Surface-treated aluminum material, method for manufacturing the same, and compressor wheel

Abstract

A surface-treated aluminum material (1) comprises a base material (2) comprising an aluminum alloy in which the content of Cu is greater than 1.8 mass% but no more than 6.8 mass%, and a protective film (3) formed on the base material (2). The protective film (3) comprises an oxide layer (31) that consists of an aluminum oxide and covers the base material (2), and a hydrated oxide layer (32) that contains a hydrated oxide of aluminum and covers the oxide layer (31). A ratio J1 / J2 of a current density J1 of the surface-treated aluminum material (1) to a current density J2 of the base material (2) at a prescribed potential is 7000×10-5 or less when performing cathode polarization measurement of the surface-treated aluminum material (1) after being heated for 4 hours at a temperature of 200°C and the base material (2) using a prescribed measurement solution.

Description

[Technical Field]

[0001] This invention relates to a surface-treated aluminum material, a method for manufacturing the same, and a compressor wheel. [Background technology]

[0002] 2000 series aluminum alloys are widely used in applications such as turbocharger compressor wheels, taking advantage of their relatively high strength at high temperatures compared to other aluminum alloys. They are also sometimes used in components placed inside vacuum chambers in semiconductor manufacturing equipment.

[0003] Incidentally, an anodic oxide film is sometimes applied to the surface of aluminum materials for purposes such as surface protection. For example, Patent Document 1 describes a component for a substrate processing apparatus that performs plasma treatment on a substrate, wherein the component is connected to the anode of a DC power supply and has a film formed on its surface by an anodic oxidation treatment in which it is immersed in a solution mainly composed of an organic acid, and the film is subjected to a semi-sealing treatment using boiling water. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-81815 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the component described in Patent Document 1 has a problem in that its durability against corrosive gases and plasma is low because the pores of the anodic oxide film are not completely sealed.

[0006] On the other hand, in the component described in Patent Document 1, a method of completely sealing the pores of the anodic oxide film can be considered to improve durability against corrosive gases and plasma. However, in this case, cracks are more likely to occur in the anodic oxide film when the temperature rises, and there is a risk that foreign matter consisting of small fragments of the anodic oxide film will be generated.

[0007] Furthermore, in applications where high-temperature environments are used and sliding properties are required, such as compressor wheels, cracks in the anodized coating can lead to a decrease in corrosion resistance and wear resistance. To suppress the occurrence of such foreign matter and cracks, it is desirable to further improve the heat resistance of aluminum materials with an anodized coating on their surface.

[0008] This invention was made in view of the above background, and aims to provide a surface-treated aluminum material, a method for manufacturing the same, and a compressor wheel that have excellent corrosion resistance to corrosive gases and plasma, and can suppress the occurrence of cracks even when the temperature rises. [Means for solving the problem]

[0009] One aspect of the present invention is a base material made of an aluminum alloy having a Cu (copper) content of more than 1.8% by mass and 6.8% by mass or less, and a protective skin formed on the base material. membrane and A surface-treated aluminum material having, The protective coating consists of an aluminum oxide, and comprises an oxide layer covering the base material, It comprises a hydrated oxide layer containing aluminum hydrated oxide and covering the oxide layer, When the cathode polarization of the base material and the surface-treated aluminum material after heating at 200°C for 4 hours was measured using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution in a volume ratio of NaCl solution:acetic acid = 1000:1, the current density at the center potential of the potential region indicating the diffusion limit current of hydrogen ions in the base material was measured, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material, J1 / J2, was found to be 7000 × 10⁻⁶.-5 The following is a surface-treated aluminum material.

[0010] Another aspect of the present invention relates to a compressor wheel made of the surface-treated aluminum material of the above aspect.

[0011] Yet another aspect of the present invention is a method for manufacturing a surface-treated aluminum material according to the above-described aspect, By subjecting the base material to anodizing treatment, the oxide layer having pores is formed on the base material. Subsequently, the base material and the oxide layer are heated at a temperature of 50°C to 350°C. The present invention relates to a method for manufacturing a surface-treated aluminum material, wherein the oxide layer is then brought into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores. [Effects of the Invention]

[0012] The surface-treated aluminum material (hereinafter referred to as "aluminum material") has a protective film on the surface of the base material comprising the oxide layer and the hydrated oxide layer. Furthermore, when the cathode polarization of the surface-treated aluminum material and the base material is measured after heating at a temperature of 200°C for 4 hours using the specific method, the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material, J1 / J2, is 7000 × 10⁻⁶. -5 The following is true: Aluminum materials possessing these properties exhibit excellent corrosion resistance to corrosive gases and plasma, as well as superior heat resistance, and can suppress crack formation even when the temperature rises.

[0013] Furthermore, since the compressor wheel is made of the aluminum material, it suppresses the occurrence of cracks in the protective coating even when it becomes hot during use, and maintains the sound condition of the protective coating for a long period of time. As a result, the protective coating is less prone to cracking, and wear of the protective coating can be suppressed over a long period of time.

[0014] Also, in the method for manufacturing the aluminum material, after subjecting the base material to an anodic oxidation treatment, the oxide layer formed by the anodic oxidation treatment is heated at a temperature within the specific range. By heating the oxide layer before sealing the pores of the oxide layer in this way, the internal stress generated during the formation of the oxide layer can be relaxed. Then, after relaxing the internal stress of the oxide layer, the oxide layer and the sealing agent are brought into contact to form a hydrated oxide layer on the oxide layer and seal the pores, thereby enhancing the corrosion resistance against corrosive gases and plasmas, improving the heat resistance, and suppressing the occurrence of cracks even when the temperature rises.

[0015] As described above, according to the above aspect, there can be provided a surface-treated aluminum material having excellent corrosion resistance against corrosive gases and plasmas, excellent heat resistance, and capable of suppressing the occurrence of cracks even when the temperature rises, a method for manufacturing the same, and a compressor wheel.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a cross-sectional view of the surface-treated aluminum material in the embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the base material on which the oxide layer is formed during the manufacturing process of the surface-treated aluminum material in the embodiment. [Figure 3] FIG. 3 is an explanatory view showing an example of the cathode polarization curve of the base material. [Figure 4] FIG. 4 is an enlarged view of the step portion in the cathode polarization curve of the base material. [Figure 5] FIG. 5 is an explanatory view showing a method for measuring the strain amount of the surface-treated aluminum material in the reference example. [Figure 6] FIG. 6 is an explanatory view showing the measurement result of the strain amount of the surface-treated aluminum material in the reference example.

Embodiments for Carrying Out the Invention

[0017] (Aluminum Material) The base material of the aforementioned aluminum material is composed of an aluminum alloy having a Cu content exceeding 1.8% by mass and not exceeding 6.8% by mass. The shape of the base material is not particularly limited and can take various shapes depending on the application of the aluminum material.

[0018] The aluminum alloy constituting the base material of the aforementioned aluminum material may be, for example, a 2000 series aluminum alloy. As the 2000 series aluminum alloy constituting the base material of the aforementioned aluminum material, for example, an aluminum alloy can be used that contains Cu (copper) in an amount exceeding 1.8 mass% and up to 6.8 mass%, and also contains one or more elements selected from the group consisting of Si (silicon), Fe (iron), Mn (manganese), Mg (magnesium), Cr (chromium), Zn (zinc), and Ti (titanium) as optional components, with the remainder being Al and unavoidable impurities.

[0019] More specifically, as 2000 series aluminum alloys, for example, aluminum alloys having chemical compositions represented by alloy numbers AA2011, AA2014, AA2014A, AA2017, AA2017A, AA2218, AA2219, AA2018, AA2025, AA2319, AA2124, AA2036, AA2117, AA2618, or AA2024 can be used.

[0020] The base material is provided with a protective coating comprising an oxide layer made of aluminum oxide and laminated on the base material, and a hydrated oxide layer containing hydrated aluminum oxide and laminated on the oxide layer. More specifically, the hydrated oxide layer may be composed of hydrated aluminum oxide. The hydrated oxide layer may also contain hydrated oxide and a metal salt. The protective coating can be obtained, for example, by anodic oxidation of the base material to form an oxide layer with numerous pores on the surface of the base material, followed by a sealing treatment to block the pores of the oxide layer with the hydrated oxide layer. Such a protective coating has excellent corrosion resistance to corrosive gases and plasma. Therefore, forming the protective coating on the base material can improve the corrosion resistance of the aluminum material.

[0021] The thickness of the protective film is preferably 2 μm or more. This further improves the corrosion resistance of the aluminum material. From the viewpoint of corrosion resistance, there is no particular upper limit to the thickness of the protective film; the thicker the protective film, the better the corrosion resistance of the aluminum material can be. From this viewpoint, the thickness of the protective film is more preferably 5 μm or more, and even more preferably 10 μm or more. The upper limit for the manufacturing thickness of the protective film is, for example, 200 μm. From the viewpoint of suppressing the occurrence of cracks in the protective film, the thickness of the protective film is preferably 100 μm or less.

[0022] When a porosity test is performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area of ​​the aluminum material is 0.3 g / dm². 2 The following is preferable: In such an aluminum material, the pores of the oxide layer are sufficiently sealed by the hydrated oxide layer, thus more reliably improving the corrosion resistance of the aluminum material.

[0023] The specific method for the porosity test is as follows: First, 35 mL of phosphoric acid and 20 g of chromic anhydride are dissolved in water to prepare 1 L of test solution. Next, a test piece containing the protective film is taken from the aluminum material, and the area of ​​the protective film on the test piece is measured. After removing any dirt from the surface of the test piece, its mass is measured. Then, the test piece is immersed in the test solution, which is maintained at a temperature of 38°C ± 1°C, for 15 minutes ± 5 seconds.

[0024] After the test specimen has been immersed in the test solution, it is washed with running water, and then with deionized water or distilled water. After the washed specimen is thoroughly dried, its mass is measured.

[0025] The area A (unit: dm²) of the protective coating on the test specimen obtained from the above is... 2 Using the mass m1 (unit: g) of the test specimen before immersion in the test solution and the mass m2 (unit: g) of the test specimen after immersion in the test solution, the mass loss per unit area δ is calculated based on the following formula (1).A (Unit: g / dm 2 It is possible to calculate ). δ A =(m1-m2) / A ···(1)

[0026] The surface-treated aluminum material was subjected to cathode polarization measurement using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution in a volume ratio of NaCl solution:acetic acid = 1000:1. The cathode polarization of the surface-treated aluminum material was measured after heating it at 200°C for 4 hours, and the current density at the center potential of the potential region showing the hydrogen ion diffusion limit current of the base material was measured. The ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material, J1 / J2, was 7000 × 10⁻⁶. -5 The aluminum material has the following characteristics: Aluminum materials in which the current density ratio J1 / J2 is within the specified range are less prone to cracking when the temperature rises. Therefore, aluminum materials equipped with the protective coating and in which the current density ratio J1 / J2 is within the specified range have excellent corrosion resistance and heat resistance. From the viewpoint of improving the heat resistance of the aluminum material, there is no lower limit to the current density ratio J1 / J2, but by definition, the current density ratio J1 / J2 is always greater than 0.

[0027] As mentioned above, the aluminum material exhibits excellent corrosion resistance to corrosive gases and plasma, and can suppress the occurrence of cracks in the protective coating even when the temperature rises. Therefore, the aluminum material is suitable for applications such as cover members installed around the fans of cooking appliances and components for semiconductor manufacturing equipment. Furthermore, the aluminum material has the characteristics of being resistant to cracking of the protective coating and being resistant to wear even at high temperatures. For this reason, the aluminum material is also suitable for applications such as compressor wheels incorporated into turbochargers.

[0028] (Manufacturing method for aluminum materials) In manufacturing the surface-treated aluminum material, first, a base material made of an aluminum alloy with a Cu content exceeding 1.8% by mass and not exceeding 6.8% by mass is prepared. The manufacturing method of the base material is not particularly limited, and known methods can be adopted. For example, the base material may be manufactured by a method appropriately combining casting, rolling, and heat treatment. Also, after manufacturing the base material, before performing anodic oxidation treatment, pretreatment for anodic oxidation such as degreasing, pickling, and polishing may be performed as necessary. Next, by subjecting the base material to anodic oxidation treatment, the oxide layer having pores is formed on the base material. In anodic oxidation treatment, an oxide layer can be formed on the surface of the base material by passing a direct current between the base material and the counter electrode while immersing the base material and the counter electrode in an electrolytic solution. The oxide layer thus formed is composed of an aluminum oxide such as alumina and has a large number of pores.

[0029] The electrolytic solution used in anodic oxidation treatment may be, for example, an acidic electrolytic solution containing an electrolyte such as sulfuric acid or phosphoric acid, or an alkaline electrolytic solution containing an electrolyte such as sodium metaborate. The electrolytic solution used in anodic oxidation treatment preferably contains an inorganic electrolyte composed of an inorganic cation and one or more anions selected from the group consisting of sulfate ions, phosphate ions, ammonium ions, and borate ions. By performing anodic oxidation treatment using an electrolytic solution containing an inorganic electrolyte, an oxide layer having a desired structure can be more easily formed.

[0030] The current density of the direct current in anodic oxidation treatment can be appropriately set, for example, from the range of 1 mA / cm 2 or more to 100 mA / cm 2 or less. Also, the temperature of the electrolytic solution in anodic oxidation treatment can be appropriately set, for example, from the range of 0°C or more to 40°C or less.

[0031] In anodizing, the thickness of the oxide layer formed is preferably 2 μm or more. By making the oxide layer 2 μm or more thick, the thickness of the protective film obtained after sealing can be sufficiently increased, making it easier to obtain aluminum material with excellent corrosion resistance and heat resistance.

[0032] In the above manufacturing method, after anodizing, the base material and the oxide layer are heated at a temperature of 50°C to 350°C. By heating the oxide layer at a temperature within the specified range after anodizing but before sealing the pores in the oxide layer, the internal stress of the oxide layer can be relieved. Then, by sealing the pores after the internal stress of the oxide layer has been relieved, the internal stress in the protective film after sealing can be reduced. As a result, the occurrence of cracks in the protective film when heated can be suppressed, and an aluminum material with excellent heat resistance can be obtained.

[0033] If the heating temperature of the oxide layer is less than 50°C, the internal stress of the oxide layer will not be sufficiently relieved, and cracks may easily occur in the protective film when the temperature of the aluminum material rises. On the other hand, if the heating temperature of the oxide layer exceeds 350°C, the oxide layer may not be able to follow the thermal expansion of the base material, and cracks may occur in the oxide film. When heating the oxide layer, heating may be stopped immediately after the oxide layer reaches the desired temperature, or the temperature may be maintained for a certain period of time after reaching the desired temperature. From the viewpoint of sufficiently relieving the internal stress of the oxide layer and more reliably improving the heat resistance of the aluminum material, it is preferable that the heating time from the start to the end of heating the oxide layer is between 1 minute and 12 hours.

[0034] After heating the oxide layer, the oxide layer is brought into contact with a sealing agent. This forms the hydrated oxide layer on the oxide layer and seals the pores with the hydrated oxide layer. As the sealing agent, for example, a substance that can react with aluminum oxide to form a hydrated oxide, such as hot water, can be used. When hot water is used for the sealing treatment, a hydrated oxide layer consisting of aluminum hydrated oxide can be formed on the oxide layer.

[0035] Furthermore, as a sealing agent, substances that react with aluminum oxides to form hydrated oxides and metal salts can be used, such as aqueous solutions of nickel acetate, cobalt acetate, chromate, and silicate. When sealing is performed using such a sealing agent, a hydrated oxide layer containing aluminum hydrated oxide and metal salt can be formed on the oxide layer.

[0036] From the viewpoint of more easily obtaining aluminum materials with excellent corrosion resistance and heat resistance, it is preferable that the sealing agent be hot water. Furthermore, by sealing the pores of the oxide layer with hot water, a hydrated oxide layer that does not contain metal salts can be formed on the oxide layer. When using hot water as a sealing agent, it is more preferable to seal the pores of the oxide layer by contacting the oxide layer with hot water at 95°C or higher for 10 minutes or more but less than 120 minutes. [Examples]

[0037] (Examples) Examples of the surface-treated aluminum material and its manufacturing method will be described with reference to Figures 1 and 2. As shown in Figure 1, the surface-treated aluminum material 1 of this example has a base material 2 made of an aluminum alloy having an aluminum or Cu content of more than 1.8% by mass and 6.8% by mass or less, and a protective film 3 formed on the base material. The protective film 3 has an oxide layer 31 made of aluminum oxide that covers the base material 2, and a hydrated oxide layer 32 containing hydrated aluminum oxide that covers the oxide layer 31. When the cathode polarization of the base material 2 and the surface-treated aluminum material 1, which was heated at 200°C for 4 hours, was measured using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution in a volume ratio of NaCl solution:acetic acid = 1000:1, the current density at the center potential of the potential region indicating the diffusion limit current of hydrogen ions in the base material 2 was measured, and the ratio of the current density J1 of the surface-treated aluminum material 1 to the current density J2 of the base material 2, J1 / J2, was found to be 7000 × 10⁻⁶. -5 The following applies:

[0038] In producing the aluminum material 1 in this example, first, the base material 2 is subjected to anodizing treatment to form an oxide layer 31 with pores 311 on the base material 2, as shown in Figure 2. Then, the base material 2 and the oxide layer 31 are heated at a temperature of 50°C to 350°C to relieve the internal stress of the oxide layer 31. After that, the oxide layer 31 is brought into contact with a sealing agent to form a hydrated oxide layer 32 on the oxide layer 31 and seal the pores 311, thereby obtaining the aluminum material 1.

[0039] Table 1 shows specific examples of aluminum material 1 (test materials A1 to A3). The manufacturing method for test materials A1 to A3 is as follows, for example. First, an aluminum plate with a thickness of 1.1 mm and having the chemical composition represented by one of the alloy numbers shown in Table 1 is prepared as the base material 2. This base material 2 is subjected to a pretreatment for anodic oxidation. Specifically, as a pretreatment, the base material 2 is first subjected to alkaline etching by immersing it in a sodium hydroxide aqueous solution with a concentration of 5 mass% at a temperature of 55°C. After that, the base material 2 is subjected to desmat treatment by immersing it in nitric acid with a concentration of 30 mass%. After that, the base material 2 is subjected to chemical polishing by immersing it in a mixed solution of phosphoric acid and sulfuric acid mixed in a volume ratio of phosphoric acid:sulfuric acid = 7:3 at a temperature of 85°C. After the chemical polishing treatment, desmat treatment is performed again under the same conditions as described above.

[0040] After pre-treating the base material 2 as described above, the base material 2 is subjected to anodizing to form an oxide layer 31 on the surface of the base material 2. The electrolyte used in the anodizing process is a 15% by mass aqueous sulfuric acid solution, and the electrolyte temperature is 5°C. The current density in the anodizing process is 10 mA / cm². 2 The processing time is set to 60 minutes. The oxide layer 31 formed in this way is a so-called porous anodized film and has numerous pores 311, as shown in Figure 2. The thickness of the oxide layer 31 formed by anodic oxidation under the above conditions is approximately 15 μm.

[0041] After anodizing, the base material 2 is heated in a heating furnace to relieve the internal stress of the oxide layer 31. The set temperature of the heating furnace is the value shown in the "Heating Temperature" column of Table 1, and the time the base material stays in the furnace, that is, the time from the start of heating to the end of heating, is the value shown in the "Heating Time" column of Table 1.

[0042] Subsequently, the base material 2 equipped with the oxide layer 31 is immersed in hot water at 100°C for 60 minutes as a sealing agent, thereby forming a hydrated oxide layer 32 made of hydrated aluminum oxide on the oxide layer 31, and sealing the pores 311 of the oxide layer 31 with the hydrated oxide layer 32. Through this process, test materials A1 to A3 shown in Table 1 can be obtained. Note that when sealing the pores 311 of the oxide layer 31 under these conditions, the mass loss per unit area of ​​the aluminum material 1 when performing a sealing degree test according to the method specified in JIS H8683-2:2013 is 0.3 g / dm². 2 The results are as follows:

[0043] Note that test materials B1 to B2 shown in Table 1 are test materials for comparison with test materials A1 to A3. The manufacturing method of test materials B1 to B2 is the same as that of test materials A1 to A3, except that after forming the oxide layer 31 on the base material 2, the oxide layer 31 is brought into contact with the sealant without heating.

[0044] Next, the method for measuring the cathode polarization of test materials A1-A3 and B1-B2 will be explained.

[0045] [Cathode Polarization Measurement] The cathode polarization of the base material and the test material heated at 200°C for 4 hours will be measured using the following method, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material, J1 / J2, will be calculated based on these cathode polarization curves. First, the test material will be heated in an oven set to 200°C for 4 hours. After removing the test material from the oven and letting it cool to room temperature, an evaluation area will be set on the protective coating, and the parts of the surface of the test material other than the evaluation area will be covered with silicone resin.

[0046] Next, prepare a 5% by mass NaCl aqueous solution and a 99.7% acetic acid solution. Prepare the measurement solution by adding the acetic acid to the NaCl aqueous solution so that the volume ratio of NaCl aqueous solution to acetic acid is 1000:1. Immerse the test specimen, counter electrode, and reference electrode, electrically connected to the potentiostat, in this solution and allow it to stand for 30 minutes to stabilize the potential of the measurement area. Do not degas the measurement solution. For example, an Ag / AgCl electrode can be used as the reference electrode.

[0047] After the potential of the measurement section stabilizes, a voltage is applied between the test specimen and the counter electrode using a potentiostat, and the potential of the measurement section is swept at a sweep rate of 20 mV / min until the potential of the measurement section reaches -2000 mV relative to the reference electrode. By measuring the current density flowing through the measurement section at this time, the cathode polarization curve of the test material after heating is obtained. Similarly, the cathode polarization curve of the base material is obtained by performing the same measurement using the base material that has undergone pretreatment for anodizing using the method described above. The cathode polarization measurements of both the test material and the base material are performed in an atmospheric environment, with the temperature of the measurement solution maintained at 25°C. Furthermore, the cathode polarization measurements of both the test material and the base material are performed without stirring the measurement solution, with the measurement solution being substantially still.

[0048] Figure 3 shows an example of the cathode polarization curve of a base material, specifically an aluminum alloy with the chemical composition represented by alloy number A6016, without a protective coating. The vertical axis in Figure 3 represents the potential of the measurement point (unit: V), and the horizontal axis represents the current density (unit: μA / cm²). 2 ). Also, the horizontal axis scale in Figure 3 is logarithmic. As shown in Figure 3, the cathode polarization curve of aluminum material without a protective coating shows a stepped shape.

[0049] In cathode polarization measurements, as the current approaches a state where it is rate-limited by hydrogen ion diffusion, the change in current becomes smaller in response to the change in potential at the measurement site. Therefore, in the cathode polarization curve shown in Figure 3, where potential is represented on the vertical axis and current density on the horizontal axis, the potential region indicating the hydrogen ion diffusion limit current is included in the part of the cathode polarization curve where the slope of the curve is steep at the step.

[0050] Figure 4 shows an enlarged view of the stepped portion of the cathode polarization curve in Figure 3. Although not shown in the figure, the cathode polarization curve of the base material also exhibits a stepped shape similar to that in Figure 3. Therefore, based on the shape of the stepped portion of the cathode polarization curve shown in Figure 4, the center of the potential region indicating the diffusion limit current of hydrogen ions can be determined. The method for determining the potential region indicating the diffusion limit current of hydrogen ions in the cathode polarization curve of the base material is as follows: First, as shown in Figure 4, a tangent line L is drawn at the stepped portion of the cathode polarization curve where the absolute value of the slope is greatest. Then, the region R where this tangent line L and the cathode polarization curve overlap is defined as the potential region indicating the diffusion limit current of hydrogen ions. The current density J2 at the center of the region R determined in this way is calculated. In addition, the current density J1 at the same potential as the center of the aforementioned potential region in the cathode polarization curve of the base material is calculated in the cathode polarization curve of the test material after heating.

[0051] The current density J1 calculated based on the cathode polarization curve of the test material after heating can be used as an indicator of the contact area between the base material and the measurement solution in the test material after heating. A larger current density value indicates a larger contact area between the base material and the measurement solution. Therefore, the ratio J1 / J2 of the current density J1 calculated using the heated test piece to the current density J2 calculated using the base material can be used as an indicator of the rate of increase in the exposed area of ​​the base material due to heating. More specifically, for example, if defects such as cracks are formed in the protective coating of the test material after heating, the base material may be exposed due to the cracks. In this case, the current density ratio J1 / J2 will be larger. Table 1 shows the current density ratio J1 / J2 for each test material.

[0052] [Table 1]

[0053] As shown in Table 1, when preparing test materials A1 to A3, an oxide layer is formed on the base material, and then the oxide layer is heated to a temperature within the specified range before sealing the pores of the oxide layer. Therefore, these test materials have a current density ratio J1 / J2 within the specified range, and the occurrence of cracks in the protective coating can be suppressed even when the temperature rises. Furthermore, since the oxide layer of the protective coating of these test materials is sealed by a hydrated oxide layer, it exhibits excellent corrosion resistance to corrosive gases and plasma.

[0054] On the other hand, when preparing test materials B1 and B2, an oxide layer is formed on the base material, and then the pores are sealed without heating the oxide layer. As a result, the current density ratio J1 / J2 of these test materials is higher than the aforementioned specific range, making them prone to cracking when the temperature rises.

[0055] (Reference example) This example describes the measurement of strain in an aluminum material having a protective coating on the base material. In this example, symbols identical to those used in previously described examples represent the same components as those in the previously described examples, unless otherwise specified.

[0056] The method for preparing the test material used in this example is as follows. First, an aluminum plate with a thickness of 1.1 mm and having the chemical composition represented by alloy number AA6016 is prepared as the base material 2. This base material 2 is subjected to a pretreatment for anodic oxidation in the same manner as in the example, and then subjected to anodic oxidation. After the anodic oxidation treatment, the base material 2 is heated in a heating furnace to relieve the internal stress of the oxide layer 31. The set temperature of the heating furnace is the value shown in the "Heating Temperature" column of Table 2, and the time the base material stays in the furnace, that is, the time from the start of heating to the end of heating, is the value shown in the "Heating Time" column of Table 2.

[0057] Subsequently, the base material 2 equipped with the oxide layer 31 is immersed in hot water at 100°C for 60 minutes as a sealing agent, thereby forming a hydrated oxide layer 32 on the oxide layer 31 and sealing the pores 311 of the oxide layer 31 with the hydrated oxide layer 32. Through this process, test materials C1 to C2 shown in Table 1 can be obtained.

[0058] Test materials D1 and E1 shown in Table 1 are test materials for comparison with test materials C1 to C2. The manufacturing method of test material D1 is the same as that of test materials C1 to C2, except that after forming an oxide layer 31 on the base material 2, the oxide layer 31 is brought into contact with a sealing agent without heating. Test material E1 is a plate material made of an aluminum alloy having the chemical composition represented by alloy number AA6016. Test material E1 is obtained by subjecting a plate material made of an aluminum alloy having the chemical composition represented by alloy number AA6016 to pretreatment for anodic oxidation treatment using the method described above.

[0059] To measure the strain of test materials C1-C2 and test material D1, as shown in Figure 5, the base material 2 is exposed on the back of the surface of the aluminum material 1 that has the protective coating 3. Then, a strain gauge 4 is attached to the exposed base material 2. By heating the aluminum material 1 with the strain gauge 4 attached in this way, the strain due to thermal expansion of the base material 2 and the protective coating 3 can be measured. Note that in Figure 5, the structure of the protective coating 3 is simplified for convenience.

[0060] Although not shown in the diagram, to measure the amount of strain in test material E1, a strain gauge should be attached to one side of test material E1 in the thickness direction, and then test material E1 should be heated.

[0061] Figure 6 shows the change in strain when test specimens C1-C2, D1, and E1 are heated for 30 minutes in a furnace set to 200°C. In Figure 6, the vertical axis represents strain, and the horizontal axis represents the elapsed time from the start of heating. Immediately after heating begins, the test specimens undergo thermal expansion as the temperature rises, so as shown in Figure 6, the strain increases rapidly for the first few minutes after the start of the test. After that, when the temperature of the test specimens reaches approximately a constant temperature, the strain of the test specimens becomes approximately constant.

[0062] Table 2 shows the maximum strain values ​​during heating of the test specimens. Table 2 also shows the difference between the maximum strain values ​​of test specimens C1-C2 and D1 (which have protective coatings) and the maximum strain value of test specimen E1 (which does not have a protective coating). The difference between the strain values ​​of test specimens C1-C2 and D1 and the strain value of test specimen D indicates the magnitude of the internal stress in the protective coating released by heating during the test. A smaller difference between the two strain values ​​indicates lower internal stress in the protective coating.

[0063] [Table 2]

[0064] As shown in Table 2, the strain of test materials C1 and C2, in which the hydrated oxide layer is formed after heating the oxide layer during the manufacturing process, is smaller than the strain of test material D1, in which the hydrated oxide layer is formed without heating the oxide layer. Therefore, these results indicate that, in the manufacturing process of aluminum, forming the hydrated oxide layer after heating the oxide layer can relieve internal stress in the protective film and improve the heat resistance of the aluminum material.

[0065] Although embodiments of the surface-treated aluminum material and its manufacturing method according to the present invention have been described above based on the examples, the specific embodiments of the surface-treated aluminum material and its manufacturing method according to the present invention are not limited to the embodiments described in the examples, and the configuration can be appropriately modified without impairing the spirit of the present invention.

[0066] For example, the surface-treated aluminum material according to the present invention may take the following embodiments: [1] to [3].

[0067] [1] A surface-treated aluminum material comprising a base material made of an aluminum alloy having an aluminum or Cu content of more than 1.8% by mass and 6.8% by mass or less, and a protective film formed on the base material, The protective coating consists of an aluminum oxide, and comprises an oxide layer covering the base material, It comprises a hydrated oxide layer containing aluminum hydrated oxide and covering the oxide layer, When the cathode polarization of the base material and the surface-treated aluminum material after heating at 200°C for 4 hours was measured using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution in a volume ratio of NaCl solution:acetic acid = 1000:1, the current density at the center potential of the potential region indicating the diffusion limit current of hydrogen ions in the base material was measured, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material, J1 / J2, was found to be 7000 × 10⁻⁶. -5 The following are surface-treated aluminum materials.

[0068] [2] When the degree of sealing test is performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area is 0.3 g / dm 2 The surface-treated aluminum material described in [1] is as follows:

[0069] Furthermore, the compressor wheel according to the present invention may take the form described in [3] below. [3] A compressor wheel made of surface-treated aluminum material as described in [1] or [2].

[0070] Furthermore, the method for manufacturing the surface-treated aluminum material according to the present invention may take the forms shown in [4] to [8] below.

[0071] A method for manufacturing a surface-treated aluminum material as described in [4], [1], or [2], By subjecting the base material to anodizing treatment, the oxide layer having pores is formed on the base material. Subsequently, the base material and the oxide layer are heated at a temperature of 50°C to 350°C. A method for manufacturing a surface-treated aluminum material, comprising subsequently bringing the oxide layer into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and sealing the pores.

[0072] [5] The method for producing a surface-treated aluminum material according to [4], wherein the heating time in the heating process, from the start of heating the oxide layer to the end of heating, is 1 minute or more and less than 12 hours. [6] The method for producing a surface-treated aluminum material according to [4] or [5], wherein the sealing agent is hot water.

[0073] [7] A method for producing a surface-treated aluminum material according to any one of [4] to [6], wherein in the sealing step, the oxide layer is brought into contact with hot water at 100°C or higher as the sealing agent for 10 minutes or more but less than 120 minutes. [8] A method for producing a surface-treated aluminum material according to any one of [4] to [7], wherein the electrolyte used in the anodic oxidation treatment comprises an inorganic electrolyte consisting of an inorganic cation and one or more anions selected from the group consisting of sulfate ions, phosphate ions, ammonium ions, and borate ions.

Claims

1. A surface-treated aluminum material comprising a base material made of an aluminum alloy having a Cu content of more than 1.8% by mass and 6.8% by mass or less, and a protective film formed on the base material, The protective coating consists of an aluminum oxide, and comprises an oxide layer covering the base material, It comprises a hydrated oxide layer containing aluminum hydrated oxide and covering the oxide layer, When the cathode polarization of the base material and the surface-treated aluminum material after heating at 200°C for 4 hours was measured using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution in a volume ratio of NaCl solution:acetic acid = 1000:1, and the current density at the center potential of the potential region indicating the diffusion limit current of hydrogen ions in the base material was measured, the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material J1 / J2 was 7000 × 10⁻¹⁰. -5 The following are surface-treated aluminum materials.

2. When a porosity test is performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area is 0.3 g / dm². 2 The surface-treated aluminum material according to claim 1, which is as follows:

3. A compressor wheel made of surface-treated aluminum material according to claim 1 or 2.

4. A method for manufacturing a surface-treated aluminum material according to claim 1 or 2, By subjecting the base material to an anodizing treatment, the oxide layer having pores is formed on the base material. Subsequently, the base material and the oxide layer are heated at a temperature of 50°C to 350°C. A method for manufacturing a surface-treated aluminum material, comprising subsequently bringing the oxide layer into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and sealing the pores.

5. The method for producing a surface-treated aluminum material according to claim 4, wherein the heating time in the heating process, from the start of heating the oxide layer to the end of heating, is 1 minute or more and less than 12 hours.

6. The method for producing a surface-treated aluminum material according to claim 4, wherein the sealing agent is hot water.

7. A method for producing a surface-treated aluminum material according to claim 4, wherein in the sealing process, the oxide layer is brought into contact with hot water at 95°C or higher as the sealing agent for 10 minutes or more but less than 120 minutes.

8. The method for producing a surface-treated aluminum material according to claim 4, wherein the electrolyte used in the anodic oxidation treatment comprises an inorganic electrolyte consisting of an inorganic cation and one or more anions selected from the group consisting of sulfate ions, phosphate ions, ammonium ions, and borate ions.

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