JPS62250607A - Manufacture of fe-si-al alloy dust core - Google Patents

Abstract

PURPOSE:To obtain an Fe-Si-Al alloy dust core, which stably has excellent magnetism and cost thereof is reduced, by gas-atomizing the molten metal of an Fe-Si-Al alloy, manufacturing spherical coarse powder and using powder having specific mean grain size and apparent density acquired by further pulverizing the spherical coarse powder as raw material powder. CONSTITUTION:Spherical coarse powder (not more than 100ppm oxygen content) is manufactured by gas atomizing from the molten metal of an Fe-Si-Al group alloy (4-13% Si, 4-7% Al and Fe as the remainder), and the surfaces of powder having mean grain size of 40-110mum and apparent density of 2. 6-3.8g/cm<3> acquired by further pulverizing the coarse powder are coated with O.4 wt. % water glass, and the powder is dust-molded at pressure of 20ton/cm<2>, and thermally treated for one hr at 700 deg.C. Accordingly, a dust core, which stably displays high permeability extending over a high frequency zone and cost of which is reduced, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a Fe-5i-Al alloy dust core.

[Conventional technology]

Conventionally, Fe-Si-Al alloy powder magnetic cores have been used in electronic equipment 8 (
High frequency noise generated from the internal power supply, that is, noise that goes back and forth between the power supply lines called normal mode, is
It has been used as a choke coil to attenuate large impedance.

The Fe-Si-Al alloy powder magnetic core has superior high frequency characteristics than the iron powder magnetic core, and also has particularly excellent DC superposition characteristics, and does not contain effective raw materials such as Ni and Mo.
Since it is cheaper than e-Ni alloy powder magnetic cores, the demand for it has been gradually increasing in recent years.

Conventionally, Fe-8i-Al alloy powder magnetic cores are made by melting an ingot, diffusion annealing it to reduce the segregation of A1 and Si, and then coarsely pulverizing it, and then going through several stages of pulverizing processes to obtain raw material powder. It has been manufactured by coating the powder surface with an inorganic insulating material, compacting it, and heating it.

[Problem that the invention seeks to solve]

However, in the process of crushing the ingot as described above, the entire process of manufacturing, annealing, and crushing the ingot is long, which increases the cost of raw material powder for force compaction, and as a result, F
The current situation is that the e-5L-AI alloy powder magnetic core itself is expensive, and its use as a choke coil is restricted.

The present invention was made in view of the above 7JL circumstances, and is based on new knowledge about the relationship between the properties of powder particles and the magnetic properties of the dust core, and is based on the following: It is an object of the present invention to provide a less expensive Fe-Si-Al alloy powder magnetic core.

[Means for solving problems]

The present invention is based on new findings regarding the relationship between the powder morphology and particle size and the magnetic properties of the powder magnetic core, which will be described later. , a molten metal of Fe-8i-Al alloy is gas atomized to produce a spherical coarse powder, and then the coarse powder is further pulverized, and the average particle size obtained is within the range of 40 to 110 μI, and Is the loading density 2.6 to 3.8 g/aI? The inventors have discovered that it is effective to use a powder having the following properties as a raw material powder, and that in order to obtain higher magnetic permeability, it is effective to reduce the amount of oxygen contained in the powder.

Note that the Fe-S L-AI alloy here refers to an alloy system known as a so-called sendust alloy, which has 5i4-13%, Al 4-7%, the balance Fe as its main components, and other elements. Refers to high permeability alloys that contain unavoidable impurities and, if necessary, additional elements below brocade.

[Effect]

First, one of the findings newly discovered by the present inventors will be explained.

In powder magnetic cores, it is most important that the effective magnetic permeability remains stably high and approximately constant up to a high frequency band. For this purpose, in the Fe-8i-Al alloy powder magnetic core, the surface of the powder particles is coated with an inorganic insulating material such as water glass and then pressure-formed to maintain a certain degree of insulation between the particles. This is used as a magnetic core, which is then heat treated to obtain the above characteristics.

The reason why a heat-resistant inorganic material is used instead of an organic material for the surface insulation of the powder particles is to enable the final heat treatment.

According to the present inventors, the biggest factors influencing the value of effective magnetic permeability and its frequency characteristics are (A) particle morphology and (B) particle size.

Regarding (A), even if the particles are covered with an insulating film, if the particles are pressed against each other during molding, the film is likely to be destroyed and the insulation will deteriorate, and the higher the frequency of the alternating magnetic field, the more likely eddy currents will flow. , the effective permeability decreases. Therefore, from the viewpoint of frequency characteristics, the particle shape is required to be difficult to cause insulation breakdown 1i due to local pressure bonding. That is, if the particle surface is disordered and irregularly shaped, dielectric breakdown will easily occur during molding, and spherical particles with a smooth surface are most preferable. Therefore, the apparent density of the powder decreases as the shape becomes more irregular, so it is desirable that the apparent density as a shape parameter be high.

However, magnetic permeability is also a parameter for the density of the powder magnetic core, and in the case of perfectly spherical particles with the highest apparent density, they are consolidated by point contact, so the density of the compact is rather low, and the demagnetizing field coefficient is This makes it somewhat difficult to achieve high magnetic permeability. Therefore, there is a trade-off between increasing the frequency at which the effective permeability begins to decrease by maintaining good insulation and increasing the initial DC effective permeability by increasing the density of the compact.
A balance needs to be struck. For this purpose, there is a suitable range for the apparent density of the powder.

On the other hand, from the viewpoint of (B), if the powder particles are too coarse, eddy currents are likely to occur due to the alternating magnetic field, the frequency characteristics of the effective magnetic permeability are likely to deteriorate, and the strength of the compact is reduced, so the particles There is an upper limit to particle size. On the other hand, if the particles are too fine, the compressibility of the powder particles decreases and the initial (DC) magnetic permeability decreases, so there is a lower limit to the particle size.

The second finding newly discovered by the present inventors is the influence of the amount of oxygen contained in the powder particles on the magnetic properties of the dust core. In other words, when the amount of oxygen contained in the powder particles decreases, the initial (
An increase in the permeability of direct current (DC) was observed. Although this is common knowledge for Fe-8i-Al alloy materials manufactured by melting, this is the first time that a similar phenomenon has been found for powder magnetic cores.

The present inventors have defined the optimum apparent density and particle size of powder particles for Fe-Si-AI alloy powder magnetic cores based on the above knowledge, and have produced powder within these defined ranges at low cost. The conditions for reducing the amount of oxygen contained and the conditions for reducing the amount of oxygen contained were further investigated.

That is, a spherical coarse powder is produced from a molten Fe-8i-AIl alloy by gas atomization, and then the coarse powder is further crushed to obtain an average particle size of 4 (hllo p
The fact that a dust core using powder with an apparent density of 2.6-3.8 g/ffl has excellent properties and can be produced at a lower cost than before, and that the oxygen content of the spherical coarse powder is is 1
It has been found that it is effective to have a PP of 100 PP or less, and the present invention has been completed.

The present invention will be explained in more detail below.

First, the reason why the upper limit of the average particle size was set to 110 μm will be described.

In Figure 1, the apparent density is 3.4±0.1 g/d? 5,5%Al-9,5%S with different average particle size
This figure shows the dependence of the high frequency characteristics of magnetic permeability on the average particle size of a powder magnetic core made of alloy powder of i-residue Fe. After adjusting the particle size, the powder was annealed at 900°C in a hydrogen stream, and the powder surface was coated with 0.8% by weight of water glass as a solid content.
0ton/cxl pressure, outer diameter 28+m, inner diameter 15n
After molding into a ring shape with a height of 8III11 m and a height of 70 m in the atmosphere.
Annealing was performed at 0°C. The magnetic permeability of this molded body was measured using an impedance meter. Figure 1: 1t on the vertical axis
e13M/ pelOK is the effective magnetic permeability μe13M in 13MH2 and 10KI+7. It is the ratio of the effective magnetic permeability μelOK at From Figure 1, the larger the average particle size, the more μe1
It can be seen that the frequency characteristics deteriorate as 3M/μelOK decreases. In particular, when the average particle size exceeds 110 μm, μe13M/μelO becomes less than 0.4, resulting in significant deterioration. Therefore, the upper limit of the average particle size was set to 110 μm. Note that when the average particle size exceeds 130 μm, the strength of the molded product is low and handling is impossible.6 Next, the reason why the lower limit of the average particle size was set to 40 μm will be described.

Figure 2 shows the effective magnetic permeability μelO at l0KIIZ of a molded body manufactured by the same method as used in Figure 1.
This shows the dependence of K on the average particle size. μeLOK increases as the particle size increases, but Fe-Si-A
Minimum value of μelOK required for I-based alloy powder magnetic core 7
It can be seen that in order to obtain a value of 0, the average particle size must be 40 μm or more.

Next, set the lower limit of the apparent density to 2.6 g/co? The reasons for this are explained below. Figure 3 shows that the average particle size is 70±5μ.
5.5% At-9, which is approximately equal to m and has a different apparent density.
The apparent density dependence of the frequency characteristics of a powder magnetic core made of a 5% Si-remaining Fe alloy powder is shown.

The method of manufacturing the magnetic core is the same as in the case of FIGS. 1 and 2. Irregularly shaped powder with low apparent density, μe13M/μ
elOK is low and frequency characteristics are poor. μc13M/μel
As mentioned in FIG. 1, the required value of OK was set as 0.4, and the lower limit of the apparent density was set as 2.6.

Furthermore, the reason why the upper limit of the apparent density was set to 3.8 g/ci will be described.

Figure 4 uses the same powder as in Figure 3 and has a length of 40+nn+
.

These are the results of measuring the transverse rupture strength of a molded body having a width of Lone and a height of 7+IIn. Powder with high apparent density.

In other words, a powder compact with a small contact area between particles and less entanglement has a lower transverse rupture strength.

F e-S i-A l alloys have low plastic deformability;
Therefore, the strength of the compacted compact is lower than that of iron or Fe-Ni alloy compacts, but it must be at least 0.2 kg/nwi" strong enough to be handled on an automatic press forming line. From this point of view, the upper limit of the apparent density of the powder is set to 3.8 g/cd.

As shown in Figures 1 to 4, in order to obtain a dust core with stable magnetic permeability and frequency characteristics, 40-11
Average particle size of 074111, 2.6-3.8 g/cd
It is clear that a powder with an apparent density of .

Naturally, the magnetic permeability and its frequency characteristics change depending on the pressure when the powder is pressure-molded, but Fe-
In the case of Si-AIl alloys, it is difficult to obtain a magnetic permeability of 70 or more unless the molding pressure is 15 tons/d- or more.

Furthermore, the molding pressure is currently limited to about 25 tons/cxl due to mold life constraints. 15 to 2
Even if the molding pressure changes up to about 5 tons/aJ, the effects on the characteristics of the particle size and apparent density of the powder particles as described above do not change as a whole.

In order to obtain powder having the particle size and apparent density specified above at a low cost, the present inventors focused on a method of producing powder directly from molten metal and conducted various studies. the result,
It has been found that the desired powder can be obtained at a low cost by producing a spherical coarse powder from a molten Fe-5i-Al alloy by gas atomization, and then further pulverizing the coarse powder.

The gas used in this gas atomization method is not particularly limited as long as it is non-oxidizing, such as ordinary argon or nitrogen.

Since the final target average particle size after pulverization is 40 to 110 μm, it is necessary to adjust the apparent density by pulverization, so the average particle size as gas atomized must be 120% or more of the final particle size after pulverization. Therefore, the average particle size as gas atomized is required to be 48 to 132 μm or more, but is it possible to adjust the particle size to this extent, for example? 8th place temperature is 160
In the case of 0°C, this can be almost achieved by setting the nozzle diameter to 4IIW11φ or more and the gas pressure to 100kg/cd or less. The average particle size as gas atomized is 300 from the point of view of pulverization efficiency.
μm is preferred; in this case, the final target powder can be easily obtained in one crushing step.

In order to make it 300 μm or less, the nozzle diameter needs to be 10 nmφ or less.

The pulverization method is not particularly limited and a wide variety of methods can be applied. For example, by carefully setting the conditions using a stamp mill, ball mill, vibration mill, jet mill, etc., it is possible to obtain a powder having the desired particle size and apparent density in a single pulverization process.

In addition, the gas atomized powder of the present invention usually has a maximum particle size of 500 μm, so it is difficult to use the conventional method.

A1. There is no segregation of Si, so diffusion annealing for reducing segregation is completely unnecessary.

The method for producing the Fe-S i-Al alloy powder of the present invention has been described above, but the method for obtaining coarse powder by gas atomization and then pulverizing it is to produce an ingot and then diffusion annealing it. However, compared to the conventional method of grinding in several steps, it is a revolutionary method that significantly shortens the process, saves energy, and reduces the cost of raw material powder.

Next, we will discuss the influence of the amount of oxygen contained in the powder to be compacted on the magnetic permeability of the powder magnetic core and its high frequency characteristics.

The amount of oxygen normally measured by gas analysis includes the solid dissolved M element and the undissolved oxygen absorbed on the powder particle surface, and it is impossible to separate the solid dissolved oxygen and the undissolved adsorbed oxygen. However, the present inventors have newly discovered that the amount of oxygen in the spherical coarse powder after atomization affects the magnetic properties of the dust core.

FIG. 5 shows the relationship between the amount of oxygen contained in the spherical coarse powder after atomization and the magnetism of the dust core. The amount of oxygen in the as-atomized coarse powder was determined mainly by adjusting the dissolution atmosphere. The average particle size of the spherical coarse powder as gas atomized was about 230 μm, and it was finely pulverized using a vibration mill to give an S11 average particle size of 72 μm and an apparent density of 3.4 g/cd. The surfaces of these powders with various initial oxygen amounts were coated with 0.4 tit% water glass, compacted at a pressure of 20 tons/i, and heat treated at 700° C. for 1 hour. According to FIG. 5, even if the amount of oxygen in the as-atomized coarse powder decreases, there is no change in the high-frequency characteristics of magnetic permeability, but it is recognized that the magnetic permeability at 10KII2 increases as the amount of oxygen decreases. Even if the amount of oxygen decreases to 140 PPM, there is no increase in magnetic permeability, but when the amount of oxygen decreases to 1001" PM or less, it improves from 97 in the case of 140 PPM or more to 103 or more, and the effect becomes apparent. In this way, the initial magnetic permeability decreases. Reducing the amount of oxygen is effective for increasing the temperature, and the effect is particularly large at 1100 PP or less.

The present inventors examined the relationship between the oxygen content of the powder after pulverization and the properties of the dust core by changing the method of pulverizing the spherical coarse powder, but no clear correlation could be recognized. This is considered to suggest that the amount of dissolved oxygen rather than the adsorbed oxygen produced by pulverization has an effect on the magnetic properties of the powder magnetic core. Specifically, in order to reduce the oxygen content in the gas atomized state to 1100 PP or less, melting and handling in a non-oxidizing atmosphere, and changing the spray medium gas to Ar
It must be atomized using a relatively large amount of gas. The most effective method is to carry out dissolution and atomization in a closed container under an inert atmosphere, according to which the oxygen-containing ffiloOP
Below PM is easily achieved.

The specific content of the present invention will be further explained below with reference to Examples.

〔Example〕

8
It was atomized with Ar gas at 0 kg/aJ to form a spherical powder with an average particle size of 210 μm. Oxygen gas content is 20
It was 0 PPM. This spherical powder was dry-pulverized using a vibration mill, with an average particle size of 83 μm and an apparent density of 3.19 g/a.
A powder of J was obtained.

This powder was subjected to strain relief treatment at 900°C for 1 hour in a hydrogen stream, the surface was insulated with 0.5.1.0, l, 5 wt% water glass, and then pressurized at a pressure of 20 tons/ci. It was molded and then heat-treated at 700° C. for 0.5 hours to obtain a powder magnetic core. μelO of the obtained dust core
K and μe13M/μelOK are as shown in Table 1, and high magnetic permeability is stably obtained up to the high frequency band.

Table 1 Example 2 120kg/an? by the same method as Example 1? The powder was atomized with Ar gas to form a spherical powder with an average particle size of 155 μm. The oxygen gas content was 250 PPM. This spherical powder was milled into a powder having an average particle size of 48 μm and an apparent density of 2.80 g/ryl. This powder was subjected to strain relief treatment at 900°C for 1 hour in a hydrogen stream.
(After insulating the surface with ht% water glass, pressure molding was performed at a pressure of 20 tons/cxl, and then 7
A powder magnetic core was obtained by heat treatment at 00°C for 0.5 hours.

μelOK and μe13M/μel of the obtained powder magnetic core
OK was 75.0.82 respectively.

Example 3 The steps after atomization were exactly the same as in Example 1, and atomization was performed in a closed container maintained in an Ar atmosphere.
Table 2 shows the properties of the powder magnetic core when the average particle size as atomized is 230±20 μna and the oxygen content is 50.80.150 PPM. The amount of water glass coated on the powder surface was 1.0%. The amount of oxygen was adjusted by the oxygen partial pressure of the atmosphere. Table 2 shows A1- in Example 1.
The case where the amount of oxygen is 200 PPM is also shown. The effect of increasing magnetic permeability by reducing the amount of oxygen is recognized.

Table 2 [Effects of the Invention] As is clear from the above, the method for manufacturing a Fe-8i-AI alloy powder magnetic core of the present invention is a method for manufacturing a powder magnetic core that stably exhibits high magnetic permeability over a high frequency band. This method provides a powder magnetic core that is optimal as a powder core and is less expensive than the conventional method of producing a powder magnetic core using powder obtained by manufacturing a molten ingot, annealing it, and then pulverizing it. It has great industrial value.

[Brief explanation of drawings]

Figure 1 is a correlation diagram between the average particle size of powder and frequency characteristics of magnetic permeability, Figure 2 is a correlation diagram between average particle size of powder and magnetic permeability, and Figure 3 is a correlation diagram between average particle size of powder and magnetic permeability.
The figure shows the correlation between the apparent density of powder and the frequency characteristics of magnetic permeability.
FIG. 4 is a correlation diagram between the apparent density and transverse rupture strength of the powder, and FIG. 5 is a correlation diagram between the oxygen content and magnetic permeability of the powder and its frequency characteristics. Figure 1 Average particle size (μm) Average particle size (pm) Apparent density (9/Cm3) Apparent density (cycm3) p610/je13M/p210

Claims (1)

[Claims] 1. Fe-Si-A made by coating the surface of Fe-Si-Al alloy powder with an inorganic insulating material and heat-treating it after pressure molding.
In the method for manufacturing an l-based alloy powder magnetic core, Fe-Si-A
A spherical coarse powder is produced by gas atomization from the molten metal of the L-based alloy, and then the coarse powder is further crushed to obtain an average particle size of 40 to 110 μm and an apparent density of 2.6 to 3.8.
Fe-S characterized by using powder of g/cm^3
A method for producing an i-Al alloy powder magnetic core. 2. The method for producing a Fe-Si-Al alloy powder magnetic core according to claim 1, wherein the spherical coarse powder produced by gas atomization contains 100 PPM or less of oxygen.