JP6865437B2 - Manufacturing method of magnet alloy powder with film - Google Patents

Description

The present invention relates to a method for producing a magnet alloy powder with a film.

Rare earth magnets, like ferrite magnets and alnico magnets, are magnetic materials used in various applications such as motors. Generally, since these magnets are manufactured by sintering, it is difficult to form them into a complicated shape. In addition, since the shrinkage during sintering is about 15% to 20%, it is not possible to obtain a product with high dimensional accuracy.

In recent years, the development of bond magnets has been promoted in order to solve these drawbacks. In the bonded magnet, a polyamide resin or a polyphenylene sulfide resin is used as a binder to solidify the magnet powder for molding. However, bond magnets using iron-based magnet powder containing rare earth elements have a problem of deterioration of magnetic properties due to heating during kneading and molding. Further, the bonded magnet may be exposed to a high temperature of 100 ° C. or higher depending on its use, and the deterioration of magnetic characteristics due to exposure to a high temperature environment during such use is also a problem.

Therefore, in order to improve the deterioration of the magnetic properties, the surface of the molded product is coated with a thermosetting resin or the like, or, for example, as disclosed in Patent Document 1, a phosphate-containing paint is applied. Although a method has been proposed, sufficient characteristics have not been obtained from the viewpoint of coercive force and the like.

At present, as disclosed in Patent Document 2, there is a method of adding phosphoric acid to an organic solvent when iron-based magnet powder containing a rare earth element is pulverized in an organic solvent to produce magnet powder. , It is said to be effective in preventing deterioration of the magnetic properties of magnet powder when heated to a high temperature. According to such a method, a film containing iron phosphate is formed on the surface of the magnet powder, and a magnet powder in which a decrease in coercive force under heating conditions is suppressed can be produced.

However, in order to further expand the application, it is necessary to further suppress the decrease in coercive force in a high temperature environment. _{Here, it is presumed that if a chromium oxide film typified by Cr 2} O ₃ can be formed on the surface of the magnet alloy powder, it is possible to improve the oxidation resistance at high temperatures and the like. As a result, it is expected that the decrease in coercive force in a high temperature environment will be further suppressed.

By forming a chromium oxide film on the surface of the magnet alloy powder in this way, it is expected that the decrease in coercive force in a high temperature environment will be significantly suppressed. Therefore, a method of forming a chromium oxide film on the surface of the magnet alloy powder is required. Has been done.

Japanese Unexamined Patent Publication No. 2000-208321 JP-A-2002-124406

The present invention has been made in view of the above circumstances, and provides a method for producing a coated magnet alloy powder obtained by forming a film containing chromium oxide on the surface of an iron-based magnet alloy powder containing a rare earth element. With the goal.

The present inventors have made extensive studies to solve the above-mentioned problems. As a result, they have found that a protective film containing chromium oxide can be formed on the surface of the magnet alloy powder by immersing the magnet alloy powder in an organic solvent containing hexavalent chromium ions, and have completed the present invention. Specifically, the present invention provides the following.

(1) In the first invention of the present invention, hexavalent chromium ions and inorganic acids are added to an organic solution having a water content of 0% by volume or more and 25% by volume or less to adjust the pH to -1.0 or more and 7 or more. A solution preparation step of adjusting the hexavalent chromium ion concentration to 0.0 or less and 0.1 g / L or more and 50 g / L or less in terms of chromium oxide (VI) to prepare a chromium solution, and 0 ° C or more and 40 ° C. In the following, an aging step of aging for a period of 5 days or more and 45 days or less, and an iron-based magnet alloy powder containing a rare earth element are immersed in the chromium solution to form a film containing chromium oxide on the surface of the iron-based magnet alloy powder. It is a method for producing a magnet alloy powder with a film, which comprises a dipping step of forming.

(2) The second invention of the present invention is a method for producing a coated magnet alloy powder, wherein the inorganic acid is one or more selected from the group consisting of phosphoric acid, sulfuric acid and nitric acid in the first invention. Is.

(3) The third invention of the present invention is the method for producing a coated magnet alloy powder in the first or second invention, wherein the organic solvent has a wider potential window than water.

(4) In the fourth invention of the present invention, in any one of the first to third inventions, the organic solvent has a molecular weight of 100 or less and contains an organic compound having a nitrile group. It is a manufacturing method of.

(5) In the fifth invention of the present invention, in any one of the first to fourth inventions, the organic solvent contains one or more selected from the group consisting of acetonitrile, propanenitrile, butanenitrile and acrylonitrile. , A method for producing a magnet alloy powder with a film.

(6) In the sixth invention of the present invention, in any one of the first to fifth inventions, a film for adjusting the pH of the chromium solution to −0.5 or more and 1.5 or less in the solution preparation step. This is a method for producing a magnet alloy powder.

(7) In the seventh invention of the present invention, in any one of the first to sixth inventions, in the solution preparation step, the hexavalent chromium ion concentration in the chromium solution is 25 g / g / in terms of chromium (VI) oxide. This is a method for producing a magnet alloy powder with a film, which is adjusted to L or more and 35 g / L or less.

(8) In the eighth invention of the present invention, in any one of the first to seventh inventions, in the solution preparation step, the organic solvent contains water in an amount of 5% by volume or more and 15% by volume or less. This is a method for producing an alloy powder.

According to the present invention, it is possible to provide a method for producing a magnet alloy powder with a film, which is formed by forming a film containing chromium oxide on the surface of an iron-based magnet alloy powder containing a rare earth element.

FIG. 5 is a transmission electron micrograph of the magnetic powder of Example 14.

Hereinafter, a specific embodiment of the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

≪1. Manufacturing method of magnet alloy powder with film ≫
In the method for producing a coated magnet alloy powder according to the present embodiment, hexavalent chromium ions and an inorganic acid are added to an organic solution having a water content of 0% by volume or more and 25% by volume or less to adjust the pH to -1. A solution preparation step for preparing a chromium solution by adjusting the hexavalent chromium ion concentration from 0.0 to 7.0 and hexavalent chromium ion concentration to 0.1 g / L or more and 50 g / L or less in terms of chromium oxide (VI), and the chromium solution at 0 ° C. An aging step of aging at 40 ° C. or lower for a period of 5 days or more and 45 days or less, and an iron-based magnet alloy powder containing rare earth elements are immersed in a chromium solution to form a film containing chromium oxide on the surface of the iron-based magnet alloy powder. Including a dipping step of forming.

In this way, hexavalent chromium ions and inorganic acids are added to the organic solvent to adjust the pH to -1.0 or more and 7.0 or less, and the hexavalent chromium ion concentration to 0.1 g / L or more and 50 g / L in terms of chromium oxide (VI). By immersing the iron-based magnet alloy powder in the chromium solution obtained by adjusting the pH to L or less and aging, the surface of the iron-based magnet alloy powder can be protected by a film containing chromium oxide. By forming a protective film containing chromium oxide on the surface of the iron-based magnet alloy powder in this way, the protective film can prevent oxidation due to the binding of oxygen to the iron-based magnet alloy powder, and the iron-based magnet alloy powder can be prevented from oxidizing. It is expected to suppress the decrease in coercive force in a high temperature environment.

[Solution preparation process]
In the solution preparation step, hexavalent chromium ions and inorganic acids are added to an organic solvent having a water content of 0% by volume or more and 25% by volume or less to adjust the pH to -1.0 or more and 7.0 or less and hexavalent chromium. This is a step of preparing a chromium solution by adjusting the ion concentration to 0.1 g / L or more and 50 g / L or less in terms of chromium oxide (VI).

The hexavalent chromium ion supply source is not particularly limited, and chromium oxide (VI) (CrO ₃ ), potassium dichromate (K ₂ Cr ₂ O ₇ ), or the like can be used.

The organic solvent is not particularly limited as long as it is a solvent containing an organic compound in which the iron-based magnet alloy containing a rare earth element does not excessively dissolve or wear, and may be mixed with another solvent within this range. ..

From the viewpoint of facilitating volatilization and removal of the organic solvent after the pulverization treatment and reducing the production cost, it is preferable to use an organic compound having a molecular weight of 100 or less. Specific examples of such organic solvents include methanol, ethanol, 1-butanol, 2-butanol, 1-propanol, 2-propanol, acetonitrile, propanenitrile, butanenitrile, acrylonitrile, N-methylformamide, N. , N-Dimethylformamide, 1-methyl-2-pyrrolidone, dimethyl sulfoxide.

Among these, it is preferable to use an organic compound having a nitrile group from the viewpoint of facilitating the formation of a protective film containing chromium oxide. Further, from the viewpoint of efficiently advancing the redox reaction, it is more preferable to use a solvent having a wider potential window than water. This makes it difficult for the organic solvent to interfere with the redox reaction in which a film containing chromium oxide is formed from hexavalent chromium ions.

As the organic solvent, for example, the above-mentioned organic compound alone or a mixed solvent of these organic compounds can be used, but the stability of hexavalent chromium ions in the solvent is improved, and the resulting film can be easily formed. From the viewpoint, it is preferable to use a mixed solvent of an organic compound and water. Specifically, the mixing amount of water is not particularly limited, and for example, it is preferably 5% by volume or more and 25% by volume or less with respect to the total amount of the organic solvent and water, and is 5% by volume or more and 20% by volume or less. Is more preferable, and 5% by volume or more and 15% by volume or less is further preferable.

In particular, as the organic solvent, it is preferable to use a mixed solvent of acetonitrile and water, which contains water in a ratio of 5% by volume or more and 15% by volume or less with respect to the total amount of the mixed solvent. As a result, a protective film containing highly stable chromium oxide can be formed on the surface of the magnet alloy powder.

The hexavalent chromium ion concentration in the chromium solution is adjusted to 0.1 g / L or more and 50 g / L or less in terms of chromium oxide (VI). As a result, a film containing chromium oxide can be formed. Further, it is preferable to use one containing chromium oxide (VI) at a concentration of 25 g / L or more and 35 g / L or less in terms of chromium oxide (VI), whereby a film having more excellent protection can be formed in a short time. Further, by setting the concentration in such a range, the coverage of the film containing chromium oxide is remarkably improved.

The inorganic acid is not particularly limited, and it is preferable to use any one or more of phosphoric acid, sulfuric acid, nitric acid and the like for adjustment. Specifically, as a method for adjusting the pH, first, the pH of the organic solvent is lowered to about 4.0 by adding nitric acid, and then one or more of phosphoric acid, sulfuric acid, and nitric acid are used. Then, a method of adding until a predetermined pH is reached can be mentioned.

The pH of the chromium solution is adjusted to -1.0 or more and 7.0 or less using the above-mentioned inorganic acid. When the pH is less than -1.0 or more than 7.0, a protective film is difficult to form.

Further, particularly when it is desired to enhance the film forming ability or when short-time treatment is required, the pH of the chromium solution is preferably adjusted to -0.8 or more and 4.0 or less, and -0.5 or more and 1. It is more preferable to adjust to 5 or less. The academic reason for the existence of such an optimum pH range is not clear, but it is presumed that the change in pH affects the reaction mechanism of film formation on the surface of the iron-based magnet alloy powder. To.

[Aging process]
The aging step is a step of aging the chromium solution obtained in the solution preparation step at 0 ° C. or higher and 40 ° C. or lower for a period of 5 days or more and 45 days or less.

By performing aging in this way, a highly protective film can be formed on the surface of the iron-based magnet alloy powder. The academic reason why a highly protective film can be obtained by aging is not clear, but it is because the existence form of chromium ions in the solvent changes when left at room temperature and affects the reaction mechanism of film formation. It is presumed that there is.

As the gas atmosphere for aging, either the atmosphere or an inert gas such as nitrogen gas or argon gas may be used. However, in order to suppress the evaporation of the solvent during aging, it is preferable to keep it in a closed state.

As described above, the aging period is not particularly limited as long as it is 5 days or more and 45 days or less, and for example, it is preferably 5 days or more and 40 days or less, more preferably 5 days or more and 30 days or less, and 20 It is more preferably 1 day or more and 30 days or less.

As described above, the aging temperature is not particularly limited as long as it is 0 ° C. or higher and 40 ° C. or lower, and may be, for example, room temperature.

The aging method is not particularly limited, and examples thereof include leaving (standing). Further, it may be allowed to stand in a constant temperature room, a refrigerator, or a water bath.

[Immersion process]
The dipping step is a step of immersing the iron-based magnet alloy powder containing a rare earth element in the chromium solution obtained as described above to form a film containing chromium oxide on the surface of the iron-based magnet alloy powder.

The iron-based magnet alloy powder containing a rare earth element has, for example, Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, TbCu ₇ type, or Nd ₂ Fe ₁₄ B type crystal structure. These are intermetallic compounds having a rhombohedral, hexagonal, and tetragonal crystal structures, and examples of the Th ₂ Zn ₁₇ type alloy powder include Sm ₂ Fe ₁₇ N ₃ alloy and Nd ₂ Fe. ₁₇ N _{3 and the} like can be mentioned. Examples of the Th ₂ Ni ₁₇ type alloy powder include Gd ₂ Fe ₁₇ N ₃ . Further, _{examples of the Nd 2} Fe ₁₄ B type alloy powder include Nd ₂ Fe ₁₄ B and the like.

Examples of the rare earth element include Sm, Nd, Pr, Y, La, Ce, Gd and the like, which may be used alone or as a mixture, but Sm or Nd is particularly preferable. .. Further, this iron-based magnet alloy powder contains iron (Fe) as an essential component as a transition metal element, and a part of this may be substituted with Co. Specifically, by substituting 20% by mass or less of Fe with Co, the Curie temperature and corrosion resistance of the fine powder can be improved.

Such iron-based magnet alloy powders include C, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au and the like may be included. The iron-based magnet alloy powder contains these components in a proportion of, for example, 3% by mass or less, preferably 0.05% by mass or more and 0.5% by mass or less, so that the iron-based magnet alloy powder is pulverized. It is possible to improve the weather resistance and heat resistance of a bonded magnet produced by using a magnet alloy powder which is a product.

The iron-based magnet alloy powder can be produced by, for example, nitriding heat treatment of an alloy powder obtained by a reduction diffusion method, a liquid quenching method, or an HDDR (Hydrogenation Decompression Decompression) method.

The average particle size of the iron-based magnet alloy powder is not particularly limited, and is, for example, preferably 1 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more. On the other hand, the average particle size is preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. When the average particle size is in such a range, the amount and thickness of the film can be appropriately controlled. The "average particle size" means a value obtained by a laser diffraction method.

The immersion time is not particularly limited, and is preferably, for example, 2 minutes or more, and more preferably 5 minutes or more. When the immersion time is 2 minutes or more, a protective film containing chromium oxide can be sufficiently formed on the surface of the iron-based magnet alloy powder. On the other hand, the immersion time is preferably 2 hours or less, more preferably 1 hour or less, and further preferably 30 minutes or less. Productivity can be improved by setting the immersion time to 2 hours or less.

The iron-based magnet alloy powder can also be wet-pulverized when immersed in the chromium solution. By wet pulverizing in a chromium solution in this way, a protective film can be uniformly formed on the surface of the iron-based magnet alloy powder, which is originally easily aggregated, thereby suppressing the aggregation of the iron-based magnet alloy powder. it can. In such a case, the amount of crushing and the time for the iron-based magnet alloy powder to be immersed in the chromium solution vary depending on the crushing machine, which may exceed 2 hours, but the quality of the obtained coated magnet alloy powder There is no problem with such things.

≪2. Manufacture of bonded magnets using coated magnet alloy powder ≫
According to the method for producing a coated magnet alloy powder according to the present embodiment, the chromium oxide film is formed on the surface of the obtained iron-based magnet alloy powder, so that the bonded magnet can be used in the manufacturing process or as a bonded magnet. Even when heated to a high temperature, it is expected that the deterioration of the coercive force due to heating, that is, the decrease in the coercive force at room temperature after heating can be suppressed.

Specifically, the method for producing a bonded magnet using the filmed magnet alloy powder obtained by the above-mentioned production method is not particularly limited, and for example, the filmed magnet alloy powder is used as a known thermoplastic resin or heat. It can be produced by mixing with a curable resin or an additive and molding the obtained composition for a bonded magnet by injection molding, compression molding, extrusion molding, rolling molding, transfer molding or the like.

The thermoplastic resin acts as a binder for the magnet alloy powder with a film, and the type thereof is not particularly limited, and conventionally known ones can be used. For example, 6 nylon, 6,6 nylon, 11 nylon, 12 nylon, 6,12 nylon, aromatic nylon, polyamide resins such as modified nylon in which these molecules are partially modified, linear polyphenylene sulfide resin, crosslinked type. Polyphenylene sulfide resin, semi-crosslinked polyphenylene sulfide resin, low density polyethylene, linear low density polyethylene resin, high density polyethylene resin, ultrahigh molecular weight polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, ethylene-ethyl acrylate copolymer Resin, ionomer resin, polymethylpentene resin, polystyrene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyvinyl alcohol resin, polyvinyl butyral Resin, polyvinylformal resin, methacrylic resin, polyvinylidene fluoride resin, polyethylene chloride trifluoride resin, ethylene tetrafluoride-propylene hexafluoride copolymer resin, ethylene-ethylene tetrafluoride copolymer resin, ethylene tetrafluoride- Perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene oxide resin, polyallyl ether allylsulfone resin, polyethersulfone resin, polyether ether ketone resin , Polyallylate resin, aromatic polyester resin, cellulose acetate resin, each resin-based elastomer mentioned above, etc., random copolymers with these copolymers and other kinds of monomers, block copolymers, graft copolymers, etc. , End group modified products with other substances, etc. can be mentioned. Further, for example, examples of the thermosetting resin include epoxy resin, vinyl ester resin, unsaturated polyester resin, phenol resin, melamine resin, urea resin, benzoguanamine resin, bismaleimide / triazine resin, diallyl phthalate resin, furan resin, and thermosetting resin. Examples thereof include polybutadiene resin, polyimide resin, polyurethane resin, silicone resin, xylene resin, etc., and of course, systems in these basic compositions, other kinds of monomers, and blends of two or more kinds of these resins are also included. Of these, epoxy resin, vinyl ester resin, or unsaturated polyester resin is particularly preferable.

In addition, as long as the properties of the manufactured magnet alloy powder with a film are not impaired, lubricants such as fatty acids such as paraffin wax and liquid paraffin, hindered amine stabilizers, and antioxidants such as phenols, phosphites, and thioethers. Stabilizers such as agents. Conventionally known additives can be blended.

The method of mixing the coated magnet alloy powder with each of the above-mentioned components is not particularly limited, and for example, a mixer such as a ribbon blender, a tumbler, a Nauter mixer, a Henschel mixer, a super mixer, or a Banbury mixer, a kneader, etc. This can be performed using a kneader such as a roll, a kneader luder, a single-screw extruder, or a twin-screw extruder.

By mixing each component in this way, a composition for a bonded magnet can be obtained. The shape of the obtained composition for a bond magnet is powder, beads, pellets, or a mixture thereof, but pellets are preferable from the viewpoint of ease of handling.

Next, the composition for a bonded magnet obtained as described above is heated and melted at the melting temperature of the thermoplastic resin, and then molded into a magnet having a desired shape. Examples of the molding method include various molding methods such as an injection molding method, an extrusion molding method, an injection compression molding method, an injection press molding method, and a transfer molding method. Among these, an injection molding method and an extrusion molding method are particularly used. The method, injection compression molding method, and injection press molding method are preferable. When a thermosetting resin is used, for example, the obtained composition for a bonded magnet is being molded into a magnet having a desired shape, or after being molded, the thermosetting resin is heated and simultaneously added to a curing agent. React.

Specifically, when molding a bond magnet using a composition for a bond magnet, it is molded by injection molding under the conditions of, for example, a molding temperature of 200 ° C. or higher and 300 ° C. or lower, and a mold temperature of 100 ° C. or higher and 150 ° C. or lower.

As described above, the magnet alloy powder is exposed to a high temperature in the manufacturing process of the bonded magnet. In this regard, according to the method for producing a magnet alloy powder with a film according to the present embodiment described above, even if the magnet alloy powder is heated to a high temperature, it is possible to suppress a decrease in the coercive force at room temperature after heating, which is stable. The magnetic properties can be maintained.

Hereinafter, examples of the present invention will be described in more detail, but the present invention is not limited to these examples.

[reagent]
Iron-based magnet alloy powder: Sm-Fe-N-based magnet alloy powder
(Average particle size 20 μm, manufactured by Sumitomo Metal Mining Co., Ltd.)
Chromium oxide (VI): 98% chromium oxide (VI)
(Product name: Chromium oxide (VI), manufactured by Kanto Chemical Co., Inc.)
Nitric acid: 60% aqueous solution
(Product name: Nitric acid, manufactured by Kanto Chemical Co., Inc.)
Sulfuric acid: 96% aqueous solution
(Product name: Sulfate, manufactured by Kanto Chemical Co., Inc.)

[Sample preparation]
An organic solvent (acetonitrile, 2-propanol, 2-hydroxyheptanenitrile, acetonitrile-2-propanol or acetonitrile-propanenitrile) is mixed with water, and the pH is adjusted with 60% nitrate and 96% sulfuric acid. A solvent was prepared. Chromium oxide (VI) was added to and dissolved in this solvent to prepare a chromium solution. Table 1 below shows the types of organic solvents contained in the chromium solution, the amount of water mixed in the organic solvent, the concentration of chromium oxide (VI) contained in the chromium solution, and the pH of the chromium solution.

Then, the chromium solution was placed in a closed container and left at room temperature in the air for a predetermined period for aging. Table 1 below shows the aging period of the chromium solution.

3 g of Sm-Fe-N-based magnet alloy powder was added to 100 mL of this chromium solution, and the mixture was immersed for 10 minutes with stirring using a glass rod.

[Sample evaluation]
The magnet alloy powder after the immersion treatment was embedded in an epoxy resin, and the cross section of the magnet alloy powder was exposed by irradiating Ar ions with a cross section polisher. Then, the cross section of the magnet alloy powder was observed with a field emission scanning electron microscope. FIG. 1 is a transmission electron micrograph of the magnetic powder of Example 14. From FIG. 1, it was found that an oxide film was formed on the surface of the magnet alloy powder.

In addition, an energy dispersive X-ray analyzer was also used to analyze the surface of the magnet alloy powder after the immersion treatment. The surface oxide film portion was analyzed, and the cation concentration of chromium (0 to 100% by mass) with respect to the detected metal element was determined. Then, when an oxide film having a chromium cation concentration of 70% by mass or more covers the entire circumference of the magnet alloy powder cross section (very good), the oxide film covers the entire circumference, but the chromium cation concentration is 50. When the mass% or more and less than 70% by mass is ○ (good), when the oxide film covers the entire circumference but the chromium cation concentration is 30% by mass or more and less than 50% by mass, Δ (slightly good), the oxide film is Table 1 shows the evaluation results of the film as x (defective) when the entire circumference is not covered or when the cation concentration of chromium is less than 30% by mass.

It was found that the iron-based magnet alloy powders obtained in Examples 1 to 19 had an oxide film containing a larger amount of chromium oxide than the iron-based magnet alloy powders obtained in Comparative Examples 1 to 5. ..

Claims (8)

Hexavalent chromium ions and inorganic acids are added to an organic solvent having a water content of 0% by volume or more and 25% by volume or less to adjust the pH to -1.0 to 7.0 and the hexavalent chromium ion concentration to chromium oxide. A solution preparation step of preparing a chromium solution by adjusting the pH to 0.1 g / L or more and 50 g / L or less in terms of (VI).
An aging step of aging the chromium solution at 0 ° C. or higher and 40 ° C. or lower for a period of 5 days or more and 45 days or less.
A method for producing a magnet alloy powder with a film, which comprises a dipping step of immersing an iron-based magnet alloy powder containing a rare earth element in the chromium solution to form a film containing chromium oxide on the surface of the iron-based magnet alloy powder. .. The method for producing a magnet alloy powder with a film according to claim 1, wherein the inorganic acid is at least one selected from the group consisting of phosphoric acid, sulfuric acid and nitric acid. The method for producing a coated magnet alloy powder according to claim 1 or 2, wherein the organic solvent has a wider potential window than water. The method for producing a coated magnet alloy powder according to any one of claims 1 to 3, wherein the organic solvent has a molecular weight of 100 or less and contains an organic compound having a nitrile group. The method for producing a coated magnet alloy powder according to any one of claims 1 to 4, wherein the organic solvent contains at least one selected from the group consisting of acetonitrile, propanenitrile, butanenitrile and acrylonitrile. The method for producing a coated magnet alloy powder according to any one of claims 1 to 5, wherein the pH of the chromium solution is adjusted to −0.5 or more and 1.5 or less in the solution preparation step. The film according to any one of claims 1 to 6 for adjusting the hexavalent chromium ion concentration in the chromium solution to 25 g / L or more and 35 g / L or less in terms of chromium oxide (VI) in the solution preparation step. Manufacturing method of magnet alloy powder. The method for producing a coated magnet alloy powder according to any one of claims 1 to 7, wherein in the solution preparation step, the organic solvent contains 5% by volume or more and 15% by volume or less of water.

Images