JPH0332886B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention mainly relates to Fe iron cores used as iron cores of power converters such as power transformers and high frequency
The present invention relates to a method for improving the magnetic properties of basic amorphous alloy ribbons, particularly iron loss.

(Prior Art) Amorphous alloy ribbons produced by rapid solidification from a molten state exhibit various excellent properties and are attracting attention for their applications. Among these, Fe-based amorphous alloys are being used as materials for various iron cores because of their high magnetic flux density and low iron loss. The reason why amorphous alloys have low core loss is that they have no anisotropy in principle and have no defects such as grain boundaries, so hysteresis loss is small, and the plate thickness is thin and electrical resistance is low. It is said that because of its large size, eddy current loss is also small. However, the eddy current loss in a broad sense, which is obtained by subtracting the DC hysteresis loss from the iron loss value, is several tens to 100 times larger than the classical eddy current loss calculated assuming uniform magnetization.
It's twice as big. This indicates that because the magnetic domain width is large, the proportion of abnormal eddy current loss caused by non-uniform magnetization changes is large.

As a method for reducing abnormal eddy current loss, the application of the method conventionally used for grain-oriented silicon steel sheets was first considered and attempted. For example, the scratch method. This is a device that uses a sharp point made of hard material to score the surface of a silicon steel plate, dividing the magnetic domains into smaller pieces and reducing iron loss. However, even when this method was applied to amorphous alloy ribbons, good results were not necessarily obtained. for example
Narita et al. Proceedings of 4th International
Conference on Rapidly Quenched Metals
(1982) reported in P1001-1004 the effect of linear strain introduced by annealing an Fe-based amorphous alloy ribbon on the surface of the ribbon with a diamond needle on the iron loss. . According to this, the effect of distortion is
Iron loss appears in the high frequency range above 5kHz, but it actually increases in the low frequency range below 100Hz, which is important for power transformers. The reason for this is that in amorphous alloys, which are thinner than silicon steel sheets, the eddy current loss is originally small in the low frequency range, so the effect of reducing iron loss due to magnetic domain refinement is slight, and rather the hysteresis loss This is presumed to be due to the increase in total iron loss.

A method of local crystallization has been proposed as a method of reducing iron loss unique to amorphous materials. This is JP-A-57
This is a method disclosed in Japanese Patent No. 97606, in which crystallized regions are formed in the form of lines or dots in the width direction of the ribbon. The crystallization method here is to irradiate laser light or electron beam, or use metal needles or
A method is adopted in which one of the metal edges is heated with electricity while being brought close to or in contact with the surface of the ribbon. Although this method of introducing local crystallized regions is an effective means for subdividing magnetic domains, it has the drawback that it does not necessarily have a certain effect on reducing iron loss in the low frequency range. For example, in the above-mentioned Japanese Patent Application Laid-Open No. 57-97606, the effect is expressed at commercial frequencies;
The above-mentioned paper by Narita et al. also describes the effect of adding a linear crystallized region, but according to it, compared to the scratch method, the effective region extends to the low frequency side, but it is ineffective below 200 Hz. In fact, it has deteriorated.

As described above, all the methods conventionally attempted to improve the core loss of amorphous magnetic alloys, particularly Fe-based amorphous alloy ribbons, have often been ineffective in commercial frequency bands.

In contrast, the present invention proposes a new method that provides a stable effect even in a low frequency band and is highly effective in reducing iron loss in amorphous alloys.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for significantly and stably reducing the core loss of an amorphous magnetic alloy.

(Means for Solving the Problems) The present invention melts the surface of an amorphous alloy ribbon locally and instantaneously, and then rapidly solidifies that part to make it amorphous again, thereby achieving a remarkable This stably achieves a reduction in iron loss. A narrowly focused pulsed laser beam is used to locally melt the surface of the ribbon.

It is preferable that the shape and distribution of the introduced local melting portions be in the form of a series of parallel points, as illustrated in FIG. The area and depth of each melted portion are determined on the condition that the melted portion and the surrounding area do not crystallize during heating or during the resolidification process after melting. When using pulsed laser light, the irradiation intensity,
Beam diameter, sweep speed, frequency, etc. are the parameters to be controlled.

When locally dissolving using pulsed laser light,
The diameter of one spot is preferably 0.5 mm or less. Exceeding these ranges may cause crystallization,
No improvement in magnetic properties can be observed either.

The direction of the dot array of the local melting portion to be introduced is preferably in the width direction of the ribbon as shown in FIG. 1, but it may be in an inclined direction up to about 30°. Also, adjacent point sequences do not need to be parallel. If the average inclination angle with respect to the ribbon width direction is less than a predetermined value and the average interval between adjacent dots is within a predetermined range, it is effective in reducing iron loss. Therefore, the sinusoidal melting section shown in FIG. 2 is also included within the scope of the present invention. It is preferable that the average spacing of the dot rows exhibiting an effect on commercial frequencies is 1 to 20 mm, and the average angle with respect to the width direction is 30 degrees or less.

In the present invention, the local melting portion may be introduced at any time before, during, or after the step of heat treating the amorphous alloy ribbon. However, the optimum conditions differ depending on the time when the melting part is introduced. For example, when a local melting zone is introduced in the width direction using the pulse mode of a YAG laser, the effective diameter of the melting zone varies depending on the time of introduction, as shown in FIGS. 3 and 4. That is, when introduced after heat treatment, the optimum spot diameter is 50 to 100 μm, but when introduced before heat treatment, the most effective spot diameter is around 200 to 250 μm. The reason for this is thought to be that the effect of introducing the melted zone is alleviated by heat treatment. The difference in effectiveness depending on the time of introduction is also reflected in the excitation characteristics. Those introduced after heat treatment showed a decrease in magnetic flux density of several to 10% at a magnetic field of 1 oersted, whereas those introduced before heat treatment showed almost no decrease in magnetic flux density.

In order to locally melt the surface of the amorphous alloy ribbon,
As mentioned above, the best way to rapidly heat the material is to irradiate it with narrowly focused pulsed laser light for a short period of time. Other methods have no effect, but rather have negative effects. Attempting to melt the material by electron beam irradiation, contact with a high-temperature object, or locally applying electricity is not preferred because the thermal influence spreads and crystallization occurs due to the low incident energy density.

The iron loss improvement effect when applying the present invention depends on the thickness of the material, and as shown in Figure 5, the greater the thickness, the greater the improvement effect (○ in the figure is before irradiation, and ● is after irradiation) . A plate thickness of 60 μm shows a 40-50% iron loss reduction effect, while a plate thickness of 30 μm or less shows a 10-20% reduction in iron loss.
That's about it. The reason for this is that in general, as the plate thickness of an amorphous alloy increases, the magnetic domain width increases, and the absolute value of the abnormal eddy current loss and its proportion in the total core loss increase. It was verified by observation using a scanning electron microscope that by introducing the local melting portion of the present invention, the magnetic domain width can be subdivided into 1/3 in the case of a plate thickness of 60 μm.

In the present invention, whether or not the part irradiated with the pulsed laser has once melted and then resolidified can be clearly distinguished by observing the irradiated part with an optical microscope or a scanning electron microscope. When irradiated with pulses, the center of the melted part becomes a depression, and the periphery is slightly raised. This is thought to be because the alloy melted by the rapid incidence of thermal energy overflows into the surrounding area. An example of a melted zone introduced by a pulsed laser is shown in FIG.

In the present invention, it was confirmed by X-ray diffraction, transmission electron microscopy, optical microscopy, etc. that the portion locally dissolved and resolidified by pulsed laser irradiation and the surrounding area were not crystallized.

Further, the method of the present invention showed similar effects even when applied before or after surface treatment for the purpose of insulation or rust prevention was applied to the surface of the ribbon.

(Example) Example 1 Composition Fe _80.5 Si _6.5 B ₁₂ C ₁ produced by single roll method,
An amorphous alloy ribbon with a thickness of 65 μm was heated to 360°C for 60 minutes with N ₂
After magnetic field annealing in gas, a YAG laser was used to introduce a localized melt onto the free surface, and an experiment was conducted to investigate the effect on iron loss. Irradiation conditions are frequency
400Hz pulse mode, sweep speed 10cm/sec, dot row direction parallel to ribbon width direction, dot row interval 5
mm, and the size of the melted part was controlled by the power of the irradiation energy and the beam diameter. Figure 3 shows the relationship between the diameter of the introduced spot-shaped melted portion and iron loss. The effect of reducing iron loss is large when the diameter of the melted part is in the range of 30 to 150 μm. Here, a single plate tester was used to measure iron loss. It was confirmed from the diffraction image obtained when X-rays were irradiated along a dot array through a slit with a width of 0.5 mm that the area irradiated under irradiation conditions with a large iron loss reduction effect and its surroundings were not crystallized.

Example 2 The free surface of an as-cast amorphous alloy ribbon in the same lot as that used in Example 1 was irradiated with a pulsed laser under the same irradiation conditions as in Example 1. 360℃ after irradiation
The relationship between iron loss and diameter of the melted part after magnetic field annealing in N ₂ gas for 60 minutes was as shown in Figure 4. The effect of reducing iron loss is remarkable when the diameter of the melted part is around 200 μm. Example 1 shows the melted part of the ribbon after magnetic field annealing.
Although X-ray diffraction was carried out using the method described in 1., the presence of crystals was not observed.

(Effects of the Invention) As explained above, according to the present invention, iron loss can be reduced even in a low frequency band, so the present invention is extremely useful.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams showing an amorphous alloy ribbon to which the method of the present invention is applied, and Figures 3 and 4 are explanatory diagrams showing the relationship between the diameter of the melted part and iron loss in the method of the present invention. , FIG. 5 is an explanatory diagram showing the relationship between plate thickness and iron loss in the method of the present invention, and FIG. 6 is a microscopic photograph showing the state of the metal structure of the melted part by the method of the present invention.

Claims (1)

[Claims] 1. By irradiating a pulsed laser in the width direction of the amorphous alloy ribbon, the surface of the amorphous alloy ribbon is locally and instantaneously melted, and then rapidly solidified to become amorphous again. A method for improving the magnetism of an amorphous alloy ribbon, characterized by introducing crystallized circular or elliptical regions in a dot array. 2. A method for improving the magnetism of an amorphous alloy ribbon according to claim 1, which comprises annealing a ribbon into which a melted portion having a diameter of 200 to 250 μm has been introduced. 3. A method for improving the magnetism of an amorphous alloy ribbon according to claim 1, which comprises introducing a melted part with a diameter of 50 to 100 μm into the annealed amorphous alloy ribbon.