JPH11241101A - Production of magnetic alloy powder for core material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic material powder excellent in high frequency characteristic as well as in saturation magnetic flux density to meet the recent demand for the miniaturization and higher level performance of a transformer core for switching power source and a smoothing choke. SOLUTION: An Fe-Si alloy or Fe-Si Al alloy powder and an Fe-Ni type 'Permalloy' (R) alloy powder, prepared by gas atomizing, are used. These powders are subjected to surface treatment with an acidic solution in a vessel having an agitation mixer and to heat treatment in an oxygen-containing atmosphere. Further, the Fe-Si alloy of Fe-Si-Al alloy powder and the Fe-Ni type 'Permalloy' (R) alloy powder, after the above treatments, are mixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic alloy powder used for a core material such as a transformer core for a switching power supply and a smoothing choke, and more particularly to a core material capable of achieving both high saturation magnetic flux density and excellent high frequency characteristics. The present invention relates to a method for producing a magnetic alloy powder.

[0002]

2. Description of the Related Art In recent years, electronic components such as a transformer core for a switching power supply and a smoothing choke have tended to be miniaturized and improved in performance. Demands for higher performance have also increased. Conventionally, powders generally used for core materials include Fe-Si alloys and Fe-Si-A
An l-based alloy (Sendust), a soft ferrite as an oxide magnetic material, and the like are known.

[0003] Among these magnetic material powders, Fe-Si
Metal alloys such as iron-based alloys and Fe-Ni-based permalloy alloys have higher saturation magnetic flux density than oxide magnetic materials, and are expected to meet the demand for miniaturization. However, there is a disadvantage that the high-frequency characteristics are deteriorated due to the high electrical conductivity of the contact portion between the powders. This is due to an increase in overcurrent loss when used in a high frequency region.

[0004] Further, Fe-Si-Al-based alloys have extremely high magnetic permeability among metal magnetic materials and are expected to be applied to cores. Therefore, there is a problem that it is extremely difficult to increase the packing density and increase the magnetic flux density as a part because the deformation is hardly caused by press molding.

On the other hand, an oxide-based magnetic material has a low electric conductivity at a contact portion between powders and has good high-frequency characteristics as compared with a metal-based magnetic material. It cannot support high performance. This disadvantage is due to the inherent properties of the oxide-based magnetic material, and is in a category where fundamental improvement is impossible.

Accordingly, in order to cope with miniaturization and high performance of parts, a metal magnetic material having a high saturation magnetic flux density and an extremely high magnetic permeability, such as an Fe-Si-Al alloy, is mainly used. Therefore, it is desired to improve the high-frequency characteristics by increasing the packing density of the powder, further increasing the magnetic flux density, and further decreasing the electric conductivity of the contact portion of the powder. On the other hand, for the purpose of achieving the above object, a proposal to lower the electric conductivity by oxidizing the surface of the metal powder by heat treatment, or combining an oxide-based magnetic material with the surface of the metal powder, for example, JP-A-6-202021
No. 6,086,045.

[0007]

However, according to the method of oxidizing the surface of the metal powder only by heat treatment, depending on the method of selecting the heat treatment temperature and the time, not only an oxide film which lowers the electric conductivity on the surface of the metal powder, but also an oxide film is formed. Since the oxide layer is formed inside the metal layer and the ratio of the metal phase that causes a high magnetic flux density is reduced, there is a risk that the characteristics of the component may deteriorate. This is because heat treatment conditions for surface oxidation, which reduce the electrical conductivity of the powder effectively, because a part of the surface of the metal powder before heat treatment reacts with oxygen in the air and partially generates oxides and nitrides. This is because the heat treatment temperature is not constant and the treatment time needs to be set longer.

According to the method of compounding an oxide-based magnetic material on the surface of a powder, high-frequency characteristics are improved as the composite ratio of the oxide-based magnetic material is increased. This is not an effective solution because the magnetic flux density as a result decreases. An object of the present invention is to solve both the above-mentioned problems of the conventional technology and to reduce the size and performance of a transformer core for a switching power supply and a smoothing choke, and to improve both the saturation magnetic flux density and the high-frequency characteristics. An object of the present invention is to provide a magnetic material exhibiting excellent characteristics.

[0009]

As a result of studying to achieve the above object, the present inventors have found that an Fe--Si alloy or Fe
-Si-Al-based alloy powder and Fe-Ni-based permalloy alloy powder are subjected to surface treatment with an acidic solution in a mixer with a stirring function, and then heat-treated in an atmosphere containing oxygen.
Further, the Fe-Si alloy or Fe-S
By mixing i-Al-based alloy powder and Fe-Ni-based permalloy powder, Fe-Si-based alloy and Fe-S
The high saturation magnetic flux density possessed by the i-Al-based magnetic material can be used to the maximum, and the soft permalloy alloy powder is filled in the gaps between these alloy powders that are not easily deformed by press compression, thereby further increasing the magnetic flux density. At the same time as finding out that it can be profitable, excellent high-frequency characteristics can be realized by an oxide layer uniformly formed on the surface of the powder.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that the surfaces of Fe-Si-based or Fe-Si-Al-based alloy powder, Fe-Ni-based alloy powder and permalloy alloy powder are acid-treated by a mixer having a stirring function. As a result, a reaction layer on the surface of the alloy powder that has reacted with oxygen or nitrogen in the air is removed, and an extremely clean and uniform metal surface is generated. The clean metal surface after the acid treatment is in an extremely active state, and forms a uniform and extremely thin oxide film at a lower temperature and a shorter heat treatment time than a powder without surface treatment. By performing such a process, it becomes possible to create an oxide layer having low electric conductivity only on the surface without reducing the alloy phase ratio.

Further, Fe-Si treated with these treatments
By mixing the Fe-Si-based powder or the Fe-Si-Al-based powder with the Fe-Si-based powder, the softness is improved by mixing the Fe-Si-based powder or the Fe-Si-Al-based powder. By being easily deformed by press compression and filling the space between the Fe-Si-based powder or the Fe-Si-Al-based powder with the Fe-Ni-based permalloy powder, the magnetic flux density can be further improved. Since these powders are covered with a very uniform and thin surface oxide film, the electric conductivity between the powders is kept low, and as a result, excellent high-frequency characteristics can be obtained.

[0012]

Example: Sendust alloy component (Fe-9.6% Si-
5.4% Al) powder and permalloy alloy component (Fe-7)
(0% Ni-2% Mo) powder was produced by Ar gas atomization, and the obtained powders were each classified into -105μ.
With respect to each of the classified powders, the powder and an acidic solution (aqueous hydrochloric acid solution having a pH of 1.0) are put into a mixer (Henschel mixer manufactured by Mitsui Mining Co., Ltd.) at a weight ratio of 1: 1 to a mixer having a rotor blade at the lower part of the processing tank. Then, the surface treatment was performed while stirring at a peripheral speed of the rotor of 10 m / sec. When the pH change was saturated (pH: around 6.5), the treatment was terminated, and the mixture was filtered and washed with pure water, and then dried at room temperature under vacuum. These surface-treated powders were kept in the air at 500 ° C. for 1 hour to perform an oxide film treatment on their surfaces, and then the two powders were mixed at a weight ratio of 1: 1 to obtain a test material powder for producing a ring sample. did.

[0013] A 1.5 wt% silicon-based binder and 0.5 w
A t% crosslinking agent was added, mixed in a mortar, press-molded at a pressure of 10 t / cm ² , and heat-treated at 700 ° C. to obtain a ring sample for measuring AC characteristics. At the same time, for comparison, the same applies to a mixture of as-atomized powder not subjected to a series of surface treatment and oxide film treatment and a mixture of powders subjected to only oxide film treatment without surface treatment. Ring samples were prepared according to the procedure, and their characteristics were compared. As an index of the characteristics, the AC initial permeability at 100 kHz was measured. The measurement results are summarized in Table 1. As shown in Table 1, as compared with the comparative example, the mixture of the powder as-atomized without the surface treatment and the oxide film treatment and the mixture of the powders with only the oxide film treatment without the surface treatment were compared. It can be seen that the present invention shows extremely excellent AC initial permeability.

[0014]

[Table 1]

[0015]

As described above, according to the present invention, the magnetic flux density and the high-frequency characteristics which cannot be achieved by the conventional method can be made compatible with the high saturation magnetic flux density and the excellent high-frequency characteristics. The application is widespread, which is extremely advantageous industrially.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/08 C22C 38/08

Claims (1)

[Claims] 1. An Fe— produced by gas atomization.
Si-based alloy or Fe-Si-Al-based alloy powder and Fe-
Ni-based permalloy powder is subjected to surface treatment with an acidic solution in a mixer equipped with a stirring function, and then heat-treated in an atmosphere containing oxygen, and further subjected to the Fe-Si-based alloy or Fe-treated alloy. A method for producing a magnetic alloy powder for a core material, comprising mixing an Si-Al alloy powder and an Fe-Ni permalloy alloy powder.