JP2894816B2 - R-TM-B permanent magnet with improved corrosion resistance and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an R-TM-B permanent magnet, wherein a chromate coating layer is further formed on a Ni plating layer coated on the surface of a magnet body. It is related to the one in which the corrosion resistance is remarkably improved by providing.

[Conventional technology]

Along with the high performance and miniaturization of electric and electronic devices, similar demands have been increasing for permanent magnets as one of the components. In other words, the strongest permanent magnets used before were rare earth cobalt (RC
o) In recent years, more powerful R-TM-B permanent magnets have emerged (JP-A-59-46008). Where R
Is one or a combination of two or more rare earth elements including Y, TM is a transition metal center such as Fe or Co, part of which is substituted with another metal element or a nonmetal element, and B is boron. It is.

However, the R-TM-B permanent magnet has a problem that it is extremely susceptible to rust. Therefore, in order to improve the corrosion resistance, means for providing an oxidation-resistant coating layer on the surface of the permanent magnet body has been taken.

Types of coating layer include Ni plating, oxidation resistant resin, Al
Ion plating has been proposed, especially for Ni
Plating is attracting attention as a simple treatment for improving the corrosion resistance of R-TM-B permanent magnets (Japanese Patent Application Laid-Open No. 60-54406).
issue). Ni plating has the advantages that the mechanical strength of the surface coating layer is superior to that of the oxidation-resistant resin, and that the coating layer itself has almost no hygroscopicity.

However, unlike the acid-resistant resin layer, there is a problem that pinholes exist on the surface of the Ni plating coating layer. Therefore, regardless of the hygroscopicity of the coating layer itself,
There has been a problem that water permeates into the magnet body through the pinholes with the passage of time and causes corrosion deterioration.

In order to solve this problem, there have been proposed to date two-layer plating in which Ni plating is further performed on the Ni plating layer, and a method of embedding pinholes by coating with an oxidation-resistant resin (Japanese Patent Application Laid-Open No. 63-163). No. -110707).

[Problems to be solved by the invention]

However, the method using two-layer plating or coating with an oxidation-resistant resin relates to the adhesion between the lower Ni plating layer and the upper Ni plating layer or the oxidation-resistant resin layer and the corrosion resistance of the upper Ni plating layer or the oxidation-resistant resin layer itself. Had problems. Therefore, the above method has a problem that the corrosion resistance can be sufficiently improved.

Therefore, an object of the present invention is to provide an R-TM-B-based permanent magnet with high reliability and improved corrosion resistance.

[Means for solving the problem]

In the present invention, R (where R is one or a combination of two or more rare earth elements including Y) 5 to 40% by weight, TM (where TM is a transition metal mainly containing Fe, Some may be replaced with other metal or non-metal elements.) 50-90%,
R-TM-B permanent magnet consisting of 0.2 to 8% of B (boron) has a Ni plating layer on the surface thereof, and further has a chromate coating layer thereon. −TM
-B-based permanent magnet.

In addition, the present invention, in the chromate treatment, sulfuric acid, hydrochloric acid,
It is characterized by using a chromic acid solution from which a strong acid such as nitric acid has been removed.

The chromate coating layer applied by the chromate treatment,
Although the film is extremely thin, it has excellent adhesion, is amorphous, has no pores, and is not easily wetted by water, and therefore has an effect of protecting the underlying metal from moisture very well. Further, it is considered that soluble hexavalent Cr ions are dissolved in the portion where the film under the chromate film is broken, and the underlying metal is protected by the corrosion inhibiting action of the ions.

The present invention is to improve the corrosion resistance of the R-TM-B permanent magnet by the anticorrosion action of the chromate film.

In the present invention, Fe, Co, Ni and other elements that substitute for a part of TM are, depending on the purpose of addition, Ga, Al, Ti, V, Cr, Mn, Zr, H
f, Nb, Ta, Mo, Ge, Sb, Sn, Bi, Ni, etc. can be added, and the present invention can be applied to any R-TM-B magnet. Further, the manufacturing method may be any of a sintering method, a molten metal quenching method, and a modification method thereof.

As a manufacturing method, plating is performed after degreasing with an organic solvent. The current density is preferably 1-2 A / dm ² , and the thickness of the plating layer is preferably 5-20 μm.

As for the pre-plating treatment, it is preferable to use an acidic solution in order to remove the deteriorated layer and activate the pre-plating. A strong acid such as sulfuric acid or hydrochloric acid is effective for pre-plating activation. However, in order to minimize the effect of the pre-plating treatment on the material, first etching with 2 to 10 vol% nitric acid and then 5 to 10 vol hydrogen peroxide %, Acetic acid 10-30 vol% is most desirable. Next, a Ni plating process is performed.

As the type of Ni plating, any of a Watt bath, a sulfamic acid bath, and an ammonium bath may be used, but bright plating is preferred. Matte plating is not preferred because it has a columnar crystal structure. However, since it has good adhesion and low stress, it is effective as a base for multilayer plating.

 Finally, a chromate treatment is performed.

After washing with water after the Ni plating treatment, immersion treatment is performed in a chromic acid solution. The chromic acid solution temperature is preferably 20 to 80 ° C, and the immersion time is preferably 1 to 10 minutes. In order to activate the immersion treatment, it is preferable to use a chromic acid solution having high acidity, but what is important here is to use a chromic acid solution excluding strong acids such as sulfuric acid, hydrochloric acid, and nitric acid. In a generally known chromate treatment, a chromate solution containing a trace amount of the above strong acid is generally used. However, the inclusion of a strong acid in the chromate solution in the chromate treatment of the present invention causes excessive activation of the chromate solution, causing the dissolution of Ni, which is a film quality, and degrading the adhesion of the chromate film. Not preferred. Further, when a strong acid penetrates the magnet body through the pinholes on the Ni plating, corrosion of the magnet body may occur. Therefore, it is desirable to use a chromic acid solution from which the strong acid has been removed for the immersion treatment.

As the type of the chromic acid solution, it is preferable to use chromic anhydride or dichromic acid having high acidity, and it is desirable that the Cr concentration be 0.01 mol / or more in order to activate the immersion treatment.

After completion of the immersion treatment, the substrate is washed with water and dried. Drying temperature is 20 ~
120 ° C is good. The drying temperature must not exceed 120 ° C., since excessive heating will result in deterioration of the corrosion resistance of the chromate film.

The EXAMPLES _{Nd (Fe 0.7 Co 0.2 B 0.07} Ga 0.03) 6.5 made of alloy composition prepared in an arc melting, and then coarsely grinding the resulting ingot by a stamp mill and a disk mill.

Thereafter, fine pulverization was carried out with a jet mill using N ₂ gas as a pulverizing medium to obtain a finely pulverized powder having a pulverized particle size of 3.5 μm (FSSS).

The obtained raw material powder was subjected to transverse magnetic field molding in a magnetic field of 15 KOe.
The molding pressure was ² Ton / cm ² . 1090
C. for 2 hours. The sintered body was cut into a size of 18 × 10 × 6 mm, heated and maintained in an argon atmosphere at 900 ° C. for 2 hours, then rapidly cooled and maintained in an argon atmosphere at 600 ° C. for 1 hour.

For the sample thus obtained,
First etching with 5vol% nitric acid, then hydrogen peroxide
Second etching was performed using a mixed acid of 10 vol% and acetic acid 25 vol%. Thereafter, various surface treatments were performed under the working conditions shown in Table 1.

In addition, the film thickness of the Ni plating layer of the sample described in Table 1 is
1, 2, 3, and 5 were 10 μm, and 4 was a lower layer 5 μm and an upper layer 5 μm.

The samples shown in Table 1 were subjected to a corrosion resistance test at 80 ° C. and 90% RH for 500 hours and a salt spray test at 35 ° C. and 5% NaCl for 100 hours. The results are shown in Table 2.

In Table 2, the corrosion resistance test results show the change in the appearance of the sample,
The results of the salt spray test indicate the time of occurrence of red rust.

Table 2 shows that the permanent magnet according to the present invention can significantly improve the corrosion resistance as compared with the conventional magnet.

〔The invention's effect〕

According to the present invention, in a magnet mainly composed of rare earth and iron, remarkable improvement in corrosion resistance, which was insufficient with conventional plating, was achieved.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01F 1 / 02,7 / 02 C23C 22/00-22/24

Claims (2)

(57) [Claims] (1) a weight ratio of R (where R is one or a combination of two or more rare earth elements including Y) 5 to 40%, and TM (where TM is a transition metal mainly containing Fe) 50 R-TM-B permanent magnet consisting of ~ 90% and B (boron) 0.2 ~ 8% has a Ni plating layer on the surface, and further has a two-layer coating layer consisting of a chromate coating layer on it An R-TM-B permanent magnet having improved corrosion resistance. 2. A weight ratio of R (where R is one or a combination of two or more rare earth elements including Y) 5 to 40%, and TM (where TM is a transition metal mainly composed of Fe) 50. 90% and B (boron) 0.2 to 8% R-TM-B permanent magnet
i.Plating, further immersion in chromic anhydride solution excluding strong acid of sulfuric acid, hydrochloric acid and nitric acid or dichromic acid solution excluding strong acid of sulfuric acid, hydrochloric acid and nitric acid, washing with water and drying A method for producing an R-TM-B-based permanent magnet having improved corrosion resistance, characterized by providing a chromate film.