WO2025041409A1 - Surface-treated aluminum material, method for producing same, and compressor wheel - Google Patents

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

The present invention relates to a surface-treated aluminum material, its manufacturing method, and a compressor wheel.

The 2000 series aluminum alloys are widely used in applications such as turbocharger compressor wheels, taking advantage of their relatively high strength at high temperatures among aluminum alloys. 2000 series aluminum alloys are also sometimes used for parts placed inside the vacuum chambers of semiconductor manufacturing equipment.

Incidentally, an anodized film may be provided on the surface of aluminum material for purposes such as surface protection. 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 source and has a film formed on the surface of the component by anodizing, in which the component is immersed in a solution mainly composed of an organic acid, and the film is subjected to a semi-sealing treatment using boiling water.

JP 2008-81815 A

However, the parts in Patent Document 1 have the problem that the pores in the anodized film are not completely blocked, making them less durable against corrosive gases and plasma.

On the other hand, in order to increase the durability of the parts in Patent Document 1 against corrosive gases and plasma, a method of completely blocking the pores in the anodized film is considered. However, in this case, cracks are more likely to occur in the anodized film when the temperature rises, and there is a risk of foreign matter consisting of small pieces of the anodized film being generated.

Furthermore, in applications such as compressor wheels that are used in high-temperature environments and require sliding properties, if cracks occur in the anodized film, this can lead to a decrease in corrosion resistance and wear resistance. In order to prevent the occurrence of such foreign matter and cracks, it is desirable to further improve the heat resistance of aluminum materials that have an anodized film on their surface.

The present invention was made in consideration of this background, and aims to provide a surface-treated aluminum material that has excellent corrosion resistance against corrosive gases and plasma and can suppress the occurrence of cracks even when the temperature rises, as well as a manufacturing method and a compressor wheel for the same.

One aspect of the present invention is a surface-treated aluminum material having a base material made of an aluminum alloy having a Cu (copper) content of more than 1.8 mass% and not more than 6.8 mass%, and a protective coating film formed on the base material,
The protective coating is made of an oxide of aluminum, and has an oxide layer covering the base material;
a hydrated oxide layer comprising a hydrated oxide of aluminum and covering the oxide layer;
The surface-treated aluminum material is characterized in that, when 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 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 NaCl solution:acetic acid = 1000:1, and the current density is measured at the central potential in the potential region showing the diffusion limiting current of the hydrogen ions of the base material, 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 or less.

Another aspect of the present invention is a compressor wheel made of the surface-treated aluminum material of the above-mentioned aspect.

Yet another aspect of the present invention is a method for producing a surface-treated aluminum material of the above aspect,
forming the oxide layer having pores on the base material by subjecting the base material to anodizing treatment;
Thereafter, the base material and the oxide layer are heated at a temperature of 50° C. or more and 350° C. or less,
Thereafter, the oxide layer is brought into contact with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores.

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. In addition, when the surface-treated aluminum material and the base material are subjected to cathodic polarization measurement after being heated at a temperature of 200°C for 4 hours by 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 is 7000 x ^10-5 or less. An aluminum material having such characteristics 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.

In addition, because the compressor wheel is made of the aluminum material, the occurrence of cracks in the protective coating is suppressed even when the temperature becomes high during use, and the healthy state of the protective coating can be maintained for a long period of time. And, because cracks are thus less likely to occur in the protective coating, wear of the protective coating can be suppressed for a long period of time.

In addition, in the manufacturing method of the 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. In this way, 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. Then, after the internal stress of 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, thereby increasing corrosion resistance against corrosive gases and plasma, improving heat resistance, and suppressing the occurrence of cracks even when the temperature rises.

As described above, according to the above-mentioned aspect, it is possible to provide a surface-treated aluminum material that has excellent corrosion resistance against corrosive gases and plasma, as well as excellent heat resistance, and is capable of suppressing the occurrence of cracks even when the temperature rises, a manufacturing method thereof, and a compressor wheel.

FIG. 1 is a cross-sectional view of a surface-treated aluminum material in an embodiment. FIG. 2 is a cross-sectional view of a base material on which an oxide layer is formed in the process for producing a surface-treated aluminum material according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing an example of a cathodic polarization curve of a 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 the surface-treated aluminum material in the reference example.

(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 may take various shapes depending on the application of the aluminum material.

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), 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, can be used.

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.

　A protective coating is provided on the base material, the protective coating including an oxide layer made of an oxide of aluminum 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. The hydrated oxide layer may also contain a hydrated oxide and a metal salt. The protective coating is obtained, for example, by subjecting the base material to an anodizing treatment to form an oxide layer with a large number of pores on the surface of the base material, and then performing a sealing treatment to block 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, by forming the protective coating on the base material, the corrosion resistance of the aluminum material can be increased.

The thickness of the protective film 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 to the thickness of the protective film, and the thicker the protective film, the more the corrosion resistance of the aluminum material can be improved. 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 manufacturing limit for the 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.

When a sealing test is performed by the method specified in JIS H8683-2: 2013, the mass loss per unit area of the aluminum material is preferably 0.3 g/ ^dm2 or less. In such an aluminum material, the pores in 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.

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 liquid. Next, a test piece including a 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 this test piece, the mass of the test piece is measured. After that, the test piece is immersed in the test liquid maintained at a temperature of 38°C ± 1°C for 15 minutes ± 5 seconds.

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

Using the area A (unit: ^dm2 ) of the protective film of the test piece obtained above, the mass _m1 (unit: g) of the test piece before immersion in the test liquid, and the mass _m2 (unit: g) of the test piece after immersion in the test liquid, the mass loss per unit area _δA (unit: g/ ^dm2 ) can be calculated based on the following formula (1).
δ _A = (m ₁ - _{m 2} )/A (1)

The surface-treated aluminum material has a characteristic that, when 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 mass % and an acetic acid with a concentration of 99.7 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 hydrogen ion of the base material is 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 is 7000 × 10 ^-5 or less. An aluminum material having a current density ratio J1/J2 within the specific range has a property of being less likely to crack when the temperature rises. Therefore, an aluminum material having the protective film and a current density ratio J1/J2 within the specific range has excellent 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 is always greater than 0 by definition.

As mentioned above, the aluminum material has excellent corrosion resistance against corrosive gases and plasma, and can suppress the occurrence of cracks in the protective film 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. In addition, the aluminum material has properties such that cracks are unlikely to occur in the protective film, and it is resistant to wear even at high temperatures. Therefore, the aluminum material is also suitable for applications such as compressor wheels incorporated in turbochargers.

(Method of manufacturing aluminum material)
In producing 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 producing the base material is not particularly limited, and a known method can be adopted. For example, the base material may be produced by a method in which casting, rolling, and heat treatment are appropriately combined. In addition, after the base material is produced, pretreatment for the anodizing treatment, such as degreasing, acid washing, and polishing, may be performed as necessary before the anodizing treatment is performed. Next, the base material is anodized to form the oxide layer having 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 the counter electrode while the base material and the counter electrode are immersed in an electrolyte. The oxide layer thus formed is composed of an oxide of aluminum, such as alumina, and has a large number of pores.

The electrolyte used in the anodizing treatment may be, for example, an acid electrolyte containing an electrolyte such as sulfuric acid or phosphoric acid, or an alkaline electrolyte containing an electrolyte such as sodium metaborate. The electrolyte 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 electrolyte containing an inorganic electrolyte, it is possible to more easily form an oxide layer having a desired structure.

The current density of the direct current in the anodizing treatment can be appropriately set, for example, in the range of 1 mA/ ^cm2 to 100 mA/ ^cm2 . The temperature of the electrolyte in the anodizing treatment can be appropriately set, for example, in the range of 0°C to 40°C.

The thickness of the oxide layer formed in the anodizing process 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 made sufficiently thick, making it easier to obtain an aluminum material with excellent corrosion resistance and heat resistance.

In the manufacturing method, after anodizing, the base material and the oxide layer are heated at a temperature of 50°C to 350°C. After anodizing, the oxide layer is heated at a temperature within the specific range before sealing the pores in the oxide layer, thereby alleviating the internal stress in the oxide layer. Then, by sealing the pores after alleviating the internal stress in the oxide layer, 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.

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 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 will 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, the heating may be terminated immediately after the temperature of the oxide layer reaches the desired temperature, or the desired temperature may be maintained for a certain period of time after the desired temperature is reached. From the viewpoint of sufficiently alleviating the internal stress of the oxide layer and more reliably increasing the heat resistance of the aluminum material, it is preferable that 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.

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. As the sealing agent, for example, a substance capable of reacting with an oxide of aluminum to form a hydrated oxide, such as hot water, can be used. When hot water is used for the sealing process, a hydrated oxide layer made of a hydrated oxide of aluminum can be formed on the oxide layer.

Also, as a sealing agent, a substance capable of reacting with an oxide of aluminum 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, or an aqueous solution of silicate, can be used. 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.

From the viewpoint of more easily obtaining an aluminum material having excellent corrosion resistance and heat resistance, it is preferable that the sealing agent is hot water. In addition, by sealing the pores in the oxide layer with hot water, a hydrated oxide layer that does not contain 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 in 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 and less than 120 minutes.

(Example)
An embodiment 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 embodiment 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 an oxide of aluminum 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 used in which a NaCl solution with a concentration of 5% by mass and acetic acid with a concentration of 99.7% by mass were mixed in a volume ratio of NaCl solution:acetic acid = 1000:1. Cathodic polarization measurements were performed on the base material 2 and the surface-treated aluminum material 1 after heating at a temperature of 200°C for 4 hours, and the current density was measured at the central potential in the potential region showing the diffusion limiting current of the hydrogen ions in the base material 2. When this was done, 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 x ^10-5 or less.

In producing the aluminum material 1 of this example, first, the base material 2 is anodized to form an oxide layer 31 having pores 311 on the base material 2 as shown in FIG. 2. The base material 2 and the oxide layer 31 are then heated at a temperature of 50°C to 350°C to relieve the internal stress of the oxide layer 31. The oxide layer 31 is then 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.

Table 1 shows specific examples of aluminum material 1 (test materials A1 to A3). The manufacturing method of test materials A1 to A3 is, 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 pretreatment for anodizing. Specifically, as pretreatment, an alkali etching treatment is performed by immersing the base material 2 in an aqueous sodium hydroxide solution with a concentration of 5 mass% and a temperature of 55°C. Then, the base material 2 is immersed in nitric acid with a concentration of 30 mass% to perform a desmutting treatment. Then, the base material 2 is immersed 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 to perform a chemical polishing treatment. After the chemical polishing treatment, a desmutting treatment is performed again under the same conditions as those described above.

After the base material 2 is 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 electrolytic solution used in the anodizing process is an aqueous sulfuric acid solution with a concentration of 15% by mass, and the temperature of the electrolytic solution is 5° C. The current density in the anodizing process is 10 mA/cm ² , and the process time is 60 minutes. The oxide layer 31 thus formed is a so-called porous type anodized aluminum film, and has a large number of pores 311 as shown in FIG. 2. The thickness of the oxide layer 31 formed by anodizing process under the above-mentioned conditions is approximately 15 μm.

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 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.

Thereafter, the base material 2 with the oxide layer 31 is immersed in hot water having a temperature of 100° C. as a sealant for 60 minutes to form a hydrated oxide layer 32 made of a hydrated oxide of aluminum on the oxide layer 31, and the pores 311 in the oxide layer 31 are sealed by the hydrated oxide layer 32. In this manner, the 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 or less when a sealing test is performed by the method specified in JIS H8683-2:2013.

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 the manufacturing method 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 the sealing agent without being heated.

Next, we will explain the method for measuring the cathodic polarization of test materials A1 to A3 and test materials B1 to B2.

[Cathode polarization measurement]
The cathodic polarization measurements are performed on the base material and the test material heated at 200° C. for 4 hours 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 is calculated based on these cathodic polarization curves. First, the test material is heated for 4 hours in an oven set at 200° C. The test material is removed from the oven and cooled to room temperature, after which an evaluation area is set on the protective coating, and the surface of the test material other than the evaluation area is covered with silicone resin.

Next, prepare a 5% by mass NaCl aqueous solution and a 99.7% by mass acetic acid, and add acetic acid to the NaCl aqueous solution so that the volume ratio of the NaCl aqueous solution to the acetic acid is NaCl aqueous solution:acetic acid = 1000:1 to prepare a measurement solution. Immerse the test piece, counter electrode, and reference electrode electrically connected to the potentiostat in this solution and leave it for 30 minutes to stabilize the potential of the measurement section. Do not degas the measurement solution. Also, an Ag/AgCl electrode, for example, can be used as the reference electrode.

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. In addition, a similar measurement is performed using the base material after pretreatment 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 the air, with the temperature of the measurement solution maintained at 25°C. In addition, the cathodic polarization measurements of the test material and base material are performed without stirring the measurement solution, and with the measurement solution substantially not flowing.

Fig. 3 shows an example of the cathodic polarization curve of a base material, which is an aluminum material having no protective coating and made of an aluminum alloy having a chemical component represented by alloy number A6016. The vertical axis of Fig. 3 shows the potential (unit: V) of the measurement part, and the horizontal axis shows the current density (unit: μA/ ^cm2 ). The horizontal axis of Fig. 3 is scaled logarithmically. As shown in Fig. 3, the cathodic polarization curve of the aluminum material having no protective coating shows a step-like shape.

In cathodic polarization measurements, 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, as shown in Figure 3, where the vertical axis represents potential and the horizontal axis represents current density, the potential region showing the limiting current for hydrogen ion diffusion is included in the steep part of the curve at the step in the cathodic polarization curve.

Figure 4 shows an enlarged view of the step portion of the cathodic polarization curve in Figure 3. Although not shown in the figure, the cathodic polarization curve of the base material also shows a step-like shape like Figure 3. Therefore, based on the shape of the step portion of the cathodic polarization curve shown in Figure 4, the center of the potential region showing the diffusion limit current of hydrogen ions can be determined. The method for determining the potential region showing the diffusion limit current of hydrogen ions 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 in the step portion of the cathodic polarization curve as shown in Figure 4. Then, the region R where this tangent line L and the cathodic polarization curve overlap is set as the potential region showing the diffusion limit current of hydrogen ions. The current density J2 in the center of the region R determined in this way is calculated. In addition, in the cathodic polarization curve of the test material after heating, the current density J1 at the same potential as the potential at the center of the above-mentioned potential region in the cathodic polarization curve of the base material is calculated.

The current density J1 calculated based on the cathodic polarization curve of the test material after heating can be used as an index of the contact area between the base material and the measurement solution in the test material after heating, and 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 test piece after heating to the current density J2 calculated using the base material can be used as an index of the increase rate of the exposed area of the base material due to heating. More specifically, for example, if defects such as cracks are formed in the protective film of the test material after heating, the base material may be exposed by the cracks. Therefore, in this case, the current density ratio J1/J2 becomes large. Table 1 shows the current density ratio J1/J2 of each test material.

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 at a temperature within the specific range before the pores in the oxide layer are sealed. As a result, these test materials have a current density ratio J1/J2 within the specific range, and are able to suppress the occurrence of cracks in the protective film even when the temperature rises. In addition, the oxide layer of the protective film of these test materials is sealed with a hydrated oxide layer, and therefore has excellent corrosion resistance against corrosive gases, plasma, etc.

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 specific range, and cracks are likely to occur when the temperature rises.

(Reference example)
In this example, an example of measuring the amount of strain in an aluminum material having a protective film 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.

The method for preparing the test material used in this example is as follows. First, an aluminum plate having a thickness of 1.1 mm and a chemical composition represented by alloy number AA6016 is prepared as the base material 2. This base material 2 is pretreated for anodizing in the same manner as in the example, and then anodized. 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 in Table 2, 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 in Table 2.

Then, the base material 2 with the oxide layer 31 is immersed in hot water at a temperature of 100°C as a sealing agent for 60 minutes to form a hydrated oxide layer 32 on the oxide layer 31 and seal the pores 311 in the oxide layer 31 with the hydrated oxide layer 32. In this way, the test materials C1 to C2 shown in Table 1 can be obtained.

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 the sealing agent without heating. Test material E1 is a plate material made of an aluminum alloy having a chemical composition represented by alloy number AA6016. Test material E1 is obtained by performing a pretreatment of anodizing treatment by the above-mentioned method on a plate material made of an aluminum alloy having a chemical composition represented by alloy number AA6016.

When measuring the amount of strain in test materials C1-C2 and 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 way, it is possible to measure the strain caused by thermal expansion of the base material 2 and protective coating 3. Note that for convenience, the structure of the protective coating 3 is shown in a simplified form in Figure 5.

Although not shown in the figure, to measure the amount of strain in the test material E1, a strain gauge is attached to one side of the test material E1 in the thickness direction, and then the test material E1 is heated.

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 the strain, and the horizontal axis represents the time elapsed from 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 test begins. After that, when the temperature of the test materials reaches an approximately constant temperature, the strain of the test materials becomes approximately constant.

Table 2 shows the maximum strain values while the test materials were being heated. Table 2 also shows the maximum strain values of test materials C1-C2 and D1, which have a protective coating, minus the maximum strain value of test material E1, which does not have a protective coating. The difference between the strain values of test materials C1-C2 and 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; the smaller the difference between the two strain values, the smaller the internal stress of the protective coating.

As shown in Table 2, the strain amount of test materials C1 and C2, which form a hydrated oxide layer after heating the oxide layer during the manufacturing process of the test materials, is smaller than the strain amount of test material D1, which forms a hydrated oxide layer without heating the oxide layer. Therefore, from these results, it can be understood that by forming a hydrated oxide layer after heating the oxide layer during the manufacturing process of the aluminum material, it is possible to reduce the internal stress of the protective film and improve the heat resistance of the aluminum material.

　Although the above describes aspects of the surface-treated aluminum material and its manufacturing method according to the present invention based on the examples, the specific aspects of the surface-treated aluminum material and its manufacturing method according to the present invention are not limited to the aspects of the examples, and the configurations can be changed as appropriate within the scope of the spirit of the present invention.

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

[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 mass% and not more than 6.8 mass%, and a protective coating film formed on the base material,
The protective coating is made of an oxide of aluminum, and has an oxide layer covering the base material;
a hydrated oxide layer comprising a hydrated oxide of aluminum and covering the oxide layer;
A surface-treated aluminum material, in which 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 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 the hydrogen ions of the base material is 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 is 7000 x ^10-5 or less.

[2] The surface-treated aluminum material according to [1], in which the mass loss per unit area is 0.3 g / dm ² or less when a sealing test is performed by the method specified in JIS H8683-2:2013.

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

　The method for manufacturing surface-treated aluminum material according to the present invention can take the following forms [4] to [8].

[4] A method for producing a surface-treated aluminum material according to [1] or [2],
forming the oxide layer having pores on the base material by subjecting the base material to anodizing treatment;
Thereafter, the base material and the oxide layer are heated at a temperature of 50° C. or more and 350° C. or less,
and then contacting the oxide layer with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores.

[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.

[7] The method for producing a surface-treated aluminum material according to any one of [4] to [6], wherein, in the sealing, the oxide layer is contacted with hot water of 100°C or higher as the sealing agent for 10 minutes or more and 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 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 (8)

A surface-treated aluminum material having a base material made of an aluminum alloy having a Cu content of more than 1.8 mass% and not more than 6.8 mass%, and a protective coating film formed on the base material,
The protective coating is made of an oxide of aluminum, and has an oxide layer covering the base material;
a hydrated oxide layer comprising a hydrated oxide of aluminum and covering the oxide layer;
A surface-treated aluminum material, in which 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 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 the hydrogen ions of the base material is 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 is 7000 x ^10-5 or less. The surface-treated aluminum material according to claim 1, wherein the mass loss per unit area is 0.3 g / dm ² or less when a sealing test is performed by the method specified in JIS H8683-2:2013. A compressor wheel made of the surface-treated aluminum material according to claim 1 or 2. A method for producing a surface-treated aluminum material according to claim 1 or 2,
forming the oxide layer having pores on the base material by subjecting the base material to anodizing treatment;
Thereafter, the base material and the oxide layer are heated at a temperature of 50° C. or more and 350° C. or less,
and then contacting the oxide layer with a sealing agent to form the hydrated oxide layer on the oxide layer and seal the pores. 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. The method for producing a surface-treated aluminum material according to claim 4 or 5, wherein the sealing agent is hot water. The method for manufacturing a surface-treated aluminum material according to any one of claims 4 to 6, wherein the oxide layer is contacted with hot water of 95°C or higher as the sealing agent for 10 minutes or more and less than 120 minutes during the sealing process. The 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 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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