JPH04328804A - Corrosion-proof permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a corrosion-proof Fe-B-R permanent magnet, on which treatment time can be cut down by not only improving the corrosion-proof property of a resist-coated Fe-B-R permanent magnet, but also by thinning off the resin-coated film. CONSTITUTION:After an Fe-B-R permanent magnet body has been ground, an aging treatment is conducted in a vacuum or inert atmosphere. Besides, by conducting a heat treatment in the atmospheric air or in an oxidizing atmosphere having the concentration of 0.1vol.% or higher, alpha-Fe is formed on a tetragon-phased surface layer which is exposed to the surface of the magnetic body, FeO and Fe3O4 are formed on the outside of the aforesaid surface layer, alpha-Fe2O3 is formed on the outermost layer, the grain boundary phase of exposed tetragonal crystal is changed to R2O3 (hexagonal), and the surface of the magnet is passivated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to Fe-B-R permanent magnets that have high magnetic properties and excellent corrosion resistance. Fe-
This invention relates to a B-R permanent magnet and its manufacturing method.

0002

[Prior art] Today, F
The e-B-R permanent magnet (Japanese Unexamined Patent Publication No. 59-46008) exhibits high magnetic properties with a structure having a main phase of a ternary tetragonal compound and an R-rich phase, and has an iHc of 25 kOe or more (
BH) max is 45MGOe or more, demonstrating much higher performance than conventional high-performance rare earth cobalt magnets. Further, Fe-BR permanent magnets with various compositions have been proposed so as to exhibit various magnetic properties selected depending on the application.

However, Fe-B-R permanent magnets having the above-mentioned excellent magnetic properties mainly contain rare earth elements and iron, which easily form oxides or hydroxides when oxidized or hydroxylated in the air. Because it contains Fe-
When a B-R permanent magnet is incorporated into a magnetic circuit, oxides or hydroxides generated on the magnet surface cause a decrease in the output of the magnetic circuit and variations in magnetism between magnetic circuits. There was a problem of contamination of peripheral equipment due to falling oxides.

[0004] Therefore, in order to improve the corrosion resistance of the above-mentioned Fe-B-R permanent magnet, the surface of the magnet body is coated with a corrosion-resistant metal plating layer by electroless plating or electrolytic plating, or a corrosion-resistant resin is coated by dipping or electroplating. Coating with a coating method, forming a corrosion-resistant metal or alloy film such as Al using a vapor deposition method, depositing a resin layer containing corrosion-resistant metal flakes, or layering different types of corrosion-resistant films. Techniques for applying corrosion-resistant coatings have been proposed.

[0005]

[Problems to be Solved by the Invention] Since electroless plating or electrolytic plating is processed in an acidic or alkaline solution, the magnet surface not only corrodes, causing deterioration and variation in magnetic properties, but also causes pins to form on the plating film. Due to the presence of holes, sufficient corrosion resistance cannot be obtained for severe tests such as salt spray tests.

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

The purpose of this invention is to improve the corrosion resistance of Fe-B-R permanent magnets, and in particular to improve the corrosion resistance of Fe-B-R permanent magnets.
The object of the present invention is to provide a corrosion-resistant Fe-BR-based permanent magnet that not only improves the corrosion resistance of the -R-based permanent magnet but also allows the reduction of surface treatment time by making the resin coating film thinner.

[0008]

[Means for Solving the Problems] This invention provides R10-3
The main phase consists of a tetragonal phase with 0 at%, B2 to 28 at%, and Fe65 to 80 at% as main components, α-Fe in the surface layer of the tetragonal phase exposed on the surface of the magnet, FeO on the outside,
Fe3O4, α-Fe2O3 is formed in the outermost layer, and the exposed tetragonal grain boundary phase is R2O3 (Hexagonal)
The present invention is a corrosion-resistant permanent magnet characterized by having a surface layer consisting of a phase with a thickness of 1 to 20 μm.

[0009] Furthermore, the present invention provides R10 to 30 atomic %,
In the method for manufacturing Fe-B-R permanent magnets whose main components are 2 to 28 at% of B and 65 to 80 at% of Fe, after grinding the magnet body and aging treatment in vacuum or inert gas, This is a method for producing a corrosion-resistant permanent magnet, which is characterized by heat treatment at 200 to 350° C. for 15 minutes to 12 hours in an oxidizing atmosphere with an oxygen concentration of 0.1 vol % or more.

0010

[Operation] As a result of various studies aimed at improving the corrosion resistance of Fe-B-R permanent magnets as well as the corrosion resistance after surface treatment, the present invention was developed by grinding the obtained magnet body and then grinding it in a vacuum or in a free environment. After aging treatment in an active atmosphere, heat treatment is performed in the air or in an oxidizing atmosphere with an oxygen concentration of 0.1 vol% or more, so that α-Fe is added to the surface layer of the tetragonal phase exposed on the surface of the magnet, and the outside thereof is FeO, Fe
3O4, α-Fe2O3 is formed in the outermost layer, and the exposed tetragonal grain boundary phase changes to R2O3 (Hexagonal), making the magnet surface passivated, which not only improves the corrosion resistance of the magnet itself, but also improves oxidation resistance. This invention was completed based on the discovery that the corrosion resistance of a plastic resin is also improved after surface treatment.

[0011] In the Fe-B-R permanent magnet according to the present invention, the main phase is a tetragonal phase, and α-Fe is formed on the surface layer of the tetragonal phase exposed on the surface of the magnet body by heat treatment, and FeO is formed on the outside thereof.
, Fe3O4, α-Fe2O3 is formed in the outermost layer, and the exposed tetragonal grain boundary phase is R2O3 (Hexagonal).
However, the total thickness of the specific four layers provided on the surface layer of the tetragonal crystal exposed on the surface and the grain boundary phase of the exposed tetragonal crystal is at least 1 μm or more in order to obtain the effect of improving corrosion resistance. thickness is required. Also, α-Fe, Fe
The thickness of O, Fe3O4, α-Fe2O3 is 1 to 10 μm
The thickness is preferable, and R2O3 (Hex
The thickness of the agonal) phase is preferably 1 to 20 μm. The reason why the thickness of the surface layer on the surface of the magnet is limited to 1 to 20 μm is that if it is less than 1 μm, the effect of improving corrosion resistance will be insufficient, and if it exceeds 20 μm, the surface layer will lose its magnetism and the magnetic properties will deteriorate. .

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

[0013] B is an essential element in the system permanent magnet, and if it is less than 2 atomic %, the rhombohedral structure becomes the main phase and high coercive force (iHc) cannot be obtained, and if it exceeds 28 atomic %, B-rich As the non-magnetic phase increases, the residual magnetic flux density (B
r) decreases, an excellent permanent magnet cannot be obtained, and B
is in the range of 2 atomic % to 28 atomic %.

[0014] Fe is an essential element in the permanent magnet, and if it is less than 65 atomic %, the residual magnetic flux density (B
If r) decreases and exceeds 80 atom %, high coercive force cannot be obtained, so Fe is contained in an amount of 65 atom % to 80 atom %. Furthermore, a part of Fe can be replaced with Co, or various additive elements can be included to improve the characteristics.

Manufacturing Method In the case of a sintered permanent magnet, the following heat treatment method is preferred for industrial production as a method for forming a surface layer of a magnet body having a specific composition and structure, which is a feature of the present invention. After the compact is sintered in a vacuum or in an inert atmosphere, it is subjected to processing steps such as cutting and grinding, and then aged in a vacuum or in an inert gas, and then in the atmosphere or at least at a low oxygen concentration. Heat treatment is performed in an oxidizing atmosphere of 0.1 vol% or more.

[0016] By aging the permanent magnet molded body at 450 to 700°C for 15 minutes or more, α-Fe is formed on the surface layer of the tetragonal phase exposed on the surface, and FeO and Fe3O are formed on the outside.
4. α-Fe2O3 is formed in the outermost layer, and the exposed tetragonal grain boundary phase changes to R2O3 (Hexagonal) phase, but the surface layer is thin, less than 1 μm, and sufficient corrosion resistance cannot be obtained. In addition, by carrying out aging treatment for a long time, the surface layer can be made thicker than 1 μm,
In industrial production, long-term aging treatment is not practical and deteriorates magnetic properties, so aging treatment at 450 to 700°C for 15 minutes to 5
After the aging treatment, the surface layer can be made to have a thickness of 1 to 20 μm without deteriorating the magnetic properties by performing a heat treatment in an oxidizing atmosphere as described below.

The heat treatment in an oxidizing atmosphere is carried out in the air or in an oxidizing atmosphere with an oxygen concentration of at least 0.1 vol% or more, and if the treatment temperature is less than 200°C, α-
Fe, FeO, Fe3O4, α-Fe2O3 and R2O
It takes a long time to make the thickness of the 3 (Hexagonal) phase 1 μm or more, which is inefficient, and the processing temperature is 35 μm or more.
If the temperature exceeds 0°C, oxidation will rapidly proceed, oxygen diffusion into the interior will increase, and the magnetic properties will deteriorate, as well as the surface layer will become brittle, which is undesirable. A more preferable treatment temperature is 250 to 300°C.

If the heat treatment time in an oxidizing atmosphere is less than 15 minutes, α-Fe, FeO, Fe3O4, α-Fe2O3
and the thickness of the R2O3 (Hexagonal) phase is 1 μm.
If it exceeds 12 hours, oxidation will progress too much and oxygen diffusion into the interior will increase, which will not only deteriorate the magnetic properties but also make the surface layer brittle, which is undesirable.
The duration is from 15 minutes to 12 hours. A more preferred treatment time is 1 to 8 hours.

The present invention significantly improves the corrosion resistance of Fe-B-R magnets, but the corrosion resistance is further improved when an oxidation-resistant resin is applied by a dipping method, a spray method, an electrodeposition method, or the like. In this invention, the resin to be deposited by dipping or spraying is preferably epoxy resin, urethane resin, fluororesin, furan resin, polysiloxane resin, etc., and the resin to be deposited by electrodeposition is preferably epoxy resin, Acrylic resin and the like are preferred.

[0020]

[Example] Example 1 Electrolytic iron with a purity of 99.9%, ferroboron alloy, and Nd, Dy, and Co with a purity of 99.7% or more were used as starting materials, and after mixing these, they were 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 with an average particle size of 3 μm. This fine powder was inserted into a mold, oriented in a magnetic field of 12 kOe, and molded at a pressure of 1.5 ton/cm2 in a direction perpendicular to the magnetic field.
A molded article with dimensions of 5 cm x 6 mm in thickness was obtained.

[0021] The obtained molded body was heated at 1100°C for 3 hours.
After sintering under the conditions of r atmosphere, after cooling, it was ground into a magnet body with dimensions of 7 cm x 3.5 cm x thickness 4 mm using a diamond grindstone, washed with a solvent, dried, and then heated in a vacuum at 530 mm.
Aging treatment was performed at ℃ for 2 hours. Then in the atmosphere, 250
A permanent magnet of the present invention was produced by heat treatment in an oxidizing atmosphere at ℃ for 2 hours. In addition, α-Fe, FeO,
The thickness of Fe3O4 and α-Fe2O3 is 5 μm, and R2O
The thickness of the 3 (Hexagonal) phase was 10 μm.

The magnetic properties of the obtained permanent magnet, and the oxidation weight gain and magnetic properties after the magnet was left in an atmosphere of 80° C. and 90% relative humidity for 100 hours were measured and are shown in Table 1. In addition, in order to prevent dew condensation on the surface of the magnet, please
After heating to 0℃, place it in an atmosphere of 80℃ and 90% relative humidity.
After being left for 00 hours, the magnet was subjected to ultrasonic cleaning in pure water to remove corrosion products on the surface of the magnet, and after drying at 100°C, the weight loss and magnet properties were investigated. The results are shown in Table 2. .

Comparative Example 1 A permanent magnet having the same composition was obtained in exactly the same manner as in Example 1, except that the heat treatment in an oxidizing atmosphere according to the present invention was not performed. Table 1 shows the measurement results of oxidation weight gain and magnet properties after a comparative magnet was left in an atmosphere of 80°C and 90% relative temperature for 100 hours.
Table 2 shows the amount of weight loss and magnetic properties measured in the same manner as in Example 1 after being left in an atmosphere of 0° C. and 90% relative temperature for 100 hours.

Example 2 An epoxy resin was coated on a permanent magnet of the present invention produced in exactly the same manner as in Example 1 by spray painting, and baked to produce a magnet having a resin layer of 20 μm. I got a body. Table 3 shows the state of rust after the obtained magnet was left in an atmosphere of 80° C. and relative temperature of 90% for 1000 hours.

Comparative Example 2 A comparative permanent magnet obtained by manufacturing in exactly the same manner as in Example 1 except that it was not heat-treated in an oxidizing atmosphere was coated with the same coating as in Example 2 to produce a similar product. A test was conducted, and the rusting conditions were investigated and are shown in Table 3.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

Effects of the Invention According to the present invention, after grinding a Fe-B-R permanent magnet body, aging treatment is performed in a vacuum or an inert atmosphere, and then in the atmosphere or in an oxygen concentration of 0.
By heat treatment in an oxidizing atmosphere of 1 vol% or more, α-Fe,
FeO, Fe3O4 on the outside, α-Fe2O on the outermost layer
3 is formed, and the exposed tetragonal grain boundary phase is R2O3(H
exagonal) and the magnet surface becomes 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 with the oxidation-resistant resin is improved. Furthermore, since the corrosion resistance of the Fe-BR-based permanent magnet itself can be improved, the thickness of the resin coating film can be reduced, and the coating treatment time and surface treatment cost can be reduced.

Claims (3)

[Claims] Claim 1: The main phase consists of a tetragonal phase with R10 to 30 at%, B2 to 28 at%, and Fe 65 to 80 at% as main components, and the surface layer of the tetragonal phase exposed on the surface of the magnet has α
-Fe, FeO on the outside, Fe3O4, α- on the outermost layer
Fe2O3 is formed and the exposed tetragonal grain boundary phase is R2
Consisting of O3 (Hexagonal) phase, thickness 1-20μ
A corrosion-resistant permanent magnet characterized by having a surface layer of m. 2. The corrosion-resistant permanent magnet according to claim 1, further comprising an oxidation-resistant resin layer on the surface of the magnet body. 3. Fe-B-R whose main components are 10 to 30 atomic % of R, 2 to 28 atomic % of B, and 65 to 80 atomic % of Fe.
In the method for manufacturing permanent magnets, after grinding the magnet body,
Corrosion resistance characterized by aging treatment in vacuum or in an inert gas, followed by heat treatment at 200 to 350°C for 15 minutes to 12 hours in the air or in an oxidizing atmosphere with an oxygen concentration of 0.1 vol% or more. A method of manufacturing permanent magnets.