JPH06151143A - Low loss magnetic core - Google Patents

Abstract

PURPOSE:To provide compactness and high performance requested to magnetic cores and also to give higher efficiency, compact size and lightweight to various electronic devices by providing low loss in the high frequency region of magnetic core and higher coercive force thereby corresponding to the trend of turning into high frequency range for power sources and providing magnetic cores having constant magnetic permeability. CONSTITUTION:Low loss magnetic core of the present invention comprises group Fe amorphous alloy sheet band having a DC rectangular ratio (Br/Bs) of less than 50%, DC coercive force of 0.2 to 10Oe and 1MHz rectangular ratio (Br/B1) of 5 to 30%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core used for a switching power supply or the like, and more particularly to a low loss magnetic core effective in a high frequency region of MHz level.

[0002]

2. Description of the Related Art In recent years, with the demand for smaller, lighter weight and higher performance of electronic devices, the magnetic parts, which are the functional parts constituting them, are also improved in performance by using materials having excellent magnetic characteristics. Is required.

For example, a switching power supply has been widely used in recent years as a stabilizing power supply for electronic equipment, but as the demand for smaller and lighter power supplies increases, higher switching frequencies are required. However, for example, in the case of a switching power supply incorporating a magnetic amplifier, even if an amorphous alloy having good high frequency characteristics is used among metal materials, the limit is practically 200 to 500 kHz, and further high frequency support is desired. It was rare.

Similarly, high frequencies are also required for transformers, choke coils and the like which are required to have constant magnetic permeability. Ferrites have been the mainstream of materials conventionally used for transformers. However, the transformer using ferrite has a problem that it is not possible to sufficiently satisfy the above-mentioned demand for higher frequency.

Further, it is generally known that by reducing the plate thickness of a metal material, iron loss can be suppressed and high frequency characteristics can be improved. Even in an amorphous alloy, the thickness can be reduced to further improve the magnetic characteristics. Is being considered.
However, although the amorphous alloy ribbon is generally produced by a liquid quenching method such as a single roll method in the atmosphere,
With this method, the reduction of the plate thickness is not sufficient, and pinholes are generated due to the inclusion of bubbles, which is problematic in terms of practicality including high frequency.

Further, the magnetic core of the present invention is required to have high coercive force as well as low loss. Usually, in order to reduce the loss, the coercive force is lowered to at least less than 0.2 Oe as a means to reduce the loss.
After obtaining the metal ribbon, after winding it in a toroidal shape at the stage of manufacturing the magnetic core, it is impregnated with a resin, cured, cut, and then subjected to a treatment such as a magnetic gap to obtain a coercive force. It was high. However, in this process, there is a problem that the magnetic characteristics of the material cannot be fully utilized because the loss increases due to various stresses, the finished state of the cut surface and the like. Furthermore, there is a problem that the provision of the gap causes leakage of magnetic flux during use, which causes noise.

[0007]

As described above, in response to the demands for high efficiency, small size and light weight of various electronic devices, and miniaturization and high performance of the magnetic core, the high frequency region of the magnetic core used for the switching power supply etc. There is a strong demand for low loss in the field.

The present invention has been made in order to solve such a problem, and achieves a low loss and a high coercive force in the high frequency region of the magnetic core, thereby responding to the high frequency of the power supply and within the use excitation range. An object of the present invention is to provide a magnetic core having constant magnetic permeability.

[0009]

The low loss magnetic core of the present invention has a DC squareness ratio (Br / Bs; Br is a residual magnetic flux density, Bs is a saturated magnetic flux density) of 50% or less and a coercive force of 0.
Squareness ratio at 2 to 10 Oe and 1 MHz (Br / B1; B1
Has a magnetic flux density of 5 to 30% when a 1 Oe magnetic field is applied.
And Fe-based amorphous alloy ribbon.

The inventors of the present invention have made earnest studies in order to obtain low loss without lowering the coercive force in the high frequency region of MHz level. As a result, the DC squareness ratio (Br / Bs) is 50% or less, and the squareness at 1 MHz is obtained. It has been found that when the ratio (Br / B1) is in the range of 5 to 30%, reduction of loss in the high frequency region of MHz level can be easily obtained in the range of coercive force of 0.2 to 10 (Oe), The present invention has been completed.

The low loss magnetic core of the present invention preferably has a DC squareness ratio (Br / Bs) of 50% or less. If the DC squareness ratio is 50% or more, the eddy current loss cannot be reduced due to the movement of the domain wall, and the loss becomes large. Therefore, it is preferably 45% or less, more preferably 30% or less.

The low loss magnetic core of the present invention is 1 MHz.
The squareness ratio (Br / B1) is preferably in the range of 5 to 30%. If Br / B1 at 1 MHz is less than 5%, the hysteresis loss and the exciting power increase.
On the other hand, when it is 30% or more, the domain wall is moved and the eddy current loss cannot be sufficiently reduced, resulting in a large loss. Therefore, it is preferably 5 to 25%, and more preferably 5 to 20%.

Further, the low loss magnetic core of the present invention preferably has a coercive force in the range of 0.2 to 10 Oe. As described above, it is preferable that the coercive force of the conventional magnetic core material is small. However, in the present invention, even if the coercive force of 1 Oe or more, which is not in the category of the magnetic core material according to the conventional conventional definition, the squareness ratio By setting the range, a sufficiently low loss is obtained. When the DC coercive force is 10 Oe or more, the hysteresis loss becomes extremely large, and the total loss becomes large. Therefore, the range of 0.3 to 8 Oe is preferable, and the range of 0.5 to 8 Oe is more preferable.

Further, in the Fe-based amorphous alloy ribbon of the present invention, a crystal containing α-Fe as a main component has an area ratio of 5 to 5.
It is preferable to deposit 50%. The precipitation of α-Fe crystals brings about the effect of reducing the magnetostriction of the Fe-based amorphous alloy, and improves the sensitivity of magnetic characteristics to handling. Further, since the resonance determined by the magnetostriction and the magnetic path length is reduced by the existence of the α-Fe crystal, there is no limitation on the usable frequency, and good magnetic characteristics can be obtained even in the high frequency region of MHz level. Further, since the α-Fe crystal hinders the movement of the domain wall, even if the hysteresis loss becomes large, the eddy current loss which makes a large contribution particularly to the high frequency iron loss can be greatly reduced. Therefore, it is preferably in the range of 8 to 40%, more preferably 10 to 30%.

Further, the average crystal grain size of the crystals containing α-Fe as a main component is preferably in the range of 5 to 100 nm. If the crystal grain size is 5 nm or less, domain wall pinning is unlikely to occur and it is difficult to reduce eddy current loss. On the other hand, when the thickness is 100 nm or more, the hysteresis loss becomes too large due to the excessive pinning effect. Therefore, in order to prevent the domain wall movement and obtain the optimum hysteresis loss, the average crystal grain size is preferably 8 to 80 nm, and more preferably 10 to 50 nm.

Here, the amount of the α-Fe crystals precipitated and the average crystal grain size can be controlled by the heat treatment conditions, that is, the heat treatment temperature and the heat treatment time. α-
Precipitation of Fe crystals can be realized by strain relief heat treatment at least at a crystallization temperature (value obtained by thermal analysis at a temperature rising rate of 10 ° C./min), but in a short time of 10 minutes or less, even at a crystallization temperature or higher. It is possible.

The crystal precipitation state and the average crystal grain size were observed with a transmission electron microscope. The ratio of the crystal phase is the amount of α-Fe crystals deposited per unit area, and the average crystal grain size is the longest diameter of the α-Fe crystals. Fe-based amorphous alloy of the present invention have the general formula _{(Fe 1-a M a)} 100-c (Si 1-b B b) c M: V, Cr, Mn, Ti, Cu, Nb, Mo, Ta,
At least one selected from W is represented by 0 ≦ a ≦ 0.1 0.2 ≦ b ≦ 1 12 ≦ c ≦ 28 (at.%). Here, the M element is an element effective for making the plate thickness extremely thin because it reduces the viscosity at the time of injecting the molten metal, but if its amount is larger than 0.1, sufficient saturation magnetization cannot be obtained. Therefore, it is preferably 0.01 to 0.08, and more preferably 0.02.
The range of 0.06 is preferable. In addition, as the M element, V, Cr, Mn, Ti, and Cu are preferable when a low loss is obtained, that is, when α-Fe is easily precipitated.
Further, Nb, Mo, Ta and W are preferable for expanding the optimum heat treatment temperature.

Si and B are elements necessary for amorphization, but when b is less than 0.2, amorphization becomes difficult. Moreover, since the Si content contributes to the crystallization temperature, b is 0.3 to 0.3 when the heat treatment is taken into consideration.
0.9 is preferable and the range of 0.4-0.8 is more preferable. Further, the amount of Si determines the amount of solid solution in the α-Fe crystal, and an ordered phase may be observed at 0.5 or more.

If the total amount of Si and B is less than 12 at%, it is difficult to amorphize, while if it is more than 28 at%, it is difficult to obtain good magnetic characteristics. In addition, Fe-Si-B
Considering as a ternary system, the value of c is 12 to 26 at.
%, And for the precipitation of α-Fe crystals, the Fe-rich side of the eutectic composition, that is, the range of 12 to 22 at% is preferable.

The above amorphous alloy can be obtained by a usual single roll method in the air, but it is preferably produced under reduced pressure or in a He atmosphere in order to improve the smoothness of the surface because there are few pinholes. The plate thickness is 3 to 12
The range of 4 μm is effective for high frequencies, and in particular, the range of 4 to 12 μm is preferable in view of the above pinholelessness, surface smoothness, and space factor at the time of manufacturing the magnetic core. The low loss magnetic core of the present invention is obtained, for example, by the following method.

That is, when the molten alloy is jetted from the nozzle onto the cooling body moving at a high speed and is rapidly cooled, the molten alloy jetted from the nozzle moves at a high speed when the amorphous alloy ribbon is manufactured. The atmosphere in contact with is to be an inert atmosphere of less than 60 torr or a reduced pressure of 0.1 torr or less.

More specifically, the surroundings of the quartz nozzle containing the mother alloy are evacuated to 0.1 torr or less, or the inert gas is replaced to 60 torr or less, and a Fe-based roll, a Ni-based roll or a Cu-based roll is used. This makes it possible to produce an ultrathin amorphous alloy having good surface smoothness with few pinholes. Here, the inert gas is H
e and Ar are preferred.

The long side in the slit shape at the tip of the nozzle determines the width of the obtained ribbon, and can be set to an appropriate value of 2 mm or more. In addition, the short side is an important value that determines the thickness of the ribbon, 0.2 mm or less is preferable, and
It is preferably 0.15 mm or less. The roll peripheral speed may be 20 m / sec or more, preferably 25 m / s or more. The upper limit is 70 m / s
, And the ribbon obtained is often cut off. Injection pressure is 0.05kg to make ultra-thin ribbon
/ cm ² It may be as follows, preferably 0.03 kg / cm ² And more preferably 0.02 kg / cm ² Is.

The low-loss magnetic core of the present invention is formed into a desired shape by winding the amorphous alloy obtained by the above-mentioned manufacturing method or laminating one or more layers, and then strained at a temperature not higher than the crystallization temperature. It is obtained by performing a heat treatment. The atmosphere for these heat treatments is not particularly limited, and may be an inert atmosphere such as nitrogen or Ar, or the air.

[0025]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 (Fe _1-x V _x ) ₈₃ (Si _0.3 B _0.7 ) ₁₇ [where x is
[0.0.02,0.04,0.06] was produced by a single roll method in vacuum to obtain an amorphous alloy ribbon having a plate thickness of 7.0 μm. After molding the obtained ribbon to an outer diameter of 15 mm, an inner diameter of 10 mm, and a height of 5 mm, at a temperature below the crystallization temperature,
Magnetic characteristics such as high frequency iron loss at 1 MHz and 0.1 T, direct current squareness ratio (Br / Bs), and direct current coercive force were evaluated by changing time and temperature. High frequency iron loss, and Br / B1
Is a magnetic measurement system (Iwasaki Tsushinki SY8617)
Then, the DC magnetic characteristics were measured using a DCBH flux meter. The results are shown in FIG. 1, and it can be seen that a low loss at high frequency is obtained in the case of the magnetic characteristics within the range of the present invention.

Examples 2 to 4: Comparative Examples 1 to 3 Amorphous alloys having a composition of (Fe _0.96 Mn _0.04 ) ₈₂ (Si _0.3 B _0.7 ) ₁₈ were produced by a single roll method in a vacuum, and had a plate thickness of 7.0 μm. An amorphous alloy ribbon was obtained. The obtained ribbon was formed into an outer diameter of 12 mm, an inner diameter of 8 mm and a height of 5 mm, and then heat-treated at each heat treatment temperature shown in Table 1 for a fixed time of 30 minutes to obtain α-Fe crystals having a grain size shown in Table 1. Were also precipitated in the proportions shown in Table 1, and the dependence of various magnetic properties on the α-Fe crystal and the heat treatment temperature was investigated. The high frequency iron loss, DC squareness ratio (Br / Bs), and DC coercive force were measured under the same conditions as in Example 1, and the frequency characteristic of permeability was L
The measurement was performed using a CR meter under the condition of an excitation magnetic field of 2 mOe.

The evaluation results of various magnetic properties are shown in Table 1 and FIG. From Table 1, the magnetic core of the present invention containing α-Fe as a main component in an area ratio of 5 to 50%, and the average particle size of the α-Fe crystal in the range of 5 to 100 nm is desirable in a high frequency region. It can be seen that the magnetic characteristics are satisfied. Also,
From FIG. 2, α-Fe satisfying the area ratio and particle size of the present invention is obtained.
It can be seen that the magnetic core of the present invention having crystals has reduced resonance due to magnetostriction.

[0029]

[Table 1]

Examples 5 to 20: Comparative Examples 4 to 5 The alloy compositions shown in Table 2 were produced in vacuum by a single roll method to obtain amorphous alloy ribbons having the plate thickness shown in Table 2. The obtained ribbon was formed into an outer diameter of 15 mm, an inner diameter of 10 mm, and a height of 5 mm, and was subjected to strain relief heat treatment for 30 minutes at each crystallization temperature or lower. After that, the magnetic characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 2, and it can be seen that the magnetic core of the present invention has extremely small high frequency loss. Further, when the anisotropic magnetic field Hs was obtained from the initial magnetization curve at direct current, a large value was obtained in the magnetic core of the present invention. It can be seen that the BH linearity up to this magnetic field is good and that it has excellent constant magnetic permeability.

[0031]

[Table 2]

[0032]

As described above, according to the present invention, the loss and the coercive force of the magnetic core in the high frequency region can be reduced, which can correspond to the high frequency of the power source and the constant permeability within the used excitation range. It is possible to provide a magnetic core with magnetic susceptibility, improve efficiency for various electronic devices, reduce size and weight,
Moreover, it is extremely useful because it can sufficiently meet the demands for miniaturization and high performance of the magnetic core.

[Brief description of drawings]

FIG. 1 is a graph of 1 MHz when various heat treatments are performed on the Fe-based amorphous alloy shown in Example 1 of the present invention.
It is a figure which shows the direct current squareness ratio (Br / Bs) in 0.1T, the direct current coercive force (Hc), and the relationship of iron loss.

FIG. 2 is a diagram showing frequency characteristics of magnetic permeability in the Fe-based amorphous alloys shown in Examples 2 to 4 and Comparative Examples 1 to 3 of the present invention for each heat treatment temperature.

Claims (3)

[Claims] 1. A Fe-based amorphous alloy having a DC squareness ratio (Br / Bs) of 50% or less, a DC coercive force of 0.2 to 10 Oe, and a squareness ratio (Br / B1) of 1 MHz in the range of 5 to 30%. A low-loss magnetic core characterized by being made of a thin strip. 2. The low loss magnetic core according to claim 1,
A low-loss magnetic core, wherein the amorphous phase of the Fe-based amorphous alloy ribbon contains 5 to 50% by area ratio of crystals containing α-Fe as a main component. 3. The low-loss magnetic core according to claim 2,
The average particle size of the crystals containing α-Fe as the main component is 5 to 10
A low loss magnetic core characterized by being in the range of 0 nm.