JPH0529116A - High corrosion-resistant rare earth magnet - Google Patents

Abstract

PURPOSE:To maintain excellent magnetic property for a long period by covering the surface of an RE-B-Fe sintered rare earth magnet or the surface of an RE-TM-B hot processed rare earth magnet with the vapor-phase plating of Al or Al alloy and the organic coating layer by electrodeposited plating. CONSTITUTION:A vapor-phased plating made of Al or Al alloy is made on the surface of an RE-B-Fe sintered rare earth magnet or the surface of an RE-TM-B hot processed rare earth magnet, and thereon an organic coating layer is made by electrodeposited plating. The plating of Al or Al alloy serves as a layer for preventing the oxidation of the surface of a magnet, and also is elevates the adhesion with the organic coating layer made by an electrodeposition-coating method, and further it has a function as a hydrogen shutoff layer which hinderes the hydrogen produced in electrodeposition coating from moving in ward the magnetic alloy and from causing hydrogen embrittlement, and this plated layer is made by vapor-phase plating method. Hereby, excellent magnetic property can be maintained for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth magnet having improved corrosion resistance. More specifically, a rare earth magnet is provided with a vapor phase plating layer made of Al or Al alloy and a corrosion resistant organic coating layer formed by electrodeposition coating on the surface of the rare earth magnet. Accordingly, the present invention relates to a highly corrosion-resistant rare earth magnet which has improved corrosion resistance and can maintain excellent magnetic properties for a long period of time.

[0002]

2. Description of the Related Art Magnet alloys are widely used as permanent magnets and the like as peripheral materials for large computers and as materials for electric or electronic parts such as various electric products for general household use. With the demand for higher performance and higher performance, the demands for magnetic alloys such as magnetic properties and corrosion resistance are becoming more and more advanced.

Among these, the RE-B-Fe system sintered rare earth magnet or the RE-TM-B system hot-worked rare earth magnet is said to have excellent magnetic properties. However, since this rare earth magnet not only contains a highly active rare earth element but also an alloy in which a RE-rich phase and an Fe-rich phase coexist, it is easily generated by the influence of the local battery due to the potential difference between the two phases. Rust. Therefore, surface treatment for rust prevention is indispensable for practical use.
a method of plating a metal such as i or Zn or an alloy thereof;
A method of applying chemical conversion treatment such as phosphate treatment or chromate treatment; a method of applying a resin coating of epoxy resin or acrylic resin by a dipping method, a spray method or the like has been proposed.

[0004]

However, satisfactory plating adhesion and corrosion resistance cannot be obtained by the method of plating a metal or alloy such as Ni or the chemical conversion treatment method. Moreover, since these rare earth magnets have a high hydrogen storage property and have the property of being brittle due to hydrogen storage, if electroplating or electroless plating is adopted, hydrogen generated during plating is stored and the magnet becomes brittle at the plating interface. It causes chemical cracking and peels off the plating, making it impossible to maintain corrosion resistance.

In order to avoid such problems, vapor phase plating methods such as vapor deposition plating have been proposed, but in this method, pinhole defects in the plating layer are a major obstacle to improvement in corrosion resistance.

In addition, it is difficult to obtain sufficient adhesion and corrosion resistance even by a method of applying a resin coating such as a dipping method or a spray method, and it is difficult to form a uniform resin coating film on the magnet surface. Corrosion resistance is apt to be insufficient at the edge portion, and corrosion progresses from this portion as a starting point.

The present invention has been made by paying attention to the above situation, and an object thereof is to obtain a high magnetic property capable of maintaining excellent magnetic characteristics for a long term without causing problems such as hydrogen absorption. It is intended to provide a corrosion resistant rare earth magnet.

[0008]

Means for Solving the Problems The constitution of the present invention which has been able to solve the above-mentioned problems is that the surface of a RE-B-Fe system sintered rare earth magnet or a RE-TM-B system hot-worked rare earth magnet is made of Al. Alternatively, the gist is that a vapor phase plating layer made of an Al alloy is formed, and an organic coating layer formed by electrodeposition coating is formed on the plating layer. The electrodeposition coating method for forming the organic coating layer may be either an anion type electrodeposition coating method or a cation type electrodeposition coating method, but it is more preferable to generate hydrogen in the electrodeposition step. There is no anion type electrodeposition coating method.

[0009]

The high corrosion resistance rare earth magnet according to the present invention is the RE-B-Fe system sintered rare earth magnet or RE-TM- magnet as described above.
A vapor phase plating layer made of Al or an Al alloy is formed on the surface of a B-system hot-working rare earth magnet, and an organic coating layer is formed thereon by electrodeposition coating. Due to the synergistic surface protection effect, the corrosion resistance of the magnet is significantly increased.

First, the Al or Al alloy plating layer formed in the present invention acts as an antioxidation layer on the surface of the magnet and enhances the adhesion of the organic coating layer formed by the electrodeposition coating method. It functions as a hydrogen barrier layer that prevents hydrogen generated during coating from moving toward the magnet alloy and causing hydrogen embrittlement, and this plated layer is formed by a vapor phase plating method.

That is, when the vapor-phase plating method is adopted, hydrogen is not generated in the plating process unlike the case where the electroplating method or the electroless plating method is adopted, and as described above, the magnet surface absorbs hydrogen. This is because there is no risk of causing problems such as embrittlement.

Further, the Al or Al alloy plated layer is appropriately etched by the electrodeposition coating liquid in the electrodeposition coating process of the organic coating layer formed on the surface thereof, and also exerts the action of enhancing the adhesiveness of the organic coating layer. . As the vapor phase plating method, a vacuum vapor deposition method, a sputtering method, an ion plating method and the like can be mentioned as preferable ones.
As an Al alloy, Mg, Si, Cu, M together with Al
Various Al alloys containing one or more metals such as n, Zn, Cr and Ni as alloy components are included.

By the way, the Al or Al alloy plating layer formed by the vapor phase plating method has a minute pinhole defect, so that a sufficient surface protection effect cannot be obtained.
Therefore, in the present invention, as a means for compensating for this pinhole defect and obtaining excellent corrosion resistance, an organic coating layer is formed thereon by electrodeposition coating.

That is, according to the electrodeposition coating method, the organic coating layer forming material is electrically adsorbed on the surface of the magnet to form a coating film, so that the coating layer forming material surely penetrates to the pinhole defect portion of the vapor phase plating layer. Thus, a surface protective film is formed, and therefore the film adhesion is remarkably enhanced as compared with the ordinary dipping method, spray method and the like.

In particular, during electrodeposition coating, the electrolytic deposition of the resin initially occurs on the entire surface to be coated, but if the resin deposition amount becomes uneven during the electrolytic deposition, the resin deposition amount In areas where there is a large amount of electrolytic resistance, the amount of electrolytic deposition decreases relatively, whereas in areas where there is a small amount of resin deposition, the amount of electrolytic deposition is low. Therefore, the finally formed electrodeposition coating film has a uniform thickness over the entire surface, and there is no fear that coating film defects such as pinholes locally remain.

Moreover, Al or Al alloy formed on the surface of the magnet by the vapor plating method has better adhesion to the rare earth magnet than Ni plating or the like, and Al or Al alloy.
The alloy is cleaned by an appropriate etching action during electrodeposition coating, and the resin is electrolytically deposited on the surface of the alloy, so these effects are combined to significantly enhance the adhesion of the surface coating and the coating is extremely dense. It becomes homogeneous and can maintain a high level of corrosion resistance for a long period of time.

The electrodeposition coating methods include anion type electrodeposition coating and cation type electrodeposition coating. Either of them may be adopted in the present invention, but anion type electrodeposition coating is more preferable.
This is because anion type electrodeposition coating does not show generation of hydrogen during electrolytic deposition, and there is no possibility of causing a problem of magnet embrittlement due to hydrogen absorption. However, in the present invention, an Al or Al alloy plating layer having a hydrogen barrier effect is formed as the underlayer, and even if some hydrogen is generated in the electrodeposition coating process, the hydrogen moves toward the magnet alloy due to the plating layer. Therefore, it is also possible to employ the cationic electrodeposition coating method.

However, when the cation-type electrodeposition coating method is adopted, hydrogen may invade toward the magnet alloy through pinhole defects in the Al or Al alloy plating layer, and the magnet may be slightly embrittled by hydrogen. Therefore, it is desired to perform a chemical conversion treatment such as a chromate treatment in advance to form a chemical conversion film on the pinhole defect portion to surely prevent the migration of hydrogen toward the magnet alloy.

The type of electrodeposition coating solution used in the present invention is not particularly limited, but preferred examples are anion type electrodeposition coating resins such as polyester type, polybutadiene type, epoxy type, acrylic type and alkyd type resins. Anionic emulsions obtained by blending or reacting one or more of the above resins with each other, and one or more of the epoxy-based or polyester-based resins as the cationic electrodeposition coating resin are blended. An example is a cationic emulsion that has been reacted or reacted. Among these, it is the highly alkaline anion type electrodeposition coating solution having a pH of 8.3 or more that can obtain particularly excellent corrosion resistance.

However, the above resins generally tend to thicken when they are made into an alkaline aqueous solution. Therefore, depending on the kind of the resin used, the molecular weight and acidity may be adjusted so that sufficient stability and electrodeposition coatability can be obtained. It is desired to adjust the valency, solid content concentration and the like as appropriate.

The above Al or Al constituting the surface protective layer
The thicknesses of the alloy layer and the organic coating layer may be appropriately determined in consideration of the required degree of corrosion resistance and economic efficiency, but if they are shown as standard values, the Al or Al alloy plating layer may have a thickness of 5 to 5. 15μm, organic coating layer is 5
It is about 20 μm.

Next, the RE-B-Fe system sintered rare earth magnet and the RE-TM-B system hot-worked rare earth magnet used in the present invention will be explained. First, the RE-B-Fe based sintered rare earth magnet contains at least one rare earth element and B and Fe as essential elements, and the rare earth element represented by RE is Pr, Nd, La, Ce, Td. , Dy, H
o, Er, Eu, Sm, Gd, Pm, Tm, Yb, L
Examples thereof include u and Y, and these may be used alone or, if necessary, may be used in combination of two or more kinds. Among the above rare earth elements, Pr and N are particularly preferable.
d.

The preferred RE content in these RE-B-Fe-based sintered rare earth magnets (hereinafter referred to as atomic% unless otherwise specified) is 8 to 30%, and if it is less than 8%, a sufficient coercive force is obtained. Is difficult to obtain, and if it exceeds 30%, the residual magnetic flux density tends to be insufficient. Further, the preferable content ratio of B is 2
If it is less than 2%, it is difficult to obtain a sufficient coercive force, and if it exceeds 28%, the residual magnetic flux density becomes insufficient. Fe is preferably in the range of 40 to 90%. If it is less than 40%, the residual magnetic flux density tends to be insufficient, while if it exceeds 90%, it becomes difficult to obtain a high level coercive force.

In the RE-B-Fe system sintered rare earth magnet, part of Fe may be replaced with Co or Ni. However, if the substitution amount of Co becomes too large, it becomes difficult to obtain a high coercive force, so the substitution amount of Fe is 50%.
The residual magnetic flux density tends to decrease when the Ni substitution amount becomes too large, so the substitution amount for Fe should be 8% or less.

Further, in this magnet, the coercive force can be further increased by substituting one or more of the following elements as Fe for substitution with Fe (provided that two or more elements are included). When used in combination, the allowable content is the upper limit of the content of each additive element that exhibits the maximum value).

Al: 9.5% or less, Ti: 4.5% or less, V: 9.5% or less, Cr: 8.5% or less, M
n: 8.0% or less, Bi: 5.0% or less, Nb: 9.
5% or less, Ta: 9.5% or less, Mo: 9.5% or less, W: 9.5% or less, Sb: 2.5% or less, G
e: 7.0% or less, Sn: 3.5% or less, Zr: 5.
5% or less, Ni: 9.0% or less, Si: 9.0% or less, Zn: 1.1% or less, Hf: 5.5% or less.

Next, the RE-TM-B hot-working rare earth magnet contains at least one rare earth element (RE) containing Y, a transition element (TM) and B as essential elements. Those listed as the constituent elements of the RE-B-Fe-based sintered rare earth magnet are exemplified again, but the highest magnetic property among these is easily obtained when Pr is used, so that it is substantially Pr. It is preferable that only 50% or more of RE is Pr. Also Dy and T
The combined use of a small amount of heavy rare earth element such as d is effective for improving the coercive force.

The RE content in the total amount of the RE-TM-B hot-worked rare earth magnets is preferably 8 to 25%, more preferably 10 to 20%, further preferably 12 to 18%.
% Range. The main phase of a magnet having RE, TM and B as its basic components is RE ₂ TM ₁₄ B (eg Pr ₂ Fe).
_14B ), if RE is insufficient, this compound is not formed and a cubic crystal structure having the same structure as α-iron is formed, so that it is difficult to obtain good magnetic properties (especially coercivity), while RE is If it is too large, the amount of non-magnetic RE rich phase increases and the residual magnetic flux density tends to decrease.

Next, the content of B is suitably 2 to 8%, more preferably 4 to 6%. If the amount of B is insufficient, R
Since it becomes an E—Fe rhombohedron, it is difficult to obtain a sufficient coercive force. On the contrary, if the coercive force is too large, for example, a nonmagnetic RE ₂ Fe ₄ B phase is precipitated and the residual magnetic flux density becomes low.

TM is 40 to 90%, more preferably 65.
90% is appropriate. If the amount of TM is insufficient, the residual magnetic flux density becomes low, and if it is too large, the coercive force becomes insufficient.
The most typical one of TM is Fe, but a part of it can be replaced with Co and / or Ni. Co is effective in raising the Curie point of the magnet,
Basically, by replacing the Fe site of the main phase, RE ₂ Co ₁₄ B
However, this compound has a small crystal anisotropy field,
Since the coercive force of the entire magnet decreases as the substitution amount of Co increases, it is preferable to suppress Fe to 50% or less, more preferably 20% or less. Further, since the residual magnetic flux density tends to decrease as the substitution amount of Ni increases, it is desirable to suppress Fe to about 8% or less.

The basic constituent elements of the RE-TM-B hot-working rare earth magnet are as described above, but if necessary, other elements such as Ag, Au, Al, Cu, Ga, Sn and P are used.
The coercive force can be further increased by containing at least one of t, Zn and the like, and the effect is effectively exhibited by the addition of 0.2% or more. However, if the amount is too large, the non-magnetic grain boundary phase increases and the magnetic properties are deteriorated. Therefore, it should be suppressed to 2% or less.

Among the above elements, particularly Ag, Au, Al,
Cu, Pt, Sn, and Zn have the effect of refining the crystal structure and suppressing the formation of a surface-deteriorated layer due to hot working for imparting anisotropy as described later, and have a thin-walled shape of, for example, about 3 mm. Even in this case, the effect of giving a magnet having excellent magnetic characteristics is exhibited.

An anisotropic permanent magnet can be obtained by hot working the RE-TM-B alloy thus obtained, preferably at a temperature of 800 ° C. or higher, and orienting it. In addition, this RE
The -TM-B hot-working rare earth magnet is particularly preferable because it has a superior effect in corrosion resistance and magnetic properties to the above-mentioned Re-B-Fe sintered rare earth magnet.

In the present invention, RE-B-Fe as described above is used.
A permanent magnet having high corrosion resistance can be obtained by applying the above-mentioned Al or Al alloy plating and anionic electro-deposition coating to the system sintered rare earth magnet or the RE-TM-B system hot worked rare earth magnet. That is, in the above magnet alloy, not only is the amount of oxygen and rare earth element oxides contained therein extremely small, and there is no fragile oxide layer with poor coating adhesion in the surface layer portion, or the protective coating formation step or Will not occlude hydrogen and then embrittle,
Combined with the above-mentioned effect of improving coating film adhesion by Al or Al alloy plating and electrodeposition coating, excellent corrosion resistance is exhibited,
A high level of magnetic properties can be maintained for a long period of time.

[0035]

Example 1 Iron powder having a purity of 99.9%, ferroboron alloy having a purity of 99.9% and Nd having a purity of 99.7% or more were used as raw materials, and these were blended and subjected to high frequency melting, and then a water-cooled copper mold was prepared. Casting was performed to obtain an ingot having a composition of Nd ₁₄ B ₇ Fe ₇₉ .

The ingot was roughly crushed with a stamp mill and then finely crushed with a ball mill to obtain a fine powder having a particle size of 2.8 to 8 μm. This fine powder was charged into a mold, oriented in a magnetic field of 10 KOe, and molded at a pressure of 1.5 t / cm ² .

This compact was sintered in an Ar atmosphere at 1000 ° C. for 1 hour, then allowed to cool, and then 600 ° C. in an Ar atmosphere.
A rare earth magnet was obtained by aging treatment for 2 hours. A test piece of 20 mm × 30 mm × 3 mm size was cut out from the obtained magnet, surface-polished (No. 150) and degreased with acetone, and then an Al plating layer was formed by the vacuum deposition method as shown in Table 1, and electrodeposition was performed thereon. The organic coating layer was formed by the coating method. In addition, in accordance with the conventional method, those plated with Ni at a current density of 8 A / dm ² using a Watt bath, only the vapor-deposited Al plating layer and only the organic electrodeposition coating are shown as comparative examples.

After electrodeposition coating or Ni plating, magnetizing treatment was carried out to obtain a test material having the following initial magnetic characteristics. Residual magnetic flux density (Br) = 12.5 KG Coercive force (iHc) = 12.0 KQe Energy product (BH) _max = 35.0 MGOe Each of the obtained test materials was subjected to a corrosion resistance test by the following method.

(Corrosion resistance test) Test material is 80 ° C. × 90% R
After standing for 600 hours in a constant temperature and humidity atmosphere of H, the appearance (visual observation), film adhesion (JIS K 5400: cross-cut tape method) and magnetic properties were examined. The results are collectively shown in Table 1.

[0040]

[Table 1]

As is apparent from Table 1, in Examples (Nos. 1 to 5), no change in appearance and no decrease in coating adhesion were observed after the corrosion resistance test, and the magnetic properties were the same as those before the test. While maintaining as it is, Comparative Example (No. 6 ~
In No. 11), appearance deterioration due to rusting and deterioration of plating adhesion are remarkable, and magnetic properties are considerably deteriorated.

Example 2 Electrolytic iron having a purity of 99.9%, ferroboron having a purity of 99.9%, and Pr having a purity of 99% or more were used as raw materials, which were blended and then subjected to high frequency melting. An ingot having the composition shown was obtained. By cutting this ingot, encapsulating it in an iron capsule, performing hot rolling with a total reduction of 76% at 950 ° C., and then heat treating it under the conditions of 1000 ° C. × 6 hours and 480 ° C. × 2 hours, The rare earth magnets having the magnetic characteristics shown in Table 2 were obtained. 20mm x 30mm x 3m from this magnet
A test piece of m was cut out, and after surface polishing (No. 150) and degreasing with acetone, vapor deposition Al plating and electrodeposition coating shown in Table 3 were performed, and a magnetization treatment and a corrosion resistance test were performed in the same manner as in Example 1 below. It was The results are shown in Table 4.

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

All the test materials shown in Tables 2 to 4 satisfy the requirements of the present invention, and the deterioration of the appearance after the corrosion resistance test, the deterioration of the coating film adhesion and the deterioration of the magnetic properties are completely recognized. Absent.

[0047]

The present invention is constructed as described above, and R
A magnet is obtained by coating the surface of an EB-Fe-based sintered rare earth magnet or a RE-TM-B-based hot-worked rare earth magnet with a vapor phase plating layer made of Al or an Al alloy and an organic coating layer by electrodeposition coating. The adhesion between the surface and the plating layer and the adhesion between the plating layer and the organic coating layer are both enhanced, and as a result, the corrosion resistance as a whole can be significantly increased, and a highly corrosion-resistant rare earth magnet that maintains excellent magnetic properties for a long time is provided. I got it.

Claims (2)

[Claims] 1. A RE-B-Fe-based sintered rare earth magnet or a RE-TM-B-based hot-worked rare earth magnet (RE represents one or more rare earth elements, and TM represents one or more transition elements: the same applies hereinafter. 1. A highly corrosion-resistant rare earth magnet, characterized in that a vapor phase plating layer made of Al or an Al alloy is formed on the surface of 1), and an organic coating layer formed by electrodeposition coating is formed on the plating layer. 2. The highly corrosion resistant rare earth magnet according to claim 1, wherein the organic coating layer is formed by anion type electrodeposition coating.