Manufacturing method for surface-treated aluminum material

Abstract

The present invention provides a surface-treated aluminum material with high surface hardness and excellent fatigue properties, as well as a method for manufacturing the same. [Solution] The surface-treated aluminum material 1 comprises 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 comprises a first layer 31 made of aluminum oxide that covers the base material 2, and a second layer 32 containing hydrated aluminum oxide that covers the first layer 31. When a tensile axial force fatigue test of the surface-treated aluminum material 1 was performed in a room temperature environment under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz, the number of cycles to fracture was 1.0 × 10⁻⁶. 6 The fatigue strength, expressed as the maximum stress under these conditions, is 160 MPa or higher.

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, Patent Document 1 describes an anodizing method for an aluminum alloy in which 4.0 to 24.0% by mass of silicon is added, with the aim of improving the hardness, elastic modulus, and corrosion resistance of the anodized film, wherein the anodizing treatment is performed for a maximum of 60 minutes, and an anodized film with a thickness of 10 μm to 25 μm is formed within the said treatment time. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-155917 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, forming an anodic oxide film on the surface of an aluminum alloy material tends to shorten the fatigue life of the aluminum alloy material. In particular, if the pores of the anodic oxide film are blocked by a sealing treatment, the fatigue life tends to be significantly shortened.

[0006] This invention was made in view of the above background, and aims to provide a surface-treated aluminum material with high surface hardness and excellent fatigue properties, as well as a method for manufacturing the same. [Means for solving the problem]

[0007] One of the present inventions reference The embodiment is 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 comprises a second layer containing aluminum hydrate oxide and covering the first layer, When a tensile axial fatigue test was performed on the surface-treated aluminum material under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz in a room temperature environment, the number of cycles to fracture was 1.0 × 10⁻⁶. 6 The surface-treated aluminum material has a fatigue strength of 160 MPa or more, expressed as the maximum stress under certain conditions.

[0008] This invention one The embodiment is a method for manufacturing a surface-treated aluminum material according to the above embodiment, Prepare the base material, 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 at a temperature of 50°C to 600°C for 3 minutes to 48 hours. The present invention relates to a method for manufacturing a surface-treated aluminum material, wherein a sealing agent is then brought into contact with the first layer to form the second layer. [Effects of the Invention]

[0009] The surface-treated aluminum material (hereinafter referred to as "aluminum material") comprises a first layer made of aluminum oxide and a second layer containing hydrated aluminum oxide that covers the first layer, and has a protective film formed on the base material. Therefore, the surface-treated aluminum material has high surface hardness.

[0010] In addition, when the aluminum material is subjected to a tensile axial force fatigue test under the specific conditions, the fatigue strength represented by the maximum stress when the number of fracture repetitions is 1.0×10 6 is 160 MPa or more. Such an aluminum material has excellent fatigue characteristics and can suppress the occurrence of cracks even when a load is repeatedly applied.

[0011] In the method for manufacturing the surface-treated aluminum material, a first layer is formed by subjecting the base material to an anodic oxidation treatment. Then, after heating the first layer under conditions within the specific range, a second layer is formed. The aluminum material thus formed has high surface strength and excellent fatigue characteristics.

[0012] As described above, according to the above aspect, it is possible to provide a surface-treated aluminum material having high surface hardness and excellent fatigue characteristics and a method for manufacturing the same.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a cross-sectional view of the surface-treated aluminum material in the embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the base material on which the first layer is formed in the manufacturing process of the surface-treated aluminum material of the embodiment. [Figure 3] FIG. 3 is an explanatory view of the S-N diagrams of test specimens A1 and B1 in the embodiment. [Figure 4] FIG. 4 is an explanatory view of the S-N diagrams of test specimens A2 and B2 in the embodiment. [Figure 5] FIG. 5 is an explanatory view of the S-N diagrams of test specimens A3 and B3 in the embodiment.

Modes for Carrying Out the Invention

[0014] (Surface-Treated Aluminum Material) The base material of the aforementioned aluminum material is made of aluminum or an aluminum alloy. The shape of the base material is not particularly limited and can take various shapes depending on the application of the aluminum material. For example, the base material may be a wrought material such as a rolled plate or an extruded material, or it may be a cast material or a forged material. The base material may also be machined to form a desired shape. If the shape of the base material is a plate, the thickness of the base material is not particularly limited. More specifically, the base material may be a cold-rolled plate with a thickness of about 1 mm, or a hot-rolled plate with a thickness of about 50 mm.

[0015] The base material is preferably an extruded material. Extruded materials are often used in applications requiring relatively high fatigue strength. Therefore, by forming the protective film on the surface of the extruded material as the base material, the aforementioned effects can be utilized more effectively.

[0016] 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. Furthermore, the base material may be a clad material in which two or more layers having different chemical compositions are laminated together.

[0017] The base material is preferably composed of a 6000 series aluminum alloy or a 7000 series aluminum alloy. These aluminum alloys have relatively high strength among aluminum alloys. Therefore, by forming the protective film on the surface of a base material composed of these alloys, the fatigue strength of the aluminum material can be further increased.

[0018] 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 surface hardness of the aluminum material can be more reliably increased, and the corrosion resistance of the aluminum material can be further improved. There is no particular upper limit to the thickness of the protective film, but the upper limit for the thickness of the protective film in manufacturing is, for example, 200 μm. From the viewpoint of further increasing 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.

[0019] 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.

[0020] 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 more easily increasing the thickness of the anodic oxide film, it is preferable that the first layer has pores. Furthermore, it is preferable that the pores of the first layer are sealed by the second layer. In this case, the surface hardness of the aluminum material can be more reliably increased, and the corrosion resistance of the aluminum material can be further improved.

[0021] The second layer contains hydrated aluminum oxide. Because hydrated aluminum oxide has high chemical stability, it is less likely to deteriorate during use of the aluminum material. In addition, hydrated aluminum oxide also has excellent corrosion resistance.

[0022] Furthermore, the second layer is formed, for example, by hydrating the aluminum oxide contained in the first layer after the first layer has been formed 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 aluminum hydrate on the first layer, the formation of defects at the interface between the first and second layers can be suppressed. As a result, by providing a second layer containing aluminum hydrate on the first layer, high corrosion resistance can be maintained over a long period of time.

[0023] More specifically, the second layer may consist of a hydrated aluminum oxide. Alternatively, the second layer may consist of a 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 oxides and / or hydroxides 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.

[0024] 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 surface hardness of the aluminum material can be increased more easily.

[0025] 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.

[0026] 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.

[0027] 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)

[0028] When a tensile axial fatigue test was performed on the surface-treated aluminum material under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz in a room temperature environment, the number of cycles to fracture was 1.0 × 10⁻⁶. 6 The fatigue strength, expressed as the maximum stress at which this occurs, is 160 MPa or higher. Such aluminum materials have excellent fatigue properties, suppressing the progression of fatigue fracture even when subjected to repeated loads, and improving fatigue life.

[0029] The tensile axial force fatigue test of the aluminum material is more specifically carried out in a room temperature environment of 25°C ± 5°C in accordance with JIS Z2271-1978. The stress applied to the test piece is tensile stress, and the stress ratio, that is, the ratio of the minimum stress to the maximum stress, is 0.1. Also, the repetition frequency of the tensile stress is 30 Hz. Under the above conditions, the tensile axial force fatigue test is carried out by variously changing the stress applied to the test piece, and the number of repetitions when the test piece breaks is defined as the breaking repetition number.

[0030] Based on these test results, an S-N curve is created with the maximum value of the stress applied to the test piece shown on the vertical axis and the number of breaking repetitions shown on the horizontal axis. Then, the S-N curve thus produced is analyzed using a continuous decline type curve model as a regression model in accordance with the Japan Society for Materials Science Standard: JSMS-SD-6-04 "Standard for Evaluating Fatigue Reliability of Metallic Materials (S-N Curve Regression Method)". In the regression curve obtained in this way, when the number of breaking repetitions is 1.0×10 6 the maximum stress is defined as the fatigue strength of the aluminum material.

[0031] (Manufacturing method of aluminum material) The surface-treated aluminum material is, for example, prepare the base material, form the first layer on the base material by subjecting the base material to an anodic oxidation treatment, then heat the base material and the first layer at a temperature of 50°C or higher and 600°C or lower for 3 minutes or longer and 48 hours or shorter, and then obtain it by bringing a sealing agent into contact with the first layer to form the second layer. Hereinafter, the manufacturing method of the aluminum material will be described in more detail.

[0032] In preparing 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. As for the casting method of the base material, either DC casting or continuous casting may be used. The base material may also be formed into a desired shape by machining a cast material, forged material, or wrought material. As mentioned above, from the viewpoint of more effectively utilizing the effect of improving fatigue properties, it is preferable to produce the base material by extruding an ingot in the preparation of the base material.

[0033] 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.

[0034] 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 an electrolyte solution. 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 solution.

[0035] 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.

[0036] The current density of the DC current in the anodizing process is, for example, 1 mA / cm². 2 More than 100mA / cm 2The 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.

[0037] The thickness of the first layer formed during the anodizing process is preferably 10 μm or more. By making the thickness of the first layer 10 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.

[0038] In the above manufacturing method, after anodizing, the base material and the first layer are heated at a temperature of 50°C to 600°C for 3 minutes to 48 hours. By heating the first layer under these specific conditions before forming the second layer on the first layer, the fatigue strength of the aluminum material can be improved.

[0039] The reason why the aforementioned effects are obtained by heating the first layer is not entirely clear at this time, but for example, the following reasons can be considered. Multiple strains exist in the first layer formed on the base material, and these strains are thought to be released when heated at a temperature corresponding to the state of each strain. Therefore, when the first layer is heated after being formed by anodizing, it is thought that the strains present in the first layer are released according to the heating temperature of the first layer, and the internal stress is relaxed. Furthermore, by forming the second layer after the internal stress of the first layer has been relaxed, it is thought that a protective film that is less prone to cracking even when a load is repeatedly applied can be formed. In this way, by improving the durability of the protective film against repeated loads, it is thought that the progression of fatigue fracture of the base material starting from cracks that occur in the protective film can be suppressed. As a result of the above, it is thought that the fatigue properties of the aluminum material can be improved.

[0040] From the viewpoint of further improving the heat resistance of the protective coating, the heating temperature of the first layer is preferably 70°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher, and particularly preferably 150°C or higher. If the heating temperature of the first layer is less than 50°C, the relaxation of internal stress in the first layer tends to be insufficient. In this case, cracks are likely to occur in the protective coating when a load is repeatedly applied, which may lead to a decrease in the fatigue properties of the aluminum material.

[0041] On the other hand, if the heating temperature of the first layer is excessively high, the base material may melt during heating, or the first layer may not be able to keep up with the thermal expansion of the base material, potentially causing cracks to form in the first layer while it is being heated. These problems can be easily avoided by setting the heating temperature of the first layer to 600°C or lower, preferably 500°C or lower, more preferably 400°C or lower, even more preferably 350°C or lower, and particularly preferably 300°C or lower.

[0042] In determining the preferred range of heating temperature for the first layer, the upper and lower limits of the heating temperature for the first layer described above can be arbitrarily combined. For example, the preferred range of heating temperature for the first layer may be 70°C to 500°C, 100°C to 400°C, 120°C to 350°C, or 150°C to 300°C.

[0043] Furthermore, by setting the heating time for the first layer to between 3 minutes and 48 hours, the internal stress of the first layer can be sufficiently relieved, thereby improving the fatigue properties of the aluminum material.

[0044] The heating of the first layer may also serve as a heat treatment for the base material. For example, during the heating of the base material and the first layer, the base material may be subjected to one of the heat treatments selected from the group consisting of solution treatment or artificial aging treatment. By performing these heat treatments simultaneously with the heating of the first layer, the strength of the base material can be further improved. As a result, the fatigue strength of the aluminum material can be further increased.

[0045] In the above manufacturing method, after heating the first layer, a sealing agent is brought into contact with the first layer to form a second layer. As the sealing agent, for example, a substance that can react 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.

[0046] 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.

[0047] 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]

[0048] Examples of the surface-treated aluminum material and its manufacturing method will be described with reference to Figures 1 to 3. As shown in Figure 1, the surface-treated aluminum material 1 of 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 has a first layer 31 made of aluminum oxide that covers the base material 2 and a second layer 32 containing hydrated aluminum oxide that covers the first layer 31. When a tensile axial force fatigue test was performed on the surface-treated aluminum material in a room temperature environment under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz, the number of cycles to fracture was 1.0 × 10⁻⁶. 6 The fatigue strength, expressed as the maximum stress under these conditions, is 160 MPa or higher.

[0049] 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 at a temperature of 50°C to 600°C for 3 minutes to 48 hours to relieve the internal stress of the first layer 31. Finally, a sealing agent is brought into contact with the heated first layer 31 to form a second layer 32, thereby obtaining the aluminum material 1.

[0050] Table 1 shows specific examples of aluminum material 1 (test materials A1 to A3). The method for preparing these test materials is as follows, for example.

[0051] (Test material A1) To prepare test material A1, first, an ingot having the chemical composition represented by alloy number A6061 is produced by DC casting. After homogenizing this ingot by holding it at a temperature of 555°C for 5 hours, a round aluminum extruded material with a diameter of 15 mm is produced by hot extrusion at a temperature of 500°C.

[0052] After cutting the extruded material into small pieces of appropriate length, these pieces are subjected to solution treatment. In the solution treatment, the pieces are heated at 525°C for 30 minutes, and then quenched by fan cooling. After the solution treatment, the pieces are held at 175°C for 8 hours to undergo artificial aging treatment. Subsequently, the pieces are machined and buffed to form a shape conforming to the shape of the test specimen specified in ASTM E446-2021. Through the above steps, base material 2 can be obtained.

[0053] Next, the base material 2 is subjected to a pretreatment for anodic oxidation. Specifically, as a pretreatment, the base material 2 is first ultrasonically cleaned in an ethanol bath. After the pretreatment of the base material 2, DC electrolysis is performed on the base material 2 as an anodic oxidation treatment to form the first layer 31 on the surface of the base material 2. The electrolyte used in the anodic oxidation treatment is a 15% by mass aqueous sulfuric acid solution, and the electrolyte temperature is 5°C. The current density in the anodic oxidation 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.

[0054] After anodizing, the base material 2 is heated in a heating furnace set to 170°C for 30 minutes to relieve the internal stress of the first layer 31.

[0055] 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, thereby forming a second layer 32 made of hydrated aluminum oxide on the first layer 31, and sealing the pores 311 of the first layer 31 with the second layer 32. This allows for the production of test material A1. The thickness of the protective film 3 formed under these conditions is approximately 15 μm. Furthermore, when sealing the pores 311 of the first layer 31 under these conditions, the mass loss per unit area of ​​the aluminum material 1 when performing a sealing degree test according to the method specified in JIS H8683-2:2013 is approximately 0.01 g / dm². 2 This is the result.

[0056] (Test material A2) Test material A2 has a composition that is generally the same as test material A1, except that the base material is made of a 7000 series alloy. In preparing test material A2, first, an ingot made of a 7000 series alloy is produced by DC casting. After homogenizing this ingot by holding it at a temperature of 470°C for 6 hours, a round aluminum extruded material with a diameter of 15 mm is produced by hot extrusion at a temperature of 450°C. After cutting this extruded material to an appropriate length, a base material 2 with a shape conforming to the shape of the test piece specified in ASTM E446-2021 is produced by machining and buffing.

[0057] Next, the base material 2 is subjected to a pretreatment for anodic oxidation. Specifically, as a pretreatment, the base material 2 is first ultrasonically cleaned in an ethanol bath. After the pretreatment of the base material 2, DC electrolysis is performed on the base material 2 as an anodic oxidation treatment to form the first layer 31 on the surface of the base material 2. The electrolyte used in the anodic oxidation treatment is a 15% by mass aqueous sulfuric acid solution, and the electrolyte temperature is 5°C. The current density in the anodic oxidation treatment is 10 mA / cm². 2 The processing time will be 60 minutes.

[0058] After anodizing, the base material 2 is heated for 24 hours in a heating furnace set to 120°C to relieve internal stress in the first layer 31 and to perform artificial aging on the base material 2.

[0059] Subsequently, the base material 2, which has the first layer 31, is immersed in hot water at 100°C as a sealing agent for 60 minutes to form a second layer 32 made of aluminum hydrated 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 material A2 can be obtained.

[0060] (Test material A3) Test material A3 has a structure that is generally similar to that of test material A2. In preparing test material A3, first, a first layer 31 is formed on the surface of the base material 2 using the same method as for preparing test material A2. Then, the base material 2 is held at a temperature of 400°C for 1 hour, and then quenched by fan cooling to relieve the internal stress of the first layer 31 and to perform solution treatment on the base material 2. After that, the base material 2 is subjected to artificial aging treatment by heating it in a heating furnace set to a temperature of 120°C for 24 hours.

[0061] Subsequently, the base material 2, which has the first layer 31, is immersed in hot water at 100°C as a sealing agent for 60 minutes to form a second layer 32 made of aluminum hydrated 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 material A3 can be obtained.

[0062] (Test material B1) Test material B1, shown in Table 1, is a test material for comparison with test material A1. The method for preparing test material B1 is the same as that for test material A1, except that the second layer is formed without heating after the first layer is formed.

[0063] (Test material B2) Test material B2, shown in Table 1, is a test material for comparison with test material A2. The method for preparing test material B2 is the same as that for test material A2, except that the base material 2 is subjected to artificial aging treatment before pretreatment for anodic oxidation, and that the second layer is formed without heating after the first layer is formed. The conditions for artificial aging treatment in test material B2 are the same as those for test material A2.

[0064] (Test material B3) Test material B3, shown in Table 1, is a test material for comparison with test material A3. The method for preparing test material B3 is the same as that for test material A3, except that the base material 2 is subjected to solution treatment and artificial aging treatment before pretreatment for anodic oxidation, and that after forming the first layer, the second layer is formed without heating. The conditions for solution treatment and artificial aging treatment in test material B3 are the same as those for test material A3.

[0065] Next, the evaluation method for the fatigue properties of test materials A1-A3 and B1-B3 will be explained. The fatigue properties of the test materials can be evaluated based on the results of the tensile axial fatigue test of the test materials. The tensile axial fatigue test is performed in a room temperature environment of 25°C ± 5°C in accordance with ASTM E446-2021. The stress applied to the test piece is tensile stress, and the stress ratio, that is, the ratio of minimum stress to maximum stress, is set to 0.1. The repetition frequency of the tensile stress is set to 30 Hz. Under the above conditions, the tensile axial fatigue test is performed by changing the stress applied to the test piece in various ways, and the number of cycles at which the test piece fractures is defined as the number of cycles to fracture.

[0066] These test results are plotted on a graph where the maximum stress applied to the specimen is on the vertical axis and the common logarithm of the number of fracture cycles is on the horizontal axis to create an S / N diagram. Figure 3 shows an example of the S / N diagrams for test specimens A1 and B1. Figure 4 shows an example of the S / N diagrams for test specimens A2 and B2. Figure 5 shows an example of the S / N diagrams for test specimens A3 and B3.

[0067] The SN curve thus prepared is analyzed using a continuously decreasing curve model as the regression model, in accordance with the Japan Society of Materials Science standard: JSMS-SD-6-04 "Standard for Evaluation of Metal Material Fatigue Reliability (SN Curve Regression Method)," thereby determining the regression curve of the aforementioned test results. In this regression curve, the number of fracture cycles is 1.0 × 10⁻⁶. 6 The maximum stress is determined when the following conditions are met. The above procedure is performed for each test material, and the number of fracture cycles in these tests is 1.0 × 10⁻⁶. 6The maximum stress at which this condition is met is defined as the fatigue strength. Table 1 shows the fatigue strength for each test material.

[0068] [Table 1]

[0069] As shown in Table 1, in the manufacturing process of test materials A1 to A3, the second layer is formed after the first layer is heated under conditions within the specified range. Therefore, the fatigue strength of these test materials is 160 MPa or higher. Consequently, these test materials have high surface hardness and excellent fatigue properties.

[0070] In contrast, in the manufacturing process of test materials B1 to B3, the second layer is formed on the base material without heating the first layer after the first layer has been formed. Therefore, the fatigue strength of these test materials is less than 160 MPa. Consequently, these test materials have inferior fatigue properties.

[0071] 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.

[0072] For example, the surface-treated aluminum material may take the following forms [1] to [3].

[0073] [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 comprises a second layer containing aluminum hydrate oxide and covering the first layer, When a tensile axial fatigue test was performed on the surface-treated aluminum material under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz in a room temperature environment, the number of cycles to fracture was 1.0 × 10⁻⁶. 6A surface-treated aluminum material whose fatigue strength, expressed as the maximum stress under certain conditions, is 160 MPa or higher.

[0074] [2] The surface-treated aluminum material according to [1], wherein the base material is composed of a 6000 series aluminum alloy or a 7000 series aluminum alloy. [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.

[0075] Furthermore, the method for manufacturing the surface-treated aluminum material may take the following forms [4] to [6].

[0076] A method for manufacturing a surface-treated aluminum material as described in any one of [4], [1] to [3], Prepare the base material, 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 at a temperature of 50°C to 600°C for 3 minutes to 48 hours. A method for manufacturing a surface-treated aluminum material, comprising the steps of subsequently bringing a sealing agent into contact with the first layer to form the second layer.

[0077] [5] The method for manufacturing a surface-treated aluminum material according to [4], wherein in the preparation of the base material, the base material is produced by extruding the ingot. [6] A method for producing a surface-treated aluminum material according to [4] or [5], wherein the base material and the first layer are subjected to at least one heat treatment selected from the group consisting of solution treatment or artificial aging treatment. [Explanation of Symbols]

[0078] 1. Surface-treated aluminum material 2 Base material 3. Protective coating 31 First layer 32 Second layer

Claims

1. It comprises a base material made of aluminum or an aluminum alloy, and a protective coating formed on the base material, The protective coating consists of an aluminum oxide and comprises a first layer covering the base material, It comprises a second layer containing aluminum hydrate oxide and covering the first layer, When a tensile axial fatigue test was performed at room temperature under conditions of a stress ratio of 0.1 and a cyclic stress frequency of 30 Hz, the number of cycles to fracture was 1.0 × 10⁻⁶. 6 A method for manufacturing a surface-treated aluminum material, wherein the fatigue strength expressed by the maximum stress at that time is 160 MPa or more, Prepare the base material, 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 at a temperature of 50°C to 600°C for 3 minutes to 48 hours. A method for manufacturing a surface-treated aluminum material, comprising the steps of subsequently bringing a sealing agent into contact with the first layer to form the second layer.

2. A method for manufacturing a surface-treated aluminum material according to claim 1, wherein the base material is composed of a 6000 series aluminum alloy or a 7000 series aluminum alloy.

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 method for manufacturing a surface-treated aluminum material according to claim 1 or 2, which is as follows:

4. A method for manufacturing a surface-treated aluminum material according to claim 1 or 2, wherein the base material is produced by extruding an ingot in the preparation of the base material.

5. A method for producing a surface-treated aluminum material according to claim 1 or 2, wherein the base material and the first layer are subjected to at least one heat treatment selected from the group consisting of solution treatment or artificial aging treatment.

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