JP2840998B2 - Surface treatment method for R-Fe-B 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 an improvement in pickling performed as a pre-process of various plating processes for improving the corrosion resistance of R-Fe-B permanent magnets. The present invention relates to a surface treatment method for an R-Fe-B-based permanent magnet in which the adhesion strength of a corrosion-resistant coating after plating is improved by using an acid pickling solution.

[0002]

2. Description of the Related Art R-Fe-B (R is at least one of rare earth elements including Y) permanent magnets are widely used in a wide range of fields because of their excellent magnetic properties. However, since the permanent magnet having the above excellent magnetic properties contains a large amount of a rare earth element and iron which are easily oxidized in air as a main component, an oxide generated on the surface of the magnet is used for a device incorporating the magnet. It degrades performance and creates the problem of contamination of peripheral equipment. In order to improve the corrosion resistance of R-Fe-B permanent magnets, a manufacturing method for obtaining a permanent magnet having various corrosion resistant coatings having corrosion resistance on the surface has been proposed (Japanese Patent Application Laid-Open No. 60-54406). JP, JP-A-61-130453, JP-A-63-11070
No. 8).

[0003] When a plating treatment such as Ni plating is performed on the surface of an R-Fe-B-based permanent magnet, there is a black scale or an oxide layer on the surface of the unprocessed magnet body. There is a problem that adhesion or corrosion resistance is poor.
Therefore, a method of pickling has been reported in order to remove the oxide layer and the work distortion layer on the surface of the magnet body.

In general, a material to be processed is pickled before a metal plating process, and sulfuric acid, hydrochloric acid, or the like is used as a pickling solution. In the case of an R-Fe-B permanent magnet, sulfuric acid,
A known pickling solution such as hydrochloric acid is appropriately selected, and at least one acid selected from sulfuric acid, hydrofluoric acid, nitric acid, hydrochloric acid, permanganic acid, oxalic acid, acetic acid, formic acid, hydroxyacetic acid, and phosphoric acid (Japanese Unexamined Patent Publication No. 1-304713) has been proposed. In addition, when activation is performed with a non-oxidizing acid, hydrogen is generated and absorbed by the R-Fe-B-based alloy and collapse occurs due to hydrogen embrittlement. Therefore, a method using an oxidizing acid such as nitric acid ( Japanese Patent Publication No. 4-13438) has also been proposed.

[0005]

As a practical corrosion resistance test for R-Fe-B permanent magnets, a temperature of 125 ° C. and a relative humidity of 8 were used.
There is a test in which the sample is left for a long time under an atmosphere condition of 5% and 2 atm (PCT test). It is required to have excellent corrosion resistance.

[0006] In order to improve the corrosion resistance of the R-Fe-B permanent magnet, it is necessary to improve the adhesion of a corrosion-resistant coating provided on the surface thereof. When an acid is used, the magnet surface after pickling becomes smooth, and the adhesion between the magnet and the plating film becomes poor. Also,
When using at least one acid from an acid solution such as sulfuric acid,
Depending on the concentration, there is a problem that the magnet surface after pickling becomes smooth or that only the grain boundary phase is preferentially dissolved.

An object of the present invention is to improve the adhesion of a corrosion-resistant coating provided on an R-Fe-B permanent magnet and to solve practical problems. C. In order to obtain an R-Fe-B-based permanent magnet having excellent corrosion resistance in a T test, R-F
It is an object of the present invention to provide a surface treatment method capable of improving the adhesion between an eB-based permanent magnet and a plating film.

[0008]

Means for Solving the Problems The present inventors have proposed R-Fe-
As a result of conducting various studies on the pickling solution for the purpose of a surface treatment method capable of improving the adhesion between the B-based permanent magnet and the plating film, as described above, the conventional pickling solution was used for the R-Fe-B-based permanent magnet. With the pickling solution, the magnet surface after pickling becomes smooth or only the grain boundary phase is dissolved preferentially. However, not only the grain boundary phase of the R-rich layer and the B-rich layer but also the tetragonal by causing pitting in the main phase, and found that it is possible to adhesion to further improve the magnet body and the coating according to the anchor effect, further with the main phase to pitting possible pickling solution composition study of As a result, they found that a mixed solution of nitrate and sulfuric acid having a required mixing ratio was optimal, and completed the present invention.

That is, according to the present invention, an aqueous solution containing 0.1 mol% to 1.0 mol% of nitrate and 0.2 vol%
A surface treatment method for an R-Fe-B-based permanent magnet, characterized in that the magnet surface is pickled using a pickling solution comprising a mixed solution of 2.0 vol%.

In other words, the present invention is to perform pickling to remove an oxidized layer and a strained layer on the surface of the magnet body which impair plating uniformity, adhesion and corrosion resistance. Not only the grain boundary phase but also the main phase, the concave part is provided on the magnet surface after pickling, and the anchor effect is given to the plating film to improve the adhesion. After pickling with a pickling solution of a specific ratio, the plate is sufficiently washed, plated with a metal or alloy having corrosion resistance, such as Ni, Cu, Zn, Cr, or Sn, or a composite plating thereof, and if necessary, Electrodeposition coating, resin coating, chromate treatment, or the like may be performed on this plating layer, and the corrosion resistance is further improved by such laminated plating.

In the present invention, sodium nitrate, potassium nitrate and the like can be used as the nitrate. When the concentration of the aqueous solution of the nitrate is less than 0.1 mol%, pitting does not occur in the main phase, and the concentration of the nitrate exceeds 1.0 mol%. Is limited to 0.1 mol% to 1.0 mol% of an aqueous nitrate solution because its effect is saturated and is not economical. If the sulfuric acid concentration of the mixed solution is less than 0.2 vol%, the etching rate is too slow, and at the same time, desired pitting does not occur.
If it exceeds 0 vol%, the etching rate is too fast to control, and the magnet surface becomes too rough. Therefore, the sulfuric acid is limited to 0.2 vol% to 2.0 vol%.

The mixture according to the present invention may contain, as an additive, 5% or less of hydrogen peroxide, 5% or less of a surfactant such as sodium sulfonate, or an inhibitor. For hydrogen peroxide, NO in pickling ^- ₂ by causing an oxidizing effect NO in H ₂ O ₂ so increases ^- ₃ varied, i.e. nitric acid pickling liquid return nitrite ions to nitrate This has the effect of keeping the amount constant and at the same time cleaning the initial magnet surface. Examples of the inhibitor include (ethyl) thiourea and butyne diol. Use of an alcohol-based compound has an effect of increasing the wettability of the magnet surface, removing oil, and cleaning the surface.

As the pickling conditions, the bath temperature is preferably room temperature to 50 ° C., and the pickling time is appropriately selected according to the etching amount, but is preferably about 30 minutes or less.
Also, at the time of pickling, ultrasonic waves or air bubbling may be used in combination. The concave portion of the magnet surface obtained after the pickling according to the present invention has a diameter of 1 to 10 μm, an average depth of 0.5 to 5 μm,
The average number is one or more per 100 μm ² of surface.

Regarding the washing after pickling, it is preferable to perform ultrasonic washing using ion exchanged water of 1 μS / cm or less. After that, it moves on to the next plating process.
Any plating of a metal or alloy having corrosion resistance, such as Ni, Cu, Zn, Cr, or Sn, or a composite plating thereof may be used. As a plating method, a method using electroless plating, electrolytic plating, or a combination of the above plating may be used. Further, if necessary, by applying electrodeposition coating, resin coating, chromate treatment or the like on the plating layer, the corrosion resistance can be further improved and improved.

[0015]

The present invention is characterized in that the surface of an R-Fe-B permanent magnet is pickled by using a mixture of a specific amount of a nitrate aqueous solution and sulfuric acid as a pickling solution. The removal of the oxidized layer and the processing strain layer on the surface is possible in a short time and a predetermined amount of grinding can be performed, and the uniformity of plating and the decrease in adhesion are prevented.
Even in the case of cylindrical or other complicated shapes, any surface can be ground uniformly.

Further, regardless of the composition of the R-Fe-B-based permanent magnet, the pickling solution composed of the above-mentioned specific mixed solution is used not only for the grain boundary phase on the magnet surface but also for the main phase. Can be generated, and the adhesion between the magnet body and the coating can be further improved by the anchor effect in which the plating coating enters the generated recess.

[0017]

【Example】

Example 1 A test piece of a 15Nd-78Fe-7B-based sintered permanent magnet was prepared at atomic%, and 0.2 mol% of sodium nitrate and 1.
Pickling is performed by dipping in a pickling solution according to the present invention consisting of a 5 vol% aqueous solution at 30 ° C. for 4 minutes.
Ultrasonic cleaning with ion exchange water of S / cm or less for about 30
After cleaning for 2 seconds, the size and the number of etching pits formed on the surface of the test piece were measured with a 1500 × electron microscope photograph. Table 1 shows the measurement results.

The test piece, which had been pickled and washed, was provided with two-layer plating under the following conditions. The adhesion and corrosion resistance of the obtained test pieces were evaluated by an adhesion strength test and a P.V. C. It was evaluated by the T test.
Table 1 shows the evaluation results. In the adhesion strength test, a square of 1 cm width and 1 cm was put on the surface of the test piece plating film, and the adhesive tape stuck on this surface was peeled off to evaluate whether or not the film was peeled off. Of the number of non-peeled squares. P. C. The T test was performed at a temperature of 12
The test was performed under the conditions of 5 ° C., 85% relative humidity, and 2 atm for a long period of time.

First layer plating Matte plating, film thickness 10 μm Plating bath nickel sulfate 250 g / l, nickel chloride 4
5 g / l, boric acid 30 g / l bath temperature 50 ° C. pH 4.0 to 4.2 current density 1 A / dm ² second layer plating bright plating, film thickness 5 μm plating bath nickel sulfate 250 g / l, nickel chloride 4
5 g / l, boric acid 30 g / l brightener sodium naphthalene sulfonate, butynediol, etc. Bath temperature 50 ° C. pH 4.0-4.2 Current density 1 A / dm ²

Comparative Example 1 For comparison, the same test piece as in Example 1 was used.
Pickling with a 0 vol% nitric acid solution was performed at 30 ° C. for 3 minutes, and after washing as in Example 1, the size and number of etching pits formed on the surface of the test piece were measured with a 1500 × electron microscope photograph. Then, two-layer plating was provided in the same plating step as in Example 1, and the adhesion and corrosion resistance were evaluated by the adhesion strength test and P.I. C. It was evaluated by the T test. Table 1 shows the evaluation results.

[0021]

[Table 1]

[0022]

According to the present invention, an R-Fe-B-based permanent magnet surface is pickled by using a mixture of a specific amount of an aqueous nitrate solution and sulfuric acid as a pickling solution, whereby only the grain boundary phase on the surface of the magnet surface is removed. Instead, pitting can also be generated in the main phase, and the adhesion between the magnet body and the coating can be further improved by the anchor effect that the plating coating enters the generated recess. As is clear from the examples, in the case of the comparative example in which the surface was smoothed after pickling using nitric acid or the like during pickling,
P. C. In the adhesion strength test before the T test, the coating was easily peeled off. C. In the T test, film blisters occur only after leaving for a short time, but when pickling with a mixed solution of nitrate aqueous solution and sulfuric acid, etching pits are generated on the magnet surface,
Nd-F, which has excellent adhesion, does not peel off during practical use, and has high corrosion resistance
An eB-based permanent magnet is obtained.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Tetsuji Hayakawa 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture Yamazaki Works, Sumitomo Special Metals Co., Ltd. (56) References JP-A-63-110708 (JP, A) JP-A-4-18791 (JP, A) JP-A-57-181395 (JP, A) JP-A-56-166393 (JP, A) JP-A-5-9784 (JP, A) (58) (Int.Cl. ⁶ , DB name) C25D 5/00-7/12 C23G 1/00-1/36

Claims (1)

(57) [Claims] 1. As a pre-step of plating of an R—Fe—B-based permanent magnet, mixing a 0.1 mol% to 1.0 mol% aqueous solution of nitrate with 0.2 vol% to 2.0 vol% of sulfuric acid A method for treating the surface of an R-Fe-B-based permanent magnet, wherein the surface of the magnet is pickled using a pickling solution comprising a liquid.