JPH05109519A - High corrosion resistant rare earth magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the cracking of the surface of magnets or the like induced by hydrogen occlusion or the like and maintain excellent magnetic properties for a long time by forming the lowest layer with Sn and a metal coated layer plated with Ni or Ni alloy on the surface layer on the surface of RE-B-Fe group sintered rare earth magnets or the surface of RE-TM-B group hot processing rare earth magnets. CONSTITUTION:An Sn layer is formed on the surface of RE-B Fe group sintered rare earth magnets or RE-TM-B group hot processing rare earth magnets as a base layer. An Ni or Ni alloy layer is formed thereon based on an electric plating process or an electroless plating process or the like. In this case, the Sn layer has an excellent hydrogen transmission inhibiting action and prevents the generation of hydrogen embrittlement as hydrogen invades into the magnets when forming the Ni or the Ni alloy layer. It is, therefore, possible to enhance the adhesion properties with composite metal coated layers and inhibit the generation of plating crack or plate separation and enhance the corrosion resistance of the magnets in its turn.

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 and a method for producing the same, and more specifically, it has a multi-layer structure in which the bottom layer of the rare earth magnet is Sn and the surface layer is a Ni or Ni alloy plating layer. The present invention relates to a highly corrosion-resistant rare-earth magnet in which a metal coating layer is formed and a composite structure thereof can enhance corrosion resistance to maintain excellent magnetic properties for a long time, and a method for producing the same.

[0002]

2. Description of the Related Art Magnet alloys are widely used as materials for electric or electronic parts such as peripherals of large computers and various electric appliances for general household use. Along with the demand for higher performance, the required properties such as magnetic properties and corrosion resistance for magnet alloys are becoming more and more advanced.

Under such circumstances, the above-mentioned rare earth magnet is expected 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 extremely rusted due to the influence of the local battery due to the potential difference between the two phases. Cheap. Therefore, for practical use, surface treatment for rust prevention is indispensable. For example, a method of plating a metal such as Ni or Zn or an alloy thereof; a method of applying a chemical conversion treatment such as a phosphate treatment or a chromate treatment; a dipping method. A method of applying a resin coating such as an epoxy resin or an acrylic resin by a spray method or the like has been proposed. Among these, the ones currently widely used are Ni plating or Ni alloy plating methods such as Ni-P, which can be carried out relatively inexpensively without requiring complicated equipment.

[0004]

However, the method of plating a metal or alloy such as Ni cannot always obtain satisfactory plating adhesion and corrosion resistance. Part 1
One reason can be thought of as follows. That is, RE-B
-Fe-based sintered rare earth magnets or RE-TM-B hot-worked rare earth magnets have a high hydrogen storage property and have the property of being brittle due to hydrogen storage. Therefore, when Ni or Ni alloy plating method is adopted, it occurs during plating. Hydrogen that is stored in the rare earth magnet causes embrittlement cracking at the plating interface, reducing the plating adhesion and rusting at the interface between the plating layer and the magnet due to long-term use, resulting in plating cracking and plating peeling. Awake,
Corrosion resistance cannot be maintained. Moreover, since the rare earth magnet, which is a sintered body, is very fragile in itself, stress generated in the plating layer causes cracks at the magnet interface and induces plating delamination, which is also a major cause of failure to maintain high corrosion resistance. Thought to be a thing.

The present invention has been made by paying attention to the above situation, and its purpose is to prevent plating cracks and plating peeling without causing problems such as cracks on the magnet surface due to hydrogen absorption. An object of the present invention is to provide a highly corrosion-resistant rare earth magnet and a method for producing the same, in which the surface protective layer can be firmly adhered to the surface protective layer without causing it, and thereby excellent magnetic properties can be maintained for a long period of time.

[0006]

The constitution of the present invention which has been able to solve the above-mentioned problems is that the RE-B-Fe system sintered rare earth magnet or the RE-TM-B system hot-worked rare earth magnet has a surface The gist is that the lower layer is a metal coating layer having a multilayer structure in which the lower layer is Sn and the surface layer is Ni or Ni alloy plating. Further, in the present invention, Ni is provided between the Sn layer and the Ni or Ni alloy layer.
Corrosion resistance can be further enhanced by forming an intermediate layer made of a metal or an alloy of the metal which is more noble in terms of potential. In addition to the Sn layer and the Ni or Ni alloy layer, a Sn-Ni alloy layer may be formed between them to further improve the coating characteristics. After a Sn layer and then a Ni or Ni alloy layer were sequentially formed on the surface of a —B—Fe-based sintered rare earth magnet or a RE-TM-B-based hot-worked rare earth magnet, this was heat-treated at a temperature lower than the melting point of Sn. It can be easily obtained by mutual diffusion.

[0007]

The basic structure of the highly corrosion-resistant rare earth magnet according to the present invention is to form a metal coating layer having a multilayer structure in which the bottom layer is Sn and the surface layer is Ni or Ni alloy on the surface of the rare earth magnet as described above. It will be done. First, the Sn layer formed as the lowermost layer has an excellent effect of suppressing hydrogen permeation, and by forming the Sn layer as an underlayer, the Ni layer is formed thereon by electroplating or electroless plating. Or N
This prevents hydrogen generated when forming the i alloy layer from penetrating into the magnet and causing hydrogen embrittlement. In addition, since Sn is soft, it does not cause internal stress in the Sn layer itself, and also has a function of relaxing the stress generated at the boundary with the Ni or Ni alloy layer formed thereon, and the additive stress between them is added. Through the synergistic effect, the adhesion of the multi-layered metal coating layer to the magnet can be remarkably enhanced, plating cracks and plating peeling can be suppressed, and the corrosion resistance of the magnet can be greatly improved.

However, the anticorrosion effect of Sn is considerably inferior to that of Ni or Ni alloy, and the Sn alone coating layer cannot sufficiently enhance the corrosion resistance of the rare earth magnet. Therefore, in the present invention, the Sn layer is formed as a base layer,
The original corrosion resistance is Ni or Ni formed as the surface layer.
It will be secured by the alloy layer. Then, the combined effect of the Sn layer and Ni or Ni alloy layer was able to dramatically improve the anticorrosion performance of the entire coating layer.

Examples of the method of forming the Sn layer include vapor deposition methods such as vacuum deposition method, ion plating method, ion deposition film formation method (IVD method), plasma deposition film formation method (CVD method), and electroplating. Various methods such as a hot dip method and a hot dip plating method can be adopted. However, the electroless plating method involving a large amount of hydrogen generation in the plating step is not preferable because it causes hydrogen embrittlement of the magnet.

When the electroplating method is adopted among the above methods, a normal Sn plating bath such as an alkaline bath, a ferrostane bath, a sulfuric acid acid bath, and a borofluoric acid acid bath may be used. The type and amount of the additive may be appropriately selected in consideration of the plating efficiency, the plating thickness, the target effect of reducing the plating stress, and the like. The thickness of the Sn layer is preferably about 2 μm or more. If it is too thin, the effect of suppressing hydrogen permeation is not sufficiently exerted, and Ni or N
Not only is the effect of suppressing hydrogen embrittlement on the magnet surface due to hydrogen generated during the formation of the i alloy layer or subsequent corrosion reaction insufficient, but also the stress relaxation effect between the Ni or Ni alloy layer and the magnet surface. Also becomes a shortage.

Next, Ni or N formed as a surface layer
As the method of forming the i alloy layer, as in the case of the Sn layer, a vacuum vapor deposition method, an ion plating method, an ion vapor deposition film formation method (IVD method), a plasma vapor deposition film formation method (CVD
Method) or an electroplating method. Further, in this plating step, since the Sn layer is formed as the underlayer, an electrolytic plating method involving a considerable amount of hydrogen generation or An electroless plating method can also be adopted.

The electrolytic plating adopted here is various Ni plating baths which are commercially available Watts baths or their improved products,
Alternatively, it can be performed using a Ni alloy plating bath such as Ni-P or Ni-B, and the plating conditions such as pH and current density of the plating bath can be appropriately selected according to the plating efficiency, the target plating thickness and the like. Good. Even when the electroless plating method is adopted, a normal electroless Ni plating bath or N
An electroless Ni alloy plating bath such as iP, Ni-B, and Ni-WP may be used. The preferable thickness of the Ni or Ni alloy layer is 2 μm or more. If it is too thin, pinhole defects cannot be completely eliminated, and it becomes difficult to obtain sufficient corrosion resistance.

The preferable total thickness of the Sn layer and the Ni or Ni alloy layer is in the range of 5 to 15 μm, and in this range, a multi-layer coating film free of pinhole defects and excellent in anticorrosion performance can be obtained. .. In this case, the thickness ratio of (Ni or Ni alloy layer) / Sn layer is desired to be 1 or less in order to more effectively exhibit the above characteristics of the present invention. The reason is that the Sn layer is Ni or Ni as described above.
This is because it is formed as a base layer for enhancing the adhesiveness of the alloy layer, and the original corrosion resistance in a corrosive environment is exhibited by the Ni or Ni alloy layer.

As described above, in the present invention, the basic idea is to form the Sn layer as the underlayer, form the Ni or Ni alloy layer on the Sn layer, and protect the magnet surface with the coating layer having a two-layer structure. However, if a metal nobler nobler than Ni, such as Cu or its alloy, is formed as an intermediate layer between the Sn layer and the Ni or Ni alloy layer, the corrosion resistance of the entire coating layer is further enhanced. It is possible to do so, which is preferable.

It is also extremely effective to enhance the corrosion resistance by forming a Sn-Ni alloy layer between the Sn layer and the Ni or Ni alloy layer to form a coating layer having a multilayer structure of three or more layers. Is. That is, it cannot be said that the adhesion of the Ni or Ni alloy layer to the Sn layer is necessarily good, and particularly when the surface of the Sn layer is oxidized, the adhesion to the Ni or Ni alloy layer tends to be insufficient, Delamination may occur at the stacking interface. However, such concerns are caused by the Sn layer and N
This can be solved by forming a Sn—Ni based alloy layer between the i or Ni alloy layer. That is, Sn-N
The i-based alloy includes Sn on the lower layer side and Ni or Ni on the upper layer side.
Since it has an excellent affinity for both alloys, not only can the adhesion between both layers be enhanced by forming this as an intermediate layer, but the stress generated in the plating layer can also be Is gradually absorbed as you go to
The peeling resistance of the plating layer is further enhanced, and the corrosion resistance is further improved. It should be noted that the Sn-Ni alloy layer may be only one layer, or may be a multi-layer having two or more layers.

The method of forming the Sn-Ni alloy layer is not particularly limited, but as a general method, when forming the Ni or Ni alloy layer on the Sn layer by the vapor phase plating method, the substrate is heated to an appropriate temperature. A method of forming a Sn—Ni based alloy layer at the laminated interface by mutual diffusion by performing heating treatment after heating or after vapor-phase plating. Further, when the Ni or Ni alloy layer is formed by the electroplating method or the electroless plating method, the Sn—Ni alloy layer may be formed at the laminated interface by the heat treatment after plating. If the heat treatment temperature at this time exceeds the melting point of Sn, not only the Sn layer will flow and the smoothness of the plating surface will decrease, but also cracks will occur in the composite plating layer and the adhesion will decrease. Therefore, it is desirable that the heat treatment temperature be kept below the melting point of Sn.

Further, the corrosion resistance of the Sn layer itself is not always sufficient as described above, and when the Ni or Ni alloy layer formed on the Sn layer is scratched, the corrosion resistance of the Sn layer is rapidly increased. It is feared that corrosion will progress. However, such a concern is caused between the Sn layer and the Ni or Ni alloy layer by using a metal that is more noble than Ni, such as C.
This can be solved by forming an anticorrosion layer made of u, Ti, Cr or alloys thereof as an intermediate layer.

The present invention is constructed as described above, and the RE-
An Sn layer is formed as a base layer on the surface of the B-Fe-based sintered rare earth magnet or the RE-TM-B hot-working rare earth magnet,
A Ni or Ni alloy plating layer is formed thereon, and more preferably, a metal or alloy layer nobler than Ni or a Sn—Ni alloy layer is formed between these layers as an intermediate layer to protect the surface. The adhesion of the layer can be remarkably enhanced, and a high level of corrosion resistance can be obtained in combination with the excellent anticorrosion effect of the Ni or Ni alloy plating layer. However, the surface of the Ni or Ni alloy plating layer can be further subjected to chromate treatment or the like. It is also effective to further enhance the corrosion resistance by applying chemical conversion treatment, oxidation treatment, organic coating treatment, or the like.

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 kind of 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.
It is d.

A preferable content of RE in these RE-B-Fe 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%, and 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 of 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 enhanced by substituting Fe with at least one of the following elements as the other element (provided that two or more elements are used in combination). The upper limit of the permissible content is the content of each additive element having 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 It is preferable to use only Pr or RE in which 50% or more of RE is Pr. Also, the combined use of a small amount of heavy rare earth elements such as Dy and Td is effective for improving the coercive force.

The RE content in the total amount of the RE-TM-B hot-worked rare earth magnet 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 ), when 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). 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 preferably 2 to 8%, more preferably 4 to 6%. If the amount of B is insufficient, R
Since it becomes an E—Fe rhombohedral, it is difficult to obtain a sufficient coercive force. On the other hand, when 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, and basically it replaces the Fe site of the main phase to form RE ₂ Co.
₁₄ B is formed, but since this compound has a small crystal anisotropy magnetic field and the coercive force of the magnet as a whole becomes smaller as the substitution amount of Co increases, it becomes 50% or less, more preferably 20% or less of Fe. It is good to suppress. Further, since the residual magnetic flux density tends to decrease as the substitution amount of Ni increases, F
It is desired to suppress it to about 8% or less of e.

The basic constituent elements of the RE-TM-B hot-worked 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 it 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, especially 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 that accompanies hot working for imparting anisotropy as described later. Even in that case, the effect of giving a magnet having excellent magnetic properties is exhibited.

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

In the present invention, RE-B-Fe as described above is used.
Sintered rare earth magnet or RE-TM-B hot-worked rare earth magnet is added to the above-mentioned Sn layer and Ni or Ni alloy plating layer (or a metal or alloy layer more noble than Ni or Sn-Ni as an intermediate layer between them). By forming the system alloy layer), a highly corrosion-resistant permanent magnet can be obtained.

That is, in the above magnet alloy, the amount of oxygen and rare earth element oxide contained therein is very small, and the Ni or Ni alloy plating layer is a Sn layer or Sn-.
Since it adheres firmly through the Ni-based alloy layer, Ni or N
The excellent surface protection effect of the i alloy layer is fully exhibited.
As a result, the surface-coated rare earth magnet of the present invention exhibits excellent corrosion resistance and can maintain a high level of magnetic characteristics for a long period of time.

[0032]

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 mixed and subjected to high frequency melting, and then a water-cooled copper mold was formed. 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 1100 ° 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, and after surface polishing (No. 150) and degreasing with acetone, a composite plating layer having a structure shown in Table 1 was formed.
A comparative example is based on the conventional method, in which a Watt bath was used to perform Ni plating at a current density of 8 A / dm ² without forming a Sn layer.

After the above plating treatment, 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

Cross-section observation, corrosion resistance test, and appearance observation after the corrosion resistance test were performed on each of the obtained test materials by the following methods. (Observation of Cross Section) Each test piece before the corrosion resistance test was cut and examined for the occurrence of cracks in the magnet at the interface between the plating layer and the substrate (◯: no crack, x: crack). (Corrosion resistance test) After leaving the test material for 90 hours in a constant temperature and humidity atmosphere of 125 ° C x 85% RH, the appearance (visual observation: ◯:
No change, △: Discoloration can be seen, ×: Rust occurred),
The plating adhesion (JIS K 5400: cross-cut tape method) and magnetic properties were examined.

The results are collectively shown in Table 1. However, the method of forming each plating layer in Table 1 is as follows. Sn layer forming method: No. 1 to 4 (electroplating method: sulfuric acid acid bath, 2 A / dm ² ), No. 5 to 7 (vapor deposition plating method) Ni (Ni alloy) layer forming method: No. 1, 5 (electroplating method: Watt bath, 8 A / dm ² ), No. 4 (electroplating method: commercially available brightener addition, 8 A / dm ² ), No. 4 2,6
(Evaporation plating method) Cu layer forming method: No. 6,7 (Electroplating method: Cyan bath, 2A / dm ² )

[0037]

[Table 1]

As is clear from Table 1, Example N
o. In Comparative Examples Nos. 1 to 7, the magnetic properties also maintained the values before the test as they were. In Nos. 1 and 2, deterioration of appearance due to rusting and deterioration of plating adhesion were remarkable, and magnetic properties were 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 subjected to high frequency melting, and then water-cooled copper molds were used. 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 × 30mm × 3m from this magnet
A test piece of m was cut out, and after surface polishing (No. 150) and degreasing with acetone, plating treatment, magnetization treatment and corrosion resistance test were performed in the same manner as in Example 1.

The results are shown in Table 3. However, the method of forming each plating layer in Table 3 is as follows. Sn layer forming method: No. 1 to 3 (electroplating method: sulfuric acid acid bath, 2 A / dm ² ), No. 4 to 7 (vapor deposition plating method) Ni (Ni alloy) layer forming method: No. 1, 6, 7 (electroplating method: Watt bath, 8 A / dm ² ), No. 2, 3 (electroplating method: commercial brightener addition, 8 A / dm ² ), N
o. 4, 5 (vapor deposition plating method) Cu layer forming method: No. 5,7 (Electroplating method: Cyan bath, 2A / dm ² )

[0041]

[Table 2]

[0042]

[Table 3]

The test materials shown in Tables 2 and 3 all satisfy the requirements of the present invention, and no deterioration of appearance and deterioration of magnetic properties are observed after the corrosion resistance test.

Example 3 A test piece of a permanent magnet obtained in the same manner as in Example 1 was subjected to the same surface polishing and degreasing with acetone, and then a composite plating layer having a structure shown in Table 4 was formed. The intermediate layer (Sn-Ni
As a method of forming the (base alloy layer), No. 1, 3, 4, 5,
For Nos. 7 and 8, a method of forming a Ni or Ni alloy layer on the Sn layer and then heat treating the plated layer at 220 ° C. for 40 minutes was adopted. For Nos. 2 and 6, a method of heating the substrate to 210 ° C. was adopted when Ni vapor deposition plating was performed on the Sn layer. Sn-Ni formed as an intermediate layer by this treatment
Layer thickness was measured by cross-section EPMA. Further, a commercially available Watt bath was used, and a magnet (Nd14% -B7% -Fe79%) plated with Ni alone at a current density of 8 A / dm ² was prepared as a comparative material.

After subjecting each of the plated test materials to the same magnetizing treatment as in Example 1, cross-section observation and corrosion resistance test were conducted in the same manner. The magnetic properties immediately after the magnetization process were as follows. Residual magnetic flux density (Br) = 12.5 KG Coercive force (iHc) = 12.0 KQe Energy product (BH) _max = 35.0 MGOe

The results are collectively shown in Table 4. However, the method of forming each plating layer in Table 4 is as follows. Sn layer forming method: No. 1-4, 8 (electroplating method: sulfuric acid acidic bath, 2 A / dm ² ), No. 5 to 7 (vapor deposition plating method) Ni (Ni alloy) layer forming method: No. 1, 5 (electroplating method: Watt bath, 8 A / dm ² ), No. 4 (electroplating method: commercially available brightener addition, 8 A / dm ² ), No. 4 2,6
(Evaporation plating method) Ni-P layer forming method: No. No. 3 (electroless plating method: commercial bath), No. 3 7, 8 (electroplating method: commercial bath, 8 A / d
m ² )

[0047]

[Table 4]

As is clear from Table 4, Comparative Example 1
In No. 2 (both Ni-only plated materials), the magnet had cracks at the plating interface, and the appearance and magnetic properties after the corrosion resistance test were clearly deteriorated. On the other hand, Example No. which satisfies the requirements of the invention. 1 to 8 have no such defects. Incidentally, FIGS.
1 and Comparative Example No. 2 is a SEM photograph showing a cross-sectional metallographic structure of each plated material obtained in 1., whereas no cracking of the magnet is observed in the former, whereas in the latter Ni-only plated material,
The magnet is cracked by hydrogen absorption on the plating interface side.

Example 4 Using RE-B-Fe rare earth magnets (magnet Nos. A to D) shown in Table 2 of Example 2 as in Example 3, a composite plating treatment and a magnetizing treatment were performed. Then, a cross-section observation of the plating interface and a corrosion resistance test were performed, and the results shown in Table 5 were obtained. However,
The method of forming each plating layer in Table 5 is as follows. Also, using a commercially available Watt bath, the current density is 8 A / dm ² and N
A single-plated magnet (Nd14% -B7% -Fe79%) was prepared as a comparative material, and the same test was conducted. Sn layer forming method: No. 1 to 5 (electroplating method: sulfuric acid acidic bath, 2 A / dm ² ), No. 6 to 9 (vapor deposition plating method) Ni (Ni alloy) layer forming method: No. 1, 4 (electroplating method: Watt bath, 8 A / dm ² ), No. 2, 7 (electroplating method: commercially available brightener addition, 8 A / dm ² ), No.
5, 6 (vapor deposition plating method) Ni-P layer forming method: No. No. 3, 8 (electroless plating method: commercial bath), No. 9 (electroplating method: commercial bath, 8 A / dm
² )

In addition, in Example No. For 5 and 6, Sn
After forming the layers, the substrate is heated to 210 ° C. and then Ni is deposited and plated to form an intermediate layer. For the other materials, the intermediate layer is formed by heating the plated material at 220 ° C. for 40 minutes after the two-layer plating. Formed.

[0051]

[Table 5]

As is clear from Table 5, Comparative Example 1,
In No. 2 (both Ni-only plated materials), the magnet had cracks at the plating interface, and the appearance and magnetic properties after the corrosion resistance test were clearly deteriorated. On the other hand, Example No. which satisfies the requirements of the invention. 1 to 9 have no such defects. Incidentally, FIGS.
3 and Comparative Example No. 2 is a SEM photograph showing a cross-sectional metallographic structure of each plated material obtained in 1., whereas no cracking of the magnet is observed in the former, whereas in the latter Ni-only plated material,
The magnet is cracked by hydrogen absorption on the plating interface side.

[0053]

The present invention is constructed as described above, and R
A Sn layer is formed as an underlayer on the surface of the EB-Fe rare earth magnet, and a Ni or Ni alloy plating layer is formed thereon, or a metal or alloy nobler than Ni is formed as an intermediate layer therebetween. By forming the layer or the Sn—Ni alloy layer, the corrosion resistance can be remarkably enhanced, and the RE—B—Fe rare earth magnet with high corrosion resistance that maintains excellent magnetic characteristics for a long time can be provided.

[Brief description of drawings]

FIG. 1 is a drawing-substitute SEM photograph showing a cross-sectional metallographic structure at a plating interface portion of a corrosion-resistant rare earth magnet obtained in an example.

FIG. 2 is a drawing-substitute SEM photograph showing a cross-sectional metallographic structure at a plating interface portion of a corrosion resistant rare earth magnet obtained in a comparative example.

FIG. 3 is a drawing-substitute SEM photograph showing a cross-sectional metallographic structure at a plating interface portion of the corrosion-resistant rare earth magnets obtained in Examples.

FIG. 4 is a drawing-substitute SEM photograph showing a cross-sectional metallographic structure at a plating interface portion of the corrosion-resistant rare earth magnet obtained in Comparative Example.

Claims (4)

[Claims] 1. A RE-B-Fe-based sintered rare earth magnet or a RE-TM-B 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). A highly corrosion-resistant rare-earth magnet having a multi-layered metal coating layer, the lowermost layer of which is Sn and the surface layer of which is made of Ni or a Ni alloy. 2. The metal coating layer comprises a Sn layer and Ni or Ni.
The highly corrosion-resistant rare-earth magnet according to claim 1, which is composed of a metal nobler than Ni or an alloy layer of the metal formed between them in addition to the alloy layers. 3. The metal coating layer comprises a Sn layer and Ni or Ni.
The highly corrosion-resistant rare earth magnet according to claim 1, comprising an Sn-Ni alloy layer formed between the alloy layers, in addition to the alloy layers. 4. A Sn layer, then Ni or Ni, on the surface of a RE-B-Fe based sintered rare earth magnet or a RE-TM-B based hot-worked rare earth magnet (RE and TM have the same meanings as before).
A high corrosion resistance rare earth magnet characterized in that after sequentially forming alloy layers, these are heat-treated at a temperature lower than the melting point of Sn to form a Sn—Ni based alloy layer between the Sn layer and Ni or Ni alloy layer. Manufacturing method.