JP5223761B2 - Method for improving salt water resistance of rare earth permanent magnets with Al film containing Mg deposited on the surface - Google Patents

Description

  The present invention relates to a method for improving the salt water resistance of a rare earth permanent magnet having an Al film containing Mg deposited on its surface.

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. In order to cope with such a problem, the present inventor disclosed in Patent Document 3 as a method for imparting salt water resistance to a rare earth permanent magnet by depositing an Al coating containing 3% by mass to 10% by mass of Mg on the surface of the magnet. A method of forming was proposed. Although this method has been recognized as an excellent method for imparting salt water resistance to rare earth permanent magnets, it has recently been recognized that rare earth permanent magnets are required to be further improved in salt water resistance.

JP 2000-150216 A JP 2000-233201 A Japanese Patent Laying-Open No. 2005-191276

  Therefore, an object of the present invention is to provide a method for improving the salt water resistance of a rare earth permanent magnet having a surface on which an Al coating containing Mg is deposited.

  As a result of intensive research in view of the above points, the present inventors have made the surface of the Al coating containing Mg deposited on the surface of the rare earth-based permanent magnet condense, so that the Mg in the coating is stained on the coating surface. It was found that the salt water resistance is improved by making it come out.

The method for improving the salt water resistance of a rare earth permanent magnet in which an Al coating containing Mg is vapor-deposited on the surface of the present invention, which has been completed based on the above findings, is characterized in that the surface of the Al coating containing Mg is condensed on the surface according to claim 1. By making it, Mg in the film is oozed out to the surface of the film.
The method according to claim 2 is characterized in that in the method according to claim 1, the surface of the coating film is condensed so that the condensation particle diameter is 10 μm or more.
The method according to claim 3 is the method according to claim 1 or 2, wherein the rare earth permanent magnet is formed by vapor-depositing an Al film containing Mg on the surface, the temperature of the film surface being at least 10 ° C to 80 ° C. The film surface is condensed by exposure to an environment having a dew point temperature of 15 ° C. to 85 ° C. (provided that the dew point temperature is higher than the temperature of the film surface).

  ADVANTAGE OF THE INVENTION According to this invention, the salt water resistance improvement method of the rare earth-type permanent magnet which vapor-deposited and formed Al film containing Mg on the surface can be provided.

It is a typical front view of an example of the vapor deposition apparatus which can be used in order to vapor-deposit and form Al film containing Mg on the surface of a rare earth system permanent magnet. It is the result of having performed the elemental mapping of the film surface before dew condensation on the surface of the Al film containing Mg in Example 1 using a field emission scanning electron microscope and an energy dispersive X-ray analyzer. It is the result of element mapping of the film surface after dew condensation.

  The method for improving the salt water resistance of a rare earth permanent magnet in which an Al coating containing Mg is vapor-deposited on the surface of the present invention causes the Mg in the coating to exude to the coating surface by dew condensation on the surface of the Al coating containing Mg. It is characterized by. According to the present invention, by dew condensation on the surface of the Al coating containing Mg, the phenomenon that Mg in the coating elutes from the coating and oozes out to the surface based on its high ionization tendency and potential difference corrosion with Al. When there are minute intercrystalline voids or film defects derived from the columnar crystal structure unique to the deposited film, which can be used as a penetration path into the magnet of chlorine ions or salt water, the defects ooze out on the film surface. By allowing Mg to enter or covering such a portion with Mg oozing out on the surface of the coating, it is possible to effectively prevent the penetration of chlorine ions or salt water into the magnet.

  The Al film containing Mg on the surface of the rare earth permanent magnet according to the present invention can be formed by vapor deposition using a method known per se. However, as a desirable method, melt evaporation by heating an Al wire containing Mg as a vapor deposition material is preferable. There is a method of forming a vapor deposition by evaporating while continuously supplying to the part. In this method, the amount of Mg contained in the Al coating (for example, 3% by mass to 10% by mass is desirable. If the amount of Mg is too small, salt water resistance may not be exhibited. If the amount of Mg is too large, high stress distribution in the coating The adhesion between the magnet and the coating may be hindered), and is performed using, for example, a surface treatment apparatus as described in JP-A-2001-32062. be able to. FIG. 1 is a schematic front view thereof. In a lower portion of a processing chamber (vacuum chamber) 1 connected to an unillustrated vacuum exhaust system, a hearth (melting deposition material is melted) for evaporating Al10 containing Mg. A plurality of containers 2) are arranged on a hearth support 4 standing on a 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 is wound around a 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 surface treatment apparatus, the rare earth permanent magnet 30 is accommodated in the workpiece holder 5, the workpiece holder 5 is rotated as indicated by the arrow, and the Al wire 11 containing Mg is omitted. The Al film containing Mg is deposited on the surface of the rare earth permanent magnet 30 in the workpiece holding part 5 by evaporating Al10 containing Mg while continuously supplying to the hearth 2 heated to a predetermined temperature by the heating means. can do.

  As for Mg density | concentration included in Al wire, 3 mass%-10 mass% are desirable. If it is less than 3% by mass, the amount of Mg contained in the Al coating deposited on the surface of the rare earth-based permanent magnet is reduced, making it difficult to form a Mg-concentrated phase that contributes to improving the salt water resistance of the Al coating. There is a possibility that excellent salt water resistance cannot be imparted to the Al coating. On the other hand, if it exceeds 10% by mass, the hardness of the wire increases, so that the workability of feeding the wire into the melting and evaporating part deteriorates, or the melting occurs in the melting and evaporating part. This is because an undeposited vapor deposition material may cause a 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. It should be noted that when the film cannot be formed or when Mg is oxidized, the amount of Mg contained in the Al film may be less than the amount of Mg contained in the vapor deposition material. .

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 amount of Mg contained in the Al coating is significantly different from the amount of Mg 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, the method of vapor-depositing and forming an Al film containing Mg on the surface of the rare earth-based permanent magnet may be a method of vapor-depositing and forming a film by simply evaporating a vapor deposition material, such as a vacuum vapor deposition method. A method of vaporizing and forming a film by ionizing the evaporated material, such as a plating method, may be used.

  As explained above, vapor deposition formation of an Al film containing Mg on the surface of a rare earth-based permanent magnet is facilitated by evaporating a hydrogen-containing Al wire containing Mg while continuously supplying it to a heated melt evaporation part. It can be carried out. However, deposition of such an Al film on the surface of a rare earth permanent magnet can also be performed by a deposition method (EB deposition method) by electron beam heating using an Al ingot containing Mg. However, in the case of the EB vapor deposition method, there is a strong possibility of causing splash, and unless measures are taken such as supplying hydrogen from outside the processing chamber, the amount of Mg contained in the Al coating is greater than the amount of Mg contained in the vapor deposition material. It should be noted that Mg having a high vapor pressure tends to be reduced, and that the metal composition of the molten vapor deposition material is likely to change with time because Mg is easily evaporated from the vapor deposition material.

  The film thickness of the Al coating containing Mg is preferably 0.1 μm to 50 μm. If it is less than 0.1 μm, sufficient salt water resistance may not be imparted. On the other hand, if it exceeds 50 μm, it is difficult to reduce the size of the magnet and secure an effective volume, and it is not desirable from the viewpoint of cost. It is. The film thickness of the Al coating is more desirably 3 μm to 25 μm.

  In addition, salt water resistance can be improved by peening the deposited Al film. This action is considered to be due to the fact that the denseness of the Al coating is increased by causing the projection material to collide with the surface of the Al coating. In the peening treatment, for example, a spherical hard powder having a hardness equal to or higher than that of an Al coating such as glass beads or steel balls is used as a projection material (in particular, glass beads are suitable), and the projection material is 0.1 MPa to 0.00 MPa. What is necessary is just to carry out by projecting about 1 minute-60 minutes with respect to an Al film with the projection pressure of 5 MPa. If the projection pressure is less than 0.1 MPa, the effect of peening may not be sufficiently obtained, while if the projection pressure exceeds 0.5 MPa, the surface roughness of the Al coating may be deteriorated.

  In the present invention, the surface of the Al coating containing Mg deposited on the surface of the rare earth-based permanent magnet as described above is condensed to allow Mg in the coating to ooze out on the coating surface. The method of dew condensation on the surface of the Al coating containing Mg is not particularly limited. For example, the rare earth permanent film in which the temperature of the coating surface is 10 ° C. to 80 ° C. and the Al coating containing Mg is deposited on the surface. Examples include a method in which the surface of the coating film is condensed by exposing the magnet to an environment having a dew point temperature of 15 ° C. to 85 ° C. (provided that the dew point temperature is higher than the temperature of the coating surface). This method utilizes the difference between at least the temperature of the surface of the magnet and the dew point temperature of the environment in which the surface of the film is condensed. At least a magnet having a surface temperature of 10 ° C. to 80 ° C. is preliminarily removed from another environment. It may be carried out by moving the set film surface to an environment where condensation occurs, or at least the temperature of the environment where a magnet with a surface of the film surface of 10 ° C to 80 ° C is placed cannot follow the temperature of the magnet. You may implement by changing to the environment which condenses the film surface by raising at a speed | rate. In order to effectively elute Mg in the coating and ooze out on the surface of the magnet, it is desirable that the coating surface is condensed so that the condensation particle size is 10 μm or more. The condensation particle size tends to increase as the difference between the temperature of at least the surface of the magnet and the dew point temperature of the environment that condenses the surface of the magnet increases. Therefore, the difference between the two is desirably 5 ° C. or more. Further, the time during which the coating surface is dewed is preferably 1 minute to 48 hours. By increasing the time for which the condensation is performed, Mg in the coating can be sufficiently oozed out on the magnet surface. On the other hand, if the time for condensation is made longer than necessary, the condensed water vapor reaches the magnet surface through the defects in the case where there are fine intercrystalline voids and film defects derived from the columnar crystal structure unique to the deposited film, and the magnet Be careful as it may cause corrosion. From this point of view, it is desirable that the condensation on the surface of the coating is performed under the condition that the decrease in the residual magnetic flux density due to condensation is 1.0% or less when the residual magnetic flux density before and after the condensation is compared. The temperature of the magnet does not necessarily have to be 10 ° C. to 80 ° C. until reaching the inside as well as the surface of the coating, but the environment in which the magnet condenses the coating surface by keeping the whole constant. It is possible to suppress rapid temperature rise of the magnet after being exposed to, and to delay evaporation of condensation on the coating surface due to the magnet temperature exceeding the dew point temperature. Further, the temperature of at least the surface of the film and the environment in which the film surface is condensed may be controlled so that the condensation and evaporation of the film surface are repeatedly performed.

  In addition, although the operation of condensing the surface of the Al coating containing Mg deposited on the surface of the rare earth-based permanent magnet may be performed using an artificially set environment, the condensation on the coating surface is spontaneous. It may happen. For example, an environment with a dew point temperature of 10 ° C. to 80 ° C. may be formed in a factory or warehouse in the rainy season, so a rare earth permanent magnet with an Al coating containing Mg deposited on the surface is like this. It is possible to adopt a mode in which the coating surface is condensed by a change in temperature caused by a change in weather after that. For example, in the transportation of magnets between Japan and Southeast Asian countries such as Thailand, Indonesia, Singapore, Philippines, Malaysia, etc., the magnets usually move from 0 ° C to 40 ° C in the middle of the environment. Since the film is transferred to an environment having a high dew point temperature, the coating surface may be condensed due to such a change in the environment.

  The rare earth permanent magnet to which the present invention is applied includes, for example, an R—Fe—B sintered magnet, but is not limited thereto.

  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 body test piece) having a size of 42 mm × 20 mm × 2 mm having a composition (at%) of 17Nd-1Pr-75Fe-7B obtained by performing the above. In addition, the vapor deposition device has two cylindrical barrels made of stainless steel mesh wire with 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% by mass of Mg having a hydrogen content of 5 ppm as a vapor deposition material (compliant with JIS A5356) is fed at a wire feed speed of 3. While being continuously supplied at 9 g / min, this was heated and evaporated (Haas temperature: 1400 ° C.), and vapor deposition was performed for 30 minutes to form an Al film containing Mg on the surface of the magnet specimen.
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 projected at a projection 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 7.3 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 amount of Mg contained in the Al coating was 6.2% by mass. A salt spray test (hereinafter the same) of 35 ° C.-5% NaCl-pH 7.0 condition (according to JIS Z 2371) was performed on the magnet body test piece having the Al coating containing Mg thus obtained on the surface. The presence or absence of rust was observed. As a result, no rusting was observed even after 240 hours from the start of the test, and excellent salt water resistance was exhibited. The elemental mapping of the surface of the Al coating containing Mg of the magnet body test piece was performed using a field emission scanning electron microscope (S-4300: manufactured by Hitachi High-Technologies Corporation) and an energy dispersive X-ray analyzer (Genesis 2000: manufactured by EDAX). FIG. 2 shows the result obtained by using (the left is a secondary electron beam image, the center is the distribution of Al, and the right is the distribution of Mg. The same applies hereinafter).
Next, a magnet body test piece having an Al coating containing Mg in a room temperature environment on a surface is formed by a constant temperature and humidity tester (LH-112: manufactured by Tabay Espec Co., Ltd.). (Wet atmosphere with a relative humidity of 90% at 80 ° C.), and the coating surface was condensed for 24 hours. As a result, the entire surface of the film was condensed after 5 minutes from the start of exposure, and the dew particle size was measured to be 10 μm or more. A magnet test piece having the coating surface dewed for 24 hours was taken out of the apparatus and allowed to dry naturally in the air, and then a salt spray test was conducted to observe the presence or absence of rusting. As a result, no rusting was observed even after 300 hours from the start of the test, and an improvement in salt water resistance was observed. FIG. 3 shows the result of elemental mapping on the surface of the Al coating containing Mg of this magnet body test piece. As is apparent from FIG. 3, it was found that the condensation on the coating surface caused the Mg in the coating to elute and ooze out on the coating surface, resulting in an increase in the surface distribution of Mg. From this, the salt water resistance was improved by dew condensation on the surface of the coating because Mg exuded on the surface of the coating had fine intercrystalline voids and coating defects derived from the columnar crystal structure unique to the deposited coating. It was presumed that the salt water resistance of the entire coating was reinforced by acting on the defects in the case and entering or covering them. The deterioration of the magnetic properties of the magnet due to the condensation on the surface of the coating was practically insignificant (reduction in residual magnetic flux density due to condensation: less than 0.5%).

  INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that it can provide a method for improving the salt water resistance of a rare earth permanent magnet having an Al film containing Mg deposited on the surface.

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 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 (3)

  A method for improving the salt water resistance of a rare earth permanent magnet in which an Al coating containing Mg is vapor-deposited on the surface, wherein the surface of the Al coating containing Mg is allowed to dew, so that the Mg in the coating oozes out to the coating surface. Feature method.   The method according to claim 1, wherein the film surface is dewed so that the dew condensation particle size is 10 μm or more. A rare earth permanent magnet having an Al film containing Mg on the surface deposited at least at a coating surface temperature of 10 ° C. to 80 ° C. in an environment having a dew point temperature of 15 ° C. to 85 ° C. (however, the dew point temperature is the temperature of the coating surface) 3. The method according to claim 1 or 2, wherein the coating surface is condensed by exposing to a higher temperature.