JP2002075767A - Rare earth permanent magnet having corrosion-resistant covering, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth permanent magnet, having a corrosion- resistant covering having the same superior characteristics as those that an aluminum covering formed by the vapor phase plating method has on the surface, and to provide the manufacturing method of the rare earth permanent magnet. SOLUTION: An aluminum fine particle (I), and a covering containing at least one type selected from chrome, molybdenum, tungsten, and phosphor (II) are provided on the surface of the rare earth permanent magnet that is representatively R-Fe-B (R is a rare earth element) magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth permanent magnet having an excellent corrosion-resistant coating on the surface and a method for producing the same.

[0002]

2. Description of the Related Art Rare-earth based magnets such as R-Fe-B permanent magnets represented by Nd-Fe-B permanent magnets and R-Fe-N permanent magnets represented by Sm-Fe-N permanent magnets Permanent magnets are made of inexpensive materials that are abundant in resources,
In particular, R-Fe-B
Permanent magnets are used in various fields today. However, rare earth permanent magnets are highly reactive rare earth metals:
Because it contains R, it is easily oxidized and corroded in the air. If used without any surface treatment, corrosion will progress from the surface due to the presence of a slight amount of acid, alkali or moisture, causing rust. As a result, deterioration and variations in magnet characteristics are caused. Further, when the rusted magnet is incorporated in a device such as a magnetic circuit, the rust may be scattered and contaminate peripheral components. In view of the above, in order to impart excellent corrosion resistance to rare earth permanent magnets, an aluminum film is formed on the surface thereof by vapor phase plating such as evaporation. The aluminum coating has excellent corrosion resistance and excellent adhesion reliability with the adhesive required at the time of assembling parts. (Between the coating and the adhesive until the fracture strength inherent in the adhesive is reached) This is widely applied to rare-earth permanent magnets that require strong adhesive strength.

[0003]

As described above, although the aluminum film formed by the vapor phase plating method exhibits excellent characteristics, the apparatus for performing the vapor phase plating method is generally large-scale and expensive. Capital investment is required. Therefore, a corrosion-resistant coating that has the same properties as the excellent properties of an aluminum coating and that can be easily formed at low cost is desired. In the present invention, such a coating is applied to the surface. It is an object of the present invention to provide a rare earth permanent magnet having the same and a method for producing the same.

[0004]

Means for Solving the Problems The present inventors have conducted various studies in view of the above points, and as a result, have found that the surface of a rare-earth permanent magnet contains aluminum fine particles and dichromic acid or chromic acid. After applying the solution, by performing a heat treatment, a corrosion-resistant coating having the same properties as the aluminum coating formed by the vapor phase plating method, and having a dense and excellent adhesion to the magnet surface. It has been found that a film can be easily formed on the magnet surface at low cost.

The present invention has been made based on this finding. According to the first aspect of the present invention, there is provided a permanent magnet having (I) aluminum fine particles, (II) chromium, It has a coating containing at least one component selected from molybdenum, tungsten, and phosphorus. A permanent magnet according to a second aspect is characterized in that, in the permanent magnet according to the first aspect, the average particle diameter of the aluminum fine particles is 0.01 μm to 50 μm. The permanent magnet according to claim 3 is
3. The permanent magnet according to claim 1, wherein (I) aluminum fine particles (II) chromium in the coating,
The composition ratio ((I) / (II)) to at least one component selected from molybdenum, tungsten, and phosphorus is 1
~ 100 (mol / mol).
A permanent magnet according to a fourth aspect is characterized in that, in the permanent magnet according to any one of the first to third aspects, the thickness of the coating is 0.1 μm to 100 μm. A permanent magnet according to a fifth aspect is characterized in that, in the permanent magnet according to any one of the first to fourth aspects, the surface of the coating film is peened. Claim 6
The permanent magnet according to any one of claims 1 to 5, wherein the rare-earth permanent magnet is R-Fe-
It is a B type permanent magnet. Further, the method of the present invention for producing a permanent magnet having a coating containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten and phosphorus is as described in claim 7. After applying a treatment liquid containing (i) aluminum fine particles and (ii) at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof to the surface of the permanent magnet And heat-treating. Claim 8
The manufacturing method according to claim 7, wherein
(I) aluminum fine particles (i) in the treatment liquid
i) The composition ratio ((i) / (ii)) to at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof is 1 to 10.
0 (mol / mol). Further, according to the method of the present invention for producing a permanent magnet having a coating whose surface is peened, after forming a coating on the rare earth permanent magnet surface by the production method of claim 7 or 8, as in claim 9, And peening the coating surface.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The permanent magnet according to the present invention has a rare-earth permanent magnet surface coated with a coating containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten and phosphorus. It is characterized by having.

The permanent magnet of the present invention comprises, for example, (i) aluminum fine particles and (ii) dichromic acid, chromic acid, molybdic acid, tungstate,
It is produced by applying a treatment liquid containing at least one selected from phosphoric acid and salts thereof, followed by heat treatment.

[0008] The treatment liquid is, for example, uniformly dispersing aluminum fine particles in water, dichromic acid, chromic acid,
It is prepared by dissolving at least one selected from molybdic acid, tungstic acid, phosphoric acid, and salts thereof.

The size and shape of the aluminum fine particles to be mixed in the treatment liquid can be appropriately selected in consideration of the thickness of the coating film to be formed. It is desirable to use one having a diameter of from 01 μm to 50 μm. When the average particle size is less than 0.01 μm, secondary aggregation of fine particles occurs in the processing liquid, and it becomes difficult to handle the processing liquid during the manufacturing process, or a film in which the fine particles are uniformly dispersed cannot be formed. This is because there is a risk of doing so. On the other hand, it is desirable to disperse a large number of small fine particles in the coating and to increase the volume content of the fine particles in the coating from the viewpoint of imparting higher corrosion resistance to the coating, and when using fine particles having an average particle diameter of more than 50 μm, This is because the volume content of the fine particles in the inside is restricted, which may affect the provision of higher corrosion resistance. The particle size distribution of the aluminum fine particles is not particularly limited as long as the maximum value is equal to or less than the film thickness. Further, as the aluminum fine particles, those having various shapes such as a spherical shape, a flaky shape, and an irregular shape can be used.

The treatment solution may contain at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof. And phosphoric acid in combination, molybdic acid and phosphoric acid in combination, or dichromic acid or chromic acid, molybdic acid and phosphoric acid in combination to form multiple components in the coating Is desirable from the viewpoint of imparting higher corrosion resistance to the coating.

The salts of dichromic acid, chromic acid, molybdic acid, tungstic acid, and phosphoric acid to be mixed in the treatment liquid include lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, and ammonium salts. No.

The composition ratio of (i) aluminum fine particles to (ii) at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof in the treatment liquid ((i) / (Ii))
Is preferably adjusted to 1 to 100 (mol / mol), and more preferably to 2 to 20 (mol / mol). If the composition ratio is less than 1 (mol / mol), the content of the aluminum fine particles contributing to the corrosion resistance of the film may be too small, so that it may be difficult to form a film having excellent corrosion resistance. On the other hand, when the composition ratio exceeds 100 (mol / mol), the voids between the aluminum fine particles and the aluminum fine particles are not sufficiently filled with other coating components, and as a result, a dense coating may not be easily formed. Because. By adjusting the composition ratio of the two in the treatment liquid as described above, the composition ratio ((I) of the aluminum fine particles in the coating to (II) at least one component selected from chromium, molybdenum, tungsten, and phosphorus (( I) / (II))
Preferably, a coating of 1 to 100 (mol / mol), more preferably 2 to 20 (mol / mol) is formed,
Demonstrates excellent properties.

The total blending ratio of (i) aluminum fine particles to the treatment liquid and (ii) at least one kind selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid and salts thereof is particularly limited. Although not necessarily, usually, at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof is added in an amount of 1 mol to 10 mol / liter of water.
mol, and aluminum fine particles may be uniformly dispersed in a desired composition ratio.

It is desirable to adjust the pH of the processing solution to 0-5. By adjusting the pH of the treatment liquid in this way, it is possible to form a dense film showing excellent adhesion to the surface of the rare-earth permanent magnet.

The treatment liquid may contain an inorganic acid such as hydrochloric acid, sulfuric acid or boric acid, or an alkali such as sodium hydroxide or ammonia as a pH adjuster. Further, an organic acid such as malic acid, malonic acid, citric acid or succinic acid may be blended as a pH buffer. In addition, magnesium oxide, magnesium hydroxide, zinc oxide, zinc hydroxide, and hydroxide are used for the purpose of adjusting the pH and viscosity of the processing solution and for improving the corrosion resistance of the coating portion formed with components other than the aluminum fine particles. A water-soluble substance such as aluminum or lithium hydroxide may be blended. Further, aluminum oxide fine particles, silicon oxide fine particles, boron carbide fine particles, silicon nitride fine particles, and the like may be blended for the purpose of enhancing the hardness of the coating film.

After the treatment liquid prepared as described above is applied to the surface of the magnet, heat treatment is performed to form a film. Here, when applying the treatment liquid to the magnet surface, a known application method such as a dip coating method, a spray method, and a spin coating method can be adopted.

The heat treatment after the treatment liquid is applied to the magnet surface is performed in various atmospheres such as the atmosphere, an inert gas, or a vacuum, and in the case of a sintered magnet, in a temperature range of 100 ° C. to 450 ° C. And more desirably in a temperature range of 200 ° C to 400 ° C. If the heat treatment temperature is lower than 100 ° C., the coating may not be sufficiently densified. On the other hand, if the heat treatment temperature exceeds 450 ° C., the magnetic properties of the magnet may be deteriorated. In the case of a bonded magnet, the heat treatment temperature must be set in consideration of the heat resistance temperature of the resin used. For example, in the case of a bonded magnet using an epoxy resin or a polyamide resin, the heat treatment temperature is set to 100 ° C. in consideration of the heat resistance temperature of these resins.
It is desirable to set it to 200 ° C. In general, the heat treatment time is preferably 1 minute to 3 hours in consideration of productivity.

The film formed as described above has the same extensibility as the aluminum film formed by the vapor phase plating method. Thus, the corrosion resistance can be improved. For example, when performing shot peening, the shot material has a Vickers hardness of 300 or more,
Glass beads, steel shots, zirconia shots, or the like having an average particle diameter of 30 μm to 1000 μm can be used. If the average particle size of the shot material is less than 30 μm, there is a possibility that a peening effect sufficient for improving the corrosion resistance of the coating may not be obtained. If the average particle size of the shot material exceeds 1000 μm, the roughness of the coating surface may be reduced. In addition to the increase in the degree of cracking, cracks may be generated from the surface of the part formed of components other than the aluminum fine particles, which may cause a reduction in corrosion resistance. The projection conditions can be appropriately selected depending on the projection material to be used, the distance between the projection nozzle and a magnet having a coating on the surface of the workpiece, and the projection pressure is usually 0.1 MPa to 0.5 MPa, The projection time is 1 minute to 1 hour.

Examples of the rare earth permanent magnet applicable to the present invention include known rare earth permanent magnets such as R—Co permanent magnet, R—Fe—B permanent magnet, and R—Fe—N permanent magnet. Is mentioned. Above all, R-Fe-B permanent magnets are desirable because they have high magnetic properties, are excellent in mass productivity and economical efficiency, and have excellent adhesion to a coating film, as described above. Rare earth elements (R) in these rare earth permanent magnets are Nd, Pr, Dy, H
at least one of o, Tb, and Sm, or La, Ce, Gd, Er, Eu, Tm, Yb, and L
Those containing at least one of u and Y are desirable. Usually, one kind of R is sufficient, but in practice, 2 kinds are preferred.
Mixtures of more than one species (such as misch metal or dymium) can also be used for reasons such as availability. Further, Al, Ti, V, Cr, Mn, Bi, Nb, T
a, Mo, W, Sb, Ge, Sn, Zr, Ni, Si,
By adding at least one of Zn, Hf, and Ga, the coercive force and the squareness of the demagnetization curve can be improved, the productivity can be improved,
It is possible to reduce the price. The rare earth permanent magnet according to the present invention includes both a sintered magnet and a bonded magnet.

The coating containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten and phosphorus formed on the surface of the rare earth permanent magnet by the above method is as follows. It has various characteristics. First, due to the presence of the aluminum fine particles, the same properties as the excellent properties of the aluminum film formed by the vapor phase plating method are exhibited. In addition, since aluminum fine particles and dichromic acid or chromic acid are chemically bonded to each other due to a chemical reaction, they are dense and a layer with excellent corrosion resistance is formed on the surface of each aluminum fine particle by a chemical reaction. It has excellent corrosion resistance. In addition, aluminum has an affinity for oxygen atoms as high as a rare earth metal, so that aluminum fine particles form an interfacial reaction layer with the magnet surface, and therefore have excellent adhesion to the magnet surface. In addition, since dichromic acid and chromic acid have the ability to react with rare earth permanent magnets to form a passive film, the water itself is used in the manufacturing process of applying a treatment liquid and heat-treating it. Has the effect of suppressing corrosion of the magnet and has excellent adhesion to the magnet surface. In addition, by utilizing the extensibility of the aluminum fine particles, a peening treatment is performed to densify the surface, thereby improving corrosion resistance. Furthermore, by adjusting the composition of the processing solution and the conditions of the heat treatment, insulation properties can be imparted. If a rare-earth permanent magnet having this coating is used for a motor, the generation of eddy current can be effectively prevented. it can.

The film containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten and phosphorus formed on the surface of the rare earth permanent magnet by the above method has a film thickness. 0.1 μm
If it is above, sufficient corrosion resistance is shown. Although the upper limit of the film thickness that can be produced by the present invention is not limited,
Due to the demand for downsizing of the magnet itself, the film thickness is 10
0 μm or less is desirable. In practice, the preferred film thickness is 1 μm or more.
30 μm.

The same film or another film may be formed on the corrosion-resistant film of the present invention. By adopting such a configuration, the characteristics of the corrosion-resistant coating of the present invention can be enhanced or supplemented, and further functionality can be imparted. Since the production method of the present invention is the same as the step of forming a resin film such as application of a treatment liquid and heat treatment, the process is continuously performed (lined), and after the corrosion-resistant film of the present invention is formed, the resin is quickly formed. It becomes possible to form a coating or the like. Therefore, it is possible to efficiently form another coating on the corrosion-resistant coating of the present invention while suppressing cracking and chipping of the magnet due to handling when the magnet is moved between processes.

[0023]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.
The following embodiment is described, for example, in US Pat.
No. 3 and U.S. Pat. No. 4,792,368, 14Nd-79Fe-6B obtained by pulverizing a known casting ingot, finely pulverizing, and then performing molding, sintering, heat treatment and surface processing. This was performed using a sintered magnet having a -1Co composition.

Example 1: 1 liter of water has an average particle size of 3
800 g of fine aluminum particles (29.65 mo
l) is uniformly dispersed, and 90 g of chromic anhydride is further added.
(0.90 mol), phosphoric acid 330 g (3.37 mol)
l), 72 g (1.79 mol) of magnesium oxide was dissolved to prepare a treatment solution (pH 0 to 5). This treatment liquid was applied to the surface of a magnet (20 mm long × 30 mm wide × 0.5 mm thick) by a spray method, and then heat-treated at 350 ° C. for 1 hour to form a film. The thickness of the film formed as described above was 18 μm (by observing the fracture surface of the film with an electron microscope). In addition, the composition ratio of the coating was analyzed by X-ray fluorescence intensity measurement (RIX manufactured by Rigaku Corporation).
-3000 is used), aluminum / chromium is 32.0
(Mol / mol), aluminum / phosphorus is 9.1 (m
ol / mol) and aluminum / (chromium + phosphorus) were 7.1 (mol / mol), which almost coincided with the respective component composition ratios in the treatment liquid. When the magnet having the coating formed as described above was left under a high-temperature and high-humidity condition of a temperature of 80 ° C. and a relative humidity of 90%, a corrosion resistance test was performed. Rust was observed up to 300 hours after the start of the test. Thus, it was found that the formed film exhibited excellent corrosion resistance.

Example 2 A film was formed on the surface of a magnet (20 mm long × 30 mm wide × 0.5 mm thick) in the same manner as described in Example 1, and shot peening was performed on the surface of the film. Was. Shot peening is performed using glass beads GB-AG (Shinto Blater, Inc.
Vickers hardness 500-550, JIS equivalent particle size 180
No. (central particle size range (80%) 53 μm to 106 μm)
And a projection pressure of 0.2 MPa and a projection time of 10 minutes. When a test similar to the corrosion resistance test described in Example 1 was performed on a magnet having a coating whose surface was peened as described above, no rust was observed until 500 hours after the start of the test. From this, it was found that by performing the peening treatment on the film surface, the corrosion resistance could be improved.

Example 3 A coating was formed on the surface of a magnet (20 mm in diameter × 7 mm in height) in the same manner as described in Example 1. The film thickness of the formed film was 19 μm. Thereafter, shot peening was performed on the film surface in the same manner as in Example 2. A corrosion resistance test and a measurement of compressive shear strength were performed on a magnet having a coating whose surface was peened as described above. As a result of the same test as the corrosion resistance test described in Example 1, no rust was observed until 500 hours after the start of the test. The compression shear strength was measured by bonding this magnet to a cast iron jig using a modified acrylate adhesive (Hard Rock G-55: manufactured by Denki Kagaku Kogyo Co., Ltd.), and after standing for 24 hours.
It exhibited an excellent value of 2.1 MPa. At this time, no dissociation was observed between the magnet and the coating. From this,
It has been found that the corrosion-resistant coating of the present invention has excellent characteristics in terms of adhesion reliability and adhesion to a magnet.

[0027]

The film formed on the surface of the rare-earth permanent magnet according to the present invention and containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten and phosphorus is a gas phase. It is a corrosion-resistant film having characteristics similar to those of an aluminum film formed by a plating method, and being dense and excellent in adhesion to a magnet surface. Further, the manufacturing method is such that (i) aluminum fine particles and (ii) at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof are applied to the surface of the rare-earth permanent magnet. This is low-cost and simple, in which a heat treatment is performed after the treatment liquid to be contained is applied.

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Claims (9)

[Claims] 1. A permanent magnet comprising a rare-earth permanent magnet surface having a coating containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten, and phosphorus. 2. The permanent magnet according to claim 1, wherein said aluminum fine particles have an average particle size of 0.01 μm to 50 μm. 3. The method according to claim 1, wherein (I) aluminum fine particles (II) of chromium, molybdenum, tungsten,
The composition ratio ((I) / (II)) to at least one component selected from phosphorus is 1 to 100 (mol / mol)
The permanent magnet according to claim 1, wherein: 4. A film having a thickness of 0.1 μm to 100 μm.
4. The permanent magnet according to claim 1, wherein m is m. 5. The permanent magnet according to claim 1, wherein the surface of the coating is peened. 6. The permanent magnet according to claim 1, wherein the rare-earth permanent magnet is an R—Fe—B permanent magnet. 7. The rare-earth permanent magnet surface contains (i) aluminum fine particles and (ii) at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof. A method for producing a permanent magnet having a coating containing (I) aluminum fine particles and (II) at least one component selected from chromium, molybdenum, tungsten, and phosphorus, which is subjected to a heat treatment after applying a treatment liquid. 8. The composition ratio of (i) aluminum fine particles to (ii) at least one selected from dichromic acid, chromic acid, molybdic acid, tungstic acid, phosphoric acid, and salts thereof in the treatment liquid (( i) / (i
The method according to claim 7, wherein i)) is 1 to 100 (mol / mol). 9. A permanent magnet having a coating whose surface has been peened, wherein a coating is formed on the surface of the rare-earth permanent magnet by the production method according to claim 7 or 8, followed by peening the surface of the coating. Manufacturing method.