JP2002231518A - Soft magnetic powder and dust core formed thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft magnetic powder which is used for manufacturing a dust core of high electrical resistivity. SOLUTION: Alloy powder is a composition which contains one element or an alloy selected out of a pure Fe, Fe-Co alloy, Fe-Co-V alloy, Fe-Si alloy, and Fe-Ni alloy; and furthermore one or more easily oxidizable elements selected from Al, Cr, Mo, Ti, Zr, Nb, Y, Cs, and rare earth elements. The easily oxidizable element content of the alloy powder ranges from 0.5 to 3 wt.%. When two or more easily oxidizable elements are contained in the alloy powder, the content of them ranges from 0.5 to 4 wt.%, and all or a part of the surface of the alloy powder is coated with an oxide film which contains easily oxidizable elements as a main component and is 0.01 to 0.15 μm in thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic powder and a dust core using the same, and more particularly, a soft magnetic powder suitable as a raw material powder for producing a dust core having a high electric resistivity. It relates to a dust core using the same.

[0002]

2. Description of the Related Art A dust core can be manufactured with a high yield even if the target product is small and has a complicated shape. It is beginning to be widely used instead. This dust core is generally manufactured as follows.

First, prior to the production of a dust core, a raw material powder having a predetermined particle size made of a soft magnetic alloy having a predetermined composition is prepared. Generally, this raw material powder is generally manufactured by the following method. First, a first method is to melt a soft magnetic alloy having a predetermined composition by, for example, a vacuum melting method, cool the molten metal into an ingot, mechanically pulverize the ingot, further classify the ingot, and classify the ingot into a predetermined particle size. This is a method for producing a soft magnetic alloy powder.

[0004] Another method is an atomizing method, in which the above-mentioned molten metal is dropped or sprayed into water or gas flowing at a high speed, and the molten metal is granulated, cooled and classified, and then classified and softened to a predetermined particle size. This is a method of forming a magnetic powder. And
The following treatment is applied to this raw material powder,
This treatment is for increasing the electrical resistivity of the dust core for the purpose of manufacturing, and at the same time, for improving the formability of the raw material powder to be described later.

For example, an Al ₂ O ₃ powder,
Electrically insulating oxide powder such as SiO ₂ powder, Al
A predetermined amount of the same electrically insulating nitride powder such as N powder, Si ₃ N ₄ powder, and BN powder is bound together with electric insulating properties such as water glass, phosphoric acid, silicone resin, phenol resin, and imide resin. A predetermined amount of a liquid binder component having an ability is mixed to form a mixture.

[0006] Therefore, in the resulting mixture:
The above-mentioned electric insulating powder is attached to the surface of each raw material powder, and at the same time, the whole surface or a part of the surface of the raw material powder is covered with the above-mentioned binder component. In other words, this mixture is an aggregate of raw material powders whose surface is entirely or partially covered with an electrically insulating film, and has electrical insulation as a whole.

As for the preparation of a mixture, a predetermined amount of the above-mentioned binder component may be directly mixed with the raw material powder without adding an electrically insulating powder to the raw material powder. Also in this case, since the surface of the raw material powder in the obtained mixture is coated with the above-described electrically insulating binder component, the mixture is electrically insulating as a whole.

[0008] The mixture thus prepared is filled in a mold having a predetermined shape, and then molded at a predetermined pressure. Finally, the temperature of the obtained molded body is 500 to 900.
By performing a heat treatment at about ° C., the strain accumulated in the raw material powder during the production of the raw material powder or the molding of the mixture is removed, and the intended dust core is manufactured. By the way, application fields of the powder magnetic core manufactured as described above include, for example, a smoothing choke coil on a DC output side of a switching power supply, a normal mode noise filter on an AC input side, an active filter for power factor improvement, There are a step-up and step-down coil of a DC-DC converter or a coil for operating an electromagnetic valve.

[0009] Since the dust core in these fields is used under a high frequency applied state, the dust core needs to have high electric resistivity, that is, excellent electrical insulation. This is because if the electrical insulation is inferior, the dust core has problems such as a decrease in magnetic permeability under a high frequency and an extremely high core loss due to eddy current flowing.

[0010] For example, Fe-Si or Fe-Ni
Powder magnetic cores made of soft magnetic powders mainly have a frequency of 10 kHz.
It is used in the high frequency range of z or higher, and low core loss is an essential requirement, but in the case of such a dust core,
Its electrical resistivity is required to be 0.03 Ω · m or more. Further, pure Fe, Fe-Co system, Fe-C
High magnetic flux densities are required for those used mainly in the low frequency range of 10 kHz or less, such as powder magnetic cores made of oV-based soft magnetic powders. Is required to have a value of several hundred μΩ · cm or more as its electrical resistivity.

[0011]

When a dust core is manufactured by the above-described series of steps, the following problems are likely to occur in the step of forming the mixture and the step of heat-treating the formed body. There is a problem that it is difficult to obtain a dust core having a high electric resistivity. First, at the time of molding the mixture, by the applied pressure, it is formed on the surface of the raw material powder,
This means that the electric insulating film that insulates the raw material powders from each other is damaged, and the raw material powders are likely to come into contact with each other. In other words, the problem is that the electrical insulation between the raw material powders is destroyed.

Further, during the heat treatment of the molded body, for example, the binder component in the electrically insulating film is thermally decomposed and the film shrinks, or the film on the surface is damaged by thermal expansion of the raw material powder. Eventually, there is a problem in that the raw material powders come into direct contact with each other and the electric insulation is destroyed. The present invention does not cause the above-described problems, and in the process of manufacturing a dust core, in the case where the electric insulating film interposed between the raw material powders is damaged and the raw material powders come into direct contact with each other. It is an object of the present invention to provide a soft magnetic powder capable of suppressing a decrease in the electrical resistivity of a manufactured dust core and a dust core using the same.

[0013]

In order to achieve the above-mentioned object, the present invention provides a pure Fe, Fe-Co alloy, Fe-Co-V alloy, Fe-Si alloy, or Fe-Ni alloy. Al, Cr, M
o, Ti, Zr, Nb, Y, Cs, an alloy powder having a composition containing one or more oxidizable elements selected from the group consisting of rare earth elements, The contents are all in the range of 0.5 to 3% by weight, and when two or more kinds are contained, the total amount thereof is in the range of 0.5 to 4% by weight, Further, a soft magnetic powder characterized in that an oxide film having a thickness of 0.01 to 0.15 μm mainly containing the oxidizable element is formed on a part or the whole of the surface of the alloy powder. Provided.

In the present invention, a dust core having a high electric resistivity is provided by using the above-mentioned soft magnetic powder.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The soft magnetic powder of the present invention may be any one of, for example, Fe-Si alloy powder or Fe-Ni alloy powder which has been conventionally used as a raw material powder for a high frequency dust core. Alloy; or, for example, pure Fe powder, Fe-
An alloy of any one of Co-based alloy powder and Fe-Co-V-based alloy powder is manufactured as a base material.

That is, first, the below-described elements are added to the above-described base material alloy, and an alloy in which these elements are uniformly dispersed in the base material alloy is melted. At this time, the elements added to the base alloy are Al, Cr, Mo, Ti, Zr, Nb,
One or more of Y, Cs, and rare earth elements are selected. All of these elements are more easily oxidizable than the constituent elements of the base metal alloy, that is, Fe, Si, Ni, Co, V, and the like.

Next, a powder having a predetermined particle size is produced from the molten metal. As the powder production method, the atomization method described above,
There are two methods of cooling the molten metal into an ingot and then mechanically pulverizing the ingot. In the case of the atomizing method, the molten metal is sprayed into the air or water, which is an oxygen-containing atmosphere, to promote granulation and pulverization. Some of the above elements are exposed on the surface of the powder and exposed to an oxygen-containing atmosphere. Since the element is more easily oxidized than the constituent elements of the base metal alloy, the element is preferentially oxidized. Therefore, the obtained powder is a powder in which the element is dissolved in the base metal alloy in the center part and the surface of which is formed with an oxide film containing the oxidizable element as a main component.

In the latter production of powder using mechanical powder, the ingot is not exposed to an oxygen-containing atmosphere at a high temperature as in the case of the above-mentioned molten metal of the atomization method. Oxidation of the distributed easily oxidizable element hardly proceeds. However, in such a case, the powder obtained by mechanical pulverization is subjected to an oxidation treatment in, for example, an oxygen-containing atmosphere at a predetermined temperature, whereby only the easily oxidizable element is preferentially oxidized to obtain a powder of the present invention. Can be

Regardless of the method used, in the case of the soft magnetic powder of the present invention, a part or all of the surface of the produced powder is coated with the oxide film containing the above-mentioned easily oxidizable element as a main component. The surface is electrically insulating. Therefore, in a dust core manufactured from this powder, even if the above-mentioned electrically insulating coating formed of a binder component or the like is damaged during the molding of the dust core or in the process of firing, the powders come into contact with each other. Since the surface of each powder is electrically insulating, the dust core can maintain a high electrical resistivity.

In the soft magnetic powder of the present invention which can be produced in this manner, first, the content of the easily oxidizable element contained in the base metal alloy is determined by adjusting the content of the above-mentioned oxide film in any element. 0.5 including the amount distributed to the membrane
It is set in the range of ３3% by weight. When two or more types of easily oxidizable elements are contained, the total amount is 0.1.
It is set in the range of 5 to 4% by weight.

The content of the easily oxidizable element is 0.5% by weight.
If the amount is smaller, the formation of an oxide film on the surface of the powder is not sufficient. If the amount is more than 3% by weight, the amount of the formed oxide film is certainly increased, and the high resistance of the dust core can be realized. Since the easily oxidizable element functions as an impurity, the magnetic flux density and the magnetic permeability of the manufactured dust core are reduced.

When two or more kinds are contained, the total amount is set to 0.5% by weight or more for the same reason as described above, and the upper limit is set to 4% by weight. The thickness of the oxide film formed by coating the powder surface is 0.01 to
It is set to 0.15 μm. In addition, this thickness is a value converted from the electron irradiation time in which an easily oxidizable element is analyzed by Auger analysis and the element is observed. Then, whether or not it is an oxide film is checked if oxygen is temporarily concentrated on the powder surface and the easily oxidizable element is similarly concentrated,
It is presumed that oxides are formed by both.

When the thickness is less than 0.01 μm, the powder may be damaged when the powders come into contact with each other at the time of molding, for example, due to the low strength of the oxide film. However, it is not suitable as a raw material powder for a dust core having a high electric resistivity. In addition, the thickness is 0.
When the thickness is more than 15 μm, the magnetic permeability of the manufactured dust core is reduced.

The above-mentioned thickness is largely determined by the amount of the easily oxidizable element added to the base metal alloy and the conditions of the oxidation treatment, but is basically determined by the conditions of the oxidation treatment. Examples of the oxidation treatment include a steam heat treatment and an air heat treatment. In this case, from an industrial viewpoint, it is preferable to control the oxygen partial pressure during the heat treatment.

[0025]

EXAMPLES Examples 1 to 4 and Comparative Examples 1 to 5 An Fe--Co--V alloy was selected as a base metal alloy, and Al was selected as an easily oxidizable element. Both were mixed at a ratio such that the composition shown in Table 1 was obtained, and the mixture was charged into a vacuum melting furnace, and an alloy having a composition shown in Table 1 was melted at 1600 ° C. in a vacuum atmosphere.

The obtained melt was powdered by the method shown in Table 1. Thereafter, each powder was subjected to the heat treatment shown in Table 1 in the air (or not to the heat treatment) to obtain powder for a dust core. To 100 parts by weight of each powder (all under 100 mesh), 1 part by weight of water glass was added,
Both were stirred and mixed to prepare a mixture for molding. In addition, 0.5 part by weight of zinc stearate (lubricant) was further added to the mixture.

Next, the mixture was press-molded at a pressure of 1670 MPa to produce a ring-shaped molded body having an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm. Next, each compact was heat-treated in vacuum at a temperature of 700 ° C. for 1 hour to obtain a dust core. Then, the magnetic flux density and the electric resistivity of the obtained dust core were measured.

The above results are shown in Table 1.

[0029]

[Table 1]

Example 5, Comparative Example 6 Co: 49% by weight, V: 2% by weight, and the balance: 100% by weight of Fe, Al: 1 part by weight, and the whole in a vacuum atmosphere. It was melted at a temperature of 1400 ° C.
The obtained molten metal was subjected to an atomizing method under a condition of a spray water nozzle pressure of 9.8 MPa.

The surface of the obtained atomized powder is SiO ₂
Is irradiated at a speed of 5 nm / min, and the energy of the excited Auger electrons is analyzed to fix the atoms on the powder surface.
The atomic concentration in the depth direction was measured from the irradiation time of iO ₂ . The result is shown in FIG. In FIG. 1, the horizontal axis represents the irradiation time of SiO ₂ , that is, the thickness of the atomic layer existing on the powder surface, and the irradiation time of 1 × 10 ³ seconds corresponds to the thickness of 0.08 μm.
m.

As shown in FIG. 1, in the case of the atomizing method of the present invention, the O component is clearly present in the surface layer from the surface to a thickness of 0.1 μm, and this surface layer becomes an oxide film. It is clear that Therefore, the thickness of this oxide film can be read as 0.1 μm. Then, in the surface layer portion, particularly on the surface side, the concentration of the Al component is abnormally high, and the concentrations of the Fe component and the Co component, which are the main components, decrease as the depth increases from the surface so as to form a pair with the Al component. . Further, the O component has a high concentration on the surface side of the surface layer portion, and the deeper the portion, the lower the concentration, as in the case of the change in the concentration of the Al component. From this, it can be seen that the surface portion up to a depth of 0.1 μm is an oxide film, and the oxide is an oxide mainly containing the added Al component.

For comparison, an atomized powder was produced under the same conditions as in Example 1 except that the Al component was not added, and the result of Auger spectroscopic analysis of the atomized powder was shown in FIG. It was shown to. As is clear from FIG. 2, no oxide such as Al ₂ O ₃ is found on the surface of the atomized powder of this comparative example.

1 part by weight of water glass was added to 100 parts by weight of each atomized powder (all under 100 mesh) of this Example and Comparative Example, and both were stirred and mixed to prepare a mixture for molding. In addition, 0.5 part by weight of zinc stearate (lubricant) was further added to the mixture. Then, the mixture was press-molded at a pressure of 1670 MPa to produce a ring-shaped molded body having an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm.

Then, each compact was subjected to a heat treatment at a temperature of 700 ° C. for 1 hour in a vacuum to obtain a dust core. And the electrical resistivity of the obtained dust core was measured. The electrical resistivity of the example was 350 μΩ · m, and that of the comparative example was 80 μΩ · m. Examples 6 to 9 and Comparative Examples 7 to 12 An Fe-Ni-based alloy was selected as a base metal alloy, and Al and Zr were selected as oxidizable elements. These were mixed at a ratio such that the composition shown in Table 2 was obtained, and charged into a vacuum melting furnace, and were melted at a temperature of 1400 ° C. in a vacuum atmosphere.

After the obtained molten metal is powdered by the method shown in Table 2, each powder is subjected to the heat treatment shown in Table 2 (or without heat treatment) in the air, and the powder for the dust core is subjected to the heat treatment. I made it. Using each powder, a dust core was manufactured under the same conditions as in Examples 1 to 4, and the thickness of the oxide film and the magnetic properties were measured. The results are shown in Table 2.

[0037]

[Table 2]

Examples 10 to 12 and Comparative Examples 13 to 18 An Fe--Si alloy was selected as a base metal alloy, and Al was selected as an easily oxidizable element. These were mixed at a ratio such that the composition shown in Table 3 was obtained, and charged into a vacuum melting furnace, and were melted at a temperature of 1400 ° C. in a vacuum atmosphere. After the obtained molten metal was powdered by the method shown in Table 3, for each powder,
The heat treatment shown in Table 3 was performed in the atmosphere (or without the heat treatment) to obtain a powder for the green compact itself.

Using each powder, a dust core was manufactured under the same conditions as in Examples 1 to 4, and the thickness of the oxide film, the electrical resistivity, and the initial permeability were measured. Table 3 shows the results.

[0040]

[Table 3]

[0041]

As is clear from the above description, the soft magnetic powder of the present invention has its surface coated with an electrically insulating oxide film, so that it can be used during molding in the manufacturing process of the dust core or burning. Even if the electric insulating film formed between the powders at the time of sintering is broken and the powders come into contact with each other, the obtained dust core shows a high electric resistivity.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of Auger spectroscopy of the soft magnetic powder of Example 1.

FIG. 2 is a graph showing the results of Auger spectroscopy of the soft magnetic powder of Comparative Example 1.

Claims (2)

[Claims] 1. Pure Fe, Fe—Co alloy, Fe—Co
-V-based alloy, Fe-Si-based alloy, or Fe-Ni-based alloy, as well as Al, Cr, Mo, Ti, Z
r, Nb, Y, Cs, an alloy powder having a composition containing one or more oxidizable elements selected from the group of rare earth elements, wherein the content of the oxidizable element is: All are in the range of 0.5 to 3% by weight, and when two or more kinds are contained, their total amount is in the range of 0.5 to 4% by weight,
A part or the whole of the surface of the alloy powder has a thickness of 0.01 to 0.15 μm containing the oxidizable element as a main component.
A soft magnetic powder characterized by having an oxide film formed thereon. 2. A dust core using the soft magnetic powder according to claim 1.