WO2016132696A1

WO2016132696A1 - Powder magnetic core and method for producing same, and magnetic member produced using same

Info

Publication number: WO2016132696A1
Application number: PCT/JP2016/000582
Authority: WO
Inventors: 井上　哲夫
Original assignee: 株式会社東芝; 東芝マテリアル株式会社
Priority date: 2015-02-16
Filing date: 2016-02-04
Publication date: 2016-08-25
Also published as: JP6606162B2; JPWO2016132696A1; CN107210120A; CN107210120B

Abstract

A powder magnetic core 1 according to an embodiment comprises a pressed powder composed of a Fe-based soft magnetic powder 2 and a glass 3, wherein the diameter of each pore in the powder magnetic core 1 is 20 μm or less (including zero) and the area occupancy rate of the soft magnetic powder 2 in the powder magnetic core 1 is 88% or more.

Description

Dust core, method for manufacturing the same, and magnetic component using the same

Embodiments of the present invention relate to a dust core, a manufacturing method thereof, and a magnetic component using the same.

The dust core is used for magnetic cores of magnetic parts such as transformers, reactors, thyristor valves, noise filters, and choke coils. The dust core is required to have low iron loss and high magnetic flux density. Furthermore, it is required that their magnetic characteristics do not deteriorate from a low frequency region to a high frequency region. Iron loss includes eddy current loss We and hysteresis loss Wh. The eddy current loss We has a large relationship with the specific resistance (specific resistance) of the magnetic core. The hysteresis loss Wh is affected by strain in the magnetic powder that occurs during the magnetic powder manufacturing process or the dust core manufacturing process. The iron loss W of the dust core can be represented by the sum of eddy current loss We and hysteresis loss Wh. The eddy current loss We increases in proportion to the square of the frequency f, and it is essential to suppress the eddy current loss We in order to improve the characteristics particularly in the high frequency region.

In order to lower the eddy current loss We, it is effective to increase the effective specific resistance value ρ by confining the eddy current in a small area. When the magnetic powder is compression-molded and the powder magnetic core has a configuration in which individual magnetic powders are insulated, the effective specific resistance value ρ increases. In such a dust core, if the insulation is insufficient, the effective specific resistance value ρ decreases and the eddy current loss We increases. On the other hand, when the insulating film is thickened to improve the insulation, the volume ratio of the magnetic powder in the magnetic core is reduced, and the magnetic flux density is reduced. In order to increase the magnetic flux density, if the magnetic powder is compacted at a high pressure to increase the density of the powder magnetic core, distortion of the magnetic powder during molding cannot be avoided, and the hysteresis loss Wh increases. In particular, since the influence of the hysteresis loss Wh becomes relatively large in the low frequency region, in order to reduce the iron loss W, it is important to reduce the hysteresis loss Wh.

As a conventional method for manufacturing a dust core, a method of compression molding a mixture of soft magnetic powder and resin is known. In the method of maintaining the binding and insulating properties with the resin, it is necessary to mix a certain amount of the resin. When resin is added, the volume ratio of the magnetic powder decreases, the magnetic flux density decreases, the magnetic coupling between the magnetic powders decreases, and it becomes close to an isolated state. There is a disadvantage that Wh becomes large. When compression molding is performed at a high pressure in order to increase the volume ratio of the magnetic powder, the formed electrical insulating layer is destroyed and the eddy current loss We increases, or the molding distortion remaining in the magnetic powder increases, resulting in hysteresis loss. This leads to an increase in Wh. As described above, in the dust core using the resin component as the binder, there is a limit in reducing the eddy current loss We and the hysteresis loss Wh.

JP 2010-114222 A

The problem to be solved by the present invention is to provide a dust core, a method of manufacturing the same, and a magnetic component using the same, which can maintain a good insulating property while improving the volume ratio of the magnetic powder There is to do.

The powder magnetic core of the embodiment is a powder magnetic core made of a powder compact including Fe-based soft magnetic powder and glass, and the pore diameter in the powder compact is 20 μm or less (including zero). The occupation ratio of the Fe-based soft magnetic powder in the powder is 88% or more in terms of area ratio.

The method of manufacturing a dust core according to the embodiment includes a step of preparing glass-coated soft magnetic powder by coating glass on Fe-based soft magnetic powder, and a step of preparing a deposit by depositing the glass-coated soft magnetic powder. And pressurizing the deposited body while heating it at a temperature not lower than the softening point and not higher than the melting point of the glass to obtain a dust core.

It is sectional drawing which shows the powder magnetic core of embodiment. It is a figure explaining the shortest distance between the magnetic powder in the powder magnetic core of embodiment.

Hereinafter, a dust core according to the present invention, a manufacturing method thereof, and a form for carrying out a magnetic component using the same will be described.

(Dust core)
The powder magnetic core of the embodiment is made of a powder compact including Fe-based soft magnetic powder and glass. In the powder magnetic core of the embodiment, the pore diameter in the powder compact is 20 μm or less (including zero), and the occupation ratio of the Fe-based soft magnetic powder in the powder compact is 88% or more in area ratio.

FIG. 1 is a cross-sectional view showing a structural example of a dust core 1 according to the embodiment. In FIG. 1, 1 is a powder magnetic core (powder), 2 is an Fe-based soft magnetic powder, 3 is glass, and 4 is a pore. The Fe-based soft magnetic powder is made of iron or an iron alloy. Fe-based soft magnetic powder
Fe _x M _100-x
(Wherein M is at least one element selected from the group consisting of silicon (Si), chromium (Cr), aluminum (Al), titanium (Ti), antimony (Sb), and tin (Sn); Satisfies 90 ≦ x ≦ 100 (mass%).)
It is preferable to have the composition represented by these. By containing the M element, the specific resistance of the Fe-based soft magnetic powder can be increased. By increasing the specific resistance of the soft magnetic powder, eddy current loss can be reduced. For this reason, the x value is more preferably in the range of 90 ≦ x ≦ 99.

Between the soft magnetic powder 2 particles, glass 3 exists. The glass 3 preferably has a softening point in the range of 500 to 800 ° C. If the softening point of the glass 3 is less than 500 ° C., it may be difficult to maintain the strength when the operating environment temperature of the dust core 1 becomes high. Further, it may be difficult to raise the temperature of the strain removing heat treatment for reducing residual stress, which will be described later, to a necessary temperature. When the softening point of the glass 3 exceeds 800 ° C., it becomes difficult to coat the soft magnetic powder 2 with the glass 3. The softening point of the glass 3 is preferably 500 to 800 ° C, more preferably 600 to 750 ° C.

The glass 3 is preferably composed mainly of one selected from silicon oxide, lead oxide, bismuth oxide, zinc oxide, vanadium oxide, tin oxide, tellurium oxide, alkali metal oxide, and fluorine. The glass 3 is preferably composed mainly of silicon oxide. Silicon oxide glass is excellent in insulation, heat resistance, and bondability.

The diameter of the pores 4 present in the powder magnetic core (powder) 1 is 20 μm or less (including zero). The occupation ratio of the soft magnetic powder 2 in the dust core (powder) 1 is 88% or more in terms of area ratio. The pores 4 are formed in contact with the gap between the soft magnetic powders 2, that is, the glass layer 3. If the pore diameter exceeds 20 μm, the occupation ratio of the soft magnetic powder 2 cannot be increased. The pore diameter is 20 μm or less, and preferably 10 μm or less. Most preferred is a state without pores (pore diameter 0 μm). The pore diameter of 20 μm or less indicates that the maximum diameter of the pores 4 is 20 μm or less.

Thus, the occupation ratio of the soft magnetic powder 2 can be increased by reducing the pore diameter. The occupation ratio of the soft magnetic powder 2 is 88% or more in area ratio. The occupation ratio of the soft magnetic powder 2 is more preferably 90% or more, and particularly preferably 92% or more and 97% or less in terms of area ratio. By increasing the occupation ratio of the soft magnetic powder 2, the magnetic flux density can be increased. As a result, the saturation magnetization of the dust core 1 can be increased. The occupation ratio of the soft magnetic powder 2 is preferably 97% or less in terms of area ratio. If the occupation ratio of the soft magnetic powder 2 exceeds 97% in terms of area ratio, the ratio of the glass 3 is relatively decreased, and thus the insulation between the soft magnetic powders 2 may be lowered.

The area ratio (area ratio) indicating the occupation ratio of the soft magnetic powder 2 is measured as follows. First, an SEM photograph per unit area is taken in an arbitrary cross section of the dust core 1. The area ratio [= (total area of soft magnetic powder 2 / unit area) × 100] of the soft magnetic powder 2 shown in the SEM photograph is obtained. This operation is performed for five arbitrary unit areas, and the average value is defined as the area ratio (%). When the average particle size of the soft magnetic powder 2 is 50 μm or less, the unit area is set to 100 μm × 100 μm. When the average particle diameter of the soft magnetic powder 2 exceeds 50 μm, the unit area is set to 300 μm × 300 μm. The magnification of the SEM photograph is 1000 times.

The soft magnetic powder 2 preferably has an average particle size of 3 μm or more and 100 μm or less. When the average particle size of the soft magnetic powder 2 is less than 3 μm, it is difficult to control the thickness of the insulating glass coating in the step of preparing a glass-coated soft magnetic powder described later. When the average particle diameter of the soft magnetic powder 2 exceeds 100 μm, the gap between the soft magnetic powders 2 tends to be large. When the gap between the soft magnetic powders 2 becomes large, a region where the glass layer 3 partially increases is formed, and the occupation rate per unit area may be out of the range. Therefore, the average particle diameter of the soft magnetic powder is preferably 3 to 100 μm, and more preferably 10 to 80 μm.

The average particle diameter of the soft magnetic powder 2 is measured as follows. First, an SEM photograph is taken at an arbitrary cross section of the dust core 1. The major axis and minor axis of the soft magnetic powder 2 shown in this SEM photograph are measured, and the value obtained by dividing the total by 2 is defined as the particle diameter. This operation is performed for 50 pieces (50 soft magnetic powders), and the average value is defined as the average particle size. Here, the major axis is the longest diameter of the flat body, and the minor axis is the length on the perpendicular at the midpoint of the major axis. The magnification of SEM imaging is a magnification that clearly shows the outline of the particle diameter. For example, a 100 μm × 100 μm SEM photograph is taken at a magnification of 1000 times and used.

The soft magnetic powder 2 preferably has a flat shape. The flat shape preferably has an average aspect ratio in the range of 1.5 to 20. The aspect ratio is measured by the major axis / minor axis using the above SEM photograph. This operation is performed for 50 pieces, and the average value is defined as the average aspect ratio. The average aspect ratio in the flat shape is more preferably in the range of 2-20. According to the soft magnetic powder 2 having a flat shape, the distance between adjacent soft magnetic powders 2 can be easily controlled.

In any cross section of the powder magnetic core (powder compact) 1, the shortest distance SD between the adjacent soft magnetic powders 2 is preferably 3 nm or more and 1000 nm or less. Thereby, the occupation ratio of the soft magnetic powder per unit area can be increased. The shortest distance between adjacent soft magnetic powders 2 is more preferably 8 nm or more and 200 nm or less, and particularly preferably 8 nm or more and 130 nm or less. Furthermore, the occupation rate of the soft magnetic powder 2 per unit area can be further increased by setting the shortest distance between adjacent soft magnetic powders 2 to 10 nm or more and 130 nm or less. By setting the shortest distance between adjacent soft magnetic powders 2 to 10 nm or more, insulation can be ensured more reliably.

FIG. 2 shows an example of a cross section of the green compact 1. In FIG. 2, 2-1 and 2-2 are soft magnetic powders, and 3 is glass. In FIG. 2, soft magnetic powder 2-2 exists around soft magnetic powder 2-1. The shortest distance between adjacent soft magnetic powders 2 means that an SEM photograph (magnification of 10,000 times) is taken at an arbitrary cross section of the green compact 1 and the soft magnetic powder 2 shown in the SEM photograph has an interval between adjacent soft magnetic powders 2. This is a value obtained by measuring the shortest distance. FIG. 2 shows the distance between the two soft magnetic powders 2. When a plurality of soft magnetic powders 2 are present in the surroundings, the distance between the soft magnetic powders 2 that is the closest among them is defined as “the shortest distance between adjacent soft magnetic powders”.

Furthermore, by controlling the shortest distance between the adjacent soft magnetic powders 2, the porosity of the powder magnetic core (powder) 1 can be reduced to 10% or less, and further to 6% or less. The measurement of the porosity is preferably performed by TEM (Transmission Electron Microscope) analysis. Further, simply, “porosity = 100−occupancy ratio of soft magnetic powder (%)” may be used. Such a calculation method is effective when the shortest distance between adjacent soft magnetic powders 2 is close to 130 nm or less, or even 50 nm or less.

In the powder magnetic core 1 of the embodiment, the glass layer 3 can be formed as an insulating layer between the soft magnetic powders 2 after increasing the occupation ratio of the soft magnetic powders 2. Therefore, it is possible to achieve both the improvement of the magnetic flux density of the dust core 1 and the reduction of the eddy current loss We. Further, the hysteresis loss Wh can be reduced by reducing the residual stress of the dust core 1 by heat treatment or the like to be described later. For this reason, the loss W can be reduced.

(Magnetic parts)
The dust core 1 of the embodiment is suitably used for various magnetic components. Examples of the magnetic component include a transformer, a reactor, a thyristor valve, a noise filter, and a choke coil. These magnetic components have a dust core. The dust core is subjected to a winding process or the like as necessary. The magnetic component is suitable for a magnetic component used in a high frequency region having a frequency of 30 kHz or more. The magnetic component of the embodiment exhibits excellent magnetic properties because it achieves both improvement in the magnetic flux density of the dust core 1 and low loss. In particular, it is effective for a transformer for a switching power source, an inductor, a reactance, etc. used at a frequency of 100 kHz or more.

(Production method of dust core)
Next, the manufacturing method of the powder magnetic core of embodiment is demonstrated. If the powder magnetic core of embodiment has the above-mentioned structure, the manufacturing method will not be specifically limited. The following method is mentioned as a method for efficiently obtaining the dust core of the embodiment. The method for manufacturing a dust core includes, for example, a step of preparing glass-coated soft magnetic powder by coating glass on Fe-based soft magnetic powder, a step of preparing a deposit by depositing glass-coated soft magnetic powder, and a deposit And pressurizing while heating at a temperature not lower than the melting point and not higher than the melting point of the glass.

First, glass is coated on Fe-based soft magnetic powder to prepare glass-coated soft magnetic powder. The Fe-based soft magnetic powder is made of iron or an iron alloy. Fe-based soft magnetic powder
Fe _x M _100-x
(M is at least one element selected from the group consisting of Si, Cr, Al, Ti, Sb, and Sn, and x satisfies 90 ≦ x ≦ 100 (mass%).)
It is preferable to have the composition represented by these. The average particle size of the Fe-based soft magnetic powder is preferably 3 μm or more and 100 μm or less. The average particle size of the raw material powder is a value determined by D _50.

The glass preferably has a softening point of 500 ° C. or higher and 800 ° C. or lower. The glass preferably contains as a main component at least one selected from the group consisting of silicon oxide, lead oxide, bismuth oxide, zinc oxide, vanadium oxide, tin oxide, tellurium oxide, alkali metal oxide, and fluorine. The coating of the Fe-based soft magnetic powder with glass is performed, for example, by a method of forming a film using hydrolysis of a metal alkoxide. The coating method using hydrolysis is performed as follows. First, soft magnetic powder and water are mixed and sufficiently stirred. Next, a metal alkoxide is added and stirred to cause a hydrolysis reaction. Thereafter, the glass-coated soft magnetic powder is prepared by sufficiently drying.

The glass coating thickness is preferably 5 nm or more and 80 nm or less. If the coating thickness of the glass is less than 5 nm, the amount of glass present between the soft magnetic powders is small, so that the insulating property may be lowered. When the glass coating thickness exceeds 80 nm, it is difficult to increase the occupation ratio of the soft magnetic powder. Therefore, the glass coating thickness is preferably 5 nm to 80 nm, and more preferably 10 nm to 50 nm.

Next, a glass-coated soft magnetic powder is deposited to prepare a deposit. The step of preparing the deposit is preferably a mold molding method or a cold spray method.

Next, a step of pressing the deposited body while heating it at a temperature not lower than the softening point of the glass and not higher than the melting point is performed. The heating and pressing step is performed by hot pressing (HP), HIP (hot isostatic pressing) or the like. The pressure in the heating and pressing step is preferably 100 MPa or more, and more preferably 200 MPa or more. The upper limit of the pressure is not particularly limited, but is preferably 2000 MPa or less. By adjusting the pressure to 200 MPa or more and 2000 MPa or less, the aspect ratio of the soft magnetic powder can be adjusted simultaneously with the production of the green compact.

By pressing the glass-coated soft magnetic powder deposit while heating, a green compact can be produced while softening the glass. As a result, the occupation ratio of the soft magnetic powder can be increased while reducing the pore diameter in the green compact. Furthermore, since the soft magnetic powder previously coated with glass is used, insulation between the soft magnetic powders can be ensured. The heating temperature in the heating and pressurizing step of the deposit is preferably equal to or higher than the temperature at which the stress of the Fe-based soft magnetic powder can be relaxed. The temperature at which stress relaxation of the Fe-based soft magnetic powder varies depending on the composition of the Fe-based soft magnetic powder, but is about 500 to 800 ° C. The heat treatment for stress relaxation of the Fe-based soft magnetic powder may be performed separately from the heating and pressing step.

Next, specific examples of the present invention and evaluation results thereof will be described.

(Examples 1-7, Comparative Examples 1-2)
FeSi alloy powder (Si content: 3.5 mass%) was prepared as the Fe-based soft magnetic powder. As glass, silicon oxide glass (Va glass, softening point 600 ° C.) was prepared. A glass-coated soft magnetic powder was prepared by coating glass on Fe-based soft magnetic powder. The average particle diameter D ₅₀ of the soft magnetic powder and the coating thickness of the glass are as shown in Table 1. The SEM image mentioned above was used for the measurement of the average particle diameter of Fe type soft magnetic powder.

Next, mold molding was performed using the glass-coated soft magnetic powders of Examples and Comparative Examples. Thereafter, the HIP treatment was performed under the conditions shown in Table 2. A green compact was produced by HIP treatment.

For the obtained green compact, the occupation ratio of the soft magnetic powder, the aspect ratio of the soft magnetic powder, the pore diameter, the porosity, and the shortest distance SD between adjacent soft magnetic powders were determined. The results are shown in Table 3. For the measurement of the occupation ratio of the soft magnetic powder, when the average particle diameter of the soft magnetic powder is 50 μm or less, an SEM photograph (unit: 1000 times) having a unit area of 100 μm × 100 μm was used. When the average particle size of the soft magnetic powder exceeded 50 μm, an SEM photograph (unit: 1000 times) having a unit area of 300 μm × 300 μm was used. The area of the soft magnetic powder shown in the SEM photograph was determined, and the average value for five unit areas was defined as the occupation ratio.

The aspect ratio, average particle diameter, and pore diameter of the soft magnetic powder were measured using the SEM photograph described above. The aspect ratio and average particle diameter of the soft magnetic powder were average values for 50 soft magnetic powders. The shortest distance SD between adjacent soft magnetic powders was measured using a SEM photograph with a magnification of 10,000 times. The SEM photograph mentioned above was used for the measurement of a pore diameter and a porosity. When it was difficult to confirm the pores in the SEM photograph, TEM observation was used. The pore diameter was the maximum diameter of the pores shown in the enlarged photograph.

It was confirmed that the green compacts (powder cores) according to each example had an area ratio of soft magnetic powder of 88% or more and a pore diameter as small as 20 μm or less.

(Examples 8 to 13, Comparative Examples 2 to 4)
FeSi alloy powder (Si content: 3.5 mass%) and FeSiAl alloy powder (Si content: 9.5 mass%, Al content: 5.5 mass%) were prepared as Fe-based soft magnetic powders. As glass, sodium-based glass (softening point 600 ° C.) and soda lime glass (softening point 730 ° C.) were prepared. Glass was coated on the soft magnetic powder to prepare a glass-coated soft magnetic powder. Table 4 shows the average particle diameter D ₅₀ measured by the SEM image of the soft magnetic powder and the coating thickness of the glass. In Table 4, sodium-based glass was expressed as Na-based, and soda-lime glass was expressed as soda-lime.

Next, mold molding was performed using the glass-coated soft magnetic powders of Examples and Comparative Examples. Thereafter, HIP treatment was performed under the conditions shown in Table 5. A green compact was produced by HIP treatment.

For the obtained green compact, the occupation ratio of the soft magnetic powder, the aspect ratio of the soft magnetic powder, the shortest distance SD between adjacent soft magnetic powders, the pore diameter, and the porosity were determined. Each measurement method was the same as that in Example 1. The results are shown in Table 6.

It was confirmed that all of the green compacts (powder magnetic cores) of the examples had a soft magnetic powder occupancy ratio of 88% or more in area ratio and a small pore diameter of 20 μm or less. Further, even if the soft magnetic material and the glass material were changed, a green compact with a high occupation ratio of the soft magnetic powder was obtained.

Next, saturation magnetization and loss were measured for each of the dust cores of Examples and Comparative Examples. The loss was measured under the conditions of 100 kHz and 0.2 T (Tesla) in the initial permeability range. The results are shown in Table 7.

As can be seen from Table 7, it was confirmed that the dust cores of the respective examples had excellent magnetic properties. On the other hand, in the dust cores of Comparative Example 1, Comparative Example 2, and Comparative Example 4, only a low value of saturation magnetization of 1.7 T or less was obtained. The dust core of Comparative Example 3 had a high loss of 5200 kW / m ³ . This is because the pore diameter is large.

In addition, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

Claims

A dust core comprising a powder compact including Fe-based soft magnetic powder and glass,
A dust core in which a pore diameter in the green compact is 20 μm or less (including zero), and an occupation ratio of the Fe-based soft magnetic powder in the green compact is 88% or more in area ratio.
2. The dust core according to claim 1, wherein a porosity of the powder compact is 10% or less (including zero).
The powder magnetic core according to claim 1 or 2, wherein an average particle diameter of the Fe-based soft magnetic powder is 3 µm or more and 100 µm or less.
The Fe-based soft magnetic powder is
Fe x M 100-x
(In the formula, M is at least one element selected from the group consisting of Si, Cr, Al, Ti, Sb, and Sn, and x satisfies 90 ≦ x ≦ 100 (mass%).)
The dust core according to claim 1, having a composition represented by:
The powder magnetic core according to any one of claims 1 to 4, wherein a shortest distance between the adjacent Fe-based soft magnetic powders in an arbitrary cross section of the powder compact is 3 nm or more and 1000 nm or less.
The dust core according to any one of claims 1 to 5, wherein the Fe-based soft magnetic powder has a flat shape.
The dust core according to any one of claims 1 to 6, wherein a softening point of the glass is 500 ° C or higher and 800 ° C or lower.
A magnetic component comprising the dust core according to any one of claims 1 to 7.
The magnetic component according to claim 8, wherein the magnetic component is a transformer, a reactor, a thyristor valve, a noise filter, or a choke coil.
The magnetic component according to claim 8 or 9, wherein the magnetic component is configured to be used in a high frequency region having a frequency of 30 kHz or more.
Coating Fe-based soft magnetic powder with glass to prepare glass-coated soft magnetic powder;
Depositing the glass-coated soft magnetic powder to prepare a deposit;
A method of producing a dust core, comprising: pressing the deposited body while heating at a temperature not lower than a melting point of the glass and not higher than a melting point to obtain a dust core.
The method of manufacturing a dust core according to claim 11, wherein the step of preparing the deposit is performed by a mold molding method or a cold spray method.
The method of manufacturing a dust core according to claim 11 or 12, wherein a heating temperature of the deposit is not less than a temperature at which stress relaxation of the Fe-based soft magnetic powder is possible.
The method of manufacturing a dust core according to any one of claims 11 to 13, wherein the glass has a softening point of 500 ° C or higher and 800 ° C or lower.
The method for manufacturing a dust core according to any one of claims 11 to 14, wherein a coating thickness of the glass is 5 nm or more and 80 nm or less.