JPH08325679A - Corrosion resistant sintered magnetic alloy - Google Patents

Abstract

PURPOSE: To provide a R-TM-B sintered magnetic alloy having highly reliable corrosion resistance by providing with the specified number of recessed part having its specified depth which exist in a grain boundary on the surface of the sintered magnetic alloy. CONSTITUTION: This sintered magnetic alloy is composed of, by wt.%, 5-40 R (R is the combination of a kind or more of rare earth elements including Y.), 50-90 TM (TM is a transition metal mainly including Fe, a part of which may be substituted by the other metal or non-metal.) and 0.2-8 B (boron). The recessed part >=102 piece/cm<2> of the depth of >=3μm<=20μm, which exist on a part of the grain boundary and its vicinity in the surface of the alloy, are formed. A chemical for etching is used so as to form the recessed part. An Ni plating layer is formed on the surface of the sintered magnetic alloy. By this method, adhesion strength between R-TM-B sintered alloy and its plating is reinforced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a sintered magnetic alloy,
The present invention relates to a sintered magnetic alloy having significantly improved corrosion resistance by improving the adhesion between the sintered magnetic alloy and a plating layer formed on the surface thereof.

[0002]

2. Description of the Related Art With the high performance and miniaturization of electric and electronic devices, the same demands have been placed on the permanent magnet, which is one of the components. In other words, the strongest permanent magnet before was the rare earth-cobalt (R-Co) system, but in recent years, the stronger RT
The emergence of MB magnetic alloys (JP-A-59-460)
08). Here, R is one kind or a combination of two or more kinds of rare earth elements including Y, TM is a transition metal center such as Fe or Co, and a part thereof is replaced with another metal element or non-metal element, B Is boron. Although the magnetic alloy is manufactured by a powder metallurgical method by a sintering method, it has a problem that it is extremely rusty. Therefore, measures have been taken to provide an oxidation resistant coating layer on the surface of the permanent magnet in order to improve the corrosion resistance. The type of coating layer is electric Ni
Plating, oxidation resistant resin, Al ion plating, and the like have been proposed, and in particular, electric Ni plating has attracted attention because it improves the corrosion resistance of the R-TM-B type permanent magnet by a simple treatment (Japanese Patent Laid-Open No. Sho-06-1999). 60-54406). The electroplating Ni has the advantages that the surface coating layer has excellent mechanical strength as compared with the oxidation resistant resin, and that the coating layer itself has almost no hygroscopicity.

[0003]

However, since the above-mentioned sintered magnetic alloy is a sintered body, there are metallic foreign substances such as black skin and oxides and voids on the surface, and the Ni-plated sintered magnetic alloy is present. No sufficient adhesion strength was obtained between the plated layer and the plating layer, and its corrosion resistance was insufficient. As a method of improving the adhesion strength, there is a method of forming a recess on the surface of the object to be plated and improving the adhesion by the so-called anchor effect. JP-A-2-112
No. 207 discloses that a diameter of 0.03 to
A recess of 0.3 mm and a depth of 10 to 100 μm is formed on the surface.
There has been proposed a method of improving the adhesion between the magnet and the plating protection layer by having one or more per cm 2. However, the method described in JP-A 2-112207 has a problem that the number of anchors is small and a sufficient anchor effect cannot be obtained because the recess diameter is relatively large, 0.03 to 0.3 mm. It was Therefore, an object of the present invention is to solve the above problems and provide a highly reliable corrosion-resistant sintered magnetic alloy by improving the adhesion between the sintered magnetic alloy and the plating layer formed on the surface thereof. is there.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that in order to obtain sufficient adhesion strength without deteriorating magnetic properties, a small amount is required on the surface of the sintered magnetic alloy. It has been found that it is sufficient to form a large number of recesses, and in order to form a large number of small recesses on the surface of the sintered magnetic alloy, it is sufficient to form recesses on the grain boundaries of the surface of the sintered magnetic alloy and in the vicinity thereof. Therefore, the present invention provides a weight ratio of R
(Where R is one or a combination of two or more rare earth elements including Y) 5 to 40%, TM (where TM is F
A transition metal mainly composed of e, which may be partially replaced by another metal or a non-metal element) and is a sintered magnetic alloy composed of 50 to 90% and B (boron) 0.2 to 8%. 10 cm 2 per 1 cm 2 of recesses having a depth of 3 μm or more and 20 μm or less existing in the grain boundaries on the surface of the sintered magnetic alloy and in the vicinity thereof.
It is a corrosion-resistant sintered magnetic alloy having one or more pieces. By forming a Ni plating layer on the surface of the sintered magnetic alloy according to the present invention, it is possible to provide a corrosion-resistant sintered magnetic alloy having excellent adhesion between the sintered magnetic alloy and plating and having high corrosion resistance. In the present invention, the element substituting a part of the transition metal TM such as Fe, Co and Ni may be added depending on the purpose of addition.
Ga, Al, Ti, V, Cr, Mn, Zr, Hf, N
b, Ta, Mo, Ge, Sb, Sn, Bi, etc. can be added, and the present invention can be applied to any R-TM-B based sintered magnetic alloy.

[0005]

According to the present invention, an anchor that works effectively can be obtained by forming macroscopic recesses in the grain boundaries of the sintered magnetic alloy and a part of the vicinity thereof, thereby improving the adhesion between the sintered magnetic alloy and the plating layer. Acts to enhance. 1 (a), (b), and (c) show schematic views of the cross-sectional shape of the recesses on the surface of the sintered magnetic alloy having the plating layer. In FIG. 1, 1 is a plating layer, 2 is a crystal grain, and 3 is a concave portion of the surface of the sintered magnetic alloy in which the plating layer has entered. Further, the grain boundary means between crystal grains.
An anchor effect cannot be obtained with a recess having a shape as shown in FIG. 1 (a), resulting in insufficient adhesion. Figure 1 (b)
Although the anchor effect can be obtained by forming the concave shape shown in (1), it is extremely difficult to form the concave shape in the shape of (b). FIG. 1 (c) is a schematic view of the grain boundaries of the sintered magnetic alloy and the recesses formed in the vicinity thereof according to the present invention. The recesses are formed macroscopically in a shape that makes it difficult for the plating layer entering the recesses to come off. As a result, an extremely strong anchor effect is obtained and the adhesion is improved. As a means for forming recesses in the grain boundaries and in the vicinity of the grain boundaries, the grain boundary phase is constituted by a so-called Nd-rich phase which is easily corroded by a chemical such as an acid, so that the grain boundaries and the vicinity of the grain boundaries are selectively etched. It may be formed by using a chemical. Further, the number of recesses formed on the surface of the sintered magnetic alloy is 10 2 or more per 1 cm,
The depth is 3 μm or more and 20 μm or less. this is,
The number of recesses is less than 10 2 / cm 2, or the depth is 3 μm
If it is less than the above range, sufficient adhesion strength cannot be obtained, and if the depth of the recess exceeds 20 μm, the magnetic properties are significantly deteriorated. Further, in order to set the number of recesses to 10 2 or more per cm 2, it is preferable that the width of the recesses on the outermost surface of the magnet is 10 μm or less in sectional shape, more preferably 5 μm or less, further preferably 5 μm or less. Is the most desirable. As the oxidation resistant coating layer formed on the surface of the sintered magnetic alloy according to the present invention, a Ni plating layer formed by a Watts bath is particularly preferable. This is because the pH of the Watt bath is weakly acidic at 4 to 5, so that the grain boundaries on the surface of the sintered magnetic alloy and the vicinity thereof are further etched during the plating by the Watt bath to reach the deep portion of the formed recess. This is because Ni plating is easily deposited and a strong anchor effect is obtained. In addition, since the ionization tendency of Ni is relatively close to that of Fe, which is the main component of the sintered magnetic alloy of the present invention, it is possible to prevent the deposition of displacement plating which deteriorates the adhesion of the plated film.

[0006]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. Nd (Fe0.7Co0.2B0.07Ga0.03) 6.5
An alloy having the following composition was prepared by arc melting, and the obtained ingot was roughly crushed by a stamp mill and a disc mill.
Then, N2 gas was used as a grinding medium to perform fine pulverization with a jet mill to obtain fine pulverized powder having a pulverized particle size of 3.5 μm. 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. The compact was sintered in vacuum at 1090 ° C for 2 hours. 18 x 10 x sintered body
Cut out to a size of 6 mm, then heat and hold in an argon atmosphere at 900 ° C for 2 hours and then rapidly cool to 600 ° C.
It was held for 1 hour in the atmosphere of argon held in. The sample thus obtained was etched with 5 vol% nitric acid as a pretreatment for plating for the purpose of removing the work strain layer and oxide film on the sample surface, and a homogeneous magnet material was exposed on the sample surface, followed by 5% citric acid. The grain boundary on the sample surface and its vicinity were selectively etched with a mixed acid of 0.5% and 0.5% sulfuric acid. By adjusting the etching time with a mixed acid of 5% citric acid and 0.5% sulfuric acid, samples having different depths and numbers of recesses at the grain boundaries of the sintered magnetic alloy and in the vicinity thereof (Examples 1 to 1 in Table 1). 3 and Comparative Examples 1 and 2) were prepared. Then, a semi-bright Ni plating layer having a thickness of 15 μm is formed with a watt Ni bath,
This was used as a test piece. Further, for comparison, as a pretreatment for plating, 5 was used for the purpose of removing the processing strain layer and oxide film on the sample surface.
After etching with nitric acid of vol%, 0.5N
A sample (Comparative Example 3 in Table 1) in which concave portions were formed by ultrasonic immersion in nitric acid was prepared. Then, in the watt Ni bath, 15μ
A semi-bright Ni plating layer of m was formed and used as a test piece. The depth and the number of concave portions of the obtained sample were measured by SEM observation after creating a cross-section sample. The adhesion test was conducted by a tensile tester (Sebastian 1), and the salt spray test was conducted at 35 ° C. and 5% saline for 100 hours. The results are shown in Table 1. From Table 1, it can be seen that in the R-TM-B system sintered magnetic alloy, the adhesion and corrosion resistance of the plated film, which were insufficient by conventional plating, were significantly improved.
Also, if the number of the formed recesses is less than 10 2 / cm 2, sufficient adhesion strength cannot be obtained, while the depth of the recesses is 25 μm.
It can be seen that when m or more, the magnetic properties are significantly deteriorated.

FIG. 2 shows a photograph of a cross section of the structure of the sintered magnetic alloy according to the present invention. As shown in FIG. 2, after forming recesses at the grain boundaries on the surface of the sintered magnetic alloy and in the vicinity thereof, a plating layer having excellent adhesion can be formed on the surface of the sintered magnetic alloy by applying metal plating. . In this example, as a means for forming recesses in the sintered magnetic alloy grain boundaries exposed on the surface of the sintered magnetic alloy and in the vicinity thereof, etching was performed with a mixed acid solution of 5% citric acid and 0.5% sulfuric acid. However, the same effect can be obtained by using other chemicals or other methods capable of forming recesses in the sintered magnetic alloy grain boundary and a part of the vicinity thereof.

[0008]

[Table 1]

[0009]

According to the present invention, the relatively easy means of forming the concave portion at the grain boundary of the sintered magnetic alloy on the surface of the sintered magnetic alloy and a part in the vicinity thereof causes no increase in cost without increasing the cost. A highly reliable corrosion resistant R-TM-B based sintered magnetic alloy is provided by increasing the adhesion strength between the -TM-B based sintered magnetic alloy and plating and improving the corrosion resistance.

[Brief description of drawings]

FIG. 1A is a schematic view showing a cross-sectional shape of a conventional sintered magnetic alloy surface. (B) It is a schematic diagram which shows the cross-sectional shape of the surface of a sintered magnetic alloy. (C) It is a schematic diagram which shows the cross-sectional shape of the surface of the sintered magnetic alloy of this invention.

FIG. 2 is a scanning electron microscope photograph of a metal microstructure of a cross section of a Ni plating layer formed by a sintered magnetic alloy according to the present invention and a Watts bath.

Claims (2)

[Claims] 1. R in a weight ratio (where R is one or a combination of two or more rare earth elements including Y) 5 to 40
%, TM (here, TM is a transition metal mainly composed of Fe and may be partially replaced with other metal or non-metal element) 50 to 90%, B (boron) 0.2 to 8 %, A corrosion-resistant sintered alloy having a depth of 3 μm or more and 20 μm or less present at a grain boundary of the surface of the sintered magnetic alloy or a part thereof in the vicinity thereof is 10 2 or more per 1 cm 2. Magnetic alloy. 2. A corrosion resistant sintered magnetic alloy having a Ni plating layer on the surface of the sintered magnetic alloy according to claim 1.