JP2968605B2 - Manufacturing method of permanent magnet - 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 permanent magnet containing R (where R is one or more rare earth elements including Y), Fe and B.

[0002]

2. Description of the Related Art As a permanent magnet having high performance, an Sm-Co magnet manufactured by powder metallurgy is used as an energy product.
32MGOe is mass-produced.

However, this has a disadvantage that the raw material prices of Sm and Co are high. Among rare earth elements, rare earth elements with a small atomic weight, such as cerium and praseodymium,
Neodymium is more abundant and cheaper than samarium.
Fe is inexpensive.

[0004] In recent years, Nd-Fe-B magnets have been developed. A sintered magnet is disclosed in Japanese Patent Application Laid-Open No. 59-46008, and a magnet by a rapid quenching method is disclosed in Japanese Patent Application Laid-Open No. 60-9852. Have been.

This magnet is a high-performance magnet having a high energy product of 25 MGOe or more. However, since it contains a rare earth element which is easily oxidized and iron as main components, it has low corrosion resistance, and has problems such as deterioration of performance and variation. It has become.

For the purpose of improving the low corrosion resistance of such R-Fe-B-based magnets, there has been proposed a permanent magnet having various corrosion-resistant protective layers on its surface or a method of manufacturing the same. JP-A-60-54406, JP-A-60-63901, JP-A-60-63902,
Nos. 61-130453, 61-150201, 61-166115, 61-1661
No. 16, No. 61-166117, No. 61-1
Nos. 85910, 61-270308, 6
No. 2-120004).

[0007] Such a protective layer is made of a material such as a metal, a compound such as a metal oxide or a metal nitride, an organic material such as glass or resin, or a mixture thereof. Examples of the layering method include liquid-phase plating such as electroplating, vapor-phase plating such as sputtering, ion plating, and vacuum deposition; dip coating, brush coating, injection, hot-dip plating, and electrodeposition coating. Has been applied.

Among the protective layers formed by these methods, the metal protective layer formed by electroplating is excellent in mass productivity and not only improves corrosion resistance but also exerts a reinforcing effect in mechanical strength. Useful.

However, the surface of the magnet body before the protective layer is provided with a deteriorated layer or an oxidized layer, the magnet body is liable to be essentially oxidized, and furthermore, it absorbs hydrogen generated in the pretreatment and plating steps. Therefore, even if a plating pretreatment used for ordinary steel or the like is applied, sufficient adhesion between the magnet and the protective layer cannot be obtained, so that reliability cannot be ensured stably.

As a method for improving the adhesion between the magnet and the protective layer, for example, a method of performing a pre-treatment by shot blasting (Japanese Patent Laid-Open Nos. 1-223711 and 1-223712).
), A method of etching after heat treatment (Japanese Patent Laid-Open No.
68004), a method for reducing the amount of dissolved oxygen in the plating bath (JP-A-1-286407), and a method for dissolving the magnet component in the plating bath in advance (JP-A-2-260).
No. 03), a method of forming a low-stress plating film by washing with an oxidizing acid (Japanese Patent Laid-Open No. 2-310395) and the like have been proposed.

The present inventors have also proposed a method of providing a concave portion on the magnet surface by applying ultrasonic waves in a nitric acid solution (Japanese Patent Laid-Open No. 2-112207).

[0012]

However, the level of adhesion obtained by the various methods for improving the adhesion as described above is still insufficient. When the pressure-sensitive adhesive tape peeling test is performed in a proper state, the pressure-sensitive adhesive tape can withstand the peeling test gradually, and when a cut is made in the protective layer to reach the magnet body, it is easily peeled off with the pressure-sensitive adhesive tape. At such a low adhesion level, it is not possible to sufficiently prevent blistering and peeling of the protective layer due to the corrosion of the magnet caused when there is any defect in the protective layer or when the protective layer is damaged.

An object of the present invention is to provide a method for manufacturing a permanent magnet having a protective layer formed by electroplating having excellent adhesion and capable of preventing blistering / peeling of the protective layer due to corrosion of the magnet over time. Aim.

[0014]

This and other objects are achieved by the present invention which is defined below as (1) to (7).

(1) R (where R is one or more rare earth elements including Y), Fe and B, and the surface of a permanent magnet body having a substantially tetragonal main phase is electroplated. In the method for producing a permanent magnet having a protective layer, a dissolution treatment of dissolving the surface layer of the permanent magnet body by 5 μm or more with a treatment liquid containing nitric acid and aldonic acid or a salt thereof is performed. A method for producing a permanent magnet, comprising providing a protective layer.

(2) The method for producing a permanent magnet according to the above (1), wherein the concentration of nitric acid contained in the treatment liquid is 1N or less.

(3) The method for producing a permanent magnet according to the above (1) or (2), wherein the treatment liquid contains aldonic acid or a salt thereof in an amount equal to or more than the amount of Fe dissolved by the dissolution treatment.

(4) The method for producing a permanent magnet according to any one of (1) to (3), wherein after the dissolution treatment, ultrasonic cleaning is performed, and then the protective layer is provided.

(5) The method for producing a permanent magnet according to any one of the above (1) to (4), wherein the melting treatment is performed at a temperature of 40 ° C. or less.

(6) The method for manufacturing a permanent magnet according to any one of the above (1) to (5), wherein the protective layer formed by the electroplating is a Ni plating layer.

(7) The method for manufacturing a permanent magnet according to any one of the above (1) to (6), wherein the Ni plating layer is formed by a sulfamic acid bath.

[0022]

According to the present invention, before forming the protective layer, the surface of the permanent magnet is pre-treated with a treatment solution containing nitric acid and aldonic acid or a salt thereof. By providing a protective layer on the surface to be treated by electroplating, a permanent magnet having sufficient corrosion resistance and adhesion can be obtained.

More specifically, a commercially available cellophane adhesive tape (average adhesive force) having a peel strength of 200 gf / cm or more in an adhesion test according to JIS H8630 and a cut reaching the magnet body in the protective layer. 150gf / c
m) It can withstand the tape peel test sufficiently. By improving the adhesion, a rare earth permanent magnet excellent in reliability, in which blistering / peeling of the protective layer due to corrosion of the magnet body does not easily occur, can be obtained.

[0024]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

In the present invention, before forming the protective layer on the permanent magnet, a pretreatment is performed using a predetermined treatment liquid.

The acid used for the plating pretreatment is hydrochloric acid,
A non-oxidizing acid such as sulfuric acid is often used. However, particularly when the permanent magnet contains a rare earth element, when the treatment is performed using these acids, hydrogen generated by the acids becomes
It is occluded on the surface of the permanent magnet, the occluded site is embrittled, and a large amount of undissolved powder is generated. Since this powdery undissolved substance causes a defect in the protective layer or causes a decrease in adhesion, it is preferable that these non-oxidizing acids are not contained in the treatment liquid if possible. Therefore, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen, as the acid to be used. By using nitric acid, the surface of the magnet is chemically etched by its oxidizing action, and a fine uneven structure that cannot be visually confirmed is formed.

In the present invention, in addition to this nitric acid,
Contains aldonic acid or a salt thereof.

When this aldonic acid or a salt thereof is contained, the Fe ion eluted by nitric acid and the aldonic acid salt form a stable chelate compound, and dissolution by the substitution reaction of Nd, which has a higher ionization tendency than Fe, with free Fe ion. Can be suppressed. Therefore, by adding aldonic acid or its salt, the chemical etching that occurs locally and suddenly with nitric acid alone proceeds more gently, and there is a uniform, locally sharply deep recess on the magnet surface. No, a fine and uniform uneven structure is formed, and the adhesion of the protective layer can be improved.

Such an improvement in adhesion can be selectively realized by aldonic acid or a salt thereof, but cannot be realized by another chelating agent such as citric acid or tartaric acid.

The amount of dissolution of the magnet body by such pretreatment is preferably 5 μm or more, more preferably 10 to 15 μm in average thickness from the surface. If the amount of dissolution is less than 5 μm, a deteriorated layer and an oxidized layer due to the processing of the magnet body surface cannot be completely removed, so that sufficient adhesion cannot be obtained.

The average depth of the unevenness (the depth from the valley to the peak) is preferably about 1 to 5 μm. The average pitch of the unevenness is preferably about 10 to 50 μm. These improve the adhesion.

It is desirable that the concentration of nitric acid in the processing solution used for such pretreatment is 1 N or lower, particularly 0.6 N or lower, more preferably 0.5 N or lower. When the nitric acid concentration exceeds 1N, the dissolution rate of the magnet body becomes extremely fast, and it is difficult to control the amount of dissolution, so that a product having desired dimensional accuracy cannot be obtained. Further, in the case of a large amount of processing such as barrel processing, the dispersion of the processing state becomes large. In addition, when the nitric acid concentration is low, the amount of the solution becomes too large, and the amount of dissolution becomes insufficient. For this reason, the nitric acid concentration is desirably 1 normal or less, particularly preferably 0.05 to 0.5 normal or less.

The amount of aldonic acid or a salt thereof added to the treatment liquid is preferably at least equimolar to Fe dissolved during the treatment. If the amount of the aldonic acid or salt thereof is less than the equimolar amount of Fe dissolved in the treatment liquid at the end of the treatment, the effect of forming irregularities is not sufficient, and the adhesion is undesirably low.

The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / liter. Thus, aldonic acid or a salt thereof is
Generally, about 0.02 to 0.2 mol / liter is contained. That is, the dissolution treatment is performed by batch processing, and when the Fe dissolution amount is reached, the treatment liquid may be discarded.

Aldonic acid or a salt thereof is HOCH ₂ (C
HOH) nCOOY (Y is H or a cation), and may be, for example, any of gluconic acid, arabonic acid, mannonic acid, galactonic acid, heptonic acid and the like in which n = 3 to 5. In this case, these alkali metal salts are preferable because a highly pure reagent can be obtained.

Of these, sodium gluconate, potassium gluconate, sodium heptonate and the like can be most preferably used, and uniform and fine irregularities can be formed without increasing powdery undissolved matter. .

In addition to aldonic acid and its salts, salts of hydroxycarboxylic acids such as citric acid, tartaric acid and oxyacetic acid may be added to the acid treatment solution. The effect of forming fine irregularities, which is observed when the salt is added, cannot be obtained, and the improvement in adhesion as in the present invention cannot be achieved. In addition, the amount of powdery undissolved matter also increases.

Further, surfactants such as sodium lauryl sulfate and polyoxyethylene nonyl phenyl ether may be added to the acid treatment liquid, but when these are added to the treatment liquid of the present invention, powdery substances may be added. This is not desirable because it causes an increase in undissolved substances and also causes adsorption to the surface of the magnet body after the treatment, thereby deteriorating the adhesion.

The processing temperature of the processing solution is preferably 40 ° C. or lower, particularly 30 ° C. or lower, more preferably 20 ° C. or lower. If the treatment temperature exceeds 40 ° C., the dissolving action of the magnet by the nitric acid becomes dominant, and the effect of adding the aldone salt is lost, which is not preferable. The treatment time may be appropriately adjusted depending on the composition of the treatment liquid, the temperature, and the desired etching amount, but is usually preferably 1 to 20 minutes.

In order to completely remove a small amount of undissolved substances and residual acid components from the pretreated magnet body surface, it is preferable to carry out cleaning using ultrasonic waves. This ultrasonic cleaning is desirably performed in water having a low chlorine ion content, such as ion-exchanged water, or a solution in which a small amount of a basic compound is dissolved for the purpose of neutralizing the residual acid. If chloride ions are contained in the cleaning solution, rust may be generated on the magnet surface.

If necessary, the same immersion cleaning with water or a basic aqueous solution may be performed before and after the ultrasonic cleaning. Further, before performing the pretreatment, mechanical polishing and immersion or electrolytic degreasing or alkali derusting, which are usually performed as plating pretreatment, may be performed according to the processing method and storage state of the magnet body. .

In the pretreatment, it is preferable not to apply ultrasonic waves. This is because the unevenness may be too large.

A protective layer is formed on the cleaned magnet surface by electroplating. By forming the protective film by electroplating, a high-performance corrosion-resistant film having excellent mass productivity can be formed.

The protective layer thus formed preferably contains Ni as a main component.

By using Ni as the protective layer, the strength of the protective layer can be increased and an excellent rust prevention effect can be obtained. Examples of the plating bath used for the electroplating of Ni include a Watt bath containing no nickel chloride component, a sulfamic acid bath, a fluorinated bath, and a nickel bromide bath. However, in this case, since the dissolution of the anode is reduced, it is necessary to replenish the bath with nickel ions. The nickel ions are preferably replenished as a solution of nickel sulfate or nickel bromide.

For example, among these, in order to exhibit higher peel strength, it is particularly preferable to use a sulfamic acid bath, and examples thereof include those having the following composition.

Ni (NH ₂ SO ₃ ) ₂ .4H ₂ O 150-600 g / l NiBr ₂ .6H ₂ O 0-30 g / l Boric acid 30-60 g / l

At this time, the water in the bath preferably does not contain chlorine, and the chlorine content in the bath is preferably 100 ppm or less. As described above, by removing the chlorine component from the plating bath, it is possible to prevent blisters mainly due to aging.

The plating conditions are pH 3 to 6, particularly preferably 4.0 to 5.0, temperature 30 to 70 ° C., and current density 0.1 to 0.1.
It may be about 10 A / m ² . If the pH is lower than this range, the magnet body will be dissolved, and if the pH is higher than this range, nickel hydroxide precipitates and the plating film becomes brittle. If the current density is less than this range, impurities such as Cu, Co and the like in the plating film are often folded, resulting in a film having poor appearance and low corrosion resistance. Hydrogen generation in the vicinity increases and is absorbed by the magnetic material, causing a decrease in adhesion.

In the present invention, if necessary, improvement of corrosion resistance of known double nickel plating, trinickel plating, etc. having different natural potentials as described in page 115 of the plating technique guidebook (published by Tokyo Plating Materials Cooperative Union). Multi-layer plating for the purpose can also be preferably used. In addition, even when a normal watt bath or a sulfamine bath containing a chloride is used, the effects of improving the adhesion and the corrosion resistance of the present invention can be obtained.

When the protective layer is formed by electroplating, a rack plating method or a barrel plating method is appropriately applied according to the size and shape of the magnet body.

In general, a magnet body having a large size, which is processed by the rack plating method, requires a large area requiring a defect-free protective layer. Therefore, it is necessary to increase the thickness of the protective layer. The preferred thickness is 20-30
μm. On the other hand, the desirable protective layer thickness by electroplating only for a magnet body having a small surface area such as being processed in large quantities by barrel plating and having a weight of several tens g or less is 10 to 2 g.
0 μm.

If necessary, a protective layer formed by another method such as an electroless plating layer or a resin layer formed by various coating methods can be provided on the protective layer formed by electroplating. In such a case, the thickness of the protective layer formed by electroplating can be reduced. According to the present invention, the peel strength according to JIS H-8630 can be 200 gf / cm or more in any of these cases.

In the present invention, the permanent magnet body on which the protective layer is provided on the surface contains R (where R is one or more rare earth elements including Y), Fe and B.

The content of R, Fe and B is preferably 5.5 at% ≦ R ≦ 30 at% 42 at% ≦ Fe ≦ 90 at% 2 at% ≦ B ≦ 28 at%.

In particular, when the permanent magnet body is manufactured by a sintering method, the following composition is preferable.

As the rare earth element R, Nd, Pr, H
o, at least one of Tb, or L
a, Sm, Ce, Gd, Er, Eu, Pm, Tm, Y
Those containing at least one of b and Y are preferable.

When two or more elements are used as R, a mixture such as misch metal can be used as a raw material.

The R content is preferably 8 to 30 at%.

When the content is less than 8 at%, a high coercive force (iHc) cannot be obtained because the crystal structure becomes a cubic structure having the same structure as that of α-iron, and when it exceeds 30 at%, many R-rich nonmagnetic phases are formed. And the residual magnetic flux density (Br) decreases.

The content of Fe is preferably 42 to 90 at%.

When Fe is less than 42 at%, Br decreases, and when it exceeds 90 at%, iHc decreases.

The content of B is preferably 2 to 28 at%.

If B is less than 2 at%, a rhombohedral structure is obtained and iHc is insufficient. If B exceeds 28 at%, the B-rich non-magnetic phase increases and Br decreases.

By replacing part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics. In this case, if the amount of Co substitution exceeds 50% of Fe, the magnetic properties deteriorate, so the amount of Co substitution is preferably set to 50% or less.

In addition to R, Fe and B, Ni, Si, Al, Cu, Ca, etc.
at% or less may be contained.

Further, by substituting a part of B with one or more of C, P, S, and Cu, it is possible to improve productivity and reduce costs. In this case, the substitution amount is preferably 4 at% or less of the whole. In order to improve coercive force, improve productivity, and reduce cost, Al, Ti,
V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb,
One or more of Ge, Sn, Zr, Ni, Si, Hf and the like may be added. In this case, it is preferable that the total amount is 10 at% or less.

The permanent magnet according to the present invention has a main phase having a substantially tetragonal crystal structure. The particle size of this main phase is
It is preferably about 1 to 100 μm. And it usually contains 1 to 50% of a non-magnetic phase by volume ratio.

Such a permanent magnet body is disclosed, for example, in the above-mentioned Japanese Patent Application Laid-Open No. 61-185910.

The above-described permanent magnet body is preferably manufactured by a sintering method as described below. First,
An alloy having a desired composition is cast to obtain an ingot. The obtained ingot is subjected to a particle size of 10 to 10 using a stamp mill or the like.
The material is roughly pulverized to about 0 μm and then finely pulverized by a ball mill or the like to a particle size of about 0.5 to 5 μm.

The powder obtained is preferably molded in a magnetic field. In this case, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 t / cm ² .

The obtained molded body was heated at 1000 to 1200 ° C.
And quenched for 0.5-5 hours. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. After that, preferably in an inert gas atmosphere,
Perform aging treatment at ~ 900 ° C for 1-5 hours.

[0073]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Example 1 14Nd-1Dy-7B- produced by powder metallurgy
A sintered body having a composition of 78Fe (the number is an atomic ratio) was subjected to an aging treatment at 600 ° C. for 2 hours in an Ar atmosphere to obtain 56 × 4
It was processed to a size of 0 × 8 (mm) and chamfered by barrel polishing to obtain a permanent magnet. Next, 10 samples of these permanent magnets were immersed in 10 liters of a treatment solution having a nitric acid concentration of 0.45N and a sodium gluconate concentration of 0.023 mol / l at 30 ° C. for 1 minute to dissolve the surface layer.

The average dissolved amount was 10 μm, and the amount of Fe in the treated solution after the treatment was 0.0052 mol / l.

The treated sample was subjected to ultrasonic cleaning in ion-exchanged water, and then plated by a rack method using a plating bath having the following composition and conditions. Plating current density is 4
A / dm ² , and the thickness of the plating film were 25 μm.

The bath temperature was 50 ° C. and the bath pH was 4.5. The film thickness was measured by Seiko Electron Fluorescence X-ray film thickness meter SFT-7.
000.

NiSO ₄ .6H ₂ O 280 g / l NiCl ₂ .6H ₂ O 50 g / l Boric acid 45 g / l Commercial brightener (sulfur-based) 15 ml / l Bath temperature 50 ° C. pH 4.5

When measured by a spiral plating stress meter (manufactured by Yamamoto Plating Test Instruments Co., Ltd.), the internal stress of the film having a thickness of 25 μm by this plating bath was a compressive stress of 8 kgf / mm ² . The ultrasonic waves were applied at a frequency of 26 kHz and 600 W using a 6361 model manufactured by Marine Electric.

A 400 times SEM image of an oblique cross section at an angle of 5 ° with respect to the surface of Sample No. 1 was observed, and the state of formation of irregularities was examined. The results are shown in FIG. As shown in FIG.
According to the present invention, it can be seen that irregularities having a depth of about 3 μm are formed uniformly at a pitch of about 30 μm. In addition,
Since this SEM photograph is an oblique cross section, in the figure, the depth direction is enlarged to about 10 times (4000 times) the horizontal direction.

The adhesion of the protective film of each of the sample Nos. 1 and 5 was measured by using an adhesion strength tester (manufactured by Yamamoto Plating Test Equipment Co., Ltd.) in accordance with JIS H8630 at a peeling speed of 25 mm / min. And the average intensity was calculated.

The corrosion resistance was evaluated by a pressure cooker test (hereinafter abbreviated as PCT) at 120 ° C., 2 atm and 100% RH.

Further, at 85 ° C. and 85% R
A moisture resistance test was performed. In the PCT and the moisture resistance test, 100 samples produced in the same manner were evaluated in the shortest time of occurrence of defects.

Table 1 shows the above results.

[0085]

[Table 1]

Further, Sample No. 1 was put into normal temperature water from silicon oil at 250 ° C. to perform a thermal shock test, and the surface of the protective layer was visually observed. As a result, no abnormality occurred in Sample No. 1.

Example 2 A sample No. 2 having the same shape was obtained and evaluated in the same manner as in Example 1 except that a plating bath having the following composition and conditions was used.

Ni (NH ₂ SO ₃ ) ₂ .4H ₂ O 600 g / l NiBr ₂ .6H ₂ O 10 g / l boric acid 40 g / l Bath temperature 50 ° C. pH 4.5

The results are shown in Table 1. The internal stress of the film having a thickness of 25 μm by the plating bath was a tensile stress of 5 kgf / mm ² .

From the results shown in Table 1, it can be seen that the use of the sulfamic acid bath improves the adhesion strength.

FIG. 2 shows a 40 × optical microscope photograph of the plating film. It can be seen that the fine irregularities formed on the magnet body are also reflected on the surface after plating.

Example 3 Sample No. 3 was prepared in the same manner as in Example 2 except that the temperature of the pretreatment liquid was 10 ° C. and the processing time was 5 minutes.
Was obtained and the same evaluation was performed.

The amount of the magnet dissolved was 12 μm, and the amount of Fe in the treated solution after the treatment was 0.0060 mol / l. Table 1 also shows the results of the evaluation.

Example 4 14Nd-1Dy-7B- produced by powder metallurgy
A sintered body having a composition of 78Fe (the number is an atomic ratio) has an outer diameter of 3
The sample was processed into a flat ring shape having a size of 5 × 20 × 2 (mm) and further subjected to barrel polishing.

The above 500 samples were prepared by using a nitric acid concentration of 0.5
The surface layer was dissolved by immersing in 50 liters of a treatment liquid having a concentration of 0.025 mol / liter of N and sodium heptonate at 10 ° C. for 3 minutes.

The average dissolution amount was 6 μm, and the amount of Fe in the treated solution after the treatment was 0.009 mol / l.

After the treated sample was subjected to ultrasonic cleaning in ion-exchanged water, the first layer of Ni plating was performed by a barrel method using a plating bath having the following composition and conditions. NiSO ₄ .6H ₂ O 280 g / l NiCl ₂ .6H ₂ O 45 g / l Boric acid 40 g / l Commercial semi-brightener (no sulfur) 1.5 ml / l Bath temperature 50 ° C. pH 4.5

The average cathode current density was 0.3 A / dm ² , and the average thickness of the plating film was 10 μm.

Further, a double Ni plating was performed on the plating film using a plating bath having the same composition and conditions as in Example 1. At this time, the average current density was 0.3 A / dm ² , and the average thickness of the plating film was 5 μm.

The same evaluation was performed on Sample No. 4. Table 1 also shows the results of the evaluation.

Example 5 A sample No. 5 having the same shape was produced in the same manner as in Example 4 except that the pretreatment immersion time in Example 4 was changed to 5 minutes.
The average amount of dissolution was 10 μm, and the amount of Fe dissolved in the treatment solution after the treatment was 0.015 mol / l. Sample No.5
Were similarly evaluated. Table 1 also shows the results of the evaluation.

Comparative Example 1 Example 1 was repeated except that the pretreatment liquid was only 0.45 N nitric acid.
A sample was prepared in the same manner as described above.

The amount of the magnet dissolved and the amount of Fe in the treatment solution after use
Both amounts were the same as in Example 1. Table 1 also shows the results of the evaluation.

FIG. 3 shows an SEM photograph of the same oblique cross section as described above. From comparison between FIG. 3 and FIG. 1, it can be seen that the irregularities of the present invention are homogeneous.

Comparative Example 2 Example 2 was repeated except that the pretreatment liquid was only 0.45 N nitric acid.
A sample was prepared in the same manner as described above.

The amount of the magnet dissolved and the amount of Fe in the treated solution after use.
Both amounts were the same as in Example 2. Table 1 also shows the results of the evaluation.

FIG. 4 shows the surface state (40 times) of this. 4 and 2 show that the unevenness of the present invention is uniform and dense. Example 6 Nitric acid concentration: 0.45 N, sodium gluconate concentration:
A powder having the same composition as the sample was added and dissolved in 10 liters of a 0.023 mol / liter treatment solution until the amount of dissolved Fe became 0.020 mol / liter, and then the concentration of free nitric acid was determined by neutralization titration. Nitric acid was added so that the nitric acid concentration became the initial value of 0.45 N.

The concentration of nitric acid thus prepared: 0.4
A sample was prepared in the same manner as in Example 3 except that 5 liters, a sodium gluconate concentration: 0.023 mol / liter, and 10 liters of a treatment liquid having a dissolved Fe amount of 0.02 mol / liter were used.

The dissolved amount of the magnet was 10 μm, and the amount of Fe in the treated solution after use was 0.0250 mol / l, which was higher than the concentration of sodium gluconate.

The results of the evaluation are also shown in Table 1.

Comparative Example 3 A sample was prepared in the same manner as in Example 3 except that the processing time was changed to 2 minutes.

The dissolved amount of the magnet body was 2 μm, and the amount of Fe in the treatment solution after use was 0.0010 mol / l.

Table 1 also shows the results of the evaluation.

Comparative Example 4 A sample was prepared in the same manner as in Example 3 except that a treatment solution to which sodium citrate was added instead of sodium gluconate was used.

The dissolved amount of the magnet body was 10 μm, and the amount of Fe in the treatment solution after use was 0.0050 mol / l.

Table 1 also shows the results of the evaluation.

Comparative Example 5 A sample was obtained in the same manner as in Comparative Example 5, except that sodium tartrate was used instead of sodium citrate. Dissolution amount is 1
It was 0 μm. The amount in the processing solution after use is 0.0050
Mol / l.

Table 1 also shows the results of the evaluation.

Comparative Example 6 A sample was prepared in the same manner as in Example 5 except that the pretreatment liquid was only 0.5N nitric acid.

The amount of dissolution and the amount of Fe in the treated solution after use were the same as in Example 5.

Table 1 also shows the results of the evaluation.

From the results shown in Table 1, the peel strength of the protective film was not sufficient for the sample of the comparative example, and was equal to or lower than the adhesive strength of a commercially available cellophane adhesive tape, whereas the comparative example of the present invention did not. It can be seen that two to three times the peel strength of the example was obtained and the corrosion resistance was also improved.

Also, a remarkable effect is exhibited in a barrel plating method in which plating speed is relatively slow and poor adhesion is likely to occur, and the peel strength of the protective film can be improved more than twice.

The corrosion resistance is also improved.

[0125]

According to the method for manufacturing a permanent magnet of the present invention,
The adhesion between the magnet surface and the protective layer becomes extremely strong. For this reason, extremely high rust resistance and corrosion resistance are obtained, and corrosion resistance does not change even under storage under bad conditions, it is resistant to mechanical shock, and a highly reliable permanent magnet with no variation in characteristics between products. can get.

[Brief description of the drawings]

FIG. 1 is a SEM photograph as a drawing showing a metallographic structure of a plating film of a permanent magnet and an oblique cross section of a permanent magnet body manufactured according to the present invention.

FIG. 2 is an optical microscope photograph showing a state of a metallographic structure on a surface of a plating film of a permanent magnet manufactured by the present invention.

FIG. 3 is a SEM photograph as a drawing showing a metallographic structure of a plating film of a permanent magnet and an oblique cross section of a permanent magnet body manufactured by a comparative method.

FIG. 4 is an optical microscope photograph as a drawing showing a state of a metallographic structure on a surface of a plating film of a permanent magnet manufactured by a comparative method.

Continuation of front page (56) References JP-A-2-112207 (JP, A) JP-A-3-233913 (JP, A) JP-A-2-293330 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) H01F 1 / 053,41 / 02

Claims (7)

(57) [Claims] 1. A permanent magnet body containing R (where R is one or more rare earth elements including Y), Fe and B and having a substantially tetragonal main phase is protected by electroplating. In the method for producing a permanent magnet having a layer, a dissolution treatment is performed in which the surface layer of the permanent magnet body is dissolved by a treatment liquid containing nitric acid and aldonic acid or a salt thereof at a concentration of 5 μm or more,
Next, a method for manufacturing a permanent magnet, comprising forming a protective layer by electroplating. 2. The method for producing a permanent magnet according to claim 1, wherein the concentration of nitric acid contained in the treatment liquid is 1 N or less. 3. The method for producing a permanent magnet according to claim 1, wherein the treatment liquid contains aldonic acid or a salt thereof in an amount equal to or more than the amount of Fe dissolved by the dissolution treatment. 4. The method for producing a permanent magnet according to claim 1, wherein after the dissolution treatment, ultrasonic cleaning is performed, and then the protective layer is provided. 5. The method for producing a permanent magnet according to claim 1, wherein the melting treatment is performed at a temperature of 40 ° C. or less. 6. The method for manufacturing a permanent magnet according to claim 1, wherein the protection layer provided by the electroplating is a Ni plating layer. 7. The method for manufacturing a permanent magnet according to claim 1, wherein the Ni plating layer is formed by a sulfamic acid bath.