JP5056267B2 - Rare earth permanent magnet having Al coating containing Mg on its surface and method for producing the same - Google Patents

Description

  The present invention relates to a rare earth permanent magnet excellent in salt water resistance and a method for producing the same. More particularly, the present invention relates to a rare earth permanent magnet having an Al coating containing Mg that exhibits excellent salt water resistance on the surface and a method for producing the same.

Rare earth permanent magnets such as R—Fe—B permanent magnets represented by Nd—Fe—B permanent magnets and R—Fe—N permanent magnets represented by Sm—Fe—N permanent magnets are In particular, R-Fe-B based permanent magnets are used in various fields today because they use abundant and inexpensive materials and have high magnetic properties.
However, since rare earth permanent magnets contain a highly reactive rare earth metal: R, they are susceptible to oxidative corrosion in the atmosphere. When used without any surface treatment, a slight amount of acid, alkali, moisture, etc. Corrosion proceeds from the surface due to the presence of rust, and rust is generated, resulting in deterioration and variation in magnetic properties. Furthermore, when a magnet in which rust is generated is incorporated in an apparatus such as a magnetic circuit, the rust may be scattered to contaminate peripheral components.
In view of the above points, for the purpose of imparting excellent corrosion resistance to a rare earth-based permanent magnet, an Al coating is formed on the surface thereof by a vapor deposition method such as a vapor deposition method. In addition to being excellent in corrosion resistance, the Al coating has excellent adhesion reliability with the adhesive required when assembling the parts (the coating film and adhesive are required to reach the breaking strength inherent in the adhesive). Is widely applied to rare earth permanent magnets that require strong adhesive strength, and rare earth permanent magnets having an Al coating on the surface are used in various motors. Yes.

  Among various motors, rare earth permanent magnets incorporated in motors for automobiles are subject to severe changes in the temperature of the usage environment, and in cold regions, they are exposed to chlorine ions contained in anti-freezing agents sprayed on the road, Since it is exposed to salt water in the vicinity, it can be said that the magnet is in the most severe use environment. Therefore, rare earth permanent magnets incorporated in motors for automobiles are required to exhibit excellent corrosion resistance even in the salt spray test, which is the most severe corrosion resistance test. Not always enough. As a method for improving the salt water resistance of a rare earth permanent magnet having an Al film on its surface, a chemical conversion film is formed on the surface of the Al film (Patent Document 1), or a metal oxide film is formed ( Although the method of patent document 2) can be considered, there still exists a problem that salt water resistance is not enough.

Therefore, one of the inventors of the present invention has proposed a method of depositing an Al coating containing 3 mass% to 10 mass% of Mg on the surface of the magnet as a method for imparting salt water resistance to the rare earth permanent magnet in Patent Document 3.
JP 2000-150216 A JP 2000-233201 A Japanese Patent Laying-Open No. 2005-191276

Although the above-mentioned method proposed by one of the inventors in Patent Document 3 is an excellent method for imparting salt water resistance to rare earth-based permanent magnets, it has been recognized by both others and others. Magnets are required to have further improved salt water resistance.
Therefore, an object of the present invention is to provide a rare earth permanent magnet having an Al coating film containing Mg that exhibits excellent salt water resistance on the surface, and a method for producing the same.

  As a result of intensive studies in view of the above points, the present inventor has formed an Al coating containing Mg on the surface of a rare earth-based permanent magnet in the processing chamber of the vapor deposition apparatus, and then cooled the magnet. The temperature is controlled accurately, and the surface of the obtained rare earth-based permanent magnet film having the Mg-containing Al film on the surface is subjected to a treatment for oxidizing and / or hydroxylating Al and / or Mg in the film. It was found that the coating formed on the surface of the magnet exhibits excellent salt water resistance.

The present invention made on the basis of the above findings is a rare earth permanent magnet having an Al coating film containing Mg on the surface thereof, as described in claim 1, wherein the texture structure of the coating contains Mg as a main component. It consists of a main phase and a Mg-concentrated phase containing Al and Mg and having a Mg concentration higher than the Mg concentration of the main phase, and the Mg concentration of the coating is higher on the outer surface side than on the interface side with the magnet body in the thickness direction. And a layer in which Al and / or Mg is oxidized and / or hydroxylated on the surface on the outer surface side of the coating.
The rare earth permanent magnet according to claim 2 is characterized in that, in the rare earth permanent magnet according to claim 1, the Mg concentration in the vicinity of the interface between the coating and the magnet body is 2 mass% to 10 mass%.
The rare earth permanent magnet according to claim 3 is the rare earth permanent magnet according to claim 1 or 2, wherein the Mg concentration in the vicinity of the interface with the layer in which the Al and / or Mg of the coating is oxidized and / or hydroxylated. Is 15 mass% to 35 mass%.
The rare earth permanent magnet according to claim 4 is the rare earth permanent magnet according to any one of claims 1 to 3, wherein the Mg concentration in the layer in which Al and / or Mg is oxidized and / or hydroxylated is 3 mass. % To 20 mass%.
The rare earth permanent magnet according to claim 5 is the rare earth permanent magnet according to any one of claims 1 to 4, wherein the oxygen concentration of the layer in which Al and / or Mg is oxidized and / or hydroxylated is 5 mass. % To 50 mass%.
The rare earth permanent magnet according to claim 6 is the rare earth permanent magnet according to any one of claims 1 to 5, wherein a layer in which Al and / or Mg is oxidized and / or hydroxylated is further Zr, P. , F, and at least one element selected from the group consisting of F.
The rare earth permanent magnet according to claim 7 is the rare earth permanent magnet according to any one of claims 1 to 6, wherein the layer thickness of the layer in which Al and / or Mg is oxidized and / or hydroxylated is 0. .01 μm to 5 μm.
The rare earth permanent magnet according to claim 8 is the rare earth permanent magnet according to any one of claims 1 to 7, wherein the film thickness is 3 μm to 30 μm.
According to a first aspect of the present invention, there is provided a method for producing a rare earth-based permanent magnet having an Al coating containing Mg on the surface, as described in the ninth aspect, Mg is deposited on the surface of the rare earth-based permanent magnet in the processing chamber of the vapor deposition apparatus. After the deposited Al coating is deposited, the magnet at a high temperature of 160 ° C. or higher is cooled by rapidly cooling at a cooling rate of 10 ° C./min or higher until the temperature of the magnet reaches at least 60 ° C. The surface of the rare earth-based permanent magnet film having an Al film containing selenium is subjected to a treatment for oxidizing and / or hydroxylating Al and / or Mg in the film.
The manufacturing method according to claim 10 is characterized in that in the manufacturing method according to claim 9, rapid cooling is performed by introducing nitrogen gas into the processing chamber.
The manufacturing method according to claim 11 is the manufacturing method according to claim 9 or 10, wherein the treatment for oxidizing and / or hydroxylating Al and / or Mg in the coating is from steam treatment, hydrothermal treatment, and chemical conversion treatment. It is at least one process selected from the group consisting of.

  ADVANTAGE OF THE INVENTION According to this invention, the rare earth-type permanent magnet which has Al film containing Mg which exhibits the outstanding salt water resistance on the surface, and its manufacturing method can be provided.

  In the rare earth-based permanent magnet having an Al coating containing Mg of the present invention on the surface, the Mg concentration of the coating is higher on the outer surface side than the interface with the magnet body in the thickness direction, and on the outer surface side of the coating. The surface has a layer in which Al and / or Mg are oxidized and / or hydroxylated.

  The rare earth-based permanent magnet having an Al coating containing Mg of the present invention on its surface is, for example, deposited at a high temperature of 160 ° C. or higher after depositing an Al coating containing Mg on the surface of the rare-earth permanent magnet in the processing chamber of the vapor deposition apparatus. A certain magnet is cooled by quenching at a cooling rate of 10 ° C./min or more until the temperature of the magnet reaches at least 60 ° C., and the obtained rare-earth permanent magnet coating having an Al coating containing Mg on the surface is obtained. It can be produced by subjecting the surface to a treatment for oxidizing and / or hydroxylating Al and / or Mg in the coating.

  As a vapor deposition apparatus that can be used for carrying out the step of vapor-depositing an Al film containing Mg on the surface of a rare earth-based permanent magnet, for example, a wire-shaped vapor deposition material described in JP-A-2001-32062 is used. A vapor deposition apparatus that forms a vapor-deposited film on the surface of the magnet by evaporating while continuously supplying to the heated melting and evaporating unit is mentioned. Hereinafter, when an Al wire containing Mg is used as a vapor deposition material, a step of vapor-depositing an Al film containing Mg on the surface of a rare earth permanent magnet using a vapor deposition apparatus described in JP-A-2001-32062 is performed. The outline of will be described.

  FIG. 5 is a schematic front view of an example of a vapor deposition apparatus. In a lower part of a processing chamber (vacuum chamber) 1 connected to an unillustrated vacuum exhaust system, a hearth is a melting evaporation unit that evaporates Al10 containing Mg. A plurality of (containers for melting the vapor deposition material) 2 are arranged on a hearth support 4 erected on the support table 3. In addition, two bowl-shaped workpiece holding parts 5 formed of a net-like member are arranged in parallel above the processing chamber 1 so as to be rotatable around a rotation shaft 6. An Al wire 11 containing Mg as a vapor deposition material is wound and held on the supply reel 20 inside the lower side of the support table 3. The winding direction of the Al wire 11 containing Mg on the feeding reel 20 is set to the horizontal direction, and the wire being fed is prevented from being twisted or shaken by being orthogonal to the feeding direction, that is, the vertical direction. It is to do. The tip of the Al wire 11 containing Mg is guided above the hearth 2 by a heat-resistant protective tube 21 facing the inner surface of the hearth 2. A cutout window 22 is provided in a part of the protective tube 21, and a pair of feeding gears 23 provided in correspondence with the cutout window 22 causes the Al wire 11 containing Mg to enter the hearth 2 in a predetermined manner. Feeding is possible at the feeding speed. According to this vapor deposition apparatus, the rare earth permanent magnet 30 is accommodated in the workpiece holder 5, and the workpiece holder 5 is rotated as indicated by the arrow, and the Al wire 11 containing Mg is omitted. An Al coating containing Mg is deposited on the surface of the rare earth permanent magnet 30 in the workpiece holder 5 by evaporating Al10 containing Mg while being continuously supplied to the hearth 2 heated to a predetermined temperature by the heating means. be able to.

  The Mg concentration contained in the Al wire is desirably 3 mass% to 10 mass%. When it is less than 3 mass%, the Mg concentration contained in the Al coating deposited on the surface of the rare earth-based permanent magnet decreases, and it becomes difficult to form a Mg-concentrated phase that contributes to improving the salt water resistance of the Al coating. While there is a possibility that excellent salt water resistance cannot be imparted to the Al coating, if the hardness exceeds 10 mass%, the workability of feeding the wire into the melting and evaporating part deteriorates or the wire is melted in the melting and evaporating part. This is because there is a risk that a non-deposited material may cause splash. If oxygen is present in the processing chamber, the surface of the vapor deposition material or rare earth permanent magnet is oxidized at the stage of melting or evaporating the vapor deposition material, and Al containing Mg with excellent adhesion to the magnet surface. This point should be noted because a film may not be formed.

In view of the above points, it is desirable that the Al wire containing Mg contains hydrogen. When the vapor deposition material is evaporated, hydrogen can be supplied into the processing chamber. Therefore, even if hydrogen is not supplied from the outside of the processing chamber by a separate means, the processing chamber is made a reducing atmosphere, for example, 10 ⁻³ Pa. This is because even under an oxygen partial pressure as described above, it is possible to prevent the vapor deposition material from being oxidized at the melted or evaporated stage. The hydrogen content of the Al wire containing Mg is desirably 1 ppm to 20 ppm, and more desirably 2 ppm to 10 ppm. This is because if it is less than 1 ppm, hydrogen may not be sufficiently supplied into the processing chamber, while if it exceeds 20 ppm, hydrogen may boiler in the melt-evaporating section and cause splash.

  As for the heating temperature of a fusion | melting evaporation part, 1300 to 1500 degreeC is desirable. This is because if it is lower than 1300 ° C., the vapor deposition material may not be efficiently melted. If the vapor deposition material cannot be efficiently melted, the difference between the vapor pressure of Al and the vapor pressure of Mg (Mg has a higher vapor pressure) will greatly affect the metal composition of the deposited Al film. A phenomenon occurs in which the Mg concentration contained in the Al coating is significantly different from the Mg concentration contained in the Al wire, and the Al coating having the intended metal composition may not be formed by vapor deposition. On the other hand, if the temperature exceeds 1500 ° C., the ambient temperature becomes too high and the wire softens and becomes clogged inside the protective tube 21 in FIG. Because there is.

  The feed rate of the Al wire containing Mg to the melt evaporation part is preferably 1 g / min to 10 g / min, and more preferably 2 g / min to 5 g / min. If it is less than 1 g / min, the vapor deposition material may not be efficiently melted, whereas if it exceeds 10 g / min, the amount of the vapor deposition material melted in the melt-evaporating part may increase, causing splash. It is.

  In addition, it is desirable to set the heating temperature of the melt evaporation part and the feed rate of the Al wire containing Mg to the melt evaporation part so that the temperature of the rare earth permanent magnet does not exceed 255 ° C. during the vapor deposition process. This is because if the temperature exceeds 255 ° C., the Al coating formed on the surface of the magnet is softened and film defects are likely to occur.

  When an Al film containing Mg with a desired film thickness is deposited on the surface of a rare earth permanent magnet under the above conditions (the Mg concentration in the Al film is preferably 3 mass% to 20 mass%), the magnet is processed. A high temperature of 160 ° C. or higher, typically 180 ° C. or higher is reached in the room. In the present invention, when the magnet at such a high temperature is cooled in the processing chamber after completion of the vapor deposition step, the magnet is rapidly cooled at a cooling rate of 10 ° C./min or more until the temperature of the magnet reaches at least 60 ° C. Thereby, the structure of the Al coating film containing Mg formed on the surface of the magnet serves as a basis for achieving excellent salt water resistance. The rapid cooling operation can be performed, for example, by introducing nitrogen gas (preferably having a temperature of 15 ° C. or less) into the processing chamber, but is allowed to cool in the atmosphere (preferably 25 ° C. or less). Can also be done. These may be performed in combination. The rapid cooling operation may be performed at a constant cooling rate from the start of the operation to the end of the operation. Further, the cooling rate may be gradually increased or decreased, or a plurality of cooling rates may be adopted to perform the process in multiple stages. In these cases, the “cooling rate of 10 ° C./min or more” in the present invention means an average cooling rate from the start of the operation to the end of the operation. The upper limit of the cooling rate is preferably 100 ° C./min, and more preferably 50 ° C./min. This is because if it exceeds 100 ° C./min, the adhesion of the Al coating formed on the surface of the magnet may be adversely affected.

  When cooling a magnet at a high temperature of 160 ° C. or higher after completion of the vapor deposition process in the processing chamber, the Al coating containing Mg can be rapidly cooled at a cooling rate of 10 ° C./min or higher until the temperature of the magnet reaches at least 60 ° C. , A structure composed of a main phase containing Al as a main component and Mg, and an Mg-concentrated phase containing Al and Mg and having a Mg concentration higher than (for example, three times or more) the Mg concentration of the main phase, specifically, an average Mg enriched in Mg composed of a main phase composed mainly of Al consisting of a crystal phase with a crystal grain size of 100 nm to 2 μm and an amorphous and / or fine crystal texture with an average crystal grain size of 20 nm or less It consists of a concentrated phase, and the Mg concentrated phase has a width of 10 nm to 500 nm and is distributed continuously or intermittently in the thickness direction of the coating from the interface side to the outer surface side with the magnet body, and the main phase is 95 mass% of Al. Including above (0.01 ass% ~5mass% of Mg solid solution), Mg concentrated phase becomes organizational structure including 10mass% ~25mass% of Mg.

  Next, the Al and / or Mg in the coating is oxidized and / or applied to the surface of the coating of the rare earth-based permanent magnet having an Al coating containing Mg with a specific structure obtained on the surface. Or the outline of the process which performs the process which hydroxylates is demonstrated.

This step can be performed, for example, by subjecting the surface of the coating to steam treatment, hot water treatment, chemical conversion treatment, and the like. By this step, Al ₃ Mg ₂ which is considered to constitute the Mg-concentrated phase present in the structure of the Al coating film containing Mg is lower in potential than Al. Is preferentially decomposed by contact with moisture on the surface of the metal and oxidized or hydroxylated. As a result, Al ₂ O ₃ , Al (OH) ₃ , MgO, Mg (OH) _2, etc. are generated and contained. For example, a layer having an oxygen concentration of 5 mass% to 50 mass% (preferably 6 mass% to 45 mass%), a layer thickness of 0.01 μm to 5 μm, and an oxidized and / or hydroxylated layer of Al and / or Mg. It is formed on the surface on the outer surface side. MgO and Mg (OH) ₂ contained in this layer are relatively poorly water-soluble and excellent in salt water resistance. As a result, this layer exhibits excellent salt water resistance. In addition, as described above, Mg in the coating is consumed on the outer surface side of the coating as a result of chemical change and consumption of Mg in the coating. By moving toward the surface of the surface side, the Mg concentration of the coating is larger in the thickness direction than the interface side with the magnet body (the interface with the layer in which Al and / or Mg is oxidized and / or hydroxylated). Side) is higher. For example, the Mg concentration in the vicinity of the interface between the coating and the magnet body is 2 mass% to 10 mass% (preferably 5 mass% to 10 mass%), whereas Al and / or Mg is oxidized and / or hydroxylated. The Mg concentration in the vicinity of the interface is 15 mass% to 35 mass% (“near the interface” means any point in the range of 0.5 μm to 3 μm in the thickness direction from the interface, provided that the magnet of the film is provided). The point near the interface with the body is always located closer to the magnet body in the thickness direction than the point near the interface with the layer in which Al and / or Mg are oxidized and / or hydroxylated, and Al and / or Mg is oxidized and / or Alternatively, the point near the interface with the hydroxylated layer is always more Al and / or in the thickness direction than the point near the interface with the magnet body of the coating. Alternatively, Mg is located on the side of the oxidized and / or hydroxylated layer, and “arbitrary point” means a range within 1 μm in diameter depending on the beam diameter of the measuring device). Such a concentration gradient is continuous or intermittent from the interface side with the magnet body toward the interface side with the layer in which Al and / or Mg is oxidized and / or hydroxylated. Further, the Mg concentration of the layer formed by oxidizing and / or hydroxylating Al and / or Mg formed on the surface on the outer surface side of the coating is, for example, 3 mass% to 20 mass%. The Mg concentration in the vicinity of the interface with the magnet body and the Mg concentration in the vicinity of the interface with the layer in which Al and / or Mg are oxidized and / or hydroxylated are in the middle (for example, 10 mass% to 15 mass%). In this case, the distribution of Mg concentration as a whole of the Al film containing Mg formed on the surface of the rare earth-based permanent magnet and the Al and / or Mg oxidized and / or hydroxylated layer formed on the surface is as follows: From the interface side with the magnet body to the outer surface side, a low region and a high region (Al coating containing Mg), and an intermediate region (a layer in which Al and / or Mg is oxidized and / or hydroxylated) Become. Such three regions having different Mg concentrations may be clearly identified as a three-layer structure by a characteristic X-ray image or the like.

  The steam treatment for forming a layer in which Al and / or Mg is oxidized and / or hydroxylated on the surface on the outer surface side of the coating is, for example, a temperature of 100 ° C. to 150 ° C. (preferably 110 ° C. to 130 ° C.) 1 hour to 50 hours at a relative humidity of 70% RH to 100% RH (desirably 80% RH to 90% RH) and a pressure of 0.1 MPa to 0.5 MPa (desirably 0.15 MPa to 0.25 MPa). (Preferably 10 hours to 30 hours) It may be performed under conditions for treating a rare earth permanent magnet having an Al film containing Mg deposited on the surface. If the conditions of the water vapor treatment are too mild, there is a risk that a layer with sufficient layer thickness of Al and / or Mg oxidized and / or hydroxylated to exhibit excellent salt water resistance on the outer surface side of the coating may not be formed. On the other hand, if the conditions of the water vapor treatment are too severe, the layer thickness of the layer in which Al and / or Mg is oxidized and / or hydroxylated becomes too thick, causing cracks on the surface or peeling. Therefore, there is a possibility that excellent salt water resistance cannot be exhibited.

  The hydrothermal treatment for forming a layer in which Al and / or Mg is oxidized and / or hydroxylated on the surface on the outer surface side of the coating is, for example, 70 ° C. to 95 ° C. (preferably 80 ° C. to 90 ° C.) What is necessary is just to give the rare earth-type permanent magnet which vapor-deposited the Al film containing Mg on the surface for 10 minutes to 120 minutes (desirably 30 minutes to 90 minutes) in pure water (ion exchange water) at a temperature. . If the conditions of the hydrothermal treatment are too mild, a layer in which Al and / or Mg are oxidized and / or hydroxylated with sufficient layer thickness to exhibit excellent salt water resistance on the outer surface side of the coating will not be formed. On the other hand, if the conditions of hydrothermal treatment are too severe, the layer thickness of the oxidized and / or hydroxylated layer of Al and / or Mg will be too thick, causing cracks on the surface or peeling. There is a possibility that the excellent salt water resistance cannot be exhibited.

  The chemical conversion treatment for forming a layer in which Al and / or Mg is oxidized and / or hydroxylated on the surface on the outer surface side of the coating is roughly divided into a chromate chemical conversion treatment and a non-chromate chemical conversion treatment. Either may be sufficient. Examples of the chromate chemical conversion treatment include known chemical conversion treatments such as hexavalent chromate chemical conversion treatment containing hexavalent chromium and trivalent chromate chemical conversion treatment containing trivalent chromium without containing hexavalent chromium. The hexavalent chromate conversion treatment can be performed using, for example, Alsurf 600N manufactured by Nippon Paint Co., Ltd. The trivalent chromate conversion treatment can be performed using, for example, Palcoat 3700 manufactured by Nippon Parkerizing Co., Ltd. As the non-chromate chemical conversion treatment, for example, in addition to the zirconium phosphate chemical conversion treatment described in the above-mentioned Patent Document 1, the zirconium acid chemical conversion treatment, the zirconium-titanic acid chemical conversion treatment, the zinc phosphate chemical conversion treatment itself, etc. A known chemical conversion treatment may be mentioned. In the non-chromate chemical conversion treatment, a metal salt having a multivalent valence, for example, Zr, Ti, Mn, is expected in the hope that the same action as the self-repairing action of hexavalent chromium in the hexavalent chromate chemical conversion treatment is expected. A salt such as zirconium phosphate is preferable from the viewpoint of reactivity with Al and film adhesion. The zirconium phosphate chemical conversion treatment can be performed using, for example, Palcoat 3756 manufactured by Nippon Parkerizing Co., Ltd. In this case, the layer formed by oxidizing and / or hydroxylating Al and / or Mg formed on the surface on the outer surface side of the coating further contains elements such as Zr, P, and F.

  The film thickness of the Al coating containing Mg formed on the surface of the rare earth permanent magnet as described above is desirably 3 μm to 30 μm. If the film thickness is less than 3 μm, excellent salt water resistance may not be exhibited. On the other hand, even if the film thickness exceeds 30 μm, the salt water resistance is not improved so much and only the cost is increased.

  In addition, as the rare earth based permanent magnet in the present invention, an R—Fe—B based sintered magnet represented by an Nd—Fe—B based sintered magnet is preferably exemplified, but the rare earth based permanent magnet in the present invention is It is not limited to R—Fe—B based sintered magnets. The Al coating containing Mg formed by vapor deposition on the surface thereof may contain a trace component that cannot be avoided.

  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 and comparative examples, for example, as described in US Pat. No. 4,770,723 and US Pat. No. 4,792,368, a known cast ingot is pulverized, and after pulverization, molding, sintering, and heat treatment are performed. This was carried out using a sintered magnet (hereinafter referred to as a magnet specimen) having a size of 42 mm × 20 mm × 2 mm having a composition (at%) of 17Nd-1Pr-75Fe-7B obtained by performing surface processing. Moreover, the vapor deposition apparatus has two cylindrical barrels made of stainless steel mesh wire mesh having a diameter of 355 mm and a length of 1200 mm as shown in FIG. In addition, a material capable of performing a vapor deposition process while continuously supplying a wire vapor deposition material to the melt evaporation part was used.

Example 1
The magnetic body test piece was subjected to sand blasting to remove the oxide layer on the surface of the test piece generated by the surface processing in the previous step. The magnet body test piece from which the oxide layer has been removed is accommodated in each cylindrical barrel by 1.5 kg, and the vacuum chamber is evacuated to 1 × 10 ⁻¹ Pa, and then Ar gas is evacuated in the vacuum chamber. The total pressure was supplied at 1.0 Pa. Thereafter, glow discharge was performed for 15 minutes under the condition of a bias voltage of 0.5 kV while rotating the rotating shaft of the barrel at 6.0 rpm to clean the surface of the magnet specimen.
Subsequently, under conditions of Ar gas pressure of 1.0 Pa and bias voltage of 1.0 kV, an Al wire containing 5 mass% of Mg having a hydrogen content of 5 ppm as a vapor deposition material (compliant with JIS A5356) is fed at a rate of 3.9 g. This was heated and evaporated while being continuously supplied at 1 min / min (Haas temperature: 1400 ° C.), and vapor deposition was performed for 30 minutes to form an Al coating containing Mg on the surface of the magnet body test piece. The temperature of the magnet specimen at the end of the vapor deposition process reached 200 ° C, but not to 255 ° C (a 255 ° C thermo crayon made by NOF Corporation was scraped to one of the magnet specimens. Then, the one wrapped in Al foil and the 200 ° C. thermo crayon were shaved and wrapped in Al foil, and only the 200 ° C. thermo crayon was melted). Immediately after completion of the vapor deposition process, nitrogen gas at 15 ° C. is introduced into the processing chamber to rapidly cool the magnet body test piece, then the processing chamber is opened to the atmosphere and the magnet body test piece is taken out in the atmosphere (25 ° C. or less). It was spread out so as not to overlap the Al bat and allowed to cool, and the temperature of the magnet specimen was measured with a radiation thermometer, and it was 43 ° C. The time from introduction of nitrogen gas into the processing chamber to measurement of the temperature of the magnet specimen was 8 minutes. Therefore, the cooling rate of the magnet body test piece was 19.6 ° C./min or more because the magnet body test piece that reached at least 200 ° C. was cooled to 43 ° C. in 8 minutes (the magnet body test piece was If the temperature reaches nearly 255 ° C, the maximum cooling rate is 26.5 ° C / min).
The magnetic body test piece having the Al coating film containing Mg on the surface, obtained as described above, was put into a blasting apparatus, and a pressurized gas composed of nitrogen gas and a Mohs hardness with an average particle diameter of 120 μm as a projection material No. 6 spherical glass bead powder was sprayed at an injection pressure of 0.15 MPa for 5 minutes, and shot peening was performed on the Al coating containing Mg. The film thickness of the Al coating film containing Mg subjected to shot peening measured using a fluorescent X-ray film thickness meter (SFT-7000: manufactured by Seiko Denshi Co., Ltd.) was 11.5 μm. In addition, an atomic emission analyzer (ICPS-7500: manufactured by Shimadzu Corporation) was used to determine the composition of an Al film deposited on the surface of a glass plate (35 mm × 10 mm × 1 mm) housed in a cylindrical barrel together with a magnet body test piece. When used and measured, the Mg concentration contained in the Al coating was 5.9 mass%.

The structure of the Al coating containing Mg immediately after shot peening was observed with a transmission electron microscope (HF2100: manufactured by Hitachi High-Technologies Corporation). The photograph is shown in FIG. Further, FIG. 2 shows electron beam diffraction images of a light-colored portion indicated by a in the drawing and a dark-colored portion indicated by b in the drawing. Further, Table 1 shows the measurement results of the coating composition using an energy dispersive X-ray analyzer (Voyager: manufactured by NORAN). From FIG. 1 and FIG. 2 and Table 1, the structure of the Al coating film containing Mg has a main phase (part indicated by a in the figure) mainly composed of Al composed of a crystal phase having an average crystal grain size of 800 nm, It consists of a Mg-concentrated phase (portion indicated by b in the figure) in which Mg is composed of amorphous and / or fine crystal textures having an average crystal grain size of 20 nm or less. It was found that the width was 10 nm to 500 nm and the film was distributed continuously or intermittently in the thickness direction of the coating from the interface side with the magnet body to the outer surface side. The main phase contains 96.1 mass% Al (2.5 mass% Mg is a solid solution), the Mg concentrated phase contains 21.6 mass% Mg, and 0.01 mass% to 5 mass% containing Al as a main component. It has been found that it has a mixed phase structure of a fine crystal phase or amorphous phase in which Mg of the solid solution is dissolved and a fine crystal phase considered to be composed of Al ₃ Mg ₂ .

Subsequently, a highly accelerated life test apparatus (PM420: manufactured by Enomoto Kasei Co., Ltd.) is used for the magnet body test piece having an Al coating film containing Mg subjected to shot peening on the surface, temperature: 125 ° C., relative humidity: 85%. RH, pressure: 0.2 MPa High-temperature and high-pressure steam treatment is performed for 12 hours to oxidize and / or hydroxylate Al and / or Mg in the coating, and the Al coating containing Mg of the present invention is applied to the surface. The magnet body test piece which has was manufactured.
Reflected electron beam (BSE) as a result of observation with a field emission scanning electron microscope (S-4300: manufactured by Hitachi High-Technologies Corporation) about the cross section of the film of the magnet specimen having the film thus obtained on the surface The image is shown in FIG. Also, characteristic X-ray images of Al-Kα ray, Mg-Kα ray, and O-Kα ray using an energy dispersive X-ray analyzer (Genesis 2000: manufactured by EDAX) are shown in FIGS. 3 (b) to 3 (d), respectively. Show. Furthermore, measurement of the coating composition of the four points in the coating cross section shown in FIG. 3A and the surface on the outer surface side of the coating by the ZAF method using an energy dispersive X-ray analyzer (Genesis 2000: manufactured by EDAX). The results are shown in Table 2. The observation was performed after a magnet specimen having a coating film on the surface was resin-filled and polished, and a sample was prepared using an ion beam cross-section processing apparatus (SM09010: manufactured by JEOL Ltd.). As is apparent from FIG. 3 and Table 2, the Mg concentration distribution of the coating formed on the surface of the magnet specimen is low (point 2) from the interface with the magnet specimen to the outer surface. And a region having a thickness of about 6 μm indicated by point 3), a high region (a region having a thickness of about 2 to 3.5 μm indicated by point 1), and an intermediate region (Al and / or Mg are oxidized and / or hydroxylated). The layer having a very high oxygen concentration: a region indicated by point 4 having a thickness of about 0.8 μm), and these three types of regions having different Mg concentrations include Al—Kα ray, Mg—Kα ray, Each characteristic X-ray image of the O-Kα ray could be clearly identified as a three-layer structure (the third layer, the second layer, the second layer in order from the interface side with the magnet specimen to the outer surface side) 1 layer).

  A salt spray test under conditions of 35 ° C. and 5% NaCl-pH 7.0 (conforming to JIS Z 2371) is performed on a magnet specimen having an Al coating containing Mg of the present invention on the surface, and the presence or absence of rusting is observed. did. As a result, no rusting was observed even after 600 hours had elapsed from the start of the test, and no deterioration in magnetic properties, which was a practical problem, was observed. The reason why the coating formed on the surface of the magnet test piece exhibits excellent salt water resistance is considered to be due to the fact that the Al coating containing Mg has the unique structure described above. It was.

(Example 2)
Instead of the high-temperature and high-pressure steam treatment in Example 1, a magnet body test piece having an Al coating containing Mg subjected to shot peening on its surface was added to a 45 ° C. chemical conversion treatment solution prepared from Palcoat 3756 manufactured by Nippon Parkerizing Co., Ltd. The magnet body test piece which has Al coating film containing Mg of this invention on the surface was manufactured by giving a zirconium phosphate chemical conversion treatment by immersing for a minute, washing with water, and drying.
High-frequency glow is applied to the Al coating containing Mg formed on the surface of the magnet specimen immediately after shot peening and the Al coating containing Mg formed on the surface of the magnet specimen after chemical conversion treatment. As a result of analyzing the film composition using a discharge light emission surface analyzer (GD-OES: manufactured by HORIBA, Ltd.), the Mg concentration inside the film immediately after shot peening was constant at about 6 mass%. On the other hand, there is a gradient in the Mg concentration inside the coating after the chemical conversion treatment, and from the interface side with the magnet specimen to the outer surface side, the low region, high region, intermediate region ( A layer having a very high oxygen concentration in which Al and / or Mg are oxidized and / or hydroxylated). Moreover, the reflected electron beam (BSE) image as a result of observing the cross section of the coating film using a field emission scanning electron microscope (S-4300: manufactured by Hitachi High-Technologies Corporation) is shown in FIG. Table 3 shows the measurement results of the coating composition at the three points in the coating cross section shown in FIG. 4 and the surface on the outer surface side of the coating by the ZAF method using an analyzer (Genesis 2000: manufactured by EDAX). The observation was performed after a magnet specimen having a coating film on the surface was resin-filled and polished, and a sample was prepared using an ion beam cross-section processing apparatus (SM09010: manufactured by JEOL Ltd.). As is apparent from Table 3, the distribution of Mg concentration in the coating formed on the surface of the magnet specimen is low (point 2 and point) from the interface side with the magnet specimen to the outer surface side. 3) It was found that the region was a high region (point 1) and an intermediate region (a layer having a very high oxygen concentration in which Al and / or Mg was oxidized and / or hydroxylated). Further, it was confirmed that P was present in a layer having a very high oxygen concentration in which Al and / or Mg on the outer surface side of the coating was oxidized and / or hydroxylated.

  A salt spray test under conditions of 35 ° C. and 5% NaCl-pH 7.0 (conforming to JIS Z 2371) is performed on a magnet specimen having an Al coating containing Mg of the present invention on the surface, and the presence or absence of rusting is observed. did. As a result, no rusting was observed even after 600 hours had elapsed from the start of the test, and no deterioration in magnetic properties, which was a practical problem, was observed. The reason why the coating formed on the surface of the magnet test piece exhibits excellent salt water resistance is considered to be due to the fact that the Al coating containing Mg has the unique structure described above. It was.

(Discussion)
The reason why the Al coating containing Mg formed on the surface of the magnet test piece in Example 1 and Example 2 exhibits excellent salt water resistance is considered as follows.
The structure of the film before the water vapor treatment or chemical conversion treatment, that is, the unique tissue structure of the film formed on the surface of the magnet by quenching the magnet after completion of the vapor deposition process gives the film water vapor treatment or chemical conversion treatment. This is a structure that can exhibit excellent salt water resistance. Since Al ₃ Mg ₂ that is considered to constitute the Mg-concentrated phase present in the structure of the film before the steam treatment or chemical conversion treatment is lower in potential than Al, the steam treatment or chemical conversion By the treatment, it is preferentially decomposed by contact with moisture on the surface on the outer surface side of the coating and is oxidized or hydroxylated. As a result, Al ₂ O ₃ , Al (OH) ₃ , MgO, Mg (OH) _2, etc. And a layer containing these (a layer in which Al and / or Mg is oxidized and / or hydroxylated) is formed on the surface on the outer surface side of the coating, thereby functioning as a barrier layer against salt water. In particular, MgO and Mg (OH) ₂ contained in this layer are relatively poorly water-soluble and excellent in salt water resistance, making the function as a barrier layer effective.
In addition, the Mg-concentrated phase present in the structure of the film before performing the steam treatment or chemical conversion treatment is continuously or intermittently in the thickness direction of the film from the interface side with the magnet specimen to the outer surface side. Since it is distributed, even if the barrier layer against salt water is broken at a place on the outer surface side of the coating, Mg is supplied to the place from Al ₃ Mg ₂ which is considered to constitute the Mg concentrated phase. Then, MgO and Mg (OH) ₂ are generated at that location, whereby the barrier layer is re-formed, and excellent salt water resistance is maintained. Therefore, Mg in the coating has a tendency to move toward the outer surface because it is supplied to the outer surface of the coating, and this tendency constitutes a unique gradient pattern of Mg concentration in the coating. .

  INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that it can provide a rare earth permanent magnet having an Al coating containing Mg that exhibits excellent salt water resistance and a method for producing the same.

It is a transmission electron microscope photograph of the structure | tissue structure of Al coating film containing Mg immediately after performing shot peening in Example 1. FIG. It is an electron beam diffraction image. It is the result of having performed cross-sectional observation of the film after performing a water vapor | steam process similarly. It is the BSE image of the film after performing a chemical conversion treatment similarly. It is a typical front view of an example of the vapor deposition apparatus which can be used in order to implement this invention.

Explanation of symbols

1 Processing chamber 2 Hearth (melting and evaporating part)
DESCRIPTION OF SYMBOLS 3 Support table 4 Hearth support stand 5 To-be-processed object holding | maintenance part 6 Rotating shaft 10 Al containing Mg (molten vapor deposition material)
11 Al wire containing Mg 20 Feeding reel 21 Protective tube 22 Notch window 23 Feeding gear 30 Rare earth permanent magnet

Claims (11)

A rare earth-based permanent magnet having an Al coating containing Mg on the surface, the texture of the coating being a main phase containing Al as a main component and containing Mg, and the Mg concentration containing Al and Mg is higher than the Mg concentration of the main phase. It consists of a high Mg concentration phase, and the Mg concentration of the coating is higher on the outer surface side than the interface with the magnet body in the thickness direction, and Al and / or Mg is oxidized and oxidized on the outer surface side surface of the coating. A rare earth-based permanent magnet having a hydroxylated layer.   The rare earth-based permanent magnet according to claim 1, wherein the Mg concentration in the vicinity of the interface of the coating with the magnet body is 2 mass% to 10 mass%.   The rare earth-based permanent magnet according to claim 1 or 2, wherein the Mg concentration in the vicinity of the interface with the layer in which Al and / or Mg of the coating is oxidized and / or hydroxylated is 15 mass% to 35 mass%.   The rare earth-based permanent magnet according to any one of claims 1 to 3, wherein the Mg concentration of the layer in which Al and / or Mg is oxidized and / or hydroxylated is 3 mass% to 20 mass%.   The rare earth-based permanent magnet according to any one of claims 1 to 4, wherein the oxygen concentration of the layer in which Al and / or Mg is oxidized and / or hydroxylated is 5 mass% to 50 mass%.   6. The layer in which Al and / or Mg is oxidized and / or hydroxylated further contains at least one element selected from the group consisting of Zr, P, and F. Rare earth permanent magnets.   7. The rare earth based permanent magnet according to claim 1, wherein the layer thickness of the layer in which Al and / or Mg is oxidized and / or hydroxylated is 0.01 to 5 [mu] m.   The rare earth-based permanent magnet according to any one of claims 1 to 7, wherein the film thickness is 3 to 30 µm.   After vapor-depositing an Al film containing Mg on the surface of the rare earth-based permanent magnet in the processing chamber of the vapor deposition apparatus, cooling the magnet at a high temperature of 160 ° C. or higher is performed at 10 ° C./min until the magnet temperature reaches at least 60 ° C. It is performed by quenching at the above cooling rate, and Al and / or Mg in the coating is oxidized and / or hydroxylated on the surface of the coating of the obtained rare earth permanent magnet having the Al coating containing Mg on the surface. The method for producing a rare earth permanent magnet having an Al coating film containing Mg according to claim 1, wherein the treatment is performed.   The manufacturing method according to claim 9, wherein quenching is performed by introducing nitrogen gas into the processing chamber.   The treatment for oxidizing and / or hydroxylating Al and / or Mg in the coating is at least one treatment selected from the group consisting of steam treatment, hydrothermal treatment, and chemical conversion treatment. The manufacturing method as described.