Surface-treated aluminum material, method for producing same, and compressor impeller

Abstract

A surface-treated aluminum material (1) comprising: a base material (2) containing an aluminum alloy having a Cu content of more than 1.8 mass% and 6.8 mass% or less; and a protective film (3) formed on the base material (2). The protective film (3) has: an oxide layer (31) that contains 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). The cathodic polarization measurement of the base material (2) and the surface-treated aluminum material (1) after heating for 4 hours at a temperature of 200 DEG C using a specific measurement solution shows that 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) at a specific potential is 7000 * 10-5 or less.

Description

Technical Field

[0001] This invention relates to surface-treated aluminum materials and their manufacturing methods, as well as compressor impellers. Background Technology

[0002] 2000 series aluminum alloys, exhibiting high strength even at high temperatures, are widely used in applications such as compressor impellers in turbochargers. Additionally, 2000 series aluminum alloys are sometimes used in components housed within vacuum chambers of semiconductor manufacturing equipment.

[0003] However, for purposes such as surface protection, an anodized coating is sometimes applied to the surface of aluminum materials. For example, Patent Document 1 describes a component for a substrate processing apparatus, characterized in that the component for plasma processing of a substrate includes a coating formed on the surface of the component by connecting the component to the anode of a DC power supply and immersing it in an anodizing process in a solution mainly composed of organic acids, and the coating undergoes a semi-sealing process using boiling water.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2008-81815 Summary of the Invention The technical problem that the invention aims to solve However, the pores in the anodized coating of the component in Patent Document 1 are not completely sealed, resulting in low durability against corrosive gases and plasma.

[0005] On the other hand, in the component of Patent Document 1, a method is considered to completely seal the pores of the anodic oxide coating in order to improve the durability against corrosive gases and plasmas. However, in this case, when the temperature has risen, it may become easy for cracks to form in the anodic oxide coating, resulting in foreign matter containing small pieces of the anodic oxide coating.

[0006] Furthermore, in applications such as compressor wheels, which operate in high-temperature environments and require smooth sliding, cracks in the anodized coating can lead to a decrease in corrosion resistance and wear resistance. To suppress the formation of such foreign matter and cracks, it is desirable to further improve the heat resistance of aluminum materials with anodized coatings on their surfaces.

[0007] The present invention was made in view of the following background, and its object is to provide a surface-treated aluminum material with excellent corrosion resistance to corrosive gases and plasmas, and which can suppress the formation of cracks even when the temperature rises, a method for manufacturing the same, and a compressor impeller.

[0008] Technical solutions for solving technical problems One aspect of the present invention is a surface-treated aluminum material comprising: a base material containing an aluminum alloy having a Cu (copper) content exceeding 1.8% by mass and less than 6.8% by mass; and a protective coating formed on the base material. The protective coating comprises: an oxide layer containing aluminum oxide and covering the base material; and Hydrated oxide layer: which comprises hydrated oxide of aluminum and covers the oxide layer. The cathodic polarization of the substrate and the surface-treated aluminum material heated at 200°C for 4 hours was measured using a test solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution at a volume ratio of NaCl solution:acetic acid = 1000:1. The current density at the central potential of the potential region exhibiting the limiting diffusion current of hydrogen ions in the substrate was measured, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the substrate, J1 / J2, was found to be 7000 × 10⁻⁶. -5 the following.

[0009] Another aspect of the invention is a compressor impeller comprising the surface-treated aluminum material of the manner described above.

[0010] Another aspect of the present invention is a method for manufacturing a surface-treated aluminum material, wherein, By performing anodizing treatment on the base material, a porous oxide layer is formed on the base material. Then, the base material and the oxide layer are heated at a temperature above 50°C and below 350°C. Then, the oxide layer is brought into contact with a sealing agent to form a hydrated oxide layer on the oxide layer while sealing the pores.

[0011] Invention Effects The surface-treated aluminum material (hereinafter referred to as "aluminum material") has a protective coating on the surface of the base material, comprising the oxide layer and the hydrated oxide layer. Furthermore, after heating the surface-treated aluminum material and the base material at 200°C for 4 hours using the specific method, the cathodic polarization measurement revealed that 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 describes the properties of aluminum materials. These materials exhibit excellent resistance to corrosive gases and plasmas, as well as superior heat resistance, which inhibits crack formation even at elevated temperatures.

[0012] Furthermore, since the compressor impeller is made of the aluminum material, it can suppress the formation of cracks at the protective coating even under high temperatures during use, and maintain the integrity of the protective coating for a long time. Moreover, by making it difficult for cracks to form in the protective coating, wear on the protective coating can be suppressed over a long period.

[0013] Furthermore, in the method for manufacturing the aluminum material, after anodizing the base material, the oxide layer formed by the anodizing process is heated within the specified temperature range. By heating the oxide layer before sealing the pores, the internal stress generated during the formation of the oxide layer can be mitigated. After mitigating the internal stress of the oxide layer, the oxide layer is brought into contact with a sealing agent, forming a hydrated oxide layer on the oxide layer while simultaneously sealing the pores. This improves resistance to corrosive gases and plasmas, enhances heat resistance, and suppresses crack formation even at elevated temperatures.

[0014] As described above, according to the aforementioned method, it is possible to provide a surface-treated aluminum material, a method for manufacturing the same, and a compressor impeller that exhibit excellent corrosion resistance to corrosive gases and plasmas, as well as excellent heat resistance and the ability to suppress crack formation even at elevated temperatures. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of the surface-treated aluminum material in the embodiment.

[0016] Figure 2 This is a cross-sectional view of the base material with an oxide layer formed during the manufacturing process of the surface-treated aluminum material in the embodiment.

[0017] Figure 3 This is an illustrative diagram showing an example of the cathodic polarization curve of the base material.

[0018] Figure 4 This is an enlarged view of the stepped portion in the cathodic polarization curve of the base material.

[0019] Figure 5 This is an explanatory diagram showing the method for determining the strain of surface-treated aluminum in the reference example.

[0020] Figure 6 This is an explanatory diagram showing the measurement results of the strain of the surface-treated aluminum material in the reference example. Detailed Implementation

[0021] (Aluminum) The base material of the aluminum material is composed of an aluminum alloy with a Cu content of more than 1.8% by mass and less than 6.8% by mass. The shape of the base material is not particularly limited and can be varied depending on the application of the aluminum material.

[0022] The aluminum alloy constituting the base material of the aluminum material may, for example, be 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 the following chemical composition can be used: containing Cu (copper): more than 1.8% by mass and less than 6.8% by mass, and containing one or more elements selected from Si (silicon), Fe (iron), Mn (manganese), Mg (magnesium), Cr (chromium), Zn (zinc), and Ti (titanium) as any component, with the remainder containing Al and unavoidable impurities.

[0023] More specifically, as a 2000 series aluminum alloy, for example, aluminum alloys with chemical compositions shown in alloy numbers AA2011, AA2014, AA2014A, AA2017, AA2017A, AA2218, AA2219, AA2018, AA2025, AA2319, AA2124, AA2036, AA2117, AA2618, or AA2024 can be used.

[0024] A protective coating is formed on the base material. The protective coating comprises: an oxide layer containing 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 also be composed of hydrated aluminum oxide. Additionally, the hydrated oxide layer may contain hydrated oxide and metal salt. The protective coating can be obtained, for example, by anodizing the base material to form an oxide layer with multiple pores on the surface of the base material, followed by a pore-sealing process, using the hydrated oxide layer to seal the pores of the oxide layer. Such a protective coating exhibits excellent corrosion resistance to corrosive gases, plasma, etc. Therefore, by forming the protective coating on the base material, the corrosion resistance of the aluminum material can be improved.

[0025] The thickness of the protective coating is preferably 2. μ The thickness of the protective coating is above 5 μm. This further improves the corrosion resistance of the aluminum. From a corrosion resistance perspective, there is no specific upper limit to the thickness of the protective coating; the thicker the protective coating, the better the corrosion resistance of the aluminum. From this perspective, a thickness of 5 μm is more preferably preferred for the protective coating. μ m or more, further preferably 10 μ m or more. It should be noted that the manufacturing upper limit for the thickness of the protective coating is, for example, 200. μ From the viewpoint of suppressing crack formation at the protective coating, the thickness of the protective coating is preferably 100 μm. μ Below m.

[0026] When the sealing degree test is performed according to the method specified in JIS H8683-2:2013, the mass reduction per unit area of ​​the aluminum material is preferably 0.3 g / dm². 2 The pores in the oxide layer of the aforementioned aluminum material are fully sealed by the hydrated oxide layer, thus reliably improving the corrosion resistance of the aluminum material.

[0027] It should be noted that the specific method for the pore sealing test is as follows. First, dissolve 35 mL of phosphoric acid and 20 g of chromic anhydride in water to prepare 1 L of test solution. Next, collect a test piece containing the protective coating from the aluminum material and measure the area of ​​the protective coating on the test piece. After removing stains from the surface of the test piece, measure the mass of the test piece. Then, immerse the test piece in the test solution maintained at a temperature of 38℃±1℃ for 15 minutes±5 seconds.

[0028] After the test piece is immersed in the test solution, it is rinsed with running water, and then further rinsed with deionized water or distilled water. After the test piece is thoroughly dried, its mass is measured.

[0029] The area A (unit: dm) of the protective coating on the test piece obtained above. 2 The mass m1 (in g) of the test piece before immersion in the test solution and the mass m2 (in g) of the test piece after immersion in the test solution can be used to calculate the mass reduction per unit area based on the following formula (1). δ A (unit: g / dm) 2 ).

[0030] δ A = (m1-m2) / A (1) The surface-treated aluminum material has the following characteristics: A test solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution at a volume ratio of NaCl solution:acetic acid = 1000:1 was used to measure the cathodic polarization of the base material and the surface-treated aluminum material after heating at 200°C for 4 hours. The current density at the center of the potential region exhibiting the limiting diffusion 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. -5The aluminum material with a current density ratio J1 / J2 within the specified range exhibits properties that make it difficult for cracks to form when the temperature rises. Therefore, aluminum material with the protective coating and a current density ratio J1 / J2 within the specified range exhibits 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 must be a value greater than 0.

[0031] As described above, the aluminum material exhibits excellent corrosion resistance to corrosive gases, plasmas, etc., and can suppress the formation of cracks at the protective coating even at elevated temperatures. Therefore, the aluminum material is suitable for applications such as shrouds around fans in heating and cooking appliances, and components for semiconductor manufacturing devices. Furthermore, the aluminum material has the characteristics of being difficult to crack in the protective coating and resistant to wear even at high temperatures. Therefore, the aluminum material is also suitable for applications such as compressor impellers assembled in turbochargers.

[0032] (Manufacturing methods for aluminum materials) In manufacturing the surface-treated aluminum material, firstly, a base material of an aluminum alloy containing a Cu content of more than 1.8% by mass and less than 6.8% by mass is prepared. The manufacturing method of the base material is not particularly limited, and known methods can be used. For example, the base material can also be manufactured by a suitable combination of casting, rolling, and heat treatment. Furthermore, during the period from manufacturing the base material to performing the anodizing treatment, pretreatments such as degreasing, acid cleaning, and polishing for anodizing can be performed as needed. Next, the base material is anodized to form a porous oxide layer. During the anodizing process, with the base material and the counter electrode immersed in an electrolyte, a direct current can be passed between the base material and the counter electrode to form an oxide layer on the surface of the base material. The oxide layer thus formed is composed of aluminum oxides such as aluminum oxide and has multiple pores.

[0033] The electrolyte used in the anodizing process can be, for example, an acidic electrolyte containing electrolytes such as sulfuric acid or phosphoric acid, or an alkaline electrolyte containing electrolytes such as sodium metaborate. Preferably, the electrolyte used in the anodizing process contains an inorganic electrolyte, which comprises: inorganic cations and one or more anions selected from sulfate ions, phosphate ions, ammonium ions, and borate ions. By using an electrolyte containing an inorganic electrolyte for anodizing, it is easier to form an oxide layer with the desired structure.

[0034] The current density of the direct current in the anodizing process, for example, can be calculated based on 1 mA / cm². 2 Above and 100mA / cm 2The following ranges should be set appropriately. Additionally, the temperature of the electrolyte in the anodizing process can be appropriately set, for example, within a range of 0°C to 40°C.

[0035] The thickness of the oxide layer formed during the anodizing process is preferably 2. μ m or more. By making the oxide layer thickness 2 μ A thickness of m or more ensures that the protective coating obtained after sealing is thick enough, making it easier to obtain aluminum materials with excellent corrosion resistance and heat resistance.

[0036] In the manufacturing method described above, after anodizing, the base material and the oxide layer are heated at a temperature between 50°C and 350°C. By heating the oxide layer at a temperature within the specific range before sealing the pores in the oxide layer after anodizing, the internal stress of the oxide layer can be mitigated. Furthermore, by sealing the pores after mitigating the internal stress of the oxide layer, the internal stress in the protective coating after sealing can be reduced. As a result, the generation of cracks at the protective coating during heating can be suppressed, and aluminum with excellent heat resistance can be obtained.

[0037] When the heating temperature of the oxide layer is below 50°C, the internal stress of the oxide layer is not adequately relieved, and the protective coating may easily crack as the temperature of the aluminum material rises. On the other hand, when the heating temperature of the oxide layer exceeds 350°C, the oxide layer cannot keep up with the thermal expansion of the base material, and the oxide coating may crack. During the heating of the oxide layer, heating can be stopped shortly after the desired temperature is reached, or the desired temperature can be maintained for a certain period of time after reaching it. From the viewpoint of adequately relieving the internal stress of the oxide layer and more reliably improving the heat resistance of the aluminum material, the heating time from the start to the end of heating the oxide layer is preferably 1 minute or more and less than 12 hours.

[0038] The oxide layer is heated, and then brought into contact with a sealing agent. This forms a hydrated oxide layer on the oxide layer, sealing the pores. As a sealing agent, for example, a substance that can react with aluminum oxide to form a hydrated oxide, such as warm water, can be used. When using warm water for sealing, a hydrated oxide layer containing aluminum hydrates can be formed on the oxide layer.

[0039] Alternatively, as sealing agents, substances that can react with aluminum oxides to form hydrated oxides and metal salts, such as aqueous solutions of nickel acetate, cobalt acetate, chromate, and silicate, can be used. When sealing with such sealing agents, a hydrated oxide layer containing aluminum hydrates and metal salts can be formed on the oxide layer.

[0040] From the viewpoint of more easily obtaining aluminum materials with excellent corrosion resistance and heat resistance, warm water is preferred as the sealing agent. Furthermore, by sealing the pores in the oxide layer with warm water, a hydrated oxide layer free of metal salts can be formed on the oxide layer. When using warm water as the sealing agent, it is more preferable to seal the pores in the oxide layer by contacting the oxide layer with warm water at 95°C or higher for 10 minutes to less than 120 minutes.

[0041] Example (Example) Reference Figures 1-2 Examples of the surface-treated aluminum material and its manufacturing method are described below. Figure 1 As shown, the surface-treated aluminum material 1 in this example comprises: a base material 2, which contains an aluminum alloy with an aluminum or Cu content of more than 1.8% by mass and less than 6.8% by mass; and a protective coating 3, which is formed on the base material. The protective coating 3 comprises: an oxide layer 31, which contains aluminum oxide and covers the base material 2; and a hydrated oxide layer 32, which contains hydrated aluminum oxide and covers the oxide layer 31. Using a test solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution at a volume ratio of NaCl solution:acetic acid = 1000:1, the cathodic polarization of the base material 2 and the surface-treated aluminum material 1, which has been heated at 200°C for 4 hours, was measured. The current density at the center of the potential region exhibiting the limiting diffusion 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.

[0042] In making aluminum material 1 in this example, firstly, as follows: Figure 2 As shown, by anodizing the base material 2, an oxide layer 31 with pores 311 is formed on the base material 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. Then, the oxide layer 31 is brought into contact with a sealing agent, and while a hydrated oxide layer 32 is formed on the oxide layer 31, the pores 311 are sealed, thereby obtaining the aluminum material 1.

[0043] Specific examples of aluminum materials 1 (test materials A1 to A3) are shown in Table 1. The manufacturing method of test materials A1 to A3 is as follows, for example. First, as the base material 2, an aluminum plate with a chemical composition indicated by any of the alloy numbers shown in Table 1 and a thickness of 1.1 mm is prepared. The base material 2 undergoes a pretreatment of anodizing. Specifically, as a pretreatment, the base material 2 is first subjected to an alkaline etching treatment by immersing it in a sodium hydroxide aqueous solution with a concentration of 5% by mass and a temperature of 55°C. Then, the base material 2 is immersed in nitric acid with a concentration of 30% by mass for decontamination 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 and a temperature of 85°C, and subjected to chemical polishing treatment. After the chemical polishing treatment, a decontamination treatment is performed again under the same conditions as described above.

[0044] After pretreating the base material 2 as described above, the base material 2 is subjected to anodizing treatment to form an oxide layer 31 on the surface of the base material 2. The electrolyte used in the anodizing treatment is a 15% by mass sulfuric acid aqueous solution, and the electrolyte temperature is set to 5°C. Furthermore, the current density in the anodizing treatment is set to 10 mA / cm². 2 The processing time is set to 60 minutes. For example... Figure 2 As shown, the oxide layer 31 thus formed is a so-called porous alumite coating, having multiple pores 311. It should be noted that the thickness of the oxide layer 31 formed by anodizing under the above conditions is approximately 15 μm. μ m.

[0045] After anodizing, the base material 2 is heated in a heating furnace to alleviate 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, i.e., the time from the start of heating to the end of heating, is the value shown in the "Heating Time" column of Table 1.

[0046] Then, by immersing the base material 2 having oxide layer 31 in warm water at 100°C (as a sealing agent) for 60 minutes, a hydrated oxide layer 32 containing hydrated aluminum oxide is formed on oxide layer 31, and the hydrated oxide layer 32 seals the pores 311 of oxide layer 31. Through the above, test materials A1 to A3 shown in Table 1 can be obtained. It should be noted that, under these conditions, when sealing the pores 311 of oxide layer 31, the mass reduction per unit area of ​​aluminum material 1 is 0.3 g / dm² when the sealing degree test is performed according to the method specified in JIS H8683-2:2013. 2 the following.

[0047] It should be noted that the test materials B1 to B2 shown in Table 1 are test materials used 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 oxide layer 31 on the base material 2, the oxide layer 31 is not heated and is brought into contact with the sealing agent.

[0048] Next, the method for measuring the cathodic polarization of test materials A1 to A3 and test materials B1 to B2 will be explained.

[0049] [Cathode Polarization Measurement] The cathodic polarization of the base material and the test material heated at 200°C for 4 hours was measured using the following method. Based on these cathodic polarization curves, 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. First, the test material was heated in an oven set at 200°C for 4 hours. After the test material was removed from the oven and cooled to room temperature, an evaluation area was set on a protective film, and the portion of the test material surface outside the evaluation area was covered with silicone resin.

[0050] Next, a 5% (w / w) NaCl aqueous solution and a 99.7% (w / w) acetic acid solution are prepared. Acetic acid is added to the NaCl aqueous solution to prepare the test solution, such that the volume ratio of NaCl aqueous solution to acetic acid is NaCl aqueous solution:acetic acid = 1000:1. The test piece, counter electrode, and reference electrode, which are electrically connected to the potentiostat, are immersed in this solution and allowed to stand for 30 minutes to stabilize the potential of the measuring section. It should be noted that the test solution is not degassed. Furthermore, an Ag / AgCl electrode can be used as the reference electrode, for example.

[0051] After the potential of the measuring section stabilizes, a voltage is applied between the test piece and the counter electrode using a potentiostat. Before the potential of the measuring section reaches -2000mV relative to the reference electrode, the potential of the measuring section is scanned at a scan rate of 20mV / min. The cathodic polarization curve of the heated test material is obtained by measuring the current density flowing through the measuring section at this time. Furthermore, the same measurement is performed using a pretreated base material that has undergone anodizing using the above method to obtain the cathodic polarization curve of the base material. It should be noted that the cathodic polarization measurements of both the test material and the base material are performed under atmospheric conditions with the temperature of the measurement solution maintained at 25°C. Additionally, the cathodic polarization measurements of both the test material and the base material are performed without stirring the measurement solution, ensuring that the measurement solution is substantially non-flowing.

[0052] As an example of the cathodic polarization curve of the base material, the cathodic polarization curve of an aluminum material containing an aluminum alloy with the chemical composition shown in alloy number A6016 and without a protective coating is shown below. Figure 3 . Figure 3 The vertical axis represents the potential of the measuring unit (unit: V), and the horizontal axis represents the current density (unit: ...). μ A / cm 2 ).in addition, Figure 3 The horizontal axis is a logarithmic scale. For example... Figure 3 As shown, the cathodic polarization curve of aluminum without a protective coating exhibits a stepped shape.

[0053] In cathodic polarization measurements, if the current approaches a state limited by the diffusion rate of hydrogen ions, the change in current relative to the change in potential at the measuring section becomes smaller. Therefore, as... Figure 3 As shown, in the cathodic polarization curve where the vertical axis represents potential and the horizontal axis represents current density, the potential region exhibiting the limiting diffusion current of hydrogen ions is contained in the steeply sloped part of the stepped section of the cathodic polarization curve.

[0054] Figure 4 express Figure 3 An enlarged view of the stepped portion of the cathodic polarization curve in the figure. Although not shown in the figure, the cathodic polarization curve of the base material is also similar. Figure 3 Similarly, it displays a stepped shape. Therefore, it is possible to base it on... Figure 4 The shape of the stepped portion of the cathodic polarization curve shown determines the center of the potential region exhibiting the limiting diffusion current of hydrogen ions. The method for determining the potential region exhibiting the limiting diffusion current of hydrogen ions in the cathodic polarization curve of the substrate is as follows. First, as... Figure 4 As shown, a tangent line L with the largest absolute value of the slope is drawn from the stepped portion of the cathodic polarization curve. Then, the region R where this tangent line L overlaps with the cathodic polarization curve is defined as the potential region exhibiting the limiting diffusion current of hydrogen ions. The current density J2 at the center of this defined region R is calculated. Furthermore, in the cathodic polarization curve of the heated test material, the current density J1 at the same potential as the center of the aforementioned potential region in the cathodic polarization curve of the parent material is calculated.

[0055] 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 measurement solution in the heated test material, showing that the larger the current density value, the larger the contact area between the base material and the measurement solution. Therefore, the ratio J1 / J2, calculated using the heated test piece relative 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, in cases where the protective coating in the heated test material has defects such as cracks, the base material may sometimes be exposed due to the cracks. Therefore, in this case, the current density ratio J1 / J2 becomes larger. The current density ratios J1 / J2 for each test material are shown in Table 1.

[0056] [Table 1] As shown in Table 1, during the fabrication of test materials A1 to A3, after forming an oxide layer on the base material, the oxide layer was heated within the specified temperature range before sealing the pores in the oxide layer. Therefore, these test materials exhibit a current density ratio J1 / J2 within the specified range, and can suppress crack formation at the protective coating even at elevated temperatures. Furthermore, the oxide layer of the protective coating in these test materials is sealed by a hydrated oxide layer, thus exhibiting excellent corrosion resistance to corrosive gases, plasmas, etc.

[0057] On the other hand, when preparing test materials B1 to B2, after forming an oxide layer on the base material, the pores are sealed without heating the oxide layer. Therefore, the current density ratio J1 / J2 of these test materials is higher than the specified range, making them prone to cracking under elevated temperatures.

[0058] (Example for reference) In this example, an example of strain measurement for aluminum material with a protective coating on the base material is described. It should be noted that, unless otherwise specified, reference numerals used in this example that are identical to those used in existing examples indicate the same constituent elements as those in existing examples.

[0059] The method for preparing the test material used in this example is as follows. First, an aluminum plate with the chemical composition shown in alloy number AA6016 and a thickness of 1.1 mm was prepared as base material 2. The base material 2 was pretreated by anodizing using the same method as in the example, followed by anodizing. After anodizing, the base material 2 was heated in a furnace to alleviate the internal stress of the oxide layer 31. The furnace setting temperature was the value shown in the "Heating Temperature" column of Table 2, and the residence time of the base material in the furnace, i.e., the time from the start to the end of heating, was the value shown in the "Heating Time" column of Table 2.

[0060] Then, by immersing the base material 2 having the oxide layer 31 in warm water at 100°C for 60 minutes as a sealing agent, a hydrated oxide layer 32 is formed on the oxide layer 31, and the pores 311 of the oxide layer 31 are sealed by the hydrated oxide layer 32. Through the above, the test materials C1 to C2 shown in Table 1 can be obtained.

[0061] It should be noted that test materials D1 and E1 shown in Table 1 are test materials used 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 not heated but brought into contact with a sealing agent. Furthermore, test material E1 is a sheet of aluminum alloy containing the chemical composition shown in alloy number AA6016. Test material E1 can be obtained by pretreatment of the sheet of aluminum alloy containing the chemical composition shown in alloy number AA6016 using the method described above.

[0062] like Figure 5 As shown, when measuring the strain of test materials C1-C2 and test material D1, the base material 2 is exposed on the reverse side of the aluminum material 1, opposite to the side with the protective coating 3. A strain gauge 4 is then mounted on the exposed base material 2. The strain caused by the thermal expansion of the base material 2 and the protective coating 3 can be measured by heating the aluminum material 1 with the strain gauge 4 mounted thereon. It should be noted that... Figure 5 For convenience, the structure of the protective coating 3 is simplified in the description.

[0063] Although not shown in the figure, when measuring the strain of test material E1, simply install a strain gauge on one side of the test material E1 in the thickness direction and then heat the test material E1.

[0064] Figure 6 This indicates the change in strain when test materials C1-C2, test material D1, and test material E1 are heated for 30 minutes in a furnace set to 200°C. Figure 6 The vertical axis represents the dependent variable, and the horizontal axis represents the elapsed time since heating began. Shortly after heating begins, the test material thermally expands as the temperature rises; therefore, as... Figure 6 As shown, the strain increases sharply from the start of the test until several minutes later. Then, if the temperature of the test material and the base material reaches a substantially constant temperature, the strain of the test material and the base material becomes a substantially constant value.

[0065] The maximum values ​​of strain during the heating of the test materials are shown in Table 2. Additionally, Table 2 shows the values ​​obtained by subtracting the maximum value of strain of test material E1 (without a protective coating) from the maximum values ​​of strain of test materials C1-C2 and test material D1 (with protective coating). The difference between the strain of test materials C1-C2 and test material D1 and the strain of test material D represents the magnitude of the internal stress of the protective coating released by heating during the test; the smaller the difference in strain, the smaller the internal stress of the protective coating.

[0066] [Table 2] As shown in Table 2, during the manufacturing process of the test materials, the strain of test materials C1 and C2, which underwent heating of the oxide layer to form a hydrated oxide layer, was smaller compared to the strain of test material D1, which formed a hydrated oxide layer without heating the oxide layer. Therefore, these results indicate that during the manufacturing process of aluminum, forming a hydrated oxide layer after heating the oxide layer can alleviate the internal stress of the protective coating and improve the heat resistance of the aluminum material.

[0067] The above description illustrates the surface-treated aluminum material and its manufacturing method according to the present invention based on the embodiments. However, the specific methods of surface-treated aluminum material and its manufacturing method according to the present invention are not limited to the embodiments, and appropriate modifications can be made without prejudice to the spirit of the present invention.

[0068] For example, the surface-treated aluminum material of the present invention can be adopted in the manner described in [1] to [3].

[0069] [1] A surface-treated aluminum material comprising: a base material comprising an aluminum alloy having an aluminum or Cu content of more than 1.8% by mass and less than 6.8% by mass; and a protective coating formed on the base material. The protective coating comprises: an oxide layer containing aluminum oxide and covering the base material; and Hydrated oxide layer: which comprises hydrated oxide of aluminum and covers the oxide layer. The cathodic polarization of the substrate and the surface-treated aluminum material heated at 200°C for 4 hours was measured using a test solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution at a volume ratio of NaCl solution:acetic acid = 1000:1. The current density at the central potential of the potential region exhibiting the limiting diffusion current of hydrogen ions in the substrate was measured, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the substrate, J1 / J2, was found to be 7000 × 10⁻⁶. -5 the following.

[0070] [2] The surface-treated aluminum material according to [1], wherein the mass reduction per unit area is 0.3 g / dm² when the sealing degree test is performed by the method specified in JIS H8683-2:2013. 2 the following.

[0071] In addition, the compressor impeller of the present invention can adopt the following scheme [3].

[0072] [3] A compressor impeller comprising the surface-treated aluminum material described in [1] or [2].

[0073] In addition, the manufacturing method of the surface-treated aluminum material involved in this invention can be carried out in the manner shown in [4] to [8].

[0074] The manufacturing method of the surface-treated aluminum material as described in [4], [1] or [2], wherein, By performing anodizing treatment on the base material, a porous oxide layer is formed on the base material. Then, the base material and the oxide layer are heated at a temperature above 50°C and below 350°C. Then, the oxide layer is brought into contact with a sealing agent to form a hydrated oxide layer on the oxide layer while sealing the pores.

[0075] [5] In the method for manufacturing surface-treated aluminum material according to [4], the heating time from the start of heating the oxide layer to the end of heating is more than 1 minute and less than 12 hours.

[0076] [6] The method for manufacturing surface-treated aluminum material according to [4] or [5], wherein the sealing agent is warm water.

[0077] [7] A method for manufacturing surface-treated aluminum material according to any one of [4] to [6], wherein, in the sealing process, the oxide layer is contacted with warm water at 100°C or higher as the sealing agent for 10 minutes or more but less than 120 minutes.

[0078] [8] The method for manufacturing surface-treated aluminum material according to any one of [4] to [7], wherein the electrolyte used in the anodizing process comprises an inorganic electrolyte, the inorganic electrolyte comprising: inorganic cations and one or more anions selected from sulfate ions, phosphate ions, ammonium ions and borate ions.

Claims

1. A surface-treated aluminum material, characterized in that, have: The base material is an aluminum alloy containing more than 1.8% by mass and less than 6.8% by mass of Cu; and A protective coating is formed on the base material. The protective coating has the following characteristics: An oxide layer comprising an aluminum oxide and covering the substrate; and Hydrated oxide layer: which comprises hydrated oxide of aluminum and covers the oxide layer. The cathodic polarization of the substrate and the surface-treated aluminum material heated at 200°C for 4 hours was measured using a test solution prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid solution at a volume ratio of NaCl solution:acetic acid = 1000:

1. The current density at the central potential of the potential region exhibiting the limiting diffusion current of hydrogen ions in the substrate was measured, and the ratio of the current density J1 of the surface-treated aluminum material to the current density J2 of the substrate, J1 / J2, was found to be 7000 × 10⁻⁶. -5 the following.

2. The surface-treated aluminum material according to claim 1, wherein, The mass reduction per unit area is 0.3 g / dm² when the pore size test is performed according to the method specified in JIS H8683-2:2013. 2 the following.

3. A compressor impeller, characterized in that, It includes the surface-treated aluminum material as described in claim 1 or 2.

4. The method for manufacturing the surface-treated aluminum material according to claim 1 or 2, characterized in that, Anodizing the base material creates a porous oxide layer on it. Then, the base material and the oxide layer are heated at a temperature above 50°C and below 350°C. Then, the oxide layer is brought into contact with a sealing agent to form a hydrated oxide layer on the oxide layer while sealing the pores.

5. The method for manufacturing 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 more than 1 minute and less than 12 hours.

6. The method for manufacturing surface-treated aluminum material according to claim 4 or 5, wherein, The sealing agent is warm water.

7. The method for manufacturing surface-treated aluminum material according to any one of claims 4 to 6, wherein, In the sealing process, the oxide layer is brought into contact with warm water at 95°C or higher as the sealing agent for 10 minutes or more but less than 120 minutes.

8. The method for manufacturing surface-treated aluminum material according to any one of claims 4 to 7, wherein, The electrolyte used in the anodic oxidation process contains an inorganic electrolyte, which includes inorganic cations and one or more anions selected from sulfate ions, phosphate ions, ammonium ions and borate ions.

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