JP4506306B2 - Corrosion-resistant rare earth permanent magnet and method for producing the same - Google Patents

Description

  The present invention relates to a corrosion-resistant rare earth permanent magnet and a method for producing the same.

Rare earth permanent magnets such as R-Fe-B permanent magnets typified by Nd-Fe-B permanent magnets have high magnetic properties and are used in various fields today. However, rare earth permanent magnets contain a rare earth element: R, which is susceptible to oxidative corrosion in the atmosphere. Therefore, when used without surface treatment, corrosion progresses from the surface due to the influence of slight acid, alkali, moisture, etc., and rust is generated, resulting in deterioration and dispersion of magnetic properties. It will be. Furthermore, when rust is generated in a magnet incorporated in a device such as a magnetic circuit, the rust may be scattered and contaminate peripheral components. Therefore, in view of the above points, for the purpose of imparting corrosion resistance to the rare earth-based permanent magnet, an Al film as a corrosion-resistant film is formed on the surface by a vapor deposition method such as a vacuum deposition method, an ion plating method, or a sputtering method. To be formed. In addition to being excellent in corrosion resistance and mass productivity, the Al coating has excellent adhesion reliability with the adhesive required at the time of component assembly. Therefore, it is widely applied to rare earth permanent magnets that require strong adhesive strength.
By the way, recently, the field of use of rare earth permanent magnets has been expanding, and along with this, the corrosion resistance required of magnets has become increasingly severe and diversified. Therefore, even an Al coating having excellent corrosion resistance is desired to be improved in high temperature and high humidity resistance, salt spray resistance, acid rain resistance, and the like. However, the Al film formed by the vapor deposition method has its surface oxidized and covered with a passive film due to the characteristics of a metal called Al, but when the passive film on the surface of the Al film is damaged, From there, the corrosion proceeds toward the surface of the magnet (pitting corrosion), and eventually the corrosion reaches the surface of the magnet. In addition, an Al film formed by vapor phase epitaxy sometimes has a defect portion such as a part where the film does not exist or a thin part with a spread of several tens of μm due to generation and lack of droplets (molten particles). However, the occurrence of pitting corrosion is further promoted in the Al film in which this occurs. Although the corrosion resistance of the Al coating formed by today's technology is very good, such corrosion can always occur. Therefore, unless the solution is established, the corrosion resistance of the Al coating should be improved. I can't.
As a solution to the above problems, as a method for reinforcing and supplementing the corrosion resistance of the Al coating, for example, the surface modification of the Al coating is performed by a chemical conversion treatment reaction described in Patent Document 1. There are aluminum-chromate treatment methods that can be used. However, this method uses a treatment liquid containing hexavalent chromium and fluorine ions, which is undesirable for the environment and the human body, and forms a chromate film while etching the surface of the Al film with fluorine ions. Since the chromate film incorporates hexavalent chromium contained in the treatment solution, there are concerns about adverse effects on the environment and the human body, as well as the problem of complicated waste liquid treatment. is there. Therefore, this method is not necessarily a desirable method today. In addition, since the chromate film is a reactive film by a chemical conversion treatment reaction on the surface of the Al film, it is difficult to increase the film thickness. There is a problem in that the portion cannot be sufficiently sealed to reinforce and supplement the corrosion resistance. Therefore, an excellent solution that can replace the aluminum-chromate treatment method is desired.
Japanese Examined Patent Publication No. 6-66173

  Accordingly, an object of the present invention is to provide a corrosion-resistant rare earth permanent magnet in which the occurrence of pitting corrosion in an Al coating is suppressed while ensuring excellent adhesion reliability and the corrosion resistance is improved, and a method for producing the same. .

  As a result of various studies in view of the above points, the present inventor has performed a substitution treatment of the surface of the Al coating formed on the surface of the rare earth-based permanent magnet with Zn and / or Sn, and then trivalent as a constituent component. By forming a chemical treatment film containing chromium and carbon and free of hexavalent chromium, it suppresses the occurrence of pitting corrosion of the Al film while ensuring excellent adhesion reliability without adversely affecting the environment and the human body. It was found that the corrosion resistance can be improved.

The corrosion-resistant rare earth-based permanent magnet of the present invention based on the above knowledge is obtained by forming an Al film having a thickness of 3 μm to 25 μm on the surface of the sintered magnet by vapor phase growth as described in claim 1. The surface is subjected to a substitution treatment with Zn and / or Sn, and then a trivalent chromium and carbon are contained as constituent components to form a hexavalent chromium-free chemical conversion coating film.
The corrosion-resistant rare earth permanent magnet according to claim 2 is the corrosion-resistant rare earth permanent magnet according to claim 1, wherein the chemical conversion coating is further selected from Co, Mo, W, Ti, Zr, Mn, and Fe as constituent components. It comprises at least one metal component.
The corrosion-resistant rare earth permanent magnet according to claim 3 is the corrosion-resistant rare earth permanent magnet according to claim 1 or 2, wherein the surface of the Al coating is replaced with Zn and / or Sn between the Al coating and the chemical conversion coating. It has a substitution processing layer based on processing.
The corrosion-resistant rare earth-based permanent magnet according to claim 4 is the corrosion-resistant rare earth-based permanent magnet according to claim 3, wherein the substitution treatment layer is made of (1) Zn and / or Sn and (2) Fe, Ni, Co, Cu. It comprises at least one metal component selected.
Further, the corrosion-resistant rare earth-based permanent magnet according to claim 5 is the corrosion-resistant rare earth-based permanent magnet according to any one of claims 1 to 4, wherein the chemical conversion treatment film has a thickness of 0.01 μm to 1 μm. To do.
The method for producing a corrosion-resistant rare earth-based permanent magnet according to the present invention includes the step of forming an Al film having a thickness of 3 μm to 25 μm on the surface of the sintered magnet by vapor phase epitaxy as described in claim 6. After the substitution treatment with Zn and / or Sn, a hexavalent chromium-free chemical conversion coating film containing trivalent chromium and carbon as constituent components is formed.
The manufacturing method according to claim 7 is the manufacturing method according to claim 6, wherein the chemical conversion coating film further comprises at least one metal component selected from Co, Mo, W, Ti, Zr, Mn, and Fe as a constituent component. It is characterized by comprising.
The manufacturing method according to claim 8 is the replacement processing layer according to claim 6 or 7, wherein a layer thickness of 0.05 μm to 5 μm on the surface of the Al coating is based on a replacement treatment with Zn and / or Sn. Then, a chemical conversion treatment film is formed on the surface.
The manufacturing method according to claim 9 is the manufacturing method according to claim 8, wherein the substitution treatment layer is at least one selected from (1) Zn and / or Sn and (2) Fe, Ni, Co, Cu. It comprises a metal component.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the pitting corrosion of Al film can be suppressed, and the corrosion resistance can be improved, and the manufacturing method can be provided, ensuring the outstanding adhesion reliability.

  In the method for producing a corrosion-resistant rare earth permanent magnet according to the present invention, the Al film may be formed on the surface of the magnet by any method, but both the rare earth permanent magnet and the Al film are susceptible to oxidative corrosion. In view of having this, it is desirable to carry out by vapor phase growth. Examples of the vapor phase growth method include a vacuum deposition method, an ion plating method, a sputtering method, and the like. It is desirable to adopt a plating method. The formation conditions of the Al coating may be in accordance with general conditions in the method employed. Needless to say, a known cleaning process such as washing, degreasing, and sputtering may be performed on the surface of the magnet before forming the Al film. The film thickness of the Al coating is desirably 3 μm to 25 μm, and more desirably 5 μm to 20 μm. If the film thickness is less than 3 μm, the corrosion resistance of the Al coating may not be improved because the Al coating is dissolved during the subsequent substitution treatment with Zn and / or Sn on the surface of the Al coating. On the other hand, if the film thickness exceeds 25 μm, it may take a long time to form the Al film, which may result in inferior productivity and may make it difficult to secure the effective volume of the magnet. . The Al coating may be an alloy coating with Cu, Mg or the like mainly composed of Al. Moreover, the metal which cannot avoid mixing may be contained as an impurity.

  The substitution treatment with Zn and / or Sn on the surface of the Al coating may be a known zinc substitution treatment, tin substitution treatment, tin / zinc substitution treatment, or the like. Examples of the treatment liquid used for the substitution treatment with Zn and / or Sn include those containing Zn ions and / or Sn ions and having a pH adjusted to 11 to 14 with an alkali such as sodium hydroxide. The treatment liquid may contain at least one metal ion selected from Fe ions, Ni ions, Co ions, and Cu ions in order to improve the surface coverage of the Al coating. The preparation of such a treatment liquid includes, for example, an aqueous sodium hydroxide solution containing zinc oxide and / or tin oxide, and at least one metal salt selected from ferric chloride, nickel sulfate, cobalt sulfate and copper sulfate. It may be performed by dissolving (such a treatment liquid is also commercially available: for example, trade names AZ301 and AZ401 manufactured by Uemura Kogyo Co., Ltd.). The concentration of these metal ions in the treatment liquid is preferably 1 g / L to 150 g / L as the total metal ion concentration in order to cause a substitution reaction on the surface of the Al coating uniformly, and 5 g / L to 100 g / L. Is more desirable. Various additives may be added to the treatment liquid for the purpose of stabilizing the treatment liquid.

  The substitution treatment of the surface of the Al coating with Zn and / or Sn is, for example, at least one selected from (1) Zn ions and / or Sn ions and (2) Fe ions, Ni ions, Co ions, and Cu ions. What is necessary is just to immerse the rare earth-based permanent magnet in which the Al film is formed on the surface of the magnet in the treatment liquid containing the metal ions. By doing this, the passive film formed on the surface of the Al film is peeled off, and metal ions are substituted and deposited on the newly exposed active surface. (1) Zn and / or Sn and (2) Fe A substitution treatment layer containing at least one metal component selected from Ni, Co and Cu is formed. At this time, the temperature of the treatment liquid is desirably room temperature to 50 ° C. If the temperature of the treatment liquid is lower than room temperature, it may be difficult to cause a substitution reaction on the surface of the Al coating uniformly. On the other hand, if the temperature of the treatment liquid is higher than 50 ° C., the substitution reaction may occur drastically. Therefore, it may be difficult to form a uniform replacement treatment layer. The processing time is preferably 5 seconds to 300 seconds. If the treatment time is less than 5 seconds, the substitution treatment layer may not be sufficiently formed. On the other hand, if the treatment time is more than 300 seconds, the dissolution of the Al coating proceeds, and in some cases, the surface of the magnet is exposed. Corrosion of the magnet may occur or it may be difficult to form a uniform replacement treatment layer. Since the component constituting the substitution treatment layer can be deposited on the surface of the substitution treatment layer thus formed, the substitution treatment layer thus formed can be thickened unlike the chromate film. Even if there is a defective part due to generation and loss of droplets in the Al coating, the sealing effect on the part is excellent. Needless to say, a known cleaning process such as cleaning, degreasing, or sputtering may be performed on the surface of the Al film before the replacement process with Zn and / or Sn on the surface of the Al film. In addition, after degreasing the surface of the Al coating with an organic solvent such as ethanol, degreasing with an alkaline solution containing sodium phosphate or sodium carbonate and a surfactant, and further adding sodium phosphate, sodium carbonate and sodium hydroxide. Etching with an alkaline solution that is contained may be followed by dipping in an aqueous nitric acid solution or an aqueous sulfuric acid solution to remove smut. Further, if the surface of the substitution treatment layer once formed is lightly etched with nitric acid and then the substitution treatment layer is formed again, a uniform substitution treatment layer can be formed on the surface of the Al coating.

  The thickness of the substitution treatment layer thus formed is desirably 0.05 μm to 5 μm. If the layer thickness is less than 0.05 μm, the surface of the Al coating formed on the surface of the rare earth-based permanent magnet in the next step contains trivalent chromium and carbon as constituent components with excellent adhesion, and hexavalent chromium. There is a risk that it is difficult to form a free chemical conversion coating, and if there are minute pinholes in the Al coating, the pinhole cannot be covered with the substitution processing layer, thereby improving the corrosion resistance of the Al coating. On the other hand, when the layer thickness exceeds 5 μm, the strength of the substitution treatment layer is lowered, and the substitution treatment layer may not be able to fully perform its function. The layer thickness of the substitution treatment layer can be adjusted by the treatment time (immersion time in the treatment liquid) and the number of treatments (number of immersion in the treatment liquid) in addition to the temperature and pH of the treatment liquid.

  The formation of a hexavalent chromium-free chemical conversion coating containing trivalent chromium and carbon as constituent components after the surface of the Al coating is replaced with Zn and / or Sn is, for example, (1) Nitrate and sulfate, etc. and (2) succinic acid, malic acid, malonic acid, oxalic acid and other carboxylic acids and their salts (sodium salt, potassium salt, etc.) dissolved in water and treated with Al coating By immersing a rare earth-based permanent magnet formed with a substitution treatment layer based on the substitution treatment with Zn and / or Sn on the surface of the surface, treatment based on pH fluctuation caused by elution of Zn and Sn contained in the substitution treatment layer The trivalent chromium ions that form a stable complex with the carboxylic acid in the liquid may be liberated, and trivalent chromium hydroxide may be generated and deposited on the surface of the substitution treatment layer. The chemical conversion film formed in this way contains carbon derived from a carboxylic acid present in the form of a salt with trivalent chromium in the film as a constituent component. Moreover, the chemical conversion treatment film thus formed may further contain at least one metal component selected from Co, Mo, W, Ti, Zr, Mn, and Fe as a constituent component. Such a metal component forms a salt that is hardly soluble or insoluble in free carboxylic acid and water, so that it is included in the chemical conversion coating in the form of a carboxylate salt, and sometimes Zn or Sn included in the substitution processing layer. It is included in the chemical conversion treatment film as a metal crystal that precipitates due to the substitution reaction with, thereby contributing to the thickening of the chemical conversion treatment film. In addition, the generation of such a carboxylate salt also contributes to the thickening of the chemical conversion coating film by promoting the generation and deposition of a hydroxide of trivalent chromium on the surface of the substitution processing layer. In addition to trivalent chromium and carbon as constituent components, at least one metal component selected from Co, Mo, W, Ti, Zr, Mn, Fe is included, and the formation of the hexavalent chromium-free chemical conversion coating film is, for example, (1) Trivalent chromium nitrates and sulfates, etc. (2) Carboxylic acids such as succinic acid, malic acid, malonic acid, oxalic acid and their salts (sodium salts, potassium salts, etc.) and (3) Co, Mo , W, Ti, Zr, Mn, Fe, a rare earth system in which a substitution treatment layer based on substitution treatment with Zn and / or Sn on the surface of the Al coating is formed in a treatment solution prepared by dissolving nitrate or sulfate in water What is necessary is just to immerse a permanent magnet. The pH of the treatment liquid is desirably 1 to 5, and more desirably 3 to 4.5. If the pH is less than 1, the formation and deposition efficiency of trivalent chromium hydroxide on the surface of the substitution treatment layer may be reduced. On the other hand, if the pH exceeds 5, the trivalent chromium carboxylic acid in the treatment solution If the stability of the complex decreases, the stability of the treatment liquid itself may decrease. The temperature of the treatment liquid is preferably 10 ° C to 80 ° C, and more preferably 25 ° C to 40 ° C. If the temperature is lower than 10 ° C, the formation and deposition efficiency of the trivalent chromium hydroxide on the surface of the substitution treatment layer may be reduced. On the other hand, if the temperature is higher than 80 ° C, the chemical conversion treatment reaction may occur extremely. In addition to the possibility of forming a uniform chemical conversion treatment film, the evaporation of water from the treatment liquid becomes prominent, the composition of the treatment liquid tends to fluctuate, and stable operation may be difficult. The processing time is preferably 5 seconds to 300 seconds. Various additives may be added to the treatment liquid for the purpose of stabilizing the treatment liquid.

  The chemical conversion coating thus formed is a reactive coating by a chemical conversion reaction on the surface of the substitution treatment layer based on the substitution treatment with Zn and / or Sn on the surface of the Al coating, but itself is hardly soluble in water. Yes, it has the property of being less susceptible to corrosion over time and less susceptible to corrosion. Further, the chemical conversion treatment film thus formed is excellent in homogeneity by being formed on the surface of the substitution treatment layer based on the substitution treatment with Zn and / or Sn on the surface of the Al coating. Therefore, this chemical conversion coating film combines these characteristics and imparts excellent corrosion resistance to the rare earth permanent magnet. Moreover, since the surface has moderate roughness, it has excellent adhesion reliability based on the anchor effect. Even if a defect occurs in the chemical conversion coating film, in addition to the chemical conversion coating film having a self-repairing action, the Al coating surface is replaced with Zn and / or Sn. Since the sacrificial anticorrosive action is added to the surface, the corrosion of the rare earth permanent magnet can be effectively prevented.

  The film thickness of the chemical conversion film thus formed is desirably 0.01 μm to 1 μm. If the film thickness is less than 0.01 μm, it may not contribute to the improvement of the corrosion resistance of the Al coating formed on the surface of the magnet. On the other hand, if the film thickness exceeds 1 μm, the trivalent chromium in the treatment liquid is formed during the formation process. If the concentration of ions greatly fluctuates, stable production over a long period of time may be difficult. The film thickness of the chemical conversion coating can be adjusted by the treatment time (immersion time in the treatment liquid) and the number of treatments (number of immersion in the treatment liquid) in addition to the temperature and pH of the treatment liquid. This chemical conversion coating is formed by a chemical conversion reaction on the surface of the substitution treatment layer based on the substitution treatment with Zn and / or Sn on the surface of the Al coating. Or by immersing the rare earth-based permanent magnet in which the substitution treatment layer based on the substitution treatment with Sn is immersed in the treatment liquid, the substitution treatment layer is dissolved and apparently formed directly on the surface of the Al coating; In some cases, the substitution treatment layer is not completely dissolved and remains on the surface of the Al coating via the substitution treatment layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to this and is not interpreted. In the following examples, as described in, for example, US Pat. No. 4,770,723 and US Pat. No. 4,792,368, a known cast ingot is pulverized, and after fine pulverization, molding, sintering, heat treatment, surface processing This was performed using a sintered magnet (hereinafter referred to as a magnet specimen) having a size of 27 mm in length, 15 mm in width, and 2 mm in height having a 17Nd-1Pr-75Fe-7B composition (at%) obtained by performing the above.

Experiment A: Production process of corrosion-resistant rare earth-based permanent magnet 1: Formation of Al coating on the surface of a magnet specimen A magnet body in a processing chamber (vacuum chamber) of a known surface treatment apparatus (internal volume 2.2 m ³ ) After accommodating the test piece, the test piece was evacuated until the total internal pressure became 1.0 × 10 ⁻¹ Pa. Thereafter, Ar gas was introduced into the vacuum chamber so that the total pressure was 1.0 MPa, and sputtering was performed to clean the surface of the magnet specimen. Thereafter, a voltage of 1.5 kV is applied to the magnet test piece, the Al wire is heated and melted, evaporated and ionized, and an Al coating with a thickness of 20 μm is formed on the surface by an ion plating method in 20 minutes. Formed (average value of N = 3).

Step 2: Zinc replacement treatment on the surface of the Al coating The surface of the Al coating formed on the surface of the magnet specimen in Step 1 is smoothed by performing a peening treatment known per se, and then degreased with ethanol as a pretreatment. Then, the zinc replacement treatment of the surface of the Al coating was performed by immersing the magnet test piece having the Al coating formed on the surface under five kinds of conditions in a zinc replacement treatment solution. The zinc replacement treatment liquid used was such that the zinc oxide concentration was 100 g / L, the ferric chloride concentration was 10 g / L, the Rochelle salt concentration was 10 g / L, and the sodium hydroxide concentration was 525 g / L. Each component was prepared by dissolving in water (pH 11.8, the total concentration of Zn ions and Fe ions in the zinc substitution treatment solution was 83.7 g / L). The obtained results (Sample 1 to Sample 5) are shown in Table 1.

  As is clear from Table 1, it was found that the layer thickness of the zinc-substituted treatment layer can be controlled by changing the treatment time. The thickness of the zinc substitution treatment layer is determined by breaking the sample before and after the formation of the zinc substitution treatment layer and detecting zinc (ZnKα) using EPMA (EPM-810: manufactured by Shimadzu Corporation, the same shall apply hereinafter). Measured (average value of N = 3). In addition, it was confirmed that the zinc substitution treatment layer contained iron by breaking the sample before and after the formation of the zinc substitution treatment layer and detecting iron (FeKα) using EPMA.

Step 3: Production of corrosion-resistant rare earth-based permanent magnets by forming a chemical conversion coating film Sample 1, sample 2, and sample 3 obtained in step 2 are each immersed in a treatment solution under three types of conditions to replace zinc. A chemical conversion coating was formed on the surface of the treatment layer. The treatment liquid used was a chromium (III) nitrate concentration of 25 g / L, a cobalt nitrate concentration of 3 g / L, a copper sulfate pentahydrate concentration of 0.004 g / L, and a silver nitrate concentration of 0.05 g / L. Each component was dissolved in water so that the concentration of L, sodium nitrate was 2 g / L, and the concentration of succinic acid was 20 g / L, and the pH was adjusted to 4 with sodium hydroxide. The obtained results (Examples 1 to 9) are shown in Table 2.

  As is clear from Table 2, in all of Examples 1 to 9, three films having a film thickness of 0.01 μm to 0.1 μm were formed on the surface of the zinc substitution treatment layer from the treatment liquid containing trivalent chromium ions. A chemical conversion coating containing hexavalent chromium and free of hexavalent chromium could be formed. The film thickness of the chemical conversion coating was measured by breaking the sample before and after the chemical conversion coating was formed and detecting chromium (CrKα) using EPMA. In addition, the sample before and after the formation of the chemical conversion coating is broken, and EPMA is used to detect cobalt (CoKα). By detecting carbon (CKα), the chemical conversion coating contains cobalt. It was confirmed that the chemical conversion coating film contained carbon. In addition, in the corrosion-resistant rare earth-based permanent magnets manufactured in Examples 1 to 3, since the layer thickness of the zinc substitution treatment layer formed in Step 2 is thin, the zinc substitution treatment layer is dissolved after the chemical conversion treatment film is formed. In the corrosion-resistant rare earth permanent magnets manufactured in Examples 4 to 9, the thickness of the zinc substitution treatment layer formed in Step 2 was so thick that the chemical conversion treatment film was formed. It was confirmed that the zinc substitution treatment layer remained by breaking the sample before and after the formation of the chemical conversion coating and detecting zinc (ZnKα) using EPMA.

Experiment B: Evaluation of Corrosion Resistance of Produced Corrosion Resistant Rare Earth Permanent Magnets After the formation of an Al film on the surface produced in Examples 1 to 9 of Experiment A, the surface was subjected to a zinc substitution treatment and then a chemical conversion treatment film Corrosion resistance was evaluated by performing a salt spray test described in JIS Z 2371 for 1000 hours on a magnet body test piece (corrosion-resistant rare earth permanent magnet) formed by forming a film. The result is a magnetic specimen (Comparative Example 1) in which an Al film having a film thickness of 20 μm is formed on the surface obtained in Step 1 of Experiment A, and Sample 1, Sample 2 and Sample obtained in Step 2 of Experiment A. 3 and according to the method described in Japanese Patent Application Laid-Open No. 2000-150216, a magnetic body test piece in which an Al film having a film thickness of 20 μm was formed on the surface obtained in Step 1 of Experiment A was obtained from Palcoat 3756MA manufactured by Nihon Parkerizing Co., Ltd. A magnet test piece (Comparative Example 2) in which a zirconium-containing chemical conversion coating was formed on the surface of an Al coating by immersion in a processing solution prepared using PALCOAT 3756MB, and a film thickness on the surface obtained in Step 1 of Experiment A Is immersed in a treatment solution prepared using Asa Roof 600N manufactured by Nippon Paint Co., Ltd., and a hexavalent cup is formed on the surface of the Al film. Shown in Table 3 together with the results of the evaluation of corrosion resistance of the magnet test piece obtained by forming a chromate coating (Comparative Example 3) containing the beam.

  As apparent from Table 3, in the salt spray test, in Comparative Example 1, the occurrence of pitting corrosion was noticeable after the lapse of 24 hours from the start of the test, leading to the occurrence of red rust on the entire surface. In Sample 1, Sample 2, and Sample 3, white rust was generated by elution of zinc after 24 hours from the start of the test, and red rust was generated on the entire surface after 100 hours. In Comparative Example 2, the occurrence of pitting corrosion and spot rust began to be noticeable after 100 hours had elapsed from the start of the test, and the entire surface reached red rust after 250 hours had elapsed. In Comparative Example 3, although generation of white rust due to elution of zinc was recognized in part, red rust was not generated on the entire surface even after 1000 hours had elapsed from the start of the test. In the corrosion-resistant rare earth permanent magnets manufactured in Examples 1 to 3, the zinc substitution treatment layer formed in Step 2 is thin, so the zinc substitution treatment layer is dissolved after the chemical conversion coating is formed. Although hardly remained, white rust was generated due to elution of zinc after 100 hours from the start of the test, but no red rust was generated even after 1000 hours from the start of the test. In the corrosion-resistant rare earth-based permanent magnets manufactured in Examples 4 to 9, generation of white rust due to elution of zinc was recognized in part, but no red rust was generated even after 1000 hours from the start of the test. . Therefore, it was found that any of the corrosion-resistant rare earth permanent magnets manufactured in Examples 1 to 9 has extremely excellent corrosion resistance in practical use. In addition, any of the corrosion-resistant rare earth permanent magnets manufactured in Examples 1 to 9 had excellent adhesion reliability after the test was completed (confirmed by evaluation of adhesion reliability with the epoxy adhesive).

Experiment C: Evaluation of Pitting Corrosion Resistance in Severe Environment of Produced Corrosion Resistant Rare Earth Permanent Magnet After forming Al coating on the surface produced in Examples 4 to 9 of Experiment A, the surface was subjected to zinc substitution treatment Then, pitting corrosion resistance was evaluated by a supersaturated high-temperature and high-pressure test (PCT: Pressure Cooker Test) for a magnet specimen (corrosion-resistant rare earth permanent magnet) formed with an inorganic coating that is hardly soluble or insoluble in water. Evaluation of pitting corrosion resistance was performed by using a pressure cooker tester (TPC-411: manufactured by Tabai Co., Ltd.) and leaving it for 12 hours under the conditions of temperature 120 ° C. × relative humidity 98% or more × pressure 0.2 MPa. The result is a magnetic specimen (Comparative Example 1) in which an Al film having a film thickness of 20 μm is formed on the surface obtained in Step 1 of Experiment A, and Sample 1, Sample 2 and Sample obtained in Step 2 of Experiment A. 3 and according to the method described in Japanese Patent Application Laid-Open No. 2000-150216, a magnetic body test piece in which an Al film having a film thickness of 20 μm was formed on the surface obtained in Step 1 of Experiment A was obtained from Palcoat 3756MA manufactured by Nihon Parkerizing Co., Ltd. A magnet specimen (Comparative Example 2) in which a zirconium-containing chemical conversion coating was formed on the surface of an Al coating by immersing it in a processing solution prepared using Palcoat 3756MB, and a film thickness on the surface obtained in Step 1 of Experiment A Is immersed in a treatment solution prepared using Asa Roof 600N manufactured by Nippon Paint Co., Ltd., and a hexavalent cup is formed on the surface of the Al film. Shown in Table 4 together with the results of the evaluation of pitting corrosion resistance of the magnet test piece obtained by forming a chromate coating (Comparative Example 3) containing the beam.

  As is apparent from Table 4, in Comparative Examples 1 to 3 and Sample 1, the occurrence of a large number of pitting corrosion was observed after the test was completed. In Sample 2 and Sample 3, no pitting corrosion was observed, but many white rusts were observed. In the corrosion-resistant rare earth permanent magnets manufactured in Examples 4 to 9, no pitting corrosion was observed after completion of the test, and the pitting corrosion resistance was extremely excellent in practical use. In addition, any of the corrosion-resistant rare earth permanent magnets manufactured in Examples 4 to 9 had excellent adhesion reliability after the test was completed (confirmed by evaluation of adhesion reliability with the epoxy adhesive).

  INDUSTRIAL APPLICABILITY The present invention provides an anti-corrosion rare earth permanent magnet in which the corrosion resistance is improved by suppressing the occurrence of pitting corrosion in an Al coating while ensuring excellent adhesion reliability, and an industrial method in that it can be provided. With the above applicability.

Claims (9)

After forming an Al film having a film thickness of 3 μm to 25 μm on the surface of the sintered magnet by vapor deposition , the surface is subjected to a substitution treatment with Zn and / or Sn, and then trivalent chromium and carbon as constituent components. A corrosion-resistant rare earth-based permanent magnet comprising a chemical conversion coating film free of hexavalent chromium.   2. The corrosion-resistant rare earth permanent magnet according to claim 1, wherein the chemical conversion coating further comprises at least one metal component selected from Co, Mo, W, Ti, Zr, Mn and Fe as a constituent component.   The corrosion-resistant rare earth permanent magnet according to claim 1 or 2, wherein a substitution treatment layer based on substitution treatment with Zn and / or Sn on the surface of the Al coating is provided between the Al coating and the chemical conversion coating. .   4. The corrosion-resistant rare earth-based permanent material according to claim 3, wherein the substitution treatment layer comprises (1) Zn and / or Sn and (2) at least one metal component selected from Fe, Ni, Co, Cu. magnet.   The corrosion-resistant rare earth-based permanent magnet according to any one of claims 1 to 4, wherein the chemical conversion coating has a thickness of 0.01 µm to 1 µm. After forming an Al film having a film thickness of 3 μm to 25 μm on the surface of the sintered magnet by vapor deposition , the surface is subjected to a substitution treatment with Zn and / or Sn, and then trivalent chromium and carbon as constituent components. And a hexavalent chromium-free chemical conversion coating is formed. A method for producing a corrosion-resistant rare earth permanent magnet.   The production method according to claim 6, wherein the chemical conversion coating further comprises at least one metal component selected from Co, Mo, W, Ti, Zr, Mn, and Fe as a constituent component.   A chemical conversion treatment film is formed on a surface of an Al coating film after forming a substitution treatment layer having a thickness of 0.05 μm to 5 μm based on a substitution treatment with Zn and / or Sn. Item 8. The manufacturing method according to Item 6 or 7.   9. The manufacturing method according to claim 8, wherein the substitution treatment layer comprises (1) Zn and / or Sn and (2) at least one metal component selected from Fe, Ni, Co, and Cu.