Surface-treated aluminum material and method for manufacturing the same

Abstract

The present invention provides a surface-treated aluminum material and a method for manufacturing the same, which can easily increase the maximum operating temperature while maintaining high corrosion resistance. [Solution] The surface-treated aluminum material 1 has a base material 2 made of aluminum or an aluminum alloy and a protective film 3 formed on the base material 2. The protective film 3 has a first layer 31 made of aluminum oxide that covers the base material 2 and a second layer 32 that covers the first layer 31. After preparing a 5% by mass aqueous sodium chloride solution in a tank open to the atmosphere and heating it at a temperature of 200°C for 1 hour, the anode made of the surface-treated aluminum material 1 and the cathode made of oxygen-free copper are electrically connected to each other and are facing each other with a distance of 3 cm between them when immersed in the sodium chloride solution, the integral value of the current density of the anode current flowing from the cathode to the anode from the time of immersion until 30 minutes have elapsed is 5000 μC / cm². 2 The following applies:

Description

[Technical Field]

[0001] The present invention relates to a surface-treated aluminum material and a method for manufacturing the same. [Background technology]

[0002] Aluminum materials, consisting of aluminum or aluminum alloys, are used in a wide variety of applications. These aluminum materials may have an anodic oxide coating applied to their surface to achieve various objectives, such as improved corrosion resistance, scratch resistance, and aesthetic appeal. Because the functions that can be imparted to aluminum materials by the anodic oxide coating are diverse, the application fields of aluminum materials with anodic oxide coatings are expanding rapidly.

[0003] For example, because anodic oxide films have excellent chemical stability, forming an anodic oxide film on the surface of an aluminum material can improve the corrosion resistance of the aluminum material. For example, Patent Document 1 describes a surface treatment method for aluminum or an aluminum alloy, characterized by comprising the steps of forming an anodic oxide film on the surface of aluminum or an aluminum alloy, a first sealing treatment step of immersing in an aqueous solution containing nickel fluoride at 20 to 35°C, and a second sealing treatment step of immersing in an aqueous solution containing nickel acetate at 80 to 93°C. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-070847 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, aluminum materials treated by the surface treatment method described in Patent Document 1 have the problem that their corrosion resistance tends to decrease when the temperature rises, and there were limitations to raising the maximum operating temperature, that is, the maximum temperature expected in the environment in which the parts are used, while maintaining high corrosion resistance.

[0006] This invention was made in view of the above background, and aims to provide a surface-treated aluminum material and a method for manufacturing the same that can easily increase the maximum operating temperature while maintaining high corrosion resistance. [Means for solving the problem]

[0007] One aspect of the present invention comprises a base material made of aluminum or an aluminum alloy, and a protective skin formed on the base material. membrane and A surface-treated aluminum material having, The protective coating consists of an aluminum oxide and comprises a first layer covering the base material, It has a second layer covering the preceding first layer, After preparing a 5% by mass aqueous sodium chloride solution in a tank open to the atmosphere, and heating the surface-treated aluminum material anode and oxygen-free copper cathode in the same tank at 200°C for 1 hour, the anode and cathode are electrically connected to each other and positioned facing each other with a distance of 3 cm between them. When these are then immersed in the aqueous sodium chloride solution, the integral value of the current density of the anode current flowing from the cathode to the anode from the time of immersion until 30 minutes have elapsed is 5000 μC / cm². 2 The following is a surface-treated aluminum material.

[0008] Another aspect of the present invention is a method for manufacturing a surface-treated aluminum material according to the above-described aspect, The first layer is formed on the base material by applying an anodizing treatment to the base material. Subsequently, the base material and the first layer are heated under conditions where the heating temperature T is 100°C or more and 450°C or less, and the product T·t of the heating temperature T and heating time t is 100°C·min or more and 5000°C·min or less. Thereafter, there is a method for manufacturing a surface-treated aluminum material in which the second layer is formed on the first layer.

Advantages of the Invention

[0009] The surface-treated aluminum material (hereinafter referred to as "aluminum material") includes a first layer made of an aluminum oxide and a second layer covering the first layer, and has a protective film formed on a base material. Further, when the anode and cathode made of the aluminum material are immersed in an aqueous sodium chloride solution under the specific conditions, the integrated value of the current density of the anode current is 5000 μC / cm 2 or less. The aluminum material having such characteristics can easily maintain high corrosion resistance even when its temperature rises.

[0010] In the method for manufacturing the surface-treated aluminum material, after subjecting the base material to an anodic oxidation treatment, the first layer formed by the anodic oxidation treatment is heated under the conditions within the above range. Thus, by heating the first layer before forming the second layer on the first layer, it is possible to easily avoid a decrease in corrosion resistance even when the temperature of the aluminum material rises.

[0011] As described above, according to the above aspect, it is possible to provide a surface-treated aluminum material and a method for manufacturing the same that can easily increase the maximum use temperature while maintaining high corrosion resistance.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a cross-sectional view of the surface-treated aluminum material in the example. [Figure 2] FIG. 2 is a cross-sectional view of the base material on which the first layer is formed in the manufacturing process of the surface-treated aluminum material of the example. [Figure 3] FIG. 3 is an explanatory view schematically showing a measuring device for the anode current in the example. [Figure 4]Figure 4 is an explanatory diagram showing the measurement results of the anode current of test material A3, test material B1, and test material B2 in the example. [Modes for carrying out the invention]

[0013] (Aluminum material) The aluminum material, when the anode made of the aluminum material and the cathode made of oxygen-free copper are immersed in an aqueous sodium chloride solution under the specified conditions, has an integrated current density of 5000 μC / cm² from the time of immersion until 30 minutes have elapsed. 2 The aluminum material possesses the following characteristics. Aluminum materials with these characteristics exhibit excellent heat resistance and corrosion resistance. Therefore, the aluminum material can easily achieve a high maximum operating temperature while maintaining high corrosion resistance.

[0014] From the perspective of increasing the maximum operating temperature of the aluminum material, the integral value of the current density of the anode current should be 2000 μC / cm². 2 Preferably, it is 1000 μC / cm². 2 It is more preferable that the following conditions are met: 500 μC / cm 2 The following is even more preferable:

[0015] The reason why aluminum materials whose integrated current density of the anode current falls within the specified range exhibit excellent heat resistance is not entirely clear at present, but the following reasons are possible. Specifically, it is thought that when the base material is anodized during the manufacturing process of the aluminum material, a first layer with internal stress is formed on the base material. Therefore, when the aluminum material is heated, the internal stress remaining in the first layer is released, and defects such as minute cracks occur within the protective film. Furthermore, if defects occur within the protective film, when the anode and cathode are immersed in a sodium chloride solution, the sodium chloride solution enters the defects and comes into contact with the base material of the aluminum material. As a result, galvanic corrosion occurs due to the difference in natural potential between the base material and oxygen-free copper, and an anode current flows from the cathode to the anode.

[0016] In contrast, aluminum materials in which the integral value of the current density of the anode current falls within the specified range are considered to have small internal stresses remaining in the first layer. Therefore, even when the aluminum material is heated and the internal stresses remaining in the first layer are released, it is considered that defects such as minute cracks are less likely to occur within the protective coating.

[0017] As a method for reducing the integral value of the current density of the anode current, for example, a method of heating the first layer before forming the second layer can be employed, as in the aluminum material manufacturing method described later.

[0018] The integral value of the current density of the anode current flowing through the surface-treated aluminum material is calculated more specifically by the following method. First, a 5% by mass aqueous solution of sodium chloride is prepared in a tank open to the atmosphere. The sodium chloride solution is not degassed. The temperature of the sodium chloride solution is 20°C.

[0019] In addition to preparing the sodium chloride aqueous solution, the anode and cathode used for measuring the anode current are prepared separately. To prepare the anode, first, the surface-treated aluminum material is heated at 200°C for 1 hour. Then, a 1 cm layer is applied to the surface of the surface-treated aluminum material. 2 A measurement area with a certain surface area is set, and the area outside the measurement area is covered with an electrically insulating coating. By doing so, an anode can be obtained.

[0020] As the cathode, an oxygen-free copper material having the chemical composition represented by alloy number C1020 and tempered to a temper symbol O is used. On the surface of this oxygen-free copper material, 1 cm 2 A cathode can be obtained by setting a measurement area having a certain surface area and covering the area outside the measurement area with an electrically insulating coating.

[0021] Electrically connect the anode and the cathode prepared as described above via a conductor wire. Then, immerse the anode and the cathode in the sodium chloride aqueous solution in a state where they are opposed to each other such that the distance between the measurement regions is 3 cm. At this time, if the base material is exposed in the measurement region of the anode, electrode reactions occur in the respective measurement regions of the anode and the cathode. As a result, an anodic current flows from the cathode to the anode.

[0022] The area of the measurement region of the anode and the area of the measurement region of the cathode are both 1 cm 2 Therefore, the value of the anodic current (unit: μA) measured by the method described above is the current density (unit: μA / cm 2 ) of the anodic current flowing per cm 2 of area. Therefore, after measuring the anodic current flowing from the cathode to the anode using a microammeter or the like, by integrating the current density of the anodic current from the time of immersion to the time when 30 minutes have elapsed with respect to time (unit: seconds), the integrated value of the current density of the anodic current (unit: μC / cm 2 ) can be calculated. The measurement interval of the anodic current may be, for example, 1 second or less.

[0023] The base material of the aluminum material is composed of aluminum or an aluminum alloy. The shape of the base material is not particularly limited and can take various shapes according to the use of the aluminum material. For example, the base material may be an extended material such as a rolled plate or an extruded material, or may be a cast material or a forged material. Further, the base material may be subjected to machining for forming it into a desired shape. When the shape of the base material is plate-like, the thickness of the base material is not particularly limited. More specifically, the base material may be, for example, a cold-rolled plate having a thickness of about 1 mm, or a hot-rolled plate having a thickness of about 50 mm.

[0024] Furthermore, the material of the base material can be appropriately selected from the group consisting of aluminum and aluminum alloys, depending on the application of the aluminum material. More specifically, for example, 1000 series aluminum can be used as the aluminum constituting the base material. For example, 2000 series aluminum alloy, 3000 series aluminum alloy, 4000 series aluminum alloy, 5000 series aluminum alloy, 6000 series aluminum alloy, 7000 series aluminum alloy, and 8000 series aluminum alloy can be used as the aluminum alloy constituting the base material. In addition, the base material may be a clad material in which two or more layers having different chemical compositions are laminated together.

[0025] A protective film is provided on the base material, comprising a first layer laminated on the base material and a second layer laminated on the first layer. The thickness of the protective film is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. In this case, the corrosion resistance of the aluminum material can be more reliably improved. From the viewpoint of improving corrosion resistance, there is no particular upper limit to the thickness of the protective film, but the manufacturing upper limit for the thickness of the protective film is, for example, 200 μm. From the viewpoint of further improving the productivity of the aluminum material, the thickness of the protective film is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 60 μm or less.

[0026] In determining the preferred range of thickness for the protective film, the upper and lower limits of the protective film described above can be arbitrarily combined. The preferred range of thickness for the protective film may be, for example, 10 μm to 200 μm, 10 μm to 150 μm, 15 μm to 100 μm, 15 μm to 60 μm, or 20 μm to 60 μm.

[0027] The first layer is composed of aluminum oxide. The first layer may have pores. That is, the first layer may be a porous type anodic oxide film. Alternatively, the first layer may be a barrier type anodic oxide film that does not have pores. From the viewpoint of making it easier to increase the thickness of the anodic oxide film, it is preferable that the first layer has pores.

[0028] The material constituting the second layer is not particularly limited. For example, the second layer may be a coating film. The second layer may also be composed of hydrated aluminum oxide. Furthermore, the second layer may be composed of hydrated aluminum oxide and oxides and / or hydroxides of metal elements other than aluminum. Examples of metal elements included in the second layer include Ni (nickel), Cr (chromium), Zr (zirconium), Si (silicon), Ti (titanium), Au (gold), Ag (silver), Co (cobalt), Mo (molybdenum), Mn (manganese), Nb (niobium), Ta (tantalum), W (tungsten), Zn (zinc), Fe (iron), Ir (iridium), and Sc (scandium). In other words, the second layer may contain a hydrated aluminum oxide and an oxide and / or hydroxide of one or more metallic elements selected from the group consisting of Ni, Cr, Zr, Si, Ti, Au, Ag, Co, Mo, Mn, Nb, Ta, W, Zn, Fe, Ir, and Sc.

[0029] The second layer preferably contains aluminum hydrate oxide. Because aluminum hydrate oxide has high chemical stability, it is less likely to deteriorate during use of the aluminum material. Furthermore, aluminum hydrate oxide also exhibits excellent corrosion resistance. Therefore, by providing a second layer containing aluminum hydrate oxide on top of the first layer, high corrosion resistance can be maintained for a longer period of time.

[0030] Furthermore, the second layer containing hydrated aluminum oxide is formed, for example, by hydrating the aluminum oxide contained in the first layer after forming the first layer by anodizing the base material. When aluminum oxide is hydrated, the hydrated oxide grows from the surface of the aluminum oxide, making it difficult for defects to form between the aluminum oxide and the hydrated oxide. Therefore, by forming a second layer containing hydrated aluminum oxide on the first layer, the formation of defects at the interface between the first and second layers can be suppressed, and the corrosion resistance of the aluminum material can be more easily improved.

[0031] When a porosity test is performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area of ​​the aluminum material is 0.3 g / dm². 2 The following is preferable: In such an aluminum material, the first layer is sufficiently covered by the second layer. Therefore, by keeping the mass loss in the porosity test within the specified range, the corrosion resistance of the aluminum material can be more easily improved.

[0032] The specific method for the porosity test is as follows: First, 35 mL of phosphoric acid and 20 g of chromic anhydride are dissolved in water to prepare 1 L of test solution. Next, a test piece containing the protective film is taken from the aluminum material, and the area of ​​the protective film on the test piece is measured. After removing any dirt from the surface of the test piece, its mass is measured. Then, the test piece is immersed in the test solution, which is maintained at a temperature of 38°C ± 1°C, for 15 minutes ± 5 seconds.

[0033] After the test specimen has been immersed in the test solution, it is washed with running water, and then with deionized water or distilled water. After the washed specimen is thoroughly dried, its mass is measured.

[0034] The area A (unit: dm²) of the protective coating on the test specimen obtained from the above is... 2 Using the mass m1 (unit: g) of the test specimen before immersion in the test solution and the mass m2 (unit: g) of the test specimen after immersion in the test solution, the mass loss per unit area δ is calculated based on the following formula (1).A (Unit: g / dm 2 It is possible to calculate ). δ A =(m1-m2) / A ···(1)

[0035] As mentioned above, the aluminum material can easily increase its maximum operating temperature while maintaining high corrosion resistance, making it suitable for applications such as bonding members that are joined to metal members made of metals other than aluminum.

[0036] (Manufacturing method for aluminum materials) The surface-treated aluminum material is, for example, The first layer is formed on the base material by applying an anodizing treatment to the base material. Subsequently, the base material and the first layer are heated under conditions where the heating temperature T is 100°C or more and 450°C or less, and the product T·t of the heating temperature T and heating time t is 100°C·min or more and 5000°C·min or less. The material is then obtained by forming the second layer on the first layer. The method for manufacturing the aluminum material will be described in more detail below.

[0037] In producing the surface-treated aluminum material, first, a base material made of aluminum or an aluminum alloy 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 produced by a method that appropriately combines casting, rolling, and heat treatment. For the casting method of the base material, either DC casting or continuous casting may be used. Furthermore, the base material may be formed into a desired shape by machining a cast material, forged material, or wrought material.

[0038] Furthermore, in the above manufacturing method, pretreatments such as degreasing, etching, desmatting, polishing, and grinding may be performed on the base material before anodizing, as necessary.

[0039] In the above manufacturing method, the first layer is formed on the base material by subjecting the base material prepared in this manner to an anodic oxidation treatment. In the anodic oxidation treatment, the first layer can be formed on the surface of the base material by DC electrolysis, that is, by passing a DC current between the base material and the counter electrode while the base material and the counter electrode are immersed in an electrolyte.

[0040] The electrolyte used in the anodic oxidation process may be an acidic electrolyte containing electrolytes such as sulfuric acid, oxalic acid, or phosphoric acid, or an alkaline electrolyte containing electrolytes such as sodium metaborate. Preferably, the electrolyte used in the anodic oxidation process contains an inorganic electrolyte consisting of inorganic cations such as metal ions or ammonium ions, and one or more anions selected from the group consisting of sulfate ions, phosphate ions, and borate ions. By performing the anodic oxidation process using an electrolyte containing an inorganic electrolyte, a first layer having the desired structure can be formed more easily.

[0041] The current density of the DC current in the anodizing process is, for example, 1 mA / cm². 2 More than 100mA / cm 2 The temperature can be set appropriately from the following range. Furthermore, the electrolyte temperature in the anodizing process can be set appropriately from, for example, a range of 0°C to 40°C.

[0042] The thickness of the first layer formed during the anodizing process is preferably 2 μm or more. By making the thickness of the first layer 2 μm or more, the thickness of the protective film obtained after sealing can be sufficiently increased, thereby further improving the corrosion resistance of the aluminum material.

[0043] In the above manufacturing method, after anodizing treatment, the base material and the first layer are heated under conditions where the heating temperature T is 100°C or more and 450°C or less, and the product T·t of the heating temperature T and heating time t is 100°C·min or more and 5000°C·min or less. In this way, it is believed that by heating the first layer under these specific conditions before forming the second layer on the first layer, the internal stress of the first layer can be relaxed. Furthermore, by forming the second layer after heating the first layer, the heat resistance of the protective film can be improved, and the maximum operating temperature of the aluminum material can be increased while maintaining high corrosion resistance.

[0044] If the heating temperature T of the first layer is less than 100°C, the relaxation of internal stress in the first layer tends to be insufficient. In this case, the heat resistance of the protective film may be insufficient, making it difficult to obtain an aluminum material with a high maximum operating temperature. From the viewpoint of further improving the heat resistance of the protective film and raising the maximum operating temperature of the aluminum material, the heating temperature T of the first layer is preferably 130°C or higher, more preferably 150°C or higher, even more preferably 180°C or higher, and particularly preferably 200°C or higher.

[0045] On the other hand, if the heating temperature T of the first layer exceeds 450°C, the first layer may not be able to keep up with the thermal expansion of the base material, and cracks may occur in the first layer while it is being heated. By setting the heating temperature T of the first layer to 450°C or lower, preferably 400°C or lower, more preferably 350°C or lower, even more preferably 330°C or lower, and particularly preferably 300°C or lower, the occurrence of cracks in the first layer during heating can be easily avoided.

[0046] In determining the preferred range for the heating temperature T of the first layer, the upper and lower limits of the heating temperature T of the first layer described above can be arbitrarily combined. For example, the preferred range for the heating temperature T of the first layer may be 130°C to 400°C, 150°C to 350°C, 180°C to 330°C, or 200°C to 300°C.

[0047] Furthermore, if the product T·t of the heating temperature T and heating time t of the first layer is less than 100°C·min, the relaxation of internal stress in the first layer tends to be insufficient. In this case, the heat resistance of the protective film may be insufficient, making it difficult to obtain an aluminum material with a high maximum operating temperature. From the viewpoint of further improving the heat resistance of the protective film and raising the maximum operating temperature of the aluminum material, the product T·t of the heating temperature T and heating time t of the first layer is preferably 150°C·min or more, more preferably 200°C·min or more, even more preferably 400°C·min or more, and particularly preferably 800°C·min or more.

[0048] On the other hand, if the product T·t of the heating temperature T and heating time t of the first layer exceeds 5000°C·min, the first layer will be overheated, and there is a risk that cracks may occur in the first layer while it is being heated. By setting the product T·t of the heating temperature T and heating time t of the first layer to 5000°C·min or less, preferably 4500°C·min or less, more preferably 4000°C·min or less, even more preferably 3500°C·min or less, and particularly preferably 3000°C·min or less, the occurrence of cracks in the first layer during heating can be easily avoided.

[0049] In determining a preferred range for the product T·t of the heating temperature T and heating time t of the first layer, the upper and lower limits of the product T·t described above can be arbitrarily combined. For example, the preferred range for the product T·t of the heating temperature T and heating time t of the first layer may be 150°C·min or more and 4500°C·min or less, 200°C·min or more and 4000°C·min or less, 400°C·min or more and 3500°C·min or less, or 800°C·min or more and 3000°C·min or less.

[0050] In the above manufacturing method, the first layer is heated, and then the second layer is formed on top of the first layer. The method for forming the second layer can be an appropriate method from known methods depending on the material constituting the second layer. For example, if the second layer is a coating, the coating can be formed by applying paint to the first layer and then drying the paint.

[0051] Furthermore, if the second layer contains a hydrated aluminum oxide, the second layer can be formed on the first layer by bringing the first layer into contact with a sealing agent. As the sealing agent, for example, a substance capable of reacting with aluminum oxide to form a hydrated oxide can be used, such as hot water or steam at a temperature of 80°C or higher, or an aqueous solution containing ions of one or more metal elements selected from the group consisting of Ni, Cr, Zr, Si, Ti, Au, Ag, Co, Mo, Mn, Nb, Ta, W, Zn, Fe, Ir, and Sc. When sealing is performed using hot water or steam, a second layer consisting of a hydrated aluminum oxide can be formed on the first layer.

[0052] Furthermore, when an aqueous solution containing ions of the metal element is used as a sealing agent, a second layer containing hydrated aluminum oxide and oxides and / or hydroxides of the metal element can be formed on the first layer. The metal element may exist as a metal ion or as a complex ion in the aqueous solution. More specifically, aqueous solutions of metal salts containing the metal element, such as aqueous nickel acetate solution, aqueous cobalt acetate solution, aqueous nickel fluoride solution, aqueous chromate solution, and aqueous silicate solution, can be used as sealing agents.

[0053] From the viewpoint of more easily obtaining aluminum materials with excellent corrosion resistance and heat resistance, it is preferable that the sealant be hot water at a temperature of 80°C or higher. When using hot water as the sealant, it is even more preferable to form the second layer by contacting the first layer with hot water at 80°C or higher for 10 minutes or more but less than 120 minutes. [Examples]

[0054] Examples of the surface-treated aluminum material and its manufacturing method will be described with reference to Figures 1 to 4. As shown in Figure 1, the surface-treated aluminum material 1 in this example has a base material 2 made of aluminum or an aluminum alloy and a protective film 3 formed on the base material. The protective film 3 is made of aluminum oxide and has a first layer 31 covering the base material 2 and a second layer 32 covering the first layer 31. As shown in Figure 3, after preparing a 5% by mass aqueous sodium chloride solution 411 in a tank 41 open to the atmosphere and heating it at a temperature of 200°C for 1 hour, an anode 42 made of the surface-treated aluminum material 1 and a cathode 43 made of oxygen-free copper are electrically connected to each other and immersed in the sodium chloride solution 411 with a distance of 3 cm between them. The integral value of the current density of the anode current flowing from the cathode 43 to the anode 42 from the time of immersion until 30 minutes have elapsed is 5000 μC / cm². 2 The following applies:

[0055] In producing the aluminum material 1 in this example, first, the base material 2 is subjected to anodizing treatment to form a first layer 31 on the base material 2, as shown in Figure 2. Then, the base material 2 and the first layer 31 are heated under conditions where the heating temperature T is between 100°C and 450°C, and the product of the heating temperature T and heating time t T·t is between 100°C·min and 5000°C·min to relieve the internal stress of the first layer 31. Finally, the aluminum material 1 can be obtained by forming a second layer 32 on the heated first layer 31.

[0056] Table 1 shows specific examples of aluminum material 1 (test materials A1 to A11). The method for preparing these test materials is as follows, for example.

[0057] (Test materials A1~A11) To prepare test materials A1 to A11, first, an aluminum plate with a thickness of 1 mm and a chemical composition represented by alloy number A5052 is prepared as base material 2. This base material 2 is subjected to a pretreatment for anodizing. Specifically, as a pretreatment, base material 2 is first subjected to alkaline etching by immersing it in a 5 mass% sodium hydroxide aqueous solution at a temperature of 55°C. After that, base material 2 is subjected to desmatt treatment by immersing it in 30 mass% nitric acid.

[0058] After pre-treating the base material 2 as described above, DC electrolysis is performed on the base material 2 as an anodizing treatment to form the first layer 31 on the surface of the base material 2. The electrolyte used in the anodizing treatment is a 15% by mass aqueous sulfuric acid solution, and the temperature of the electrolyte is 5°C. The current density in the anodizing treatment is 10 mA / cm². 2 The processing time is set to 60 minutes. The first layer 31 formed in this way is a so-called porous anodized film and has numerous pores 311, as shown in Figure 2. The thickness of the first layer 31 formed by anodic oxidation under the above conditions is approximately 15 μm.

[0059] After anodizing, the base material 2 is heated in a heating furnace to relieve the internal stress of the first layer 31. The set temperature of the heating furnace (unit: °C) is the value shown in the "Heating Temperature T" column of Table 1, and the time the base material 2 stays in the furnace, that is, the time from the start of heating to the end of heating (unit: minutes), is the value shown in the "Heating Time t" column of Table 1. Note that the "T·t" column of Table 1 shows the product of the heating temperature T and the heating time t (unit: °C·minutes).

[0060] Subsequently, the base material 2 with the first layer 31 is immersed in hot water at 100°C for 60 minutes as a sealing agent to form a second layer 32 made of hydrated aluminum oxide on the first layer 31, and the pores 311 of the first layer 31 are sealed by the second layer 32. Through this process, test materials A1 to A11 shown in Table 1 can be obtained. When the pores 311 of the first layer 31 are sealed under these conditions, the mass loss per unit area of ​​the aluminum material 1 when a sealing degree test is performed according to the method specified in JIS H8683-2:2013 is approximately 0.01 g / dm². 2 This is the result.

[0061] (Test materials B1-B4) Test specimens B1 to B4 are for comparison with test specimens A1 to A11. The preparation method for test specimen B1 is the same as that for test specimens A1 to A11, except that the second layer is formed without heating after the first layer is formed. The preparation method for test specimens B2 to B4 is the same as that for test specimens A1 to A11, except that the heating temperature T and heating time t of the first layer are changed as shown in Table 1.

[0062] Table 1 shows the measurement results of the anode current for test materials A1-A11 and B1-B4 after heating. The specific test method is as follows.

[0063] Figure 3 shows the anode current measuring device 4. First, a 5% by mass sodium chloride aqueous solution 411 is prepared in a tank 41 that is open to the atmosphere. The sodium chloride aqueous solution 411 is not degassed. The temperature of the sodium chloride aqueous solution 411 is set to 20°C.

[0064] In addition to preparing the sodium chloride aqueous solution 411, the anode 42 and cathode 43 are prepared separately. To prepare the anode 42, first, each test material is heated in a heating furnace at 200°C for 1 hour. Then, a 1 cm layer is applied to the surface of the test material. 2 A measurement area (not shown) having the specified area is set up, and the area outside the measurement area is covered with an electrically insulating coating (not shown). This yields the anode 42.

[0065] Furthermore, in preparing cathode 43, an oxygen-free copper material having the chemical composition represented by alloy number C1020 and tempered to a temper symbol O is prepared. On the surface of this oxygen-free copper material, 1 cm 2 A measurement area (not shown) having a certain area is set up, and the area outside the measurement area is covered with an electrically insulating coating (not shown) to obtain a cathode 43. Conductor wires 44 (44a, 44c) are connected to the anode 42 and cathode 43, respectively, and these conductor wires 44 are connected to a minute ammeter 45. This electrically connects the anode 42 and cathode 43.

[0066] Next, the anode 42 and cathode 43, which are electrically connected to each other, are immersed in a sodium chloride aqueous solution 411 with the measurement areas facing each other at a distance of 3 cm. The anode current flowing from cathode 43 to anode 42 is then measured at 0.5-second intervals. Figure 4 shows graphs of the anode currents for test material A3, test material B1, and test material B2 as an example. The vertical axis of Figure 4 represents the anode current (unit: μA), and the horizontal axis represents the elapsed time (unit: seconds) from the time when anode 42 and cathode 43 were immersed.

[0067] The measurement area of ​​both anode 42 and cathode 43 is 1 cm². 2 Therefore, the anode current value (unit: μA) measured by the method described above is for an area of ​​1 cm². 2 Current density of the anode current flowing per unit area (unit: μA / cm²) 2 This is equal to the value of ). Therefore, by accumulating the product of the anode current value at each measurement point and the measurement interval of the anode current from the time the anode 42 and cathode 43 are immersed until 30 minutes have elapsed, the integral value of the anode current density (unit: μC / cm²) can be obtained. 2 ) can be calculated. Table 1 shows the integral value of the anode current density calculated in this way.

[0068] [Table 1]

[0069] As shown in Table 1, test materials A1 to A11 were prepared by heating the first layer on the base material under conditions within the specified range, and then forming a second layer. Therefore, when these test materials were heated at a temperature of 200°C for 1 hour and the anode current was measured using the specified method, the integral value of the anode current density was 5000 μC / cm². 2 The following applies: Such protective coatings have excellent heat resistance and corrosion resistance. Therefore, these test materials can easily have their maximum operating temperature increased while maintaining high corrosion resistance.

[0070] In contrast, the integral value of the current density of the anode current in test material B1 is 5000 μC / cm². 2 It is larger than [value missing]. Therefore, test material B1 may experience a decrease in corrosion resistance when its temperature rises. Possible reasons for the low heat resistance of test material B1 include the fact that the second layer was formed without heating the first layer on the base material, making it prone to defects in the protective coating when the temperature rises.

[0071] Furthermore, the integral value of the current density of the anode current in test materials B2 to B4 is 5000 μC / cm². 2 It is larger than that. Therefore, these test materials may experience a decrease in corrosion resistance when their temperature rises. Thus, the reason why test materials B2 to B4 have low heat resistance is thought to be that the product T·t of the heating temperature T and heating time t of the first layer is too large, making it easy for minute defects to occur when the first layer is heated.

[0072] Although embodiments of the surface-treated aluminum material and its manufacturing method have been described above based on the examples, the specific embodiments of the surface-treated aluminum material and its manufacturing method according to the present invention are not limited to those of the examples, and the configuration can be appropriately modified without impairing the spirit of the present invention.

[0073] For example, the surface-treated aluminum material may take the following forms [1] to [5].

[0074] [1] A surface-treated aluminum material having a base material made of aluminum or an aluminum alloy, and a protective film formed on the base material, The protective coating consists of an aluminum oxide and comprises a first layer covering the base material, It has a second layer covering the preceding first layer, After preparing a 5% by mass aqueous sodium chloride solution in a tank open to the atmosphere, and heating the surface-treated aluminum material anode and oxygen-free copper cathode in the same tank at 200°C for 1 hour, the anode and cathode are electrically connected to each other and positioned facing each other with a distance of 3 cm between them. When these are then immersed in the aqueous sodium chloride solution, the integral value of the current density of the anode current flowing from the cathode to the anode from the time of immersion until 30 minutes have elapsed is 5000 μC / cm². 2 The following are surface-treated aluminum materials. [2] The surface-treated aluminum material according to [1], wherein the thickness of the protective coating is 10 μm or more.

[0075] [3] When the degree of sealing test is performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area is 0.3 g / dm 2 The surface-treated aluminum material described in [1] or [2] below. [4] The surface-treated aluminum material according to any one of [1] to [3], wherein the second layer contains a hydrated aluminum oxide. [5] The surface-treated aluminum material according to any one of [4], wherein the second layer further comprises an oxide and / or hydroxide of one or more metal elements selected from the group consisting of Ni, Cr, Zr, Si, Ti, Au, Ag, Co, Mo, Mn, Nb, Ta, W, Zn, Fe, Ir, and Sc.

[0076] Furthermore, the method for manufacturing the surface-treated aluminum material may take the form described in [6] below. A method for manufacturing a surface-treated aluminum material as described in any one of [6] [1] to [5], The first layer is formed on the base material by applying an anodizing treatment to the base material. Subsequently, the base material and the first layer are heated under conditions where the heating temperature T is 100°C or more and 450°C or less, and the product T·t of the heating temperature T and heating time t is 100°C·min or more and 5000°C·min or less. A method for manufacturing a surface-treated aluminum material, comprising subsequently forming the second layer on top of the first layer. [Explanation of symbols]

[0077] 1. Surface-treated aluminum material 2 Base material 3. Protective coating 31 First layer 32 Second layer

Claims

1. A surface-treated aluminum material having a base material made of aluminum or an aluminum alloy, and a protective film formed on the base material, The protective coating consists of an aluminum oxide and comprises a first layer covering the base material, It has a second layer covering the preceding first layer, After preparing a 5% by mass aqueous sodium chloride solution in a tank open to the atmosphere, and heating the surface-treated aluminum material anode and oxygen-free copper cathode in the same tank at 200°C for 1 hour, the anode and cathode are electrically connected to each other and positioned facing each other with a distance of 3 cm between them. When these are then immersed in the aqueous sodium chloride solution, the integral value of the current density of the anode current flowing from the cathode to the anode from the time of immersion until 30 minutes have elapsed is 5000 μC / cm². 2 The following are surface-treated aluminum materials.

2. The surface-treated aluminum material according to claim 1, wherein the thickness of the protective film is 10 μm or more.

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

4. The surface-treated aluminum material according to claim 1, wherein the second layer contains a hydrated oxide of aluminum.

5. The surface-treated aluminum material according to claim 4, wherein the second layer further comprises an oxide and / or hydroxide of one or more metal elements selected from the group consisting of Ni, Cr, Zr, Ti, Au, Ag, Co, Mo, Mn, Nb, Ta, W, Zn, Fe, Ir, and Sc.

6. A method for manufacturing a surface-treated aluminum material according to any one of claims 1 to 5, The first layer is formed on the base material by applying an anodizing treatment to the base material. Subsequently, the base material and the first layer are heated under conditions where the heating temperature T is 100°C or more and 450°C or less, and the product T·t of the heating temperature T and heating time t is 100°C·min or more and 5000°C·min or less. A method for manufacturing a surface-treated aluminum material, comprising subsequently forming the second layer on the first layer.

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