Fe-Co alloy coated substrate and laminated core member

Abstract

The present invention provides a Fe-Co alloy base material capable of obtaining good magnetic characteristics while ensuring insulating properties and adhesion. An Fe-Co alloy-coated base material and a laminated core member, the Fe-Co alloy-coated base material having an oxide layer on at least one of the front surface and the back surface of an Fe-Co alloy base material, the Fe-Co alloy-coated base material being characterized in that the thickness of the oxide layer is 280-500 nm when the oxide layer is formed only on the front surface or the back surface, and the thickness of the oxide layer is not greater than 500 nm when the oxide layer is formed on the front surface and the back surface. The thickness of the oxide layer on the front surface side and the thickness of the oxide layer on the back surface side are respectively 140 nm to 500 nm, and the maximum height difference of irregularities of the oxide layer at the interface between the oxide layer and the Fe-Co alloy substrate in a cross section in the thickness direction of the Fe-Co alloy coated substrate is 300 nm or less.

Description

Technical Field

[0001] This invention relates to an Fe-Co alloy coated substrate and a laminated core component. Background Technology

[0002] Due to increased environmental awareness in recent years, efforts toward the electrification of automobiles and the hybridization of aircraft have become active. Among the key technologies for these advancements are high output, miniaturization, and low loss in electric motors. Regarding the shape of the motor core used in these electric motors, a stacked core with a structure formed by stacking multiple sheets of soft magnetic alloy is used, which maximizes magnetization per unit volume and facilitates core miniaturization.

[0003] As a method to further miniaturize the laminated core, it is effective to use a soft magnetic material with high saturation magnetic flux density. As a method to further reduce losses, it is effective to improve the electrical insulation (hereinafter, simply referred to as insulation) between the laminated single plates. For example, Patent Document 1 discloses a laminated core formed by stacking a single layer of permendur (Fe-Co alloy) material with high saturation magnetic flux density, and proposes to form a ceramic layer such as magnesium oxide, zirconium oxide, or aluminum oxide on the surface of the single layer material as an insulating film.

[0004] On the other hand, since the coating process of the insulating layer is easy, there are also known methods that form an oxide layer mainly composed of Fe and Co on the surface of a substrate and produce an insulating layer by means of heat treatment or the like. Patent Document 2 describes that for a board material, an oxidation annealing is performed after the final recrystallization annealing process to produce an oxide layer of 0.5 μm to 10 μm, thereby ensuring electrical insulation when laminated.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2012-521649

[0008] Patent Document 2: Japanese Patent Publication No. 2018-529021 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The magnesium oxide insulating film described in Patent Document 1 has good insulation properties, but it requires a separate vapor deposition or coating process, which increases the processing time. Furthermore, the Fe-Co alloy substrate used as the core material in the laminate requires a tight seal to prevent the insulation layer from peeling off during core manufacturing and causing electrical conduction between the laminated boards. Neither Patent Document 1 nor Patent Document 2 addressed maintaining good insulation, seal, and magnetic properties.

[0011] Therefore, the purpose of this invention is to provide an Fe-Co alloy substrate and a laminated core component that can obtain good magnetic properties while ensuring insulation and sealing.

[0012] Technical means to solve the problem

[0013] The present invention was made in view of the aforementioned issues.

[0014] That is, one embodiment of the present invention is an Fe-Co alloy coated substrate, which has an oxide layer on at least one of the surface and back sides of the Fe-Co alloy substrate. The Fe-Co alloy coated substrate is characterized in that, when the oxide layer is formed on either the surface or the back side of the substrate, the thickness of the oxide layer is 280 nm to 500 nm; when the oxide layer is formed on both the surface and the back side, the thicknesses of the oxide layer on the surface side and the back side are 140 nm to 500 nm, respectively; and in the thickness direction cross-section of the Fe-Co alloy coated substrate, the maximum height difference of the oxide layer at the interface between the oxide layer and the Fe-Co alloy substrate is less than 300 nm.

[0015] Preferably, the lower limit of the thickness of the oxide layer on the surface side and the back side is set to 250 nm.

[0016] Another embodiment of the present invention is a laminated core component having the Fe-Co alloy coated substrate laminated thereon.

[0017] The effects of the invention

[0018] According to the present invention, Fe-Co alloy coated substrates and high-performance laminated core components can be obtained that can obtain good magnetic properties while ensuring insulation and sealing. Attached Figure Description

[0019] [ Figure 1 [ ] represents the STEM image and elemental mapping image of the sample cross-section of an example of the present invention.

[0020] [ Figure 2 [] represents the STEM image and elemental mapping image of the sample cross-section of the comparative example.

[0021] [ Figure 3[Image] is a photograph showing the corrosion resistance test results of the examples and comparative examples of the present invention. Detailed Implementation

[0022] The Fe-Co alloy substrate of the present invention refers to a strip-shaped (coil) substrate or a thin plate in a rectangular (sheet) or part shape. Furthermore, the thickness of the Fe-Co alloy substrate of the present invention can be, for example, 0.5 mm or less. Preferably, the thickness is 0.25 mm or less. Here, the Fe-Co alloy in the present invention refers to an alloy material containing 95% or more Fe + Co by mass and 25% to 60% Co. Preferably, the lower limit of the Co content is 40%. This allows for high magnetic flux density.

[0023] Next, the elements that may be contained in the Fe-Co alloy substrate of the present invention will be described. To improve magnetic properties or cold workability, the Fe-Co alloy of the present invention may contain, on the basis of V: ​​1.70% to 2.10% and Mn: 0.01% to 0.40%, a total of one or more of the following elements by mass% up to 2.5%. In addition, as unavoidable impurity elements, examples include C, S, P, and O, and it is preferred that their respective upper limits be set to 0.1%.

[0024] The Fe-Co alloy coated substrate of the present invention has an oxide layer on at least one of the surface and back sides of the Fe-Co alloy substrate having the aforementioned composition. Furthermore, in the present invention, the oxide layer is characterized in that, when the oxide layer is formed on either the surface or the back side of the substrate, the thickness of the oxide layer is 280 nm to 500 nm; and when the oxide layer is formed on both the surface and the back side of the substrate, the thicknesses of the oxide layer on the surface side and the back side are respectively in the range of 140 nm to 500 nm. By including the oxide layer, a minimum thickness is set as required to ensure the insulation of the Fe-Co alloy substrate of the present invention, thereby without compromising magnetic properties. In addition, by forming an oxide layer with a larger lattice constant than that of Fe-Co alloys on the substrate surface, and applying a certain tensile stress to the substrate surface, the DC magnetic properties of the positively magnetostrictive Fe-Co alloy tend to be improved. When the oxide layer thickness 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 of the substrate, i.e., the surface and back sides), the oxide layer thickness is insufficient, and the iron loss may worsen when current is applied between the laminated boards in the laminated core. Furthermore, when the oxide layer thickness exceeds 500 nm, there are concerns that the difference in thermal expansion coefficients between the Fe-Co alloy substrate and the oxide layer increases, significantly reducing adhesion and causing the oxide layer to peel off during core manufacturing. Moreover, if the oxide layer thickness exceeds 500 nm, the magnetic flux density tends to decrease due to the increase in the non-strongly magnetic oxide layer. Here, in this embodiment, the reason for the different preferred lower limit of the thickness when the oxide layer is formed only on one side (either the surface or the back side) of the substrate versus when 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 the laminated core. That is, when Fe-Co alloy coated substrates with oxide layers on both sides are stacked, the thickness of the oxide layer between the coated substrates is the sum of the thickness of the oxide layer on the back side of the substrate and the thickness of the oxide layer on the surface of the substrate. Therefore, the oxide layer of a coated substrate with oxide layers on both sides can be thinner compared to a coated substrate with an oxide layer on only one side. In a coated substrate with an oxide layer on only one side of the substrate, the preferred lower limit of the oxide layer thickness is 300 nm, and more preferably 310 nm. In addition, in a coated substrate with oxide layers on both sides of the substrate, the preferred lower limit of the oxide layer thickness is 150 nm, more preferably 160 nm, and more preferably 180 nm, 200 nm, and 220 nm. In addition, the preferred upper limit of the oxide layer thickness is 400 nm, and more preferably 350 nm.

[0025] In the Fe-Co alloy-coated substrate of the present invention, when the oxide layer is formed on both the surface and back side of the substrate, it is more preferable to set the minimum thickness of the oxide layer on both the surface and back sides to 250 nm. With this structure, a stable oxide layer can be used to coat the Fe-Co alloy substrate, further improving the inhibition effect against rust that may occur during material storage. From this perspective, a minimum oxide layer thickness of 280 nm is more preferable, and even more preferably, a minimum oxide layer thickness of 300 nm or more. The laminated core member obtained by stacking the Fe-Co alloy-coated substrates exhibits excellent magnetic properties.

[0026] Furthermore, in the Fe-Co alloy-coated substrate of the present invention, a key feature is that, in the thickness direction section of the substrate, the maximum height difference between the oxide layer and the substrate at the interface is 300 nm or less. By having the aforementioned feature, the Fe-Co alloy-coated substrate of the present invention tends to improve the adhesion between the oxide layer and the substrate. When the maximum height difference between the oxide layer and the substrate at the interface exceeds 300 nm, uneven stress is generated between the oxide layer and the substrate, and the adhesion of the oxide layer tends to decrease. Moreover, the thickness of the oxide layer and the maximum height difference between the oxide layer and the substrate in the present invention can be measured, for example, by using elemental mapping based on a field emission-transmission electron microscope (FE-TEM) and the length measurement function of the FE-TEM analysis tool. Furthermore, the adhesion in the present invention can be measured, for example, by performing a cross-cutting test as specified in Japanese Industrial Standards (JIS) K5400 (1990) or JIS K5600.

[0027] Next, an example of a method for manufacturing the Fe-Co alloy substrate of the present invention will be described. In the manufacturing method of the present invention, firstly, an intermediate billet having the Fe-Co alloy composition and having undergone rapid cooling and disordering from an ordering temperature of around 730°C is cold-rolled. The intermediate billet can be hot-rolled material or a strip billet formed by pre-cooling hot-rolled material. Furthermore, if an oxide layer is formed on the surface of the intermediate billet, the oxide layer can be removed, for example, mechanically or chemically. Next, in the manufacturing method of the present invention, to obtain the desired plate thickness, the intermediate billet is cold-rolled to obtain a cold-rolled material with a plate thickness of 0.5 mm or less, and then magnetically annealed to produce a sufficiently coarse recrystallized grain structure, thereby obtaining an Fe-Co alloy substrate with good magnetic properties. Furthermore, before and after magnetic annealing, it can be processed into part shapes using methods such as stamping, wire cutting, or laser processing.

[0028] Furthermore, in the manufacturing method of the present invention, the annealed material subjected to magnetic annealing is subjected to an oxidation heat treatment to achieve a thickness of 200 nm to 500 nm and a maximum height difference between the oxide layer and the substrate at the interface in the thickness direction section of 200 nm or less. Here, the thickness of the oxide layer or the maximum height difference between the oxide layer and the substrate can be controlled primarily by adjusting the heating temperature and heating time of the oxidation heat treatment. Additionally, the oxygen partial pressure can be adjusted to form an oxide layer of the desired thickness. For example, by heat treatment at 450°C in an atmospheric environment for 0.5 to 4 hours, the Fe-Co alloy coated substrate with an oxide layer as specified in the present invention can be obtained.

[0029] Example

[0030] A cold-rolled billet with the Fe-Co alloy composition shown in Table 1 was prepared and subjected to multiple cold rolling processes to produce a cold-rolled material with a thickness of 0.2 mm. This material was then magnetically annealed at 850°C for 3 hours in a hydrogen atmosphere to obtain an annealed Fe-Co alloy substrate. Subsequently, an oxidation heat treatment was performed under the conditions shown in Table 2 to obtain Fe-Co alloy coated substrates of the present invention and comparative examples, in which oxide layers were formed on both the front and back surfaces of the substrate. The oxide layers of each obtained sample were observed, and the adhesion, insulation, and DC magnetic properties were evaluated.

[0031] [Table 1]

[0032]

[0033] [Table 2]

[0034]

[0035] In the observation of the oxide layer, a C film was used to protect the sample surface. A focused ion beam scanning electron microscope (FIB-SEM) was used to process the film-like cross-section of the sample, starting from the outermost surface and parallel to the width direction. The film was then observed using a scanning transmission electron microscope (STEM) with an FE-TEM. Elemental mapping for O, Fe, Co, and V was also performed. The results are shown below. Figure 1In addition, the lower side of the image is the Fe-Co alloy substrate side. Furthermore, the thickness of the oxide layer and the maximum height difference at the interface between the oxide layer and the substrate were measured using the length measurement function of the FE-TEM analysis tool. For the evaluation of adhesion, the cross-cutting test specified in JIS K5400 (1990) was performed to confirm whether the insulating layer had peeled off. For the evaluation of insulation, the sheet resistance (surface resistivity) of the surface was measured using a four-probe method based on a resistivity measuring machine. The measurement results of the oxide layer thickness, the maximum height difference at the interface between the oxide layer and the substrate, the presence or absence of peeling, and the sheet resistance are shown in Table 3. Furthermore, the term "maximum height difference" in Table 3 refers to the maximum height difference at the interface between the oxide layer and the substrate. Also, all the measurement results in Table 3 are based on the oxide layer on the surface side of the substrate. In the actual sample, an oxide layer was also formed on the back side of the substrate, and its thickness or maximum height difference was the same as that on the surface side.

[0036] [Table 3]

[0037]

[0038] DC magnetic properties were measured using a sample prepared by cutting a 0.2 mm thick cold-rolled material into sections 110 mm in the rolling direction and 25 mm in the right-angle direction, followed by magnetic annealing at 850°C for 3 hours in a hydrogen atmosphere. Subsequently, the same sample was subjected to oxidative heat treatment under the conditions shown in Table 2, and the DC magnetic properties were measured again. The changes in magnetic retention force, maximum permeability, and magnetic flux density before and after the oxidative heat treatment were also measured. The results are shown in Table 4.

[0039] [Table 4]

[0040]

[0041] according to Figure 1 The results in Table 3 confirm that the thickness or morphology (maximum height difference of the oxide layer) varies depending on the heating temperature and time of the oxidation heat treatment. Samples 1-3 and 11-12, where the maximum height difference at the oxide layer-substrate interface is less than 300 nm, exhibit good adhesion and no film peeling. Sample 13, where the maximum height difference at the oxide layer-substrate interface exceeds 300 nm, shows poor adhesion and film peeling. Poor adhesion of the oxide layer can lead to insulation peeling during core fabrication, resulting in electrical conduction between the laminated boards and potentially worsening iron losses, thus detrimental to the overall performance.

[0042] Regarding the sheet resistance, samples No. 2, No. 3, and No. 13 showed excellent values ​​and were found to exhibit good insulation properties. Sample No. 1 had a lower sheet resistance compared to samples No. 2 and No. 3. When used as a laminated core, since oxide layers are formed on both surfaces of the substrate, the film thickness is the sum of the film thickness on the surface side and the film thickness on the back side. Therefore, the oxide layer thickness of Sample No. 1 was approximately twice the thickness (approximately 490 nm) when used as a laminated core, resulting in sufficient insulation properties. On the other hand, the oxide layers of the comparative examples Samples No. 11 and No. 12 were too thin. Therefore, even assuming a laminated structure and setting the thickness to twice the thickness, it did not reach the oxide layer thickness of Sample No. 1, thus failing to achieve sufficient insulation properties. Furthermore, according to Table 4, the DC magnetic properties of Samples 1 to 3, whose oxide layers fall within the range of the present invention examples, were improved. Regarding the DC magnetic properties of soft magnetic materials, the lower the magnetic retention force, the higher the maximum permeability, and the higher the magnetic flux density, the better. In Examples 1 to 3 of the present invention, a significant improvement was particularly observed in the maximum permeability.

[0043] Next, the rust resistance of samples No. 1 to No. 3 and samples No. 11 to No. 13 was evaluated. Accelerated temperature and humidity tests (85℃ / 85%RH) were conducted on each sample after oxidative heat treatment. Photographs at 0 h, 560 h, and 760 h are shown below. Figure 3 At the 560-hour time point, pitting rust appeared in samples No. 1, No. 11, and No. 12. In contrast, pitting rust was hardly detected in samples No. 2, No. 3, and No. 13, which had an oxide layer thickness of 250 nm or more, confirming good rust resistance. Furthermore, at the 760-hour time point, pitting rust was also hardly detected in samples No. 2, No. 3, and No. 13, confirming very good rust resistance. Based on the above results, it is confirmed that the Fe-Co alloy coated substrate of the present invention has better insulation, adhesion, and magnetic properties compared to the Fe-Co alloy coated substrate of the comparative example. In particular, the rust resistance of samples No. 2 and No. 3 of the present invention, with an oxide layer thickness of 250 nm or more, is also excellent.

Claims

1. An Fe-Co alloy-coated substrate, wherein at least one of the surface and back sides of the Fe-Co alloy substrate has an oxide layer, and the Fe-Co alloy-coated substrate is characterized in that, When the oxide layer is formed only on the surface or the back side, the thickness of the oxide layer is 280 nm to 500 nm. When the oxide layer is formed on both the surface and the back side, the thickness of the oxide layer on the surface side and the back side is 140 nm to 500 nm, respectively. In the thickness direction cross-section of the Fe-Co alloy-coated substrate, the maximum height difference of the oxide layer at the interface between the oxide layer and the Fe-Co alloy substrate is less than 300 nm.

2. The Fe-Co alloy coated substrate according to claim 1, wherein, When the oxide layer is formed on both the surface and the back side, the lower limit of the thickness of the oxide layer on the surface side and the back side is 250 nm, respectively.

3. A laminated core component having a Fe-Co alloy coated substrate as described in claim 1 or 2 laminated thereon.

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