness of a resin coating film.

[0008]

According to the present invention, R10-3
The main phase is composed of a tetragonal phase containing 0 atomic%, B2 to 28 atomic% and Fe65 to 80 atomic% as main components, and α-Fe is formed on the surface of the tetragonal phase exposed on the surface of the magnet body, and FeO is formed on the outside thereof.
Next, Fe ₃ O ₄ and α-Fe ₂ O ₃ are sequentially formed in the outermost layer,
The exposed tetragonal grain boundary phase is R ₂ O ₃ (Hexagona).
1) having a surface layer having a thickness of 1 to 20 μm comprising a phase ,
Alternatively, the magnet body has an oxidation-resistant resin layer on the surface.
A corrosion-resistant permanent magnet, characterized in that that.

Further, the present invention provides a method for producing a compound comprising:
B-28 at%, Fe 65-80 at% as main components
In a method of manufacturing an Fe-BR based permanent magnet,
After grinding, aging treatment in vacuum or inert gas
After that, in the atmosphere or oxygen concentration 0.1 vol% or more
15 minutes to 12:00 at 200 to 350 ° C in an oxidizing atmosphere
Heat treatment duringThe tetragonal crystal exposed on the magnet body surface
Α-Fe on the surface of the phase, FeO on the outside, then Fe
_Three O _Four , The outermost layer is α-Fe _Two O _Three Are sequentially formed and exposed
The tetragonal grain boundary phase is R _Two O _Three (Hexagonal) phase
Corrosion-resistant permanent magnet having a surface layer having a thickness of 1 to 20 μm
Or an oxidation-resistant resin
Obtain a corrosion-resistant permanent magnet by coating a grease layerIt is characterized by
This is a method for producing a corrosion-resistant permanent magnet.

[0010]

The present invention has been studied in order to improve the corrosion resistance of Fe-BR permanent magnets and the corrosion resistance after surface treatment. After aging treatment in an active atmosphere, heat treatment is performed in the air or in an oxidizing atmosphere having an oxygen concentration of 0.1 vol% or more, so that the surface layer of the tetragonal phase exposed on the surface of the magnet body has α-Fe, FeO, F
e ₃ O ₄ , α-Fe ₂ O ₃ is formed in the outermost layer, the exposed tetragonal grain boundary phase changes to R ₂ O ₃ (Hexagonal), the magnet surface is passivated, and the corrosion resistance of the magnet body itself The present invention has been found not only to improve the corrosion resistance, but also to improve the corrosion resistance after the surface treatment of the oxidation-resistant resin.

In the Fe-BR-based permanent magnet according to the present invention, the main phase consists of a tetragonal phase, α-Fe is exposed on the surface of the tetragonal phase exposed on the surface of the magnet body by heat treatment, and Fe is
O, Fe ₃ O ₄ , α-Fe ₂ O ₃ formed in the outermost layer, and the exposed tetragonal grain boundary phase was changed to an R ₂ O ₃ (Hexagonal) phase. The total thickness of the specific four layers and the exposed tetragonal grain boundary phase provided on the tetragonal surface layer to be formed is at least 1 μm in order to obtain the effect of improving corrosion resistance.
m or more. Also, α-Fe, FeO,
The thickness of Fe ₃ O ₄ and α-Fe ₂ O ₃ is preferably 1 to 10 μm, and R ₂ O ₃ (Hexagona) formed in the grain boundary phase is preferable.
l) The thickness of the phase is preferably 1 to 20 μm. The reason for limiting the thickness of the surface layer on the surface of the magnet body to 1 to 20 μm is as follows.
If less than μm, the effect of improving corrosion resistance is insufficient, and
If it exceeds m, the magnetism of the surface layer is lost and the magnetic properties deteriorate.

Reasons for limiting composition R is an essential element in the Fe-BR based permanent magnet. If it is less than 10 atomic%, high magnetic properties, especially high coercive force cannot be obtained, and if it exceeds 30 atomic%, it becomes R-rich. The non-magnetic phase increases, the residual magnetic flux density (Br) decreases, and a permanent magnet with excellent characteristics cannot be obtained, and R is set in the range of 10 to 30 atomic%. R is Nd, Pr, Dy, Ho,
At least one of Tb, or La, C
Those containing at least one of e, Sm, Gd, Er, Eu, Tm, Yb, Lu, and Y are preferable.

B is an essential element in the permanent magnet. If the content is less than 2 atomic%, the rhombohedral structure becomes the main phase and a high coercive force (iHc) cannot be obtained. Non-magnetic phase increases and residual magnetic flux density (Br)
, A good permanent magnet could not be obtained, and B was 2
The range is from atomic% to 28 atomic%.

[0014] Fe is an essential element in the permanent magnet, and when it is less than 65 atomic%, the residual magnetic flux density (Br)
Is reduced, and if it exceeds 80 atomic%, a high coercive force cannot be obtained, so Fe is contained in an amount of 65 atomic% to 80 atomic%. Further, a part of Fe can be replaced by Co, or various additive elements can be contained for improving characteristics.

Manufacturing Method As a method of forming a magnet body surface layer having a specific composition and structure, which is a feature of the present invention, in the case of a sintered permanent magnet, the following heat treatment method is preferable for industrial production. After sintering the molded body in a vacuum or an inert atmosphere, after performing processing steps such as cutting and grinding, aging treatment is performed in a vacuum or an inert gas, and further in the air or at least an oxygen concentration. Heat treatment is performed in an oxidizing atmosphere of 0.1 vol% or more.

By aging treatment of the permanent magnet compact at 450 to 700 ° C. for 15 minutes or more, α-Fe is exposed on the surface of the tetragonal phase exposed on the surface, and FeO and Fe
₃ O ₄ , α-Fe ₂ O ₃ is formed in the outermost layer, and the exposed tetragonal grain boundary phase changes to R ₂ O ₃ (Hexagonal) phase, but the thickness of the surface layer is less than 1 μm and is sufficiently small. Corrosion resistance cannot be obtained. Further, by performing the aging treatment for a long time, the surface layer can be made to have a thickness of 1 μm or more. However, in industrial production, the aging treatment for a long time is not practical and deteriorates the magnet properties. After the aging treatment for 15 minutes to 5 hours, a heat treatment in an oxidizing atmosphere described below can be performed to reduce the surface layer thickness to 1 to 20 μm without deteriorating the magnet characteristics.

The heat treatment in an oxidizing atmosphere is performed in the air or in an oxidizing atmosphere having an oxygen concentration of at least 0.1 vol%.
Fe, FeO, Fe ₃ O ₄ , α-Fe ₂ O ₃ and R ₂ O ₃ (H
It takes a long time to make the thickness of the exagonal phase 1 μm or more, resulting in poor efficiency. When the treatment temperature exceeds 350 ° C., oxidation proceeds rapidly, and oxygen diffusion into the inside increases, so that magnet properties are increased. Not only deteriorates but also the surface layer becomes brittle, which is not preferable. A more preferred processing temperature is from 250 to 300 ° C.

If the heat treatment time in the oxidizing atmosphere is less than 15 minutes, the thickness of the α-Fe, FeO, Fe ₃ O ₄ , α-Fe ₂ O ₃ and R ₂ O ₃ (Hexagonal) phases should be 1 μm or more. If it exceeds 12 hours, oxidation proceeds too much and oxygen diffusion to the inside increases, not only deteriorating the magnet properties, but also making the surface layer brittle, which is not preferable. I do. A more preferred treatment time is 1 to
8 hours.

According to the present invention, the corrosion resistance of the Fe—BR magnet is remarkably improved. However, when an oxidation resistant resin is further applied by a dipping method, a spray method, an electrodeposition method or the like, the corrosion resistance is further improved. In the present invention, as the resin to be applied by the immersion method or the spray method, an epoxy resin, a urethane resin, a fluorine resin, a furan resin, a polysiloxane resin, or the like is preferable. As the resin to be applied by the electrodeposition method, an epoxy resin, Acrylic resin and the like are preferred.

[0020]

EXAMPLES Example 1 As starting materials, electrolytic iron having a purity of 99.9%, ferroboron alloy, Nd, Dy, and Co having a purity of 99.7% or more were blended, and then high-frequency melted and cast. , 14Nd
An ingot having a composition of -0.5Dy-7B-3Co-remaining Fe (at%) was obtained. Thereafter, the ingot was coarsely ground and then finely ground to obtain a fine powder having an average particle size of 3 μm. This fine powder is inserted into a mold, oriented in a magnetic field of 12 kOe, molded at a pressure of 1.5 ton / cm ^{2 in} a direction perpendicular to the magnetic field, and
A molded body having dimensions of 5 cm x 6 mm was obtained.

The obtained molded body was heated at 1100 ° C. for 3 hours at A
After sintering under the condition in an atmosphere of r, cooling and grinding into a magnet having a size of 7 cm × 3.5 cm × 4 mm in thickness with a diamond grindstone, washing and drying with a solvent,
Aging treatment was performed at 2 ° C. for 2 hours. Then in the atmosphere, 250
The permanent magnet of the present invention was manufactured by performing heat treatment in an oxidizing atmosphere at 2 ° C. × 2 hours. It should be noted that α-Fe, FeO, generated on the tetragonal surface exposed on the obtained permanent magnet surface,
The thicknesses of Fe ₃ O ₄ and α-Fe ₂ O ₃ are 5 μm, and R ₂ O ₃ (H
The thickness of the exagonal phase was 10 μm.

The magnet properties of the obtained permanent magnet body and the increase in oxidation and the magnet properties after the magnet body was left in an atmosphere at 80 ° C. and a relative humidity of 90% for 100 hours were measured, and the results are shown in Table 1. In order to prevent dew condensation on the magnet body surface,
After heating to 0 ° C., the atmosphere was placed at 80 ° C. and 90% relative humidity.
After standing for 00 hours, ultrasonic cleaning was performed in pure water to remove corrosion products on the surface of the magnet body, and the weight loss and the magnet properties after drying at 100 ° C. were examined. .

Comparative Example 1 A permanent magnet having the same composition was obtained in the same manner as in Example 1 except that the heat treatment was not performed in an oxidizing atmosphere according to the present invention. Table 1 shows the results of measurement of the increase in oxidation and magnet properties after leaving the comparative magnet in an atmosphere at 80 ° C. and a relative temperature of 90% for 100 hours.
Table 2 shows the weight loss and magnet properties measured in the same manner as in Example 1 after being left in an atmosphere at 80 ° C. and a relative temperature of 90% for 100 hours.

Embodiment 2 An epoxy resin is applied to the permanent magnet body of the present invention obtained by the same method as that of Embodiment 1 by spray coating and baked to form a magnet having a resin layer of 20 μm. I got a body. Table 3 shows the rusting state after leaving the obtained magnet body in an atmosphere at 80 ° C. and a relative temperature of 90% for 1000 hours.

Comparative Example 2 A comparative permanent magnet body produced and produced in exactly the same manner as in Example 1 except that no heat treatment was performed in an oxidizing atmosphere was subjected to the same coating as in Example 2, A test was conducted, and the rusting state was examined.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

According to the present invention, after the Fe-BR-based permanent magnet body is ground, it is subjected to aging treatment in a vacuum or in an inert atmosphere, and is further subjected to aging treatment in the atmosphere or at an oxygen concentration of 0.
By performing a heat treatment in an oxidizing atmosphere of 1 vol% or more, α-Fe,
FeO and Fe ₃ O ₄ are formed on the outside and α-Fe ₂ O ₃ is formed on the outermost layer, and the exposed tetragonal grain boundary phase is R ₂ O ₃ (Hexa
gonal) and the surface of the magnet is passivated. As is clear from the examples, not only the corrosion resistance of the magnet body itself is significantly improved, but also the corrosion resistance after the surface treatment of the oxidation-resistant resin is improved. Furthermore, since the corrosion resistance of the Fe-BR based permanent magnet itself could be improved, the thickness of the resin coating film can be reduced, and the coating processing time can be reduced and the surface treatment cost can be reduced.

Claims (4)

(57) [Claims] 1. A tetragonal phase mainly composed of 10 to 30 atomic% of R, 2 to 28 atomic% of B and 65 to 80 atomic% of Fe, and α is formed on the surface of the tetragonal phase exposed on the surface of the magnet body.
-Fe, FeO on the outside, then Fe ₃ O ₄ , α on the outermost layer
-Fe ₂ O ₃ is sequentially formed, and the exposed tetragonal grain boundary phase has an R ₂ O ₃ (Hexagonal) phase having a thickness of 1 to 20.
A corrosion-resistant permanent magnet having a surface layer of μm. 2. 10 to 30 atom% of R, 2 to 28 atom of B
%, The main phase is tetragonal with 65 to 80 atomic% Fe
Phase, and the surface layer of the tetragonal phase exposed on the magnet body surface has α
-Fe, FeO on the outside, then Fe ₃ O ₄ , α on the outermost layer
-Fe ₂ O ₃ is sequentially formed, and the exposed tetragonal grain boundary phase is
R ₂ O ₃ (Hexagonal) phase thickness 1 to 20
A corrosion-resistant permanent magnet having a μm surface layer and further having an oxidation-resistant resin layer on the surface of the magnet body. 3. An Fe—BR containing R 10 to 30 at%, B 2 to 28 at%, and Fe 65 to 80 at% as main components.
In the method of manufacturing a permanent magnet, after grinding the magnet body,
After had in vacuo the aging treatment in an inert gas, the corrosion resistance, characterized in that the heat treatment 15 minutes to 12 hours at 200 to 350 ° C. in or oxygen concentration 0.1 vol% or more oxidizing atmosphere in the air Manufacturing method of permanent magnet. 4. R10 to 30 atom%, B2 to 28 atom
%, Fe-BR with Fe-80 atomic% as a main component
In the method of manufacturing a permanent magnet, after grinding the magnet body,
After aging in vacuum or inert gas,
Or in an oxidizing atmosphere with an oxygen concentration of 0.1 vol% or more
And heat treated at 200-350 ° C. for 15 minutes to 12 hours
After that, the surface of the obtained magnet body is coated with an oxidation-resistant resin layer.
A method for producing a corrosion-resistant permanent magnet, comprising: