Coating member

Abstract

To provide a coating member which can keep insulative after discharge processing is performed and can suppress welding of laminated members at the time of thermal processing.SOLUTION: The method for manufacturing a coating member includes: an application step of applying a magnesium hydroxide fluid on a surface of an Fe-Co-based alloy base material; a baking step of baking the base material at temperatures of 600-900°C and forming a magnesium oxide coating on the base material. The coating member has a baked coating film of magnesium oxide with a lattice constant of 4.20-4.23 Å on the Fe-Co-based alloy base material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a coating member.

Background Art

[0002] Due to the recent increase in environmental protection awareness, efforts have been actively made towards the electrification of automobiles and the hybridization of aircraft. As these key technologies, there are the improvement of the 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 is used because the magnetization amount per unit volume is large and it is advantageous for miniaturization of the core.

[0003] As a method for further miniaturizing this laminated core, applying a soft magnetic material having a high saturation magnetic flux density, and as a method for further reducing losses, improving the electrical insulation (hereinafter, also simply referred to as insulation) between the laminated single plates is effective. For example, Patent Document 1 discloses a laminated core in which a single layer of permendur (Fe-Co alloy) having a high saturation magnetic flux density is 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. Patent Document 2 also discloses that a cold-rolled Fe-Co alloy material is subjected to a two-step heat treatment to produce a laminated core from the heat-treated alloy material, and it is also described that a magnesium oxide coating may be formed by heat treatment to prevent welding of the alloy material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The laminated core obtained by laminating the permendur coated with the ceramic layer disclosed in Patent Document 1 or Patent Document 2 described above is excellent in insulation. On the other hand, Patent Document 1 discloses a method of machining the shape of a single-layer material of a permendur coated with a ceramic layer (hereinafter also referred to as a coated member) by electrical discharge machining. However, as a result of the study by the present inventor, it was confirmed that the insulating layer discolored when the coated member was machined by electrical discharge machining. This discoloration is caused by the elution of the ceramic layer which is the insulating layer, and there is a fear that the insulation cannot be ensured and the loss of the laminated core increases. Such a problem has not been recognized in Patent Document 1 or Patent Document 2, and there is room for further study. Further, as a problem occurring in the laminated core, welding between single-layer materials can be cited. This welding occurs during magnetic annealing and causes a significant increase in iron loss. In addition, when peeling the welded single-layer material, a defective shape of the single-layer material occurs, and there is also concern about the deterioration of magnetic properties associated therewith. Therefore, it is necessary to suppress the occurrence of welding. Therefore, an object of the present invention is to provide a coated member, a manufacturing method thereof, which can maintain the insulation even when shape machining by electrical discharge machining is performed and can also suppress welding when laminated and heat-treated.

Means for Solving the Problems

[0006] The present inventor found that when the baking temperature is not appropriate, the lattice constituting magnesium oxide becomes unstable, and considered that the elution of the coating film occurs due to the instability. Then, the present inventor earnestly studied the appropriate baking temperature and reached the present invention. That is, one aspect of the present invention is a coated member having a baked film of magnesium oxide with a lattice constant of 4.20 to 4.23 Å on an Fe-Co alloy base material in which Fe + Co is 95% or more by mass% and contains 25 to 60% of Co, and having a coercive force of 31.2 A / m or less and a maximum relative permeability of 25,000 or more. The coercive force and the maximum relative permeability are obtained by taking a cold-rolled material of an Fe-Co alloy with a plate thickness of 0.2 mm in which Fe + Co is 95% or more by mass% and contains 25 to 60% of Co as a ring-shaped sample with an outer diameter of 45 mm and an inner diameter of 33 mm by electrical discharge machining, heating it at a heating rate of 250 °C / h in a nitrogen atmosphere, holding it at 700 °C for 30 minutes, and then performing heat treatment simulating baking by furnace cooling to room temperature over 120 minutes, performing magnetic annealing at 850 °C for 3 hours in a hydrogen atmosphere, stacking 5 ring-shaped samples each after the magnetic annealing, winding with 100 turns of the primary winding and 50 turns of the secondary winding, and measuring in a state where a DC magnetic field with a maximum applied magnetic field of 5000 A / m is applied. It is.

Effect of the Invention

[0007] According to the present invention, it is possible to provide a coated member that maintains insulation even when electrical discharge machining is performed and suppresses welding during heat treatment by lamination.

Embodiments for Carrying Out the Invention

[0008] First, a method for manufacturing the coated member of the present invention will be described. In the present invention, an Fe-Co alloy base material is used as the base material that becomes a soft magnetic material. 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. Thereby, a high magnetic flux density can be exhibited.

[0009] Next, elements that may be contained in the Fe-Co-based alloy of the present invention will be described. In order to improve the magnetic properties and cold workability of the Fe-Co-based alloy of the present invention, one or more elements of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr may be contained in a total amount of up to 5.0% by mass. In addition, as inevitable impurity elements, for example, C, S, P, and O can be mentioned, and it is preferable to set the upper limit of each of them to 0.1%, for example.

[0010] In the method for manufacturing the coated member of the present invention, first, in order to form a film made of magnesium oxide (hereinafter also referred to as MgO) on the surface of the Fe-Co alloy substrate, a coating step of applying a solution containing magnesium hydroxide (hereinafter also referred to as Mg(OH)2) is performed. The reason for selecting the MgO film is that MgO is excellent in electrical insulation and adhesion to the Fe-Co-based alloy as the substrate. Further, when the coated member is subjected to magnetic annealing to obtain desired magnetic properties, the insulating film is exposed to a reducing atmosphere such as hydrogen at about 850°C. However, MgO is difficult to be reduced by hydrogen, hardly evaporates even at high temperatures, and is unlikely to cause deterioration of properties due to thermal diffusion. Therefore, it is also excellent in terms of insulation and weld resistance.

[0011] In the present invention, as a coating solution for forming the film made of MgO described above, a Mg(OH)2 solution (hereinafter also referred to as a slurry) in which powder of Mg(OH)2 serving as a precursor of MgO is used as a solute and dispersed in a solvent is used. By using this slurry as the coating solution, the slurry can be uniformly applied to the surface of the metal substrate with a stable film thickness. Since Mg(OH)2 used as the solute of the slurry is thermally decomposed by heating to become MgO, an MgO film can be easily formed. Further, since the thermal decomposition temperature of Mg(OH)2 is as low as about 500°C, an MgO film can be stably formed at a low temperature. Here, magnesium carbonate (MgCO3) can also be used as a precursor other than Mg(OH)2. Further, as the solvent of the slurry, amphoteric solvents such as water and alcohol, and organic solvents can be used, and as a method of applying the slurry to the metal substrate, roll coating in which the slurry is applied to the substrate with a roller, dip coating in which the substrate is immersed in the slurry and pulled up, and screen printing can be used.

[0012] In the present invention, after the coating step, a baking step is carried out in which the substrate coated with the slurry is baked at 600 to 900°C to form an MgO film on the substrate (hereinafter, the step of thermally decomposing the precursor to form an MgO film is also simply referred to as "baking"). Electrical discharge machining, which is used as a machining method for producing a laminated core, machines the workpiece in water. However, elution of the MgO film tends to occur during this process, and there is a risk that the film thickness of the MgO film will become thinner due to this elution, resulting in the inability to ensure electrical insulation. In the present invention, by setting the baking temperature of Mg(OH)₂ to 600 to 900 °C, elution of the MgO film generated when the coated member is machined by electrical discharge machining can be suppressed, and an MgO film excellent in insulation and weld resistance can be formed. One of the reasons for obtaining the elution suppression effect of the present invention is considered to be that the stability of the lattice constituting the MgO film is improved by an appropriate baking temperature. When the baking temperature is less than 600 °C, elution of the MgO film occurs. When the baking temperature exceeds 900 °C, fine crystal grains due to the precipitation of the gamma phase precipitate at the grain boundaries of the Fe-Co-based metal substrate, and these fine crystal grains inhibit domain wall movement and increase the coercive force, which may deteriorate the soft magnetic properties. The upper limit of the preferable baking temperature is 850 °C, more preferably 800 °C, and even more preferably 700 °C. The above-mentioned elution of the MgO film appears as color unevenness and can be easily observed from the appearance of the coated member.

[0013] In the baking process of the present invention, the baking time can be appropriately set while considering the relationship with the baking temperature as long as the effects of the present invention are not impaired. If the baking temperature is high, the baking time can be shortened. For example, when the baking temperature is 600 °C, the baking time can be set to 1 to 30 minutes. Also, by setting the heating rate of the baking process to 200 °C / h to 300 °C / h, the stability of the lattice constituting the MgO film tends to be improved, which is preferable. Furthermore, it is preferable to cool the furnace slowly, and it is preferable to apply slow cooling from the baking temperature to room temperature over 90 to 180 minutes. The atmosphere during baking is preferably an inert gas atmosphere or a vacuum atmosphere. This is to prevent deterioration of the soft magnetic properties of the Fe-Co-based metal substrate due to excessive oxidation of the coated member and oxidation up to the Fe-Co-based metal substrate when baking is performed in the atmosphere. Examples of the inert gas atmosphere include a nitrogen gas atmosphere and an Ar gas atmosphere.

[0014] In the present invention, after applying a slurry to the surface of a metal substrate, baking is performed. However, a drying step for evaporating the solvent may be provided before baking. Since the drying step can be carried out at a low temperature near the boiling point of the solvent, the slurry can be quickly dried, suppressing dripping and enabling the formation of a uniform film thickness. Also, since the drying step can be carried out at a low temperature, it has the advantage of being able to be carried out in the atmosphere.

[0015] The coated member of the present invention obtained by the manufacturing method of the present invention described above has a baked film of magnesium oxide with a lattice constant of 4.20 to 4.23 Å on the substrate. By approaching the lattice constant of MgO to the theoretical value of 4.213 Å, the elution of the MgO film after electrical discharge machining can be suppressed. This is because Mg(OH)2, which is a precursor of MgO, has a hexagonal crystal system, while MgO formed by baking has a cubic crystal system. In the present invention, MgO is generated by the thermal decomposition reaction of Mg(OH)2 in the baking step. However, for example, when the baking temperature is as low as 500 °C, the thermal decomposition reaction does not proceed sufficiently, so MgO with a lattice constant larger than the theoretical value is generated. Since this MgO with a large lattice constant is easily eluted in water, it is considered that color unevenness occurs due to electrical discharge machining in water. Here, the lattice constant of MgO can be measured by the X-ray diffraction method. Whether the film of the present invention is a baked film formed through the application and baking of a solution can be determined from a cross-sectional photograph of the film (for example, a cross-sectional photograph of the film observed at a magnification of 1 million times with a transmission electron microscope). That is, in the baked film, voids with an equivalent circle diameter of about 10 to 50 nm are observed in the film structure, while such voids are not observed in the film formed by the physical vapor deposition method. Therefore, the baked film can be specified from this difference.

[0016] Also, the film thickness of the film formed on the coated member may be set within a range that can ensure electrical insulation. Electrical insulation improves as the film becomes thicker, but if the film is made overly thick, the occupancy ratio of the laminated core may decrease, leading to possible characteristic degradation. Therefore, the film thickness may be set considering insulation and occupancy ratio. For example, a preferable film thickness is 10 to 1000 nm.

Example

[0017] (Example 1) As the metal substrate, three cold-rolled materials of Fe-Co alloy having the composition shown in Table 1 (length 110 mm × width 60 mm × plate thickness 0.2 mm) were prepared and subjected to alkaline degreasing. Next, a slurry in which Mg(OH)2 powder as a solute was dispersed in water as a solvent was prepared, and the slurry was applied onto the substrate by the dip coating method. The substrate after the application of the slurry was dried by heating at 110 °C for 5 minutes in the atmosphere. <Example 1 of the present invention> The dried substrate was heated in a nitrogen atmosphere at a heating rate of 250 °C / h until it reached 600 °C, held at 600 °C for 30 minutes, and then subjected to a baking process of furnace cooling to room temperature over 160 minutes, to produce a coated member of Example 1 of the present invention coated with an MgO film having a film thickness of 0.1 μm. <Example 2 of the present invention> The dried substrate was heated in a nitrogen atmosphere at a heating rate of 250 °C / h until it reached 700 °C, held at 700 °C for 30 minutes, and then subjected to a baking process of furnace cooling to room temperature over 170 minutes, to produce a coated member of Example 2 of the present invention coated with an MgO film having a film thickness of 0.1 μm. <Comparative Example 1> The dried substrate was heated in a nitrogen atmosphere at a heating rate of 250 °C / h until it reached 500 °C, held at 500 °C for 30 minutes, and then subjected to a baking process of furnace cooling to room temperature over 150 minutes, to produce a coated member of Comparative Example 1 coated with an MgO film having a film thickness of 0.1 μm.

[0018]

Table 1

[0019] After processing each of the coating members produced above into a ring-shaped sample with an outer diameter of 45 mm and an inner diameter of 33 mm by electrical discharge machining, the presence or absence of color unevenness was visually determined. Also, as an evaluation of the lattice constant, using a Rigaku Corporation X-ray diffractometer RINT2500V, with CoKα as the radiation source, the lattice constant a of the MgO film formed on the surface of the metal substrate by the thin film method was determined. The results are shown in Table 2. From the results in Table 2, the lattice constant a of the MgO film of the coating member of Comparative Example 1 was larger than that of the present invention examples, and color unevenness occurred after electrical discharge machining. On the other hand, the lattice constant a of MgO in the coating members of the present invention examples 1 and 2 was close to the theoretical value, and it was confirmed that no color unevenness occurred in any of the samples after electrical discharge machining.

[0020]

Table 2

[0021] (Example 2) Subsequently, the weld resistance of the coating member of the present invention was confirmed. Two cold-rolled materials of Fe-Co alloy (A substrate) with a length of 50 mm × width of 50 mm × plate thickness of 0.2 mm having the composition shown in Table 1 of Example 1, and two cold-rolled materials of Fe-Co alloy (B substrate) with a length of 40 mm × width of 50 mm × plate thickness of 0.2 mm having the same composition as shown in Table 1 of Example 1 were prepared. <Example 3 of the Present Invention> MgO films were formed on both the A substrate and the B substrate under the same conditions as in Example 1 of the present invention to obtain coating members A and B. Subsequently, they were overlapped so that the coating member B did not protrude from the coating member A, and the overlapped coating members were sandwiched between alumina plates and heated in a heat treatment furnace at 850 °C for 3 hours to prepare a sample of Example 3 of the present invention. At this time, the surface pressure applied to the overlapped coating members A and B was 0.1 g / cm 2 was. <Comparative Example 2> Samples of Comparative Example 2 were prepared by overlapping the A substrate and the B substrate without coating, and the other conditions were the same as those of Example 3 of the present invention.

[0022] As a result of observing the heated sample, it was confirmed that welding occurred in Comparative Example 2 and the A base material and the B base material were adhered to each other. On the other hand, no welding occurred after heating in Invention Example 3. Also, this result was the same even when the surface pressure applied to the coating members A and B was changed to 0.075 g / cm 2 The same was true even when the experiment was carried out with the change. From the above results, it was confirmed that the coating member of the present invention does not cause welding even when laminated and subjected to magnetic annealing, and is a member suitable for laminated core applications.

[0023] (Example 3) In order to confirm the influence of the baking temperature on the soft magnetic properties of the Fe-Co-based alloy, an evaluation was carried out using a cold-rolled material of the Fe-Co-based alloy without MgO coating. As the metal base material, a cold-rolled material of the Fe-Co-based alloy having the composition shown in Table 3 with a thickness of 0.2 mm was prepared, and a ring-shaped sample with an outer diameter of 45 mm and an inner diameter of 33 mm was prepared by electrical discharge machining. Subsequently, the temperature was raised at a rate of 250 °C / h in a nitrogen atmosphere, held at 700 °C for 30 minutes, and then heat treatment simulating baking was performed by furnace cooling to room temperature over a period of 120 minutes. After that, magnetic annealing was performed at 850 °C for 3 hours in a hydrogen atmosphere to obtain a sample of Invention Example 4. Also, with the same sample shape and ring sample processing method, the temperature was raised at a rate of 250 °C / h in a nitrogen atmosphere, held at 950 °C for 30 minutes, and then heat treatment simulating baking was performed by furnace cooling to room temperature over a period of 180 minutes. After that, magnetic annealing was performed at 850 °C for 3 hours in a hydrogen atmosphere to obtain a sample of Comparative Example 3. Incidentally, five ring-shaped samples were prepared for each of the invention examples and comparative examples.

[0024] [Table 3]

[0025] Subsequently, for magnetic property evaluation, five ring-shaped samples of Invention Example 4 and Comparative Example 3 were stacked respectively, and windings were made with 100 turns for the primary winding and 50 turns for the secondary winding. Then, a DC magnetic field with a maximum applied magnetic field of 5000 A / m was applied to the ring-shaped sample, and the coercive force H c , the maximum relative permeability μ mwas measured. The results are shown in Table 4. From Table 4, the sample of Example 4 of the present invention has a small H c and a large μ m , indicating excellent soft magnetic properties. On the other hand, the sample of Comparative Example 3 has a large H c and a small μ m , clearly showing that its soft magnetic properties are deteriorated. From the above, it was confirmed that baking at a temperature exceeding 900°C is unsuitable as the baking temperature because the soft magnetic properties of the Fe-Co alloy deteriorate.

[0026]

Table 4

Claims

【Claim 1】 On an Fe-Co alloy substrate containing 95% or more of Fe + Co in mass% and containing 25 to 60% of Co, there is a baked film of magnesium oxide having a lattice constant of 4.20 to 4.23 Å, A coated member having a coercive force of 31.2 A / m or less and a maximum relative permeability of 25,000 or more. However, the coercive force and the maximum relative permeability are obtained by using a cold-rolled material of an Fe-Co alloy with a plate thickness of 0.2 mm containing 95% or more of Fe + Co in mass% and containing 25 to 60% of Co, and by electrical discharge machining it into a ring-shaped sample with an outer diameter of 45 mm and an inner diameter of 33 mm, Heating is carried out in a nitrogen atmosphere at a heating rate of 250 °C / h, held at 700 °C for 30 minutes, and then furnace-cooled to room temperature over 120 minutes to simulate baking, followed by Magnetic annealing is carried out at 850 °C for 3 hours in a hydrogen atmosphere, The values are measured in a state where five ring-shaped samples after the magnetic annealing are stacked together, wound with 100 turns of the primary winding and 50 turns of the secondary winding, and a DC magnetic field with a maximum applied magnetic field of 5000 A / m is applied.

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