Surface-treated aluminum material, method for producing 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

Surface-treated aluminum material, its manufacturing method, and compressor wheel

[0001] The present invention relates to a surface-treated aluminum material, a manufacturing method thereof, and a compressor wheel.

[0002] 2000 series aluminum alloys, which have relatively high strength at high temperatures among aluminum alloys, are widely used in applications such as turbocharger compressor wheels, etc. 2000 series aluminum alloys are also sometimes used for parts placed inside the vacuum chamber of semiconductor manufacturing equipment.

[0003] Incidentally, an anodized film is sometimes provided on the surface of an aluminum material for the purpose of surface protection, etc. For example, Patent Document 1 describes a component for a substrate processing apparatus that performs plasma processing on a substrate, characterized in that the component is connected to the anode of a DC power supply and has a film formed on the surface of the component by anodizing treatment in which the component is immersed in a solution mainly containing an organic acid, and the film is subjected to a semi-sealing treatment using boiling water.

[0004] JP 2008-81815 A

[0005] However, the component of Patent Document 1 has a problem in that the pores of the anodized film are not completely closed, resulting in low durability against corrosive gases and plasma.

[0006] On the other hand, in order to improve the durability of the component disclosed in Patent Document 1 against corrosive gases and plasma, it is conceivable to completely block the pores in the anodized film. However, in this case, cracks are likely to occur in the anodized film when the temperature rises, and there is a risk of generating foreign matter consisting of small pieces of the anodized film.

[0007] Furthermore, in applications such as compressor wheels that are used in high-temperature environments and require good sliding properties, the occurrence of cracks in the anodized film can lead to a decrease in corrosion resistance and wear resistance. To prevent the occurrence of such foreign matter and cracks, it is desirable to further improve the heat resistance of aluminum materials having an anodized film on their surfaces.

[0008] The present invention has been made in view of the above background, and aims to provide a surface-treated aluminum material that has excellent corrosion resistance against corrosive gases and plasma and is capable of suppressing the occurrence of cracks even when the temperature rises, a manufacturing method thereof, and a compressor wheel.

[0009] One aspect of the present invention is a surface-treated aluminum material having a base material made of an aluminum alloy containing more than 1.8% by mass and not more than 6.8% by mass of Cu (copper), and a protective coating formed on the base material, wherein the protective coating has an oxide layer made of an oxide of aluminum and covering the base material, and a hydrated oxide layer containing a hydrated oxide of aluminum and covering the oxide layer, wherein cathodic polarization measurements were performed on the base material and the surface-treated aluminum material after heating at a temperature of 200°C for 4 hours using a measurement solution obtained by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of the NaCl solution:the acetic acid = 1000:1, and the current density at the center potential of a potential region showing the diffusion limiting current of hydrogen ions in the base material was measured, and it was found that the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 7000 x 10 -5 The following surface-treated aluminum materials are available.

[0010] Another aspect of the present invention is 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 producing a surface-treated aluminum material according to the above aspect, comprising the steps of: anodizing the base material to form the oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 50°C or higher and 350°C or lower; and bringing the oxide layer into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores.

[0012] The surface-treated aluminum material (hereinafter referred to as "aluminum material") has a protective coating comprising the oxide layer and the hydrated oxide layer on the surface of a base material. Furthermore, when cathodic polarization measurements were performed on the surface-treated aluminum material and the base material after heating at a temperature of 200°C for 4 hours using the specific method, the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 7000 x 10 -5 The aluminum material having these properties has excellent corrosion resistance against corrosive gases and plasma, as well as excellent heat resistance, and can suppress the occurrence of cracks even when the temperature rises.

[0013] Furthermore, because the compressor wheel is made of the aluminum material, the occurrence of cracks in the protective coating can be suppressed even when the temperature becomes high during use, and the sound state of the protective coating can be maintained for a long period of time. Furthermore, since the protective coating is less susceptible to cracks, wear of the protective coating can be suppressed for a long period of time.

[0014] In addition, in the method for producing an aluminum material, the base material is anodized, and then the oxide layer formed by the anodization is heated at a temperature within the specific range. By heating the oxide layer before sealing the pores in the oxide layer, the internal stress generated during the formation of the oxide layer can be alleviated. After the internal stress in the oxide layer is alleviated, the oxide layer is brought into contact with a sealant to form a hydrated oxide layer on the oxide layer and seal the pores. This increases corrosion resistance against corrosive gases and plasma, improves heat resistance, and suppresses the occurrence of cracks even when the temperature rises.

[0015] As described above, according to the above-described aspects, it is possible to provide a surface-treated aluminum material that has excellent corrosion resistance against corrosive gases and plasmas, as well as excellent heat resistance, and that can suppress the occurrence of cracks even when the temperature rises, a manufacturing method thereof, and a compressor wheel.

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

[0017] (Aluminum Material) The base material of the aluminum material is made of an aluminum alloy having a Cu content of more than 1.8 mass% and not more than 6.8 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 aluminum material may be, for example, a 2000 series aluminum alloy. As the 2000 series aluminum alloy constituting the base material of the aluminum material, for example, an aluminum alloy having a chemical composition containing more than 1.8 mass % and not more than 6.8 mass % Cu (copper), and containing 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 balance being Al and unavoidable impurities, can be used.

[0019] More specifically, examples of 2000 series aluminum alloys that can be used include aluminum alloys having chemical components represented by alloy numbers AA2011, AA2014, AA2014A, AA2017, AA2017A, AA2218, AA2219, AA2018, AA2025, AA2319, AA2124, AA2036, AA2117, AA2618, and AA2024.

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

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

[0022] When a sealing test was performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area of ​​the aluminum material was 0.3 g / dm 2 In such an aluminum material, the pores of the oxide layer are sufficiently sealed by the hydrated oxide layer, so that the corrosion resistance of the aluminum material can be more reliably improved.

[0023] The specific method for the pore sealing 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 including a protective coating is taken from the aluminum material, and the area of ​​the protective coating on the test piece is measured. After removing any dirt from the surface of this test piece, the mass of the test piece is measured. Thereafter, the test piece is immersed in the test solution maintained at a temperature of 38°C ± 1°C for 15 minutes ± 5 seconds.

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

[0025] The area A (unit: dm ２ ), the mass m of the test piece before immersion in the test liquid １ (unit: g) and the mass m of the test piece after immersion in the test liquid ２ (unit: g) and calculated the mass loss per unit area δ based on the following formula (1): Ａ (unit: g / dm ２ ) can be calculated. Ａ = (m １ -m ２ ) / A...(1)

[0026] The surface-treated aluminum material was subjected to cathodic polarization measurement of the base material and the surface-treated aluminum material after heating at a temperature of 200°C for 4 hours using a measurement solution obtained by mixing a NaCl solution with a concentration of 5% by mass and acetic acid with a concentration of 99.7% by mass at a volume ratio of the NaCl solution:acetic acid = 1000:1, and when the current density at the central potential in the potential region showing the diffusion limiting current of hydrogen ions in the base material was measured, the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 7000 × 10 -5The aluminum material has the following characteristics: An aluminum material having a current density ratio J1 / J2 within the specific range is less likely to crack when the temperature rises. Therefore, an aluminum material having the protective coating and a current density ratio J1 / J2 within the specific range is excellent in both 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 the current density ratio J1 / J2 must, by definition, be a value greater than 0.

[0027] As described above, the aluminum material has excellent corrosion resistance against corrosive gases, plasma, and the like, 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 provided around the fans of cooking appliances and components for semiconductor manufacturing equipment. Furthermore, the aluminum material has properties such as being less susceptible to cracks in the protective coating and being less susceptible to wear even at high temperatures. Therefore, the aluminum material is also suitable for applications such as compressor wheels incorporated into turbochargers.

[0028] (Method for Manufacturing Aluminum Material) In manufacturing the surface-treated aluminum material, first, a base material made of an aluminum alloy having a Cu content of more than 1.8% by mass and not more than 6.8% by mass is prepared. The method for manufacturing the base material is not particularly limited, and known methods can be used. For example, the base material may be manufactured by a method that appropriately combines casting, rolling, and heat treatment. Furthermore, after manufacturing the base material, pretreatments for the anodizing treatment, such as degreasing, acid cleaning, and polishing, may be performed as necessary before the anodizing treatment. Next, the base material is anodized to form the oxide layer with pores on the base material. In the anodizing treatment, an oxide layer can be formed on the surface of the base material by passing a direct current between the base material and a counter electrode while the base material and the counter electrode are immersed in an electrolyte. The oxide layer formed in this manner is composed of an aluminum oxide, such as alumina, and has numerous pores.

[0029] The electrolytic solution used in the anodizing 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 the anodizing treatment preferably contains 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. By performing the anodizing 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 the anodizing treatment is, for example, 1 mA / cm ２ 100mA / cm or more ２ The temperature of the electrolytic solution in the anodizing treatment can be appropriately set within the range of 0°C or higher and 40°C or lower.

[0031] The thickness of the oxide layer formed in the anodizing treatment is preferably 2 μm or more. By making the thickness of the oxide layer 2 μm or more, the thickness of the protective coating obtained after sealing can be made sufficiently thick, and an aluminum material having excellent corrosion resistance and heat resistance can be more easily obtained.

[0032] In the manufacturing method, after anodizing, the base material and the oxide layer are heated at a temperature of 50°C or higher and 350°C or lower. By heating the oxide layer at a temperature within the specific range after anodizing and before sealing the pores in the oxide layer, the internal stress in the oxide layer can be alleviated. Then, by sealing the pores after alleviating the internal stress in the oxide layer, the internal stress in the protective coating after sealing can be reduced. As a result, the occurrence of cracks in the protective coating 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 alleviated, and cracks may easily occur in the protective coating when the temperature of the aluminum material increases. On the other hand, if the heating temperature of the oxide layer exceeds 350°C, the oxide layer will not be able to follow the thermal expansion of the base material, and cracks may occur in the oxide coating. When heating the oxide layer, the heating may be terminated immediately after the temperature of 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 alleviating the internal stress of the oxide layer and more reliably increasing the heat resistance of the aluminum material, the heating time from the start of heating the oxide layer to the end of heating is preferably 1 minute or more and less than 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 the pores are sealed by the hydrated oxide layer. The sealing agent may be, for example, a substance capable of reacting with an aluminum oxide to form a hydrated oxide, such as hot water. When hot water is used for the sealing treatment, a hydrated oxide layer made of a hydrated oxide of aluminum can be formed on the oxide layer.

[0035] Furthermore, as the sealing agent, a substance capable of reacting with an aluminum oxide to form a hydrated oxide and a metal salt, such as an aqueous solution of nickel acetate, an aqueous solution of cobalt acetate, an aqueous solution of chromate, an aqueous solution of silicate, etc. When sealing is performed using such a sealing agent, a hydrated oxide layer containing a hydrated oxide of aluminum and a metal salt can be formed on the oxide layer.

[0036] From the viewpoint of more easily obtaining an aluminum material having 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 using hot water, a hydrated oxide layer containing no metal salts can be formed on the oxide layer. When hot water is used as the sealing agent, it is more preferable to seal the pores of the oxide layer by contacting the oxide layer with hot water of 95°C or higher as the sealing agent for 10 minutes or more but less than 120 minutes.

[0037] Example An example 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 with an aluminum or Cu content of more than 1.8 mass% and not more than 6.8 mass%, and a protective coating 3 formed on the base material. The protective coating 3 has an oxide layer 31 made of aluminum oxide that 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 measurement solution was prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of 1000:1. The base material 2 and the surface-treated aluminum material 1 were heated at 200°C for 4 hours, and the cathodic polarization measurement was carried out using the measurement solution. The measurement was carried out using a measurement solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of 1000:1. The current density was measured at the central potential in the potential region showing the diffusion limiting current of hydrogen ions in the base material 2. The ratio J1 / J2 of the current density J1 of the surface-treated aluminum material 1 to the current density J2 of the base material 2 was 7000×10 -5 The following is the result.

[0038] In producing the aluminum material 1 of this example, first, an anodizing treatment is performed on the base material 2 to form an oxide layer 31 having pores 311 on the base material 2, as shown in Fig. 2. Then, the base material 2 and the oxide layer 31 are heated at a temperature of 50°C or higher and 350°C or lower to relieve internal stress in the oxide layer 31. Then, 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). Test materials A1 to A3 are manufactured, for example, as follows. First, an aluminum plate having a thickness of 1.1 mm and a chemical composition represented by one of the alloy numbers shown in Table 1 is prepared as base material 2. This base material 2 is subjected to a pretreatment for anodizing. Specifically, as a pretreatment, an alkali etching treatment is performed by immersing the base material 2 in a sodium hydroxide aqueous solution with a concentration of 5% by mass and a temperature of 55°C. Subsequently, the base material 2 is subjected to a desmutting treatment by immersing it in nitric acid with a concentration of 30% by mass. Subsequently, a chemical polishing treatment is performed by immersing the base material 2 in a mixed solution of phosphoric acid and sulfuric acid at a volume ratio of phosphoric acid:sulfuric acid = 7:3 at a temperature of 85°C. After the chemical polishing treatment, a desmutting treatment is performed again under the same conditions as described above.

[0040] After the base material 2 has been pretreated as described above, the base material 2 is anodized to form an oxide layer 31 on the surface of the base material 2. The electrolyte used in the anodization is a sulfuric acid aqueous solution with a concentration of 15% by mass, and the temperature of the electrolyte is 5°C. The current density in the anodization is 10 mA / cm ２ The anodizing treatment was carried out under the above-mentioned conditions for 60 minutes. The oxide layer 31 thus formed is a porous alumite coating, and has a large number of pores 311, as shown in Fig. 2. The thickness of the oxide layer 31 formed by anodizing treatment under the above-mentioned conditions is approximately 15 µm.

[0041] After the anodizing 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 1, and the residence time of the base material 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] Thereafter, the base material 2 provided with the oxide layer 31 is immersed in hot water at a temperature of 100°C as a sealant for 60 minutes, thereby forming a hydrated oxide layer 32 made of a hydrated oxide of aluminum on the oxide layer 31, and sealing the pores 311 in the oxide layer 31 with the hydrated oxide layer 32. In this manner, test materials A1 to A3 shown in Table 1 can be obtained. When the pores 311 in the oxide layer 31 are sealed under these conditions, the mass loss per unit area of ​​the aluminum material 1 is 0.3 g / dm² when a sealing test is carried out according to the method specified in JIS H8683-2:2013. 2 The following is the result.

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

[0044] Next, the method for measuring the cathodic polarization of the test materials A1 to A3 and the test materials B1 and B2 will be described.

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

[0046] Next, a 5% by mass NaCl aqueous solution and a 99.7% by mass acetic acid solution are prepared, and acetic acid is added to the NaCl aqueous solution so that the volume ratio of the NaCl aqueous solution to the acetic acid is 1000:1. A test piece, counter electrode, and reference electrode electrically connected to a potentiostat are immersed in this solution and allowed to stand for 30 minutes to stabilize the potential of the measurement section. The test solution is not degassed. An Ag / AgCl electrode, for example, can be used as the reference electrode.

[0047] After the potential of the measurement section has stabilized, a voltage is applied between the test piece 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. The current density flowing through the measurement section at this time is measured to obtain a cathodic polarization curve of the test material after heating. Furthermore, a similar measurement is performed using a base material after pre-treatment for anodizing using the method described above to obtain a cathodic polarization curve of the base material. Note that the cathodic polarization measurements of the test material and base material are both performed in an air atmosphere, with the temperature of the measurement solution maintained at 25°C. Furthermore, the cathodic polarization measurements of the test material and base material are performed without stirring the measurement solution, and in a state where the measurement solution is substantially not flowing.

[0048] As an example of the cathodic polarization curve of a base material, Fig. 3 shows the cathodic polarization curve of an aluminum material made of an aluminum alloy having a chemical composition represented by alloy number A6016 and having no protective coating. The vertical axis of Fig. 3 represents the potential (unit: V) at the measurement point, and the horizontal axis represents the current density (unit: μA / cm 2 ) The horizontal axis in Fig. 3 is scaled logarithmically. As shown in Fig. 3, the cathodic polarization curve of the aluminum material without a protective coating exhibits a step-like shape.

[0049] In cathodic polarization measurement, when the current approaches a state where it is rate-limited by the diffusion of hydrogen ions, the change in current becomes smaller relative to the change in potential at the measurement point. Therefore, in a cathodic polarization curve shown in Fig. 3, where the vertical axis represents potential and the horizontal axis represents current density, the potential region showing the diffusion-limited current of hydrogen ions is included in the steeply sloped portion of the cathodic polarization curve.

[0050] FIG. 4 shows an enlarged view of the step portion of the cathodic polarization curve in FIG. 3 . Although not shown in the figure, the cathodic polarization curve of the base material also exhibits a step-like shape, similar to FIG. 3 . Therefore, the center of the potential region showing the hydrogen ion diffusion-limiting current can be determined based on the shape of the step portion of the cathodic polarization curve shown in FIG. 4 . The method for determining the potential region showing the hydrogen ion diffusion-limiting current in the cathodic polarization curve of the base material is as follows. First, a tangent line L with the largest absolute value of the slope is drawn to the step portion of the cathodic polarization curve, as shown in FIG. 4 . Then, the region R where this tangent line L overlaps with the cathodic polarization curve is defined as the potential region showing the hydrogen ion diffusion-limiting current. The current density J2 at the center of the region R determined in this way is calculated. Furthermore, the current density J1 at the same potential as the center potential of the aforementioned potential region in the cathodic polarization curve of the base material is calculated in the cathodic polarization curve of the heated test material.

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

[0052]

[0053] As shown in Table 1, when preparing test materials A1 to A3, an oxide layer was formed on a base material, and then the oxide layer was heated at a temperature within the specified range before the pores in the oxide layer were sealed. Therefore, these test materials have a current density ratio J1 / J2 within the specified range, and are able to suppress the occurrence of cracks in the protective coating even when the temperature rises. Furthermore, because the oxide layer of the protective coating of these test materials is sealed with a hydrated oxide layer, they have excellent corrosion resistance against corrosive gases, plasma, and the like.

[0054] On the other hand, when preparing test materials B1 and B2, an oxide layer was formed on the base material, and then the pores were sealed without heating the oxide layer. Therefore, the current density ratio J1 / J2 of these test materials was higher than the specific range, and cracks were likely to occur when the temperature rose.

[0055] (Reference Example) In this example, an example of measuring the amount of strain in an aluminum material having a protective coating on the base material will be described. Note that, among the symbols used in this example, the same symbols as those used in the previous examples represent the same components as those in the previous examples unless otherwise specified.

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

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

[0058] Note that test material D1 and test material 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 base material 2, the oxide layer 31 is brought into contact with a sealing agent without heating. Furthermore, test material E1 is a plate made of an aluminum alloy having the chemical composition represented by alloy number AA6016. Test material E1 is obtained by subjecting a plate made of an aluminum alloy having the chemical composition represented by alloy number AA6016 to a pretreatment of anodizing by the method described above.

[0059] To measure the amount of strain in test materials C1-C2 and test material D1, as shown in Figure 5, the base material 2 is exposed on the back side of the surface of the aluminum material 1 that has the protective coating 3. A strain gauge 4 is then attached to the exposed base material 2. By heating the aluminum material 1 with the strain gauge 4 attached in this manner, it is possible to measure the strain caused by thermal expansion of the base material 2 and the protective coating 3. Note that for convenience, the structure of the protective coating 3 is depicted in a simplified form in Figure 5.

[0060] Although not shown in the figure, the amount of strain in the test material E1 can be measured by attaching a strain gauge to one surface of the test material E1 in the thickness direction, and then heating the test material E1.

[0061] Figure 6 shows the change in strain when test materials C1-C2, D1, and E1 are heated for 30 minutes in a heating furnace set at 200°C. The vertical axis in Figure 6 represents strain, and the horizontal axis represents the time elapsed since the start of heating. Immediately after heating begins, the test materials thermally expand as the temperature rises, so as shown in Figure 6, the strain increases rapidly for several minutes after the start of the test. After that, when the temperature of the test materials reaches a roughly constant temperature, the strain of the test materials becomes a roughly constant value.

[0062] Table 2 shows the maximum strain values ​​while the test materials were heated. Table 2 also shows the values ​​obtained by subtracting the maximum strain value of test material E1, which does not have a protective coating, from the maximum strain values ​​of test materials C1-C2 and test material D1, which have a protective coating. The difference between the strain values ​​of test materials C1-C2 and test material D1 and the strain value of test material D indicates the magnitude of the internal stress of the protective coating that was released by heating during the test, and the smaller the difference between the two strain values, the smaller the internal stress of the protective coating.

[0063]

[0064] As shown in Table 2, the strain amounts of test materials C1 and C2, in which a hydrated oxide layer was formed after heating the oxide layer during the manufacturing process of the test materials, were smaller than the strain amount of test material D1, in which a hydrated oxide layer was formed without heating the oxide layer. Therefore, from these results, it can be seen that by forming a hydrated oxide layer after heating the oxide layer during the manufacturing process of an aluminum material, it is possible to alleviate the internal stress of the protective coating and improve the heat resistance of the aluminum material.

[0065] The above has described aspects of the surface-treated aluminum material and the method for manufacturing the same according to the present invention based on the examples, but the specific aspects of the surface-treated aluminum material and the method for manufacturing the same according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not impair the intent of the present invention.

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

[0067] [1] A surface-treated aluminum material having a base material made of an aluminum alloy having an aluminum or Cu content of more than 1.8% by mass and not more than 6.8% by mass, and a protective coating formed on the base material, wherein the protective coating has an oxide layer made of an oxide of aluminum and covering the base material, and a hydrated oxide layer containing a hydrated oxide of aluminum and covering the oxide layer, wherein cathodic polarization measurements are performed on the base material and the surface-treated aluminum material after heating at a temperature of 200°C for 4 hours using a measurement solution obtained by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of the NaCl solution:the acetic acid = 1000:1, and the current density at the central potential of a potential region showing the diffusion limiting current of hydrogen ions in the base material is measured, and the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material is 7000 x 10 -5 The surface-treated aluminum material is as follows:

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

[0069] The compressor wheel according to the present invention may take the following form [3]: [3] A compressor wheel made of the surface-treated aluminum material according to [1] or [2].

[0070] Furthermore, the method for producing a surface-treated aluminum material according to the present invention can take the following aspects [4] to [8].

[0071] [4] A method for producing a surface-treated aluminum material according to [1] or [2], comprising the steps of: anodizing the base material to form the oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 50°C or higher and 350°C or lower; and bringing the oxide layer into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores.

[0072] [5] The method for producing a surface-treated aluminum material according to [4], wherein the heating time 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] The method for producing a surface-treated aluminum material according to any one of [4] to [6], wherein the sealing step involves contacting the oxide layer with hot water at 100°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 any one of [4] to [7], wherein the electrolytic solution used in the anodizing treatment contains an inorganic electrolyte comprising inorganic cations 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 having a base material made of an aluminum alloy having a Cu content of more than 1.8% by mass and not more than 6.8% by mass, and a protective film formed on the base material, wherein the protective film has an oxide layer made of an oxide of aluminum and covering the base material, and a hydrated oxide layer containing a hydrated oxide of aluminum and covering the oxide layer, wherein a cathodic polarization measurement is performed on the base material and the surface-treated aluminum material after heating at a temperature of 200°C for 4 hours using a measurement solution obtained by mixing a NaCl solution with a concentration of 5% by mass and acetic acid with a concentration of 99.7% by mass in a volume ratio of the NaCl solution:the acetic acid = 1000:1, and the current density at the central potential of the potential region showing the diffusion limit current of the base material is measured, and the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material is 7000 x 10 -5 The surface-treated aluminum material is as follows.

2. When a sealing test was conducted according to the method specified in JIS H8683-2:2013, the mass loss per unit area was 0.3 g / dm 2 The surface-treated aluminum material according to claim 1, wherein:

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

4. A method for producing a surface-treated aluminum material as defined in claim 1 or 2, comprising the steps of: anodizing the base material to form an oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 50°C or higher and 350°C or lower; and contacting the oxide layer with a sealing agent to form a hydrated oxide layer on the oxide layer and seal the pores.

5. The method for producing a surface-treated aluminum material according to claim 4, wherein the heating time 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 or 5, wherein the sealing agent is hot water.

7. A method for producing a surface-treated aluminum material according to any one of claims 4 to 6, wherein the sealing step involves contacting the oxide layer with hot water of 95°C or higher as the sealing agent for 10 minutes or more and less than 120 minutes.

8. A method for producing a surface-treated aluminum material according to any one of claims 4 to 7, wherein the electrolytic solution used in the anodizing treatment contains an inorganic electrolyte consisting of inorganic cations and one or more anions selected from the group consisting of sulfate ions, phosphate ions, ammonium ions and borate ions.

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