JPH09320826A - Highly anticorrosive rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve anticorrosive property by forming a multilayer film composed of an alkaline electroless nickel plating layer as an underlying layer, an alkaline electroless copper plating layer as an intermediate layer, and an electroless nickel- phosphorus plating layer as a surface layer, with each of these layers having a specified thickness, on the surface of a rare earth, transition metal, boron-based sintered permanent magnet body. SOLUTION: A multilayer film composed of an underlying layer, an intermediate layer and a surface layer which are made of electroless plating layers on the surface of a rare earth, transition metal, boron based sintered permanent magnet body. The underlying layer is an alkaline electroless nickel plating layer having a thickness of 0.1-5μm and the intermediate layer is an alkaline electroless copper plating layer having a thickness of 5-15μm, while the surface layer is an electroless nickel-phosphorus plating layer having a thickness of 5-15μm, thus forming a high anticorrosive rare earth magnet. Thus, a uniform plating film thickness may be obtained, and the adhesiveness between the plating film and the sintered permanent magnet body may be improved. In addition, a magnet may be provided which exhibits a high anticorrosive property and has no temporal change in magnetic property at the time of plating and after plating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a multi-layer coating of only an electroless plating layer on the surface of a rare earth / transition metal / boron-based sintered permanent magnet body to improve corrosion resistance and uniform plating with excellent adhesion. TECHNICAL FIELD The present invention relates to a highly corrosion-resistant rare earth magnet coated with a layer.

[0002]

2. Description of the Related Art A rare earth / transition metal / boron-based sintered permanent magnet is a rare earth / cobalt-based permanent magnet, which has R (where R is at least one of rare earth elements including Y), B, and Fe as main components. Magnetic properties are significantly superior to those of sintered permanent magnets.
It is widely used not only in the electronic equipment field but also in a wide range of fields.

This rare earth / transition metal / boron-based sintered permanent magnet has the above-mentioned advantages, but on the other hand, an R-rich phase such as an Nd-rich phase, which is present in the grain boundary and has a multiphase structure, is extremely potential. Since it is base, intergranular corrosion is likely to occur due to the action of the local battery, and the corrosion resistance is poor.

Therefore, in order to improve the corrosion resistance of the rare earth / transition metal / boron-based sintered permanent magnet, a surface treatment technique for forming various corrosion-resistant coatings on the surface of the magnet body has been proposed,
Many are put to practical use in industrial scale production. For example, the above-mentioned surface treatment techniques include a method of forming a resin film by electrodeposition coating / spray coating, a method of forming a vapor phase coating film such as ion plating / sputtering / vacuum deposition, electroplating / electroless plating. There is known a method of forming a wet plating film such as.
However, there are merits and demerits, and they do not necessarily meet the demands from various fields.

[0005]

Among the above-mentioned surface treatment techniques, a method of forming a wet plating film, which is excellent in cost and corrosion resistance, has become mainstream today (Japanese Patent Publication No.
-74012). Especially in industrial scale production,
Electroplating is widely used because it is superior to electroless plating in terms of cost and control of plating solution. For example, a three-layer electroplating film consisting of an electronickel plating layer as an underlayer, an electrocopper plating layer as an intermediate layer, and an electronickel / phosphorus plating layer as a surface layer is formed on the surface of a rare earth / transition metal / boron-based sintered permanent magnet body. The structure of the corrosion-resistant coating is proposed (Japanese Patent Laid-Open No. 7-331486).

[0006] This three-layer electroplating structure can suppress the formation of pinholes in the plating film and can improve the corrosion resistance, but it does not solve the essential drawbacks of electroplating. . That is, since the coating film formed by electroplating is biased due to the current distribution to the material to be plated, for example, in a cylindrical magnet body, the sticking to the inner peripheral portion of the magnet body is poor and compared with the outer peripheral portion. The plating film thickness of the inner peripheral portion becomes thin, and in the thin flat magnet body, the electric current is concentrated at the edge portion of the magnet body and the plating film at the edge portion becomes too thick compared to the central portion,
In any case, it is difficult to obtain a uniform plating film thickness. Therefore, it has a problem that it cannot be used in applications requiring high dimensional accuracy.

In order to obtain a uniform plating film thickness even with the above magnet shape, it is desirable to form the plating film only by electroless plating. For example, an electrically noble electroless copper plating layer (plating solution has a pH of 8 to 14) is deposited as a base layer on the surface of a rare earth / transition metal / boron-based sintered permanent magnet body, and an electrically baseless layer is formed on it. A configuration has been proposed in which an electroless nickel-phosphorus plating layer (plating solution has a pH of 3 to 13) is deposited to form a two-layer coating of only electroless plating (Japanese Patent Publication No. 7-2005, Japanese Patent Publication No. 7-56849).
issue).

With this two-layer electroless plating structure, it is possible to obtain a uniform plating film thickness, but since the electroless copper plating layer is essentially the underlayer, the adhesion to the magnet body is improved. In the so-called cross-cut substrate test, the coating cut by the knife floats up.

[0009] In the case of electroless copper plating, this film peeling phenomenon occurs because the initial precipitation portion first precipitates in the form of particles, and then the film grows so as to fill the spaces between the particles, so that even the grain boundary portion of the material (magnet body) It is presumed that the precipitation of the powder does not occur easily, and the anchor effect is low (New Ceramics (1991) No. 11 P88-P9, issued by TIC Co., Ltd.).
6 "Conductive coating of ceramic substrates by electroless plating").

Furthermore, there has been proposed a structure in which a three-layer plating film is formed by using an electroless plating film and an electroplating film together. That is, the surface of a rare earth / transition metal / boron-based sintered permanent magnet body is neutralized as a base layer to prevent the corrosion deterioration due to aging, and an alkaline electroless copper plating layer or nickel / phosphorus is used. A configuration has been proposed in which, after forming a plating layer, a three-layer plating film including an electrolytic copper plating layer or a nickel plating layer as an intermediate layer and an electrolytic nickel / phosphorus plating layer as a surface layer is formed (Japanese Patent Laid-Open No. 8-3763). ).

Even in the three-layer electroless plating and electroplating structure, it is difficult to obtain a uniform plating film thickness because the main constituent of the plating film is the electroplating film. Since it is a composite plating of plating, it is complicated in terms of plating work.

The present invention solves the above problems and, in particular, positively utilizes the advantages of electroless plating to obtain a uniform coating film thickness, and the plating film and rare earth /
Improves adhesion with transition metal / boron-based sintered permanent magnets,
Further, it is an object of the present invention to provide a highly corrosion-resistant rare earth magnet which exhibits excellent corrosion resistance and has no change over time in magnetic characteristics (deterioration of characteristics) during and after plating.

[0013]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors have paid attention to a structure in which a multi-layer coating is formed only by an electroless plating layer, and as a result of various experiments, particularly rare earth / transition metal / In order to improve the adhesiveness with the boron-based sintered permanent magnet body, an electroless nickel plating layer was deposited as an underlayer. That is, in the case of electroless nickel plating, smooth and dense deposition is performed from an extremely thin film state,
It has been confirmed that uniform growth continues thereafter, and it is presumed that precipitation easily up to the grain boundary part of the material (magnet body) and that it enhances the anchoring effect of the formed coating ( New Ceramics (1991) N
o. 11).

However, among the electroless nickel plating, the electroless nickel / phosphorus plating solution uses hypophosphorous acid as a reducing agent, so that phosphorous acid and hydrogen gas are generated as a side reaction, and phosphorus (P ) And hydrogen (H ₂ ) are contained in the nickel plating film. In particular, a rare earth / transition metal / boron-based sintered permanent magnet is very likely to absorb hydrogen, and if a large amount of hydrogen is absorbed, grain boundaries will drop and the adhesion to the plating film will be significantly reduced. Further, also in the case of the electroless nickel / boron plating solution, boron (B) and hydrogen (H ₂ ) are contained in the nickel plating film by the side reaction, and a similar phenomenon occurs.

Therefore, the pH of the electroless nickel plating solution is
As a result of various studies, it was found that when the plating solution is an alkaline solution, hydrogen absorption in the magnet body is significantly reduced and at the same time the grain boundaries of the magnet body are not corroded. It has been found that the configuration in which the plating layer is formed has excellent adhesion as compared with the configuration in which the conventional electroless copper plating layer (plating solution has a pH of 8 to 14) is formed. In the case of nickel-phosphorus plating, the thickness of the underlayer is 0.1 to 5 μm because it becomes harder and brittle as the film becomes thicker because it contains phosphorus.
It was confirmed that it was necessary to select from the range of m. Also in the case of nickel / boron plating, it was confirmed that it is necessary to select from the range of 0.1 to 5 μm for the same reason because it contains boron.

The surface layer is an acidic or alkaline electroless nickel-phosphorus plating layer which forms a dense film without pinholes from the viewpoint of corrosion resistance and surface properties, and the thickness of the surface layer is It was confirmed that it is necessary to select from the range of 5 to 15 μm in order to eliminate pinholes. In addition, this electroless nickel
Since the phosphorus plating layer has a very large hydrogen attack on the magnet body, it may penetrate the alkaline electroless nickel plating layer, which is the underlayer, and cause hydrogen absorption, resulting in loss of grain boundaries of the magnet body. Therefore, it is necessary to form an intermediate layer effective as a hydrogen barrier.

In addition to the function as a hydrogen barrier, the present inventors have also provided an anticorrosion mechanism and an effect of softening the heat resistance of the plating film to alleviate the heat shock, and further, through the pinhole of the alkaline electroless layer nickel plating as the underlayer. From the viewpoint of preventing corrosion of the magnet body, an alkaline electroless copper plating layer is formed as the intermediate layer. The film thickness of the intermediate layer is 5 to 1 in order to function as a hydrogen barrier.
It was confirmed that it was necessary to select from the range of 5 μm.

The present invention has been completed on the basis of the above-described examination results, and an underlayer consisting of an electroless plating layer, an intermediate layer and a surface layer are formed on the surface of a rare earth / transition metal / boron based sintered permanent magnet body. Of the alkaline electroless nickel plating layer having a film thickness of 0.1 to 5 μm, the intermediate layer having an alkaline electroless copper plating layer having a film thickness of 5 to 15 μm, and the surface layer having a film thickness of 5 to 15 μm. Of electroless nickel
It is a highly corrosion-resistant rare earth magnet characterized by being a phosphorus-plated layer.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the corrosion resistant rare earth magnet of the present invention, the rare earth / transition metal / boron based sintered permanent magnet body is
R (where R is at least one of the rare earth elements including Y
Seed) and a known sintered permanent magnet body containing Fe and B as main components, and in particular, a sintered permanent body having a composition containing R8 to 30 atom%, B2 to 28 atom% and Fe42 to 90 atom% as main components. A magnet body is preferred. As R, a light rare earth is sufficient, and Nd and Pr are particularly preferable. Usually, one type of R is sufficient, but if necessary, a mixture of two or more types (Misch metal, didymium, etc.) can be used.

By substituting 50% or less (preferably 20% or less) of Fe with Co, temperature characteristics and corrosion resistance can be improved. In addition, Al (9.5 atom% or less), Ti (4.5 atom%) for the purpose of increasing the coercive force.
Below), V (9.5 atom% or less), Cr (8.5 atom%)
Below), Mn (8.0 atom% or less), Bi (5 atom% or less), Nb (12.5 atom% or less), Ta (10.5 atom% or less), Mo (9.5 atom% or less) , W (9.5 atom% or less), Sb (2.5 atom% or less), Ge (7 atom% or less), Sn (3.5 atom% or less), Zr (5.5 atom% or less), Hf At least 1 of (5.5 atomic% or less)
It is also possible to additionally contain a seed.

It is desirable that the content of each of the additive elements such as R, Fe, B, Co and Al is appropriately selected according to the required magnetic characteristics and the like. Furthermore, C, O, P, S
The presence of impurities that are unavoidable in industrial production such as

In the corrosion-resistant rare earth magnet of the present invention, the sintered rare earth / transition metal / boron based permanent magnet body may be a sintered permanent magnet having the above composition and obtained by a known powder metallurgy method. The intended effect is not impaired by the manufacturing method, molding method, sintering method, aging treatment method and the like.

In the corrosion-resistant rare earth magnet of the present invention, the main feature of the multi-layer coating consisting of only the electroless plating layer is that the base layer is an alkaline electroless nickel plating layer and the intermediate layer is an alkaline electroless copper based on the above-mentioned findings. The plating layer and the surface layer are formed of an electroless nickel / phosphorus plating layer.

Although it is necessary that each plating layer has a required film thickness as described above, in order to further improve the function of each plating layer, the alkaline electroless nickel plating layer forming the underlayer is formed. The thickness is in the range of 0.3 to 3 μm, the thickness of the alkaline electroless copper plating layer forming the intermediate layer is in the range of 8 to 12 μm, and the thickness of the electroless nickel-phosphorus plating layer forming the surface layer is 8 to 12 μm. It is particularly preferable to select from the range.

The total thickness of the three layers including the underlayer, the intermediate layer and the surface layer is preferably 35 μm or less in view of the strength of the entire coating, the dimensional accuracy of the product, the cost, etc., but is required. It is preferably 30 μm or less, or even 25 μm or less, depending on various characteristics.

The underlayer is formed by an alkaline electroless nickel plating bath, but a known nickel / phosphorus plating bath or nickel / boron plating bath can be adopted. The composition of these alkaline electroless nickel plating baths includes nickel sulfate as a nickel source, sodium hypophosphite / sodium borohydride as a reducing agent, sodium citrate as a complexing agent, and other required components (stability). A known alkaline electroless nickel plating bath containing an agent) can be used, and an alkaline electroless nickel plating layer suitable for the underlayer of the present invention is formed by plating under the plating conditions according to the ordinary method. can do.

When a nickel-phosphorus plating bath is used, the phosphorus content in the underlayer is not particularly limited, but 2
It is preferably at least wt%, and particularly preferably at 3 to 10 wt%. When a nickel-boron plating bath is used, the boron content in the underlayer is not particularly limited,
It is preferably 0.5% by weight or more, and particularly preferably 3 to 6% by weight. These alkaline electroless nickel plating baths preferably have pH ≧ 9 for the reason of preventing intergranular corrosion of the rare earth / transition metal / boron-based sintered permanent magnet body.

The intermediate layer is formed by an alkaline electroless copper plating bath. The composition of the bath is copper sulfate as a copper source, formalin / paraformaldehyde as a reducing agent, and Rochelle salt / EDTA as a complexing agent. A known chemical copper plating containing other necessary components (sodium hydroxide, stabilizer, wetting agent, etc.) can be used, and the intermediate layer of the present invention can be obtained by plating under the plating conditions according to the conventional method. A suitable alkaline electroless copper plating layer can be formed.

Since this electroless copper plating bath may corrode the grain boundaries of the rare earth / transition metal / boron based sintered permanent magnet body through the pinholes of the electroless nickel plating layer of the underlayer, in order to prevent this Alkaline and pH ≧ 9
It is preferable that

The surface layer is formed by an electroless nickel / phosphorus plating bath. The composition of the bath is nickel sulfate as a nickel source, sodium hypophosphite as a reducing agent, and the like.
As the complexing agent, a known acid bath or alkali bath containing other required components (stabilizer, etc.) such as sodium citrate can be used. By plating under the plating conditions according to the usual method, the present invention can be used. An electroless nickel / phosphorus plating layer suitable for the surface layer of can be formed. The phosphorus content in the surface layer is not particularly limited, but is preferably 2% by weight or more, and particularly preferably 7 to 12% by weight.

For this electroless nickel / phosphorus plating, either an acidic bath or an alkaline bath can be used.
Since the plating film formation rate is high, and the plating bath is stable and easy to use, the composition formed in an acidic bath having pH ≦ 5 is preferable.

As a method of immersing the magnet body in each of the above plating baths, a known method such as a barrel method or a hooking jig method can be adopted. Furthermore, it is preferable to carry out a pretreatment such as a pickling treatment, a surface activation treatment and a smut removing treatment, if necessary.

[0033]

EXAMPLE 12.6Nd-1.2Dy-7.2B-0.
An alloy having a composition of 5Al-1.1Co-balance Fe was prepared by high frequency melting, the obtained ingot was coarsely pulverized by a stamp mill and a disc mill, and then finely divided by a jet mill using N ₂ gas as a pulverizing medium. Grain size 3.5μ
m raw material powder was obtained. The obtained raw material powder was molded under a pressure of 1.5 ton / cm ² while orienting in a magnetic field of 10 kOe. This molded body was heated at 1100 ° C in an argon atmosphere.
Sintering was performed for 1 hour, and after further cooling, aging treatment was performed at 600 ° C. for 2 hours in an argon atmosphere to obtain a rare earth / transition metal / boron-based sintered permanent magnet body.

30 mm × 12 from the above sintered permanent magnet body
The material was cut into a size of 3 mm × 3 mm to obtain the following plating test pieces. Before subjecting to electroless plating, the test piece is surface-ground by immersing the test piece in a pickling solution having a solution temperature of 30 ° C. and containing an aqueous solution of sodium nitrate 0.2 mol% and sulfuric acid 1.5 vol% for 4 minutes. It was Then, it was washed with water and further ultrasonically washed in water for 30 seconds to remove the smut attached to the test piece.

Subsequently, each test piece was subjected to electroless plating under the conditions shown in Table 1. The composition of the alkaline electroless nickel / phosphorus plating bath is nickel sulfate 25 g /
1, sodium hypophosphite 20 g / l, sodium citrate 60 g / l, and a trace amount of stabilizer, pH 9 (ammonia water adjustment), liquid temperature 60 ° C., film formation rate 6 μm
/ Hour to obtain a plating layer having a target film thickness. The phosphorus content in the formed alkaline electroless nickel / phosphorus plating layer was 5% by weight.

Similarly, the composition of the alkaline electroless copper plating bath is as follows: copper sulfate (CuSO ₄ .5H ₂ O) 10 g / l, formalin (37% HCHO) 20 ml / l, sodium hydroxide (NaOH) 10 g / l, EDTA4Na
25g / l, consisting of a small amount of stabilizer and wetting agent, pH 1
2. The liquid temperature was set to 65 ° C. and the film formation rate was adjusted to 2.5 μm / hour to obtain a plating layer having a target film thickness.

Further, the composition of the acidic electroless nickel-phosphorus plating bath is as follows: nickel sulfate 20 g / l, sodium hypophosphite 24 g / l, lactic acid 27 g / l, propionic acid 2 g / l.
1, consisting of a small amount of stabilizer, pH 4.5, liquid temperature 90 ℃
Then, the film forming rate was adjusted to 15 μm / hour to obtain a plating layer having a target film thickness. The phosphorus content in the formed acidic electroless nickel / phosphorus plating layer was 8% by weight.

A pressure cooker test, a salt spray test, a constant temperature and constant humidity test, a cross-cut substrate test, and an electroless plating treatment were carried out under the conditions shown in Table 1.
Tests such as a cooling test after heating in air and a hydrogen gas releasing test were performed, and the corrosion resistance and adhesion of each test piece were compared, and the results are shown in Table 2. Further, the change in the magnetic property of each test piece was measured before the plating treatment, after the plating treatment, and after the constant temperature and constant humidity test, and the results are shown in Table 3.

Table 4 shows a comparison between the high corrosion resistance rare earth magnet of the present invention and the conventional high corrosion resistance rare earth magnet obtained by electroplating in the plating thickness distribution and hydrogen gas release test. In the highly corrosion-resistant rare-earth magnet of the present invention, the variation of the coating size of each test piece (the variation of the coating size in the final product)
Was 5 μm or less (20 ± 3 μm). The rare earth / transition metal / boron-based sintered permanent magnet body used in this test was also obtained by the same composition and manufacturing method as the magnet body used in the previous test. In addition, the composition and working conditions of the plating bath for forming the three electroless plating layers of the highly corrosion-resistant rare earth magnet of the present invention were the same as in the previous test. The hydrogen gas release test conditions are also the same.

In the above examples, a highly corrosion-resistant rare earth magnet having a base layer of an alkaline electroless nickel / phosphorus plating layer, an intermediate layer of an alkaline electroless copper plating layer, and a surface layer of an acidic electroless nickel / phosphorus plating layer. However, even in the case of a highly corrosion-resistant rare earth magnet with a base layer consisting of an alkaline electroless nickel / boron plating layer, an intermediate layer consisting of an alkaline electroless copper plating layer, and a surface layer consisting of an alkaline electroless nickel / phosphorus plating layer, It was confirmed that there was no great difference in the evaluation characteristics and that the same action and effect could be obtained, only by changing the chemical liquid (composition) and working conditions that compose the bath.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

The high corrosion resistance rare earth magnet of the present invention has an electroless copper plating layer and a surface layer as an underlayer as in Comparative Examples 1, 2 and 3 corresponding to the prior art, as is clear from the above-mentioned Examples. As a result, it was confirmed that the pressure cooker test, the salt spray test, and the constant temperature and constant humidity test were better than those of the magnet having the electroless nickel-phosphorus plated layer, and that it had excellent corrosion resistance. Similarly, in the cross-cut substrate test, it was confirmed that the coating did not lift and had excellent adhesion.

Furthermore, since the highly corrosion-resistant rare earth magnet of the present invention withstands the cooling test after heating in the air, it is found that the plating film is rich in flexibility and has excellent adhesion to the material. Further, the results of the hydrogen gas release test confirmed that the film had the same level as in the case of electroplating, had a very small hydrogen storage amount, and had a high adhesion film with no drop of grain boundaries. Further, there is no change with time in the magnetic characteristics after the plating treatment and after the constant temperature and humidity test, and the highly corrosion-resistant rare earth magnet of the present invention in which a multi-layer coating consisting of an underlayer consisting of an electroless plating layer and an intermediate layer and a surface layer is formed, It was confirmed to be effective in a wide range of applications.

That is, the highly corrosion-resistant rare earth magnet of the present invention obtains a uniform coating film thickness by positively utilizing the advantages of electroless plating, and the plated coating and the rare earth / transition metal / boron based sintered permanent magnet body. It is possible to provide a magnet that has improved adhesion with and that exhibits excellent corrosion resistance and that has no change in magnetic characteristics over time (deterioration of characteristics) during and after plating.

Claims (4)

[Claims] 1. A rare earth / transition metal / boron-based sintered permanent magnet body is provided with a multi-layer coating consisting of an undercoat layer consisting of an electroless plating layer, an intermediate layer and a surface layer on the surface thereof, and the undercoat layer having a thickness of 0.
An alkaline electroless nickel plating layer having a thickness of 1 to 5 μm, an intermediate electroless copper plating layer having a thickness of 5 to 15 μm,
A highly corrosion-resistant rare earth magnet, wherein the surface layer is an electroless nickel-phosphorus plated layer having a film thickness of 5 to 15 μm. 2. The highly corrosion-resistant rare earth magnet according to claim 1, wherein the underlayer has a thickness of 0.3 to 3 μm, the intermediate layer has a thickness of 8 to 12 μm, and the surface layer has a thickness of 8 to 12 μm. 3. The method according to claim 1, wherein the underlayer is formed by an alkaline electroless nickel plating bath, the intermediate layer is formed by an alkaline electroless copper plating bath, and the surface layer is formed by an electroless nickel-phosphorus plating bath. High corrosion resistance rare earth magnet. 4. The rare earth / transition metal / boron-based sintered permanent magnet body has 8 to 30 atomic% of R (where R is at least one of rare earth elements including Y), B2 to 28 atomic% and Fe42.
The highly corrosion resistant rare earth magnet according to claim 1, wherein the main component is ˜90 atomic%.