Fe-Co alloy-coated substrate and laminated core member

Abstract

Provided is an Fe-Co based alloy substrate with which good magnetic characteristics can be obtained while ensuring insulation and adhesion. This Fe-Co based alloy coated substrate comprises an oxide layer on at least one of a front surface and a back surface of an Fe-Co based alloy substrate, the Fe-Co based alloy coated substrate being characterized in that: when the oxide layer is formed only on the front surface or the back surface, the thickness of the oxide layer is 280-500 nm; when the oxide layer is formed on the front surface and the back surface, the thicknesses of the oxide layers on the front surface side and the back surface side are 140-500 nm; and, in a cross section in the thickness direction of the Fe-Co based alloy coated substrate, the maximum height difference of unevenness of the oxide layer at an interface between the oxide layer and the Fe-Co based alloy substrate is 300 nm or less. A laminated core member is also provided.

Description

Technical Field

[0001] The present invention relates to an Fe-Co alloy-coated substrate and a laminated core member.

Background Art

[0002] Due to the increasing environmental awareness in recent years, efforts towards the electrification of automobiles and the hybridization of aircraft have been active. As these key technologies, there are the improvement of high output, miniaturization, and low loss of electric motors. As the shape of the motor core used in this electric motor, a laminated core having a structure in which a large number of soft magnetic alloy thin plates are laminated has a large magnetization amount per unit volume and is advantageous for miniaturization of the core and is therefore used.

[0003] As a method for further miniaturizing this laminated core, it is effective to apply a soft magnetic material having a high saturation magnetic flux density. As a method for further reducing the loss, improvement of the electrical insulation between the laminated single plates (hereinafter, also simply referred to as insulation) is effective. For example, Patent Document 1 discloses a laminated core in which permendur (Fe-Co alloy) single-layer materials having a high saturation magnetic flux density are laminated, and it is proposed to form a ceramic layer such as magnesium oxide, zirconium oxide, or aluminum oxide as an insulating film on the surface of the single-layer material.

[0004] On the other hand, since the coating treatment of the insulating layer is easy, a method of forming an oxide layer mainly composed of Fe and Co on the surface of the substrate by heat treatment or the like to form an insulating layer is also known. Patent Document 2 describes performing oxidation annealing on a plate material after the final recrystallization annealing step to create an oxide layer of 0.5 to 10 μm and ensuring the electrical insulation when laminated.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The insulating film such as magnesium oxide described in Patent Document 1 has good insulation properties, but requires a separate process of vapor deposition or coating with a solution, which is a factor increasing the man-hours. In addition, when manufacturing a laminated core, adhesion is also required for the Fe-Co-based alloy substrate that is the material of the laminated core so that the insulating layer does not peel off and electricity does not flow between the single plates laminated. Patent Document 1 and Patent Document 2 have not considered maintaining all of insulation, adhesion, and magnetic properties at good levels. Therefore, an object of the present invention is to provide an Fe-Co-based alloy substrate and a laminated core member that can obtain good magnetic properties while ensuring insulation and adhesion.

Means for Solving the Problems

[0007] The present invention has been made in view of the above-described problems. That is, one aspect of the present invention is an Fe-Co-based alloy-coated substrate having an oxide layer on at least one of the front and back surfaces of the Fe-Co-based alloy substrate, wherein when the oxide layer is formed on either the front or back surface of the substrate, the thickness of the oxide layer is 280 to 500 nm, and when the oxide layer is formed on both the front and back surfaces, the thicknesses of the oxide layers on the front surface side and the back surface side are each 140 to 500 nm, and in the cross-section in the thickness direction of the Fe-Co-based alloy-coated substrate, the maximum height difference of the unevenness of the oxide layer at the interface between the oxide layer and the Fe-Co-based alloy substrate is 300 nm or less. It is an Fe-Co-based alloy-coated substrate characterized by the above. Preferably, the lower limits of the thicknesses of the oxide layers on the front surface side and the back surface side are each 250 nm. Another aspect of the present invention is a laminated core member in which the above-described Fe-Co-based coated alloy substrate is laminated.

Effects of the Invention

[0008] According to the present invention, it is possible to obtain an Fe-Co alloy-coated substrate that can achieve good magnetic properties while ensuring insulation and adhesion, and a high-performance laminated core member.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] The Fe-Co alloy substrate of the present invention refers to a strip (coil), a rectangular shape (sheet), or a thin plate in the shape of a part. And the plate thickness of the Fe-Co alloy substrate of the present invention can be, for example, 0.5 mm or less. A preferable plate thickness is 0.25 mm or less. Here, the Fe-Co alloy in the present invention refers to an alloy material in which Fe + Co is 95% or more by mass% and contains 25 to 60% of Co. The lower limit of the preferable Co amount is 40%. Thereby, a high magnetic flux density can be exhibited.

[0011] Next, the elements that may be contained in the Fe-Co alloy substrate of the present invention will be described. In order to improve the magnetic properties and cold workability of the Fe-Co alloy of the present invention, after containing V: 1.70 to 2.10% and Mn: 0.01 to 0.40%, one or more elements of Si, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr may be contained in a total amount of up to 2.5% by mass%. In addition, as inevitable impurity elements, for example, C, S, P, and O are mentioned, and for example, it is preferable that the upper limit of each of them is 0.1%.

[0012] The Fe-Co alloy coated substrate of the present invention has an oxide layer on at least one of the front and back surfaces of the Fe-Co alloy substrate having the above-described composition. In the present invention, when the oxide layer is formed on either the front or back surface of the substrate, the thickness of the oxide layer is 280 to 500 nm. When the oxide layer is formed on both the front and back surfaces of the substrate, the thicknesses of the oxide layers on the front surface side and the back surface side are each in the range of 140 to 500 nm. By providing this oxide layer, the minimum thickness required to ensure the insulation of the Fe-Co alloy substrate of the present invention is achieved, and the magnetic properties are not impaired. In addition, since an oxide layer having a lattice constant larger than that of the Fe-Co alloy is formed on the substrate surface, a slight tensile stress is applied to the substrate surface, and the DC magnetic properties of the Fe-Co alloy having positive magnetostriction tend to improve. When the thickness of the oxide layer is less than 280 nm (when the oxide layer is formed only on one side of the substrate) or 140 nm (when the oxide layer is formed on both sides (front and back) of the substrate), the thickness of the oxide layer is insufficient, and current may flow between the single plates laminated in the laminated core, and the iron loss may deteriorate. When the thickness of the oxide layer exceeds 500 nm, the difference in the thermal expansion coefficients between the Fe-Co alloy substrate and the oxide layer becomes large, the adhesion greatly decreases, and there is a risk that the oxide layer peels off during core manufacturing. Furthermore, when the thickness of the oxide layer exceeds 500 nm, the magnetic flux density tends to decrease due to the increase in the non-ferromagnetic oxide layer. Here, in the present embodiment, the reason why the lower limit of the preferable thickness is different between the case where the oxide layer is formed on only one side (either the front or back surface) of the substrate and the case where it is formed on both sides is that it is assumed that the Fe-Co alloy coated substrate of the present invention is applied to a laminated core. That is, when Fe-Co alloy coated substrates having oxide layers on both sides are laminated, the thickness of the oxide layer between the coated substrates is the sum of the thickness of the oxide layer on the back surface of the substrate and the thickness of the oxide layer on the front surface of the substrate. Therefore, a coated substrate having oxide layers on both sides of the substrate can have a thinner oxide layer than a coated substrate having an oxide layer on only one side. In a coated substrate having an oxide layer on only one side of the substrate, the preferable lower limit of the oxide layer is 300 nm, and the more preferable lower limit of the oxide layer is 310 nm.Also, in the coated substrate having oxide layers on both sides of the substrate, the lower limit of the thickness of the preferred oxide layer is 150 nm, the lower limit of the more preferred oxide layer is 160 nm, the lower limit of the further preferred oxide layer is 180 nm, 200 nm, and 220 nm. Also, the upper limit of the preferred oxide layer is 400 nm, and the upper limit of the more preferred oxide layer is 350 nm.

[0013] In the Fe—Co based alloy coated substrate of the present invention, when oxide layers are formed on the front and back surfaces of the substrate, it is more preferable that the lower limit of the thickness of the oxide layer on the front surface side and the back surface side is 250 nm each. With this configuration, the Fe—Co based alloy substrate can be coated with a stable oxide layer, and it is possible to further enhance the effect of suppressing rust that may occur during material storage or the like. From the above viewpoints, the lower limit of the more preferable oxide layer thickness is 280 nm, and the lower limit of the further preferable oxide layer is 300 nm or more. The laminated core member obtained by laminating the above-described Fe—Co based alloy coated substrates has good magnetic properties.

[0014] Also, in the Fe—Co based alloy coated substrate of the present invention, in the cross section in the thickness direction of the substrate, it is also a feature that the maximum height difference of irregularities at the interface between the oxide layer and the substrate is 300 nm or less. By having this requirement, the Fe—Co based alloy coated substrate of the present invention tends to improve the adhesion between the oxide layer and the substrate. When the maximum height difference of irregularities at the interface between the oxide layer and the substrate exceeds 300 nm, non-uniform stress is generated between the oxide layer and the substrate, and the adhesion of the oxide layer tends to decrease. The thickness of the oxide layer in the present invention and the maximum height difference of irregularities at the interface between the oxide layer and the substrate can be measured, for example, by using elemental mapping by FE-TEM and the length measuring function of the FE-TEM analysis tool. Also, the adhesion in the present invention can be measured, for example, by performing a cross cut test defined in JIS K5400 (1990) or JIS K5600.

[0015] Next, an example of the manufacturing method for obtaining the Fe-Co alloy base material of the present invention will be described. The manufacturing method according to the present invention first performs cold rolling on an intermediate material that has the above-described Fe-Co alloy composition and has been irregularized by quenching from a normalization temperature around 730°C or higher. As this intermediate material, a hot-rolled material or a strip-shaped material obtained by subjecting a hot-rolled material to preliminary cold rolling can be used. Also, when an oxide layer is formed on the surface of the intermediate material, the oxide layer may be removed mechanically or chemically, for example. Subsequently, in the manufacturing method according to the present invention, in order to obtain a desired plate thickness, cold rolling is performed on the intermediate material to obtain a cold-rolled material with a plate thickness of 0.5 mm or less, and then magnetic annealing is performed to obtain a sufficiently coarse recrystallized grain structure, whereby an Fe-Co alloy base material having good magnetic properties can be obtained. Note that before and after magnetic annealing, processing into a component shape may be performed using press punching, wire cutting, laser processing, or the like.

[0016] Then, in the manufacturing method according to the present invention, an oxidation heat treatment is performed on the annealed material that has been subjected to the above-described magnetic annealing so that the thickness is 200 to 500 nm and the maximum height difference of the unevenness at the interface between the oxide layer and the base material in the cross section in the thickness direction is 300 nm or less. Here, the thickness of the oxide layer and the maximum height difference of the unevenness can be mainly controlled by adjusting the heating temperature and heating time of the oxidation heat treatment. Also, in order to form an oxide layer with a desired thickness, the oxygen partial pressure may be adjusted. For example, by performing heat treatment in an air atmosphere at 450°C for 0.5 to 4 hours, it is possible to obtain an Fe-Co alloy coated base material having an oxide layer defined in the present invention.

Example

[0017] A cold-rolled material having the Fe-Co alloy composition shown in Table 1 was prepared, and cold rolling was performed a plurality of times to obtain a cold-rolled material with a thickness of 0.2 mm. Then, magnetic annealing was performed in a hydrogen atmosphere at 850°C for 3 hours to obtain an annealed material (Fe-Co alloy base material) of the Fe-Co alloy. Thereafter, oxidation heat treatment was performed under the conditions shown in Table 2 to obtain Fe-Co alloy coated base materials of the present invention example and comparative example in which oxide layers were formed on the front and back surfaces of the base material. For each of the obtained samples, observation of the oxide layer and evaluation of adhesion, insulation, and DC magnetic properties were performed.

[0018]

Table 1

[0019]

Table 2

[0020] Observation of the oxide layer: The surface of the sample was protected with a C film, and the outermost surface of the specimen was processed into a film-shaped cross-sectional specimen parallel to the width direction from the outermost surface by FIB-SEM, and STEM observation was performed by FE-TEM. Also, elemental mapping of each of O, Fe, Co, and V was performed. The results are shown in Fig. 1. Note that the lower side of the image is the Fe-Co alloy substrate side. Also, the thickness of the oxide layer and the maximum height difference of the unevenness at the interface between the oxide layer and the substrate were measured using the length measurement function of the FE-TEM analysis tool. Evaluation of adhesion was carried out by performing a cross-cut test specified in JIS K5400 (1990), and the presence or absence of film peeling of the insulating layer was confirmed. Evaluation of insulation was determined by measuring the sheet resistance (surface resistivity) of the surface using the four-probe method with a resistivity measuring machine. The measurement results of the film thickness of the oxide layer, the maximum height difference of the unevenness at the interface between the oxide layer and the substrate, the presence or absence of film peeling, and the sheet resistance are shown in Table 3. Note that the "maximum height difference of the unevenness" in Table 3 indicates the maximum height difference of the unevenness at the interface between the oxide layer and the substrate. Also, all the measurement results in Table 3 are for the oxide layer on the substrate surface side. In the actual sample, an oxide layer was also formed on the back surface of the substrate, and its thickness and maximum height difference of the unevenness were of the same order as those on the surface side.

[0021]

Table 3

[0022] The DC magnetic properties were measured on samples obtained by cutting a cold-rolled material with a thickness of 0.2 mm into pieces with a length of 110 mm in the rolling direction and a width of 25 mm in the direction perpendicular to rolling, followed by magnetic annealing at 850 °C for 3 hours in a hydrogen atmosphere. Subsequently, the same samples were subjected to oxidation heat treatment under the conditions shown in Table 2, and then DC magnetic measurements were performed again to measure the changes in coercive force, maximum permeability, and magnetic flux density before and after the oxidation heat treatment. The results are shown in Table 4.

[0023]

Table 4

[0024] From the results in Fig. 1 and Table 3, it can be confirmed that there are differences in the thickness and morphology (maximum step difference of unevenness) of the oxide layer depending on the heating temperature and heating time of the oxidation heat treatment. Samples 1 to 3 and 11 to 12, where the maximum height difference of the unevenness at the interface between the oxide layer and the substrate is 300 nm or less, have good adhesion and no film peeling. In Sample 13, where the maximum height difference of the unevenness at the interface between the oxide layer and the substrate exceeds 300 nm, the adhesion is poor and film peeling occurs. Poor adhesion of the oxide layer is not preferable because it may cause the insulating layer to peel off during the manufacture of the laminated core, resulting in electrical conduction between the laminated single plates and deterioration of the iron loss. Regarding the sheet resistance, Samples No. 2, 3, and 13 showed excellent values, indicating that they exhibit good insulation properties. Sample No. 1 has a smaller sheet resistance than No. 2 and No. 3. However, when actually used as a laminated core, oxide layers are formed on both surfaces of the substrate. Therefore, the film thickness of Sample No. 1 is the sum of the film thicknesses on the front and back surfaces of the substrate. Thus, it can be seen that the oxide layer thickness of No. 1 is also about twice as thick (about 490 nm) when used as a laminated core, and it can exhibit sufficient insulation properties. On the other hand, in Comparative Examples No. 11 and No. 12, since the oxide layer is too thin, even if the thickness is doubled assuming lamination, it cannot reach the oxide layer thickness of No. 1, indicating that sufficient insulation properties cannot be exhibited. And from Table 4, the DC magnetic properties of Samples 1 to 3, where the oxide layer is within the range of the present invention examples, were improved. For the DC magnetic properties of soft magnetic materials, the lower the coercive force, the higher the maximum permeability, and the higher the magnetic flux density, the better. In Invention Examples 1 to 3, a significant improvement was confirmed particularly in the maximum permeability.

[0025] Next, the rust resistance of Sample Nos. 1 to 3 and Nos. 11 to 13 was evaluated. After the oxidation heat treatment, For each sample, a temperature and humidity accelerated test (85°C / 85%RH) was conducted. Photographs of the materials at the time points of 0 h, 560 h, and 760 h are shown in Figure 3. At the 560 h time point, pitting occurred in Nos. 1, 11, and 12, while in Nos. 2, 3, and 13 where the thickness of the oxide layer was 250 nm or more, almost no pitting was confirmed, indicating good rust resistance. Also, in Nos. 2, 3, and 13, almost no pitting was confirmed even at the 760 h time point, indicating very good rust resistance. From the above results, it was confirmed that the Fe-Co-based alloy-coated substrate of the present invention example has better insulation, adhesion, and magnetic properties than the Fe-Co-based alloy-coated substrate of the comparative example. In particular, Nos. 2 and 3 of the present invention example where the thickness of the oxide layer is 250 nm or more have excellent rust resistance.

Claims

1. An Fe—Co alloy coated substrate having an oxide layer on at least one of the front and back surfaces of an Fe—Co alloy base material, when the oxide layer is formed only on the front or back surface, the thickness of the oxide layer is 280 to 500 nm, when the oxide layer is formed on both the front and back surfaces, the thicknesses of the oxide layers on the front surface side and the back surface side are each 140 to 500 nm, in a cross section in the thickness direction of the Fe—Co alloy coated substrate, the maximum height difference of the unevenness of the oxide layer at the interface between the oxide layer and the Fe—Co alloy base material is 300 nm or less. An Fe—Co alloy coated substrate characterized by this.

2. The Fe—Co alloy coated substrate according to claim 1, wherein when the oxide layer is formed on both the front and back surfaces, the lower limit of the thickness of the oxide layers on the front surface side and the back surface side is 250 nm each.

3. A laminated core member in which the Fe—Co alloy coated substrates according to claim 1 or 2 are laminated.

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