Surface-treated aluminum material, method for producing same, metal housing, and kitchen device

Abstract

A 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) comprises an oxide layer (31) that is made of an aluminum oxide and covers the base material (2), and a hydrated oxide layer (32) that covers the oxide layer (31). The hydrated oxide layer (32) contains a hydroxide of aluminum and an oxide and / or hydroxide of a predetermined metal element. When cathode polarization measurements are performed on the base material (2) and on the surface-treated aluminum material (1) after being heated for 4 hours at a temperature of 200°C using a predetermined measurement solution, 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 predetermined potential is 90 × 10-5 or below.

Description

Surface-treated aluminum material, its manufacturing method, metal housing and kitchen equipment

[0001] The present invention relates to a surface-treated aluminum material, a manufacturing method thereof, a metal housing, and a kitchen appliance.

[0002] Aluminum materials made of aluminum or aluminum alloys are used in a variety of applications. An anodized film is sometimes formed on the surface of these aluminum materials for purposes such as surface protection. In addition, a sealing treatment is sometimes performed to close pores formed in the anodized film and improve the corrosion resistance of the aluminum material.

[0003] For example, Patent Document 1 describes a surface treatment method for aluminum or an aluminum alloy, which is characterized by comprising a step of forming an anodized film on the surface of aluminum or an aluminum alloy, a first sealing treatment step of immersing the aluminum or aluminum alloy in an aqueous solution containing nickel fluoride at 20 to 35°C, and a second sealing treatment step of immersing the aluminum or aluminum alloy in an aqueous solution containing nickel acetate at 80 to 93°C.

[0004] Japanese Patent Application Laid-Open No. 2021-70847

[0005] However, the aluminum material obtained by the manufacturing method described in Patent Document 1 is prone to cracking in the anodized film when the temperature rises, which may result in the generation of foreign matter consisting of small pieces of the anodized film. In order to prevent the generation of such foreign matter, it is desirable to further improve the heat resistance of aluminum materials having an anodized film on their surfaces.

[0006] The present invention has been made in view of the above background, and aims to provide a surface-treated aluminum material that can suppress the occurrence of cracks even when the temperature rises, a manufacturing method thereof, a metal casing, and a kitchen appliance.

[0007] A first aspect of the present invention is a surface-treated aluminum material having a base material made of aluminum or an aluminum alloy and a protective coating formed on the base material, wherein the protective coating is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer comprises a hydrated oxide of aluminum, and a metal oxide and / or metal hydroxide containing one or more metal elements selected from the group consisting of 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), A measurement solution was prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of 1000:1. The base material and the surface-treated aluminum material were heated at 200°C for 4 hours to carry out cathodic polarization measurement. The current density was measured at a central potential in a potential region showing the diffusion limiting current of hydrogen ions in the base material. The ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 90×10 -5 The following surface-treated aluminum materials are available.

[0008] A second aspect of the present invention is a surface-treated aluminum material having a base material made of aluminum or an aluminum alloy and a protective coating formed on the base material, wherein the protective coating is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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, and wherein a sample having the protective coating on one side of the base material is prepared from the surface-treated aluminum material, and a strain gauge is attached to the back side of the surface of the sample having the protective coating, and the difference ε1 - ε2 between the amount of strain of the sample at a temperature of 200°C and the amount of strain of the base material at a temperature of 200°C is 100 x 10 -6 The following surface-treated aluminum materials are available.

[0009] A third aspect of the present invention is a metal housing made of the surface-treated aluminum material of the above aspect.

[0010] A fourth aspect of the present invention is a kitchen appliance including the metal casing.

[0011] A fifth aspect of the present invention is a method for producing a surface-treated aluminum material according to the above aspect, comprising the steps of: anodizing the base material to form the oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 200°C or higher and 400°C or lower; and bringing the oxide layer into contact with a sealing agent containing the metal element to form the hydrated oxide layer on the oxide layer and seal the pores.

[0012] The surface-treated aluminum material (hereinafter referred to as "aluminum material") of the first embodiment has a protective coating comprising the oxide layer and the hydrated oxide layer on the surface of a base material. Furthermore, when cathodic polarization measurements were performed on the surface-treated aluminum material and the base material after heating at 200°C for 4 hours using the specific method, the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 90 x 10 -5 The aluminum material having these properties has excellent heat resistance, and can suppress the occurrence of cracks even when the temperature rises.

[0013] The aluminum material of the second embodiment has a protective coating film on the surface of the base material, the protective coating film including the oxide layer and the hydrated oxide layer. Also, the difference ε1-ε2 between the strain amount ε1 of the sample at a temperature of 200°C and the strain amount ε2 of the base material at a temperature of 200°C measured by the specific method is 100×10 -6 The aluminum material having these properties has excellent heat resistance, and can suppress the occurrence of cracks even when the temperature rises.

[0014] The metal housing of the third aspect is made of the aluminum material, and therefore has excellent heat resistance, and can suppress the occurrence of cracks even when the temperature rises.

[0015] The metal casing of the kitchen appliance of the fourth aspect is made of the aluminum material. As described above, the aluminum material has excellent heat resistance, so that the occurrence of cracks in the metal casing of the kitchen appliance can be suppressed even when the temperature rises.

[0016] In addition, in the fifth aspect of the method for producing an aluminum material, the base material is anodized, and then the oxide layer formed by the anodization is heated at a temperature within the specific range. By heating the oxide layer before sealing the pores in the oxide layer, the internal stress generated during the formation of the oxide layer can be alleviated. After the internal stress in the oxide layer is alleviated, the oxide layer is brought into contact with a sealing agent to form a hydrated oxide layer on the oxide layer and seal the pores, thereby improving heat resistance and suppressing the occurrence of cracks even when the temperature rises.

[0017] As described above, according to the above-described aspects, it is possible to provide a surface-treated aluminum material that has excellent heat resistance and can suppress the occurrence of cracks even when the temperature rises, a manufacturing method thereof, a metal casing, and a kitchen appliance.

[0018] Fig. 1 is a cross-sectional view of a surface-treated aluminum material in Example 1. Fig. 2 is a cross-sectional view of a base material on which an oxide layer is formed during the manufacturing process of the surface-treated aluminum material in Example 1. Fig. 3 is an explanatory diagram showing the cathodic polarization curve of the base material in Example 1. Fig. 4 is an enlarged view of a step portion in the cathodic polarization curve of the base material. Fig. 5 is an explanatory diagram showing a method for measuring the amount of strain of a surface-treated aluminum material in a reference example. Fig. 6 is an explanatory diagram showing the measurement results of the amount of strain of a surface-treated aluminum material in a reference example.

[0019] (Aluminum Material) The base material of the aluminum material is made of aluminum or an aluminum alloy. The shape of the base material is not particularly limited, and various shapes can be used depending on the application of the aluminum material. 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. Furthermore, for example, 2000 series aluminum alloys, 3000 series aluminum alloys, 4000 series aluminum alloys, 5000 series aluminum alloys, 6000 series aluminum alloys, 7000 series aluminum alloys, and 8000 series aluminum alloys can be used as the aluminum alloy constituting the base material.

[0020] A protective coating made of aluminum oxide is provided on the base material, and the protective coating includes an oxide layer laminated on the base material and a hydrated oxide layer laminated on the oxide layer. The hydrated oxide layer includes a hydrated oxide of aluminum and one or more metal compounds selected from the group consisting of metal oxides and metal hydroxides containing the metal element. The protective coating can be obtained, for example, by anodizing the base material to form an oxide layer with numerous pores on the surface of the base material, followed by a sealing treatment to block the pores in the oxide layer with the hydrated oxide layer. Such a protective coating has excellent corrosion resistance against corrosive gases. Therefore, forming the protective coating on the base material can improve the corrosion resistance of the aluminum material.

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

[0022] The integrated value A of the hydrogen emission intensity in the range from the surface of the aluminum material to a depth of 500 nm, as measured by glow discharge optical emission spectroscopy (hereinafter referred to as "GD-OES"). H The integrated value A of the luminescence intensity of the metal element M Ratio A M / A H is preferably 0.1 or more and 5.0 or less. The emission intensity of an element measured by GD-OES represents the content of that element, and the higher the emission intensity, the more that element is contained. Furthermore, most of the hydrated oxide layer is composed of aluminum hydroxide. Therefore, the ratio A M / A H The value of represents the content of the metal element normalized by the amount of aluminum hydroxide. M / A H By setting the value of within the above-mentioned specific range, the effect of improving corrosion resistance can be more reliably obtained.

[0023] The ratio A M / A H The value of can be calculated by the following method. First, in the depth profile of the hydrogen emission intensity of the aluminum material obtained by GD-OES, the hydrogen emission intensity at each measurement point within a range from the surface to a depth of 500 nm is added up, and this value is taken as the integrated value A of the hydrogen emission intensity. H Similarly, in the depth profile of the metal element emission intensity of the aluminum material, the emission intensities of the metal elements at each measurement point within a range from the surface to a depth of 500 nm are added together, and this value is taken as the integrated value A of the emission intensity of the metal elements. M The integrated value A of the luminous intensity of the metal element thus obtained is M The integrated value A of the hydrogen emission intensity H By dividing by the ratio A M / A H The value of can be obtained.

[0024] When a sealing test was performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area of ​​the aluminum material was 0.3 g / dm 2 In such an aluminum material, the pores of the oxide layer are sufficiently sealed by the hydrated oxide layer. Therefore, by setting the mass loss per unit area of ​​the aluminum material within the above-mentioned specific range, the corrosion resistance of the aluminum material can be more reliably improved.

[0025] The specific method for the pore sealing test is as follows. First, 35 mL of phosphoric acid and 20 g of chromic anhydride are dissolved in water to prepare 1 L of test solution. Next, a test piece including a protective coating is taken from the aluminum material, and the area of ​​the protective coating on the test piece is measured. After removing any dirt from the surface of this test piece, the mass of the test piece is measured. Thereafter, the test piece is immersed in the test solution maintained at a temperature of 38°C ± 1°C for 15 minutes ± 5 seconds.

[0026] After the test piece has been immersed in the test solution, it is washed with running water and then with deionized or distilled water. After the test piece has been washed, it is thoroughly dried and its mass is measured.

[0027] The area S (unit: dm ２ ), the mass m of the test piece before immersion in the test liquid １ (unit: g) and the mass m of the test piece after immersion in the test liquid ２ (unit: g) and calculated the mass loss per unit area δ based on the following formula (1): Ｓ (unit: g / dm ２ ) can be calculated. Ｓ = (m １ -m ２ ) / S...(1)

[0028] In the surface-treated aluminum material according to the first aspect, cathodic polarization measurement is performed on the base material and the surface-treated aluminum material after heating at a temperature of 200°C for 4 hours using a measurement solution obtained by mixing a NaCl solution with a concentration of 5% by mass and acetic acid with a concentration of 99.7% by mass at a volume ratio of the NaCl solution:the acetic acid = 1000:1, and when the current density at the central potential in the potential region showing the diffusion limiting current of hydrogen ions in the base material is measured, the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material is 90 × 10 -5 The aluminum material having a ratio J1 / J2 of the current density J1 within the above-mentioned specific range is less likely to crack when the temperature rises, and has excellent heat resistance.

[0029] From the viewpoint of further improving the heat resistance of the aluminum material, the current density ratio J1 / J2 is 70 × 10 -5 Preferably, it is 50×10 or less. -5 More preferably, it is 30×10 or less. -5 From the viewpoint of improving the heat resistance of the aluminum material, there is no lower limit to the current density ratio J1 / J2, but the current density ratio J1 / J2 is always greater than 0 by definition.

[0030] In addition, in the surface-treated aluminum material according to the second aspect, a sample having the protective coating on one side of the base material is prepared from the surface-treated aluminum material, and a strain gauge is attached to the back side of the surface having the protective coating in the sample, and the difference ε1-ε2 between the amount of strain ε1 of the sample at a temperature of 200°C and the amount of strain ε2 of the base material at a temperature of 200°C is measured, and the difference ε1-ε2 is 100×10 -6 The aluminum material having the difference in strain amount ε1-ε2 within the above-mentioned specific range is less likely to crack when the temperature rises, and has excellent heat resistance. The lower limit of the difference in strain amount ε1-ε2 of a sample made from the aluminum material is usually -100×10 -6 That's all.

[0031] The method for preparing a sample from a surface-treated aluminum material is not particularly limited, and various methods can be used as long as they do not affect the amount of strain in the sample. For example, when the surface-treated aluminum material is a plate having a protective coating on only one side of the base material, a small piece obtained by cutting the surface-treated aluminum material to an appropriate size can be used as the sample. Furthermore, when the surface-treated aluminum material is a plate having a protective coating on both sides of the base material, the surface-treated aluminum material can be cut to an appropriate size to prepare a small piece, and then one of the two protective coatings on the small piece can be removed to obtain a sample. As a method for removing the protective coating, for example, a method of dissolving the protective coating using an acid or alkali can be used.

[0032] As described above, the aluminum material can suppress the occurrence of cracks in the protective coating even when the temperature rises. Therefore, the aluminum material is suitable for applications such as the housing of equipment that becomes hot during use, such as kitchen equipment. More specifically, the aluminum material is suitable for use in, for example, metal housings of kitchen equipment. Examples of kitchen equipment include cooking appliances such as ovens, microwave ovens, gas stoves, and fryers, as well as hot food showcases.

[0033] (Method for manufacturing aluminum material) In manufacturing 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 manufactured by a method that appropriately combines casting, rolling, and heat treatment. After manufacturing the base material, pretreatments for the anodizing treatment, such as degreasing, acid cleaning, and polishing, may be performed as necessary before the anodizing treatment. Next, the base material is anodized to form the oxide layer with pores on the base material. In the anodizing treatment, an oxide layer can be formed on the surface of the base material by passing a direct current between the base material and a counter electrode while the base material and the counter electrode are immersed in an electrolyte. The oxide layer formed in this manner is composed of an aluminum oxide such as alumina and has numerous pores.

[0034] The electrolytic solution used in the anodizing treatment may be, for example, an acidic electrolytic solution containing an electrolyte such as sulfuric acid or phosphoric acid, or an alkaline electrolytic solution containing an electrolyte such as sodium metaborate. The electrolytic solution used in the anodizing treatment preferably contains an inorganic electrolyte consisting of 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 anodizing treatment using an electrolytic solution containing an inorganic electrolyte, an oxide layer having a desired structure can be more easily formed.

[0035] The current density of the direct current in the anodizing treatment is, for example, 1 mA / cm ２ 100mA / cm or more ２ The temperature of the electrolytic solution in the anodizing treatment can be appropriately set within the range of 0°C or higher and 40°C or lower.

[0036] The thickness of the oxide layer formed in the anodizing treatment is preferably 2 μm or more. By making the thickness of the oxide layer 2 μm or more, the thickness of the protective coating obtained after sealing can be made sufficiently thick, and an aluminum material having excellent corrosion resistance and heat resistance can be more easily obtained.

[0037] In the manufacturing method, after anodizing, the base material and the oxide layer are heated at a temperature of 200°C or higher and 400°C or lower. By heating the oxide layer at a temperature within the specific range after anodizing and before sealing the pores in the oxide layer, the internal stress in the oxide layer can be alleviated. Then, by sealing the pores after alleviating the internal stress in the oxide layer, the internal stress in the protective coating after sealing can be reduced. As a result, the occurrence of cracks in the protective coating when heated can be suppressed, and the heat resistance of the aluminum material can be improved.

[0038] If the heating temperature of the oxide layer is too low, the internal stress of the oxide layer will not be sufficiently alleviated, and cracks may easily occur in the protective coating when the temperature of the aluminum material increases. To easily avoid this problem, the heating temperature of the oxide layer is set to 200°C or higher. On the other hand, if the heating temperature of the oxide layer is too high, the oxide layer will not be able to follow the thermal expansion of the base material, and cracks may occur in the oxide coating. To easily avoid this problem, the heating temperature of the oxide layer is set to 400°C or lower.

[0039] In heating the oxide layer, the heating may be terminated immediately after the temperature of the oxide layer reaches a desired temperature, or the temperature may be maintained for a certain period of time after the desired temperature is reached. From the viewpoint of sufficiently alleviating the internal stress of the oxide layer and more reliably increasing the heat resistance of the aluminum material, the heating time from the start of heating the oxide layer to the end of heating is preferably 3 minutes or more and less than 12 hours.

[0040] After heating the oxide layer, the oxide layer is brought into contact with a sealing agent. This forms the hydrated oxide layer on the oxide layer, and the pores are sealed by the hydrated oxide layer. The sealing agent can be, for example, an aqueous solution containing 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 the aqueous solution containing the metal elements is used as the sealing agent and brought into contact with the oxide layer, the hydration reaction of aluminum oxide and the precipitation reaction of the metal element proceed in parallel. As a result, a hydrated oxide layer containing hydrated aluminum oxide and oxides and / or hydroxides of the metal elements can be formed on the oxide layer.

[0041] The sealing agent is preferably an aqueous solution containing ions of the metal element. Use of such a sealing agent allows for more reliable formation of a hydrated oxide layer. The metal element in the sealing agent may exist as a metal ion or a complex ion. Examples of the sealing agent that can be used include aqueous solutions of metal salts containing the metal element, such as an aqueous nickel acetate solution, an aqueous cobalt acetate solution, an aqueous chromate solution, and an aqueous silicate solution.

[0042] Example 1 An example of the surface-treated aluminum material and its manufacturing method will be described with reference to Figures 1 and 2. As shown in Figure 1, the surface-treated aluminum material 1 of this example has a base material 2 made of aluminum or an aluminum alloy and a protective coating 3 formed on the base material. The protective coating 3 is made of an oxide of aluminum and has an oxide layer 31 covering the base material 2 and a hydrated oxide layer 32 covering the oxide layer 31. The hydrated oxide layer 32 contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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. A measurement solution was prepared by mixing a 5 mass % NaCl solution and a 99.7 mass % acetic acid at a volume ratio of 1000:1. The base material 2 and the surface-treated aluminum material 1 were heated at 200°C for 4 hours and then subjected to cathodic polarization measurement. The current density was measured at the central potential in the potential region showing the diffusion limiting current of hydrogen ions in the base material 2. The ratio J1 / J2 of the current density J1 of the surface-treated aluminum material 1 to the current density J2 of the base material 2 was 90×10 -5 The following is the result.

[0043] In producing the aluminum material 1 of this example, first, an oxide layer 31 having pores 311 is formed on the base material 2 by anodizing the base material 2 as shown in Fig. 2. Then, the base material 2 and the oxide layer 31 are heated at a temperature of 200°C or higher and 400°C or lower to relieve internal stress in the oxide layer 31. Then, the oxide layer 31 is brought into contact with a sealing agent to form a hydrated oxide layer 32 on the oxide layer 31 and seal the pores 311, thereby obtaining the aluminum material 1.

[0044] Table 1 shows specific examples of aluminum material 1 (test materials A1 to A12). Test materials A1 to A12 were produced, for example, as follows. First, an aluminum plate having a thickness of 1.1 mm and a chemical composition represented by one of the alloy numbers shown in Table 1 is prepared as base material 2. This base material 2 is subjected to pretreatment for anodizing. Specifically, as pretreatment, base material 2 is first subjected to alkali etching treatment by immersing it in an aqueous sodium hydroxide solution with a concentration of 5% by mass and a temperature of 55°C. Thereafter, base material 2 is immersed in nitric acid with a concentration of 30% by mass to perform desmutting treatment.

[0045] After the base material 2 has been pretreated as described above, the base material 2 is anodized to form an oxide layer 31 on the surface of the base material 2. The electrolyte used in the anodization is a sulfuric acid aqueous solution with a concentration of 15% by mass, and the temperature of the electrolyte is 5°C. The current density in the anodization is 10 mA / cm ２ The treatment time is 60 minutes. The oxide layer 31 formed in this manner is a so-called porous anodized aluminum coating, and has a large number of pores 311, as shown in Fig. 2. The thickness of the oxide layer 31 formed by anodizing under the above-mentioned conditions is approximately 19 µm.

[0046] After the anodizing treatment, the base material 2 is heated in a heating furnace to relieve the internal stress of the oxide layer 31. The set temperature of the heating furnace is the value shown in the "Heating Temperature" column of Table 1, and the residence time of the base material in the furnace, that is, the time from the start of heating to the end of heating, is the value shown in the "Heating Time" column of Table 1.

[0047] The base material 2 having the oxide layer 31 is then immersed in a sealing agent for 60 minutes to form a hydrated oxide layer 32 made of a hydrated oxide of aluminum on the oxide layer 31, and the pores 311 in the oxide layer 31 are sealed by the hydrated oxide layer 32. Specifically, the sealing agent used in this example is either an aqueous solution obtained by diluting "Topseal (registered trademark) H-298" manufactured by Okuno Pharmaceutical Industries Co., Ltd. with water to a concentration of 40 mL / L, or an aqueous solution obtained by dissolving "Topseal L-100" manufactured by Okuno Pharmaceutical Industries Co., Ltd. in water to a concentration of 5 g / L. "Topseal H-298" is an aqueous solution primarily composed of nickel acetate. "Topseal L-100" is a solid primarily composed of nickel fluoride. In Table 1, "Topseal H-298" is referred to as "H-298," and "Topseal L-100" is referred to as "L-100."

[0048] As a result of the above, test materials A1 to A12 shown in Table 1 can be obtained. Note that test materials B1 to B7 shown in Table 1 are test materials for comparison with test materials A1 to A12. The method for producing test materials B1 to B2 and B5 to B7 is the same as the method for producing test material A1, except that after forming oxide layer 31 on base material 2, oxide layer 31 is brought into contact with the sealing agent without being heated. Furthermore, the method for producing test materials B3 and B4 is the same as the method for producing test material A1, except that the heating conditions in the heating furnace are changed as shown in Table 1.

[0049] Next, the method for measuring the cathodic polarization of the test materials A1 to A12 and the test materials B1 to B7 will be described.

[0050] [Cathode polarization measurement] The cathode polarization of the base material and the test material heated at 200°C for 4 hours was measured by the following method, and the ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was calculated based on these cathode polarization curves. First, the test material was heated for 4 hours in an oven set at 200°C. After removing the test material from the oven and cooling it to room temperature, an evaluation area was set on the protective coating, and the surface of the test material other than the evaluation area was covered with silicone resin.

[0051] Next, a 5% by mass NaCl aqueous solution and a 99.7% by mass acetic acid solution are prepared, and acetic acid is added to the NaCl aqueous solution so that the volume ratio of the NaCl aqueous solution to the acetic acid is 1000:1. A test piece, counter electrode, and reference electrode electrically connected to a potentiostat are immersed in the test solution and allowed to stand for 30 minutes to stabilize the potential of the measurement section. The test solution is not degassed. An Ag / AgCl electrode, for example, can be used as the reference electrode.

[0052] After the potential of the measurement section has stabilized, a voltage is applied between the test piece and the counter electrode using a potentiostat, and the potential of the measurement section is swept at a sweep rate of 20 mV / min until the potential of the measurement section reaches -2000 mV relative to the reference electrode. The current density flowing through the measurement section at this time is measured to obtain a cathodic polarization curve of the test material after heating. Furthermore, a similar measurement is performed using a base material after pre-treatment for anodizing using the method described above to obtain a cathodic polarization curve of the base material. Note that the cathodic polarization measurements of the test material and base material are both performed in an air atmosphere, with the temperature of the measurement solution maintained at 25°C. Furthermore, the cathodic polarization measurements of the test material and base material are performed without stirring the measurement solution, and in a state where the measurement solution is substantially not flowing.

[0053] An example of the cathodic polarization curve of the base material is shown in Figure 3. The vertical axis of Figure 3 represents the potential (unit: V) at the measurement point, and the horizontal axis represents the current density (unit: μA / cm 2 ) The horizontal axis in FIG. 3 is a logarithmic scale. As shown in FIG. 3, the cathodic polarization curve of the base material has a stepped shape. In cathodic polarization measurement, as the current approaches a state where it is rate-limited by the diffusion of hydrogen ions, the change in current becomes smaller relative to the change in potential at the measurement point. Therefore, in the cathodic polarization curve shown in FIG. 3, where the vertical axis represents potential and the horizontal axis represents current density, the potential region showing the diffusion-limited current of hydrogen ions is included in the steep portion of the stepped portion of the cathodic polarization curve.

[0054] Fig. 4 shows an enlarged view of the step portion of the cathodic polarization curve in Fig. 3. The method for determining the potential region showing the hydrogen ion diffusion limiting current in the cathodic polarization curve of the base material is as follows. First, as shown in Fig. 4, a tangent line L having the largest absolute value of slope is drawn to the step portion of the cathodic polarization curve. Then, the region R where this tangent line L overlaps with the cathodic polarization curve is determined as the potential region showing the hydrogen ion diffusion limiting current. The current density J2 at the central potential of the region R determined in this way is calculated. Furthermore, in the cathodic polarization curve of the heated test material, the current density J1 is calculated at the same potential as the central potential of the aforementioned potential region in the cathodic polarization curve of the base material.

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

[0056]

[0057] As shown in Table 1, when preparing test materials A1 to A12, an oxide layer was formed on the base material, and then the oxide layer was heated at a temperature within the specified range before the pores in the oxide layer were sealed. Therefore, these test materials have a current density ratio J1 / J2 within the specified range, and are able to suppress the occurrence of cracks in the protective coating even when the temperature rises. Furthermore, these test materials have excellent corrosion resistance because the oxide layer of the protective coating is sealed with a hydrated oxide layer.

[0058] On the other hand, when preparing test materials B1 to B2 and B5 to B7, an oxide layer was formed on the base material, and then the pores were sealed without heating the oxide layer. Therefore, the current density ratio J1 / J2 of these test materials was higher than the specific range, and cracks were likely to occur when the temperature rose.

[0059] The heating temperature for heating the oxide layer in preparing the test material B3 was too low, so the current density ratio J1 / J2 of the test material B3 was higher than the specific range, and cracks were likely to occur when the temperature rose.

[0060] The heating temperature when heating the oxide layer in preparing the test material B4 was too high, so the current density ratio J1 / J2 of the test material B4 was higher than the specific range, and cracks were likely to occur when the temperature rose.

[0061] Table 2 shows the mass loss per unit area obtained by the sealing test specified in JIS H8683-2:2013 for test material A1 and test material A10 among test materials A1 to A12 of this example, and the integrated value A of the hydrogen emission intensity obtained by glow discharge optical emission spectroscopy. H The integrated value A of the Ni emission intensity Ni Ratio A Ni / A H The specific method for the pore sealing test is as described above.

[0062] The measuring device used for glow discharge optical emission spectroscopy is a "GDA750" manufactured by SPECTRUMA. Argon gas is used for sputtering in GD-OES, and the sputtering conditions are an anode diameter of 2.5 mm, a power of 25 W, and a gas pressure of 350 Pa. Under these conditions, the sputtering rate of the test material is approximately 40 nm / sec. In addition, in GD-OES, the emission intensities of hydrogen and Ni during sputtering are acquired at 0.005 second intervals to create a depth profile of the emission intensity of each element.

[0063] Then, in the depth direction profile of the hydrogen emission intensity, the hydrogen emission intensities at each measurement point within a range from the surface to a depth of 500 nm were added together, and this value was taken as the integrated value A of the hydrogen emission intensity. HSimilarly, in the depth profile of the nickel emission intensity, the nickel emission intensities at each measurement point within a range from the surface to a depth of 500 nm are added together, and this value is taken as the integrated value A of the nickel emission intensity. Ni The integrated value A of the luminous intensity of the metal element thus obtained is Ni The integrated value A of the hydrogen emission intensity H By dividing by the ratio A Ni / A H The value of can be obtained.

[0064] Note that test materials C1 and C2 in Table 2 are test materials for comparison with test material A1 and test material A10. The method for preparing test material C1 is the same as that for test material A1, except that no sealing agent is used. The method for preparing test material C2 is the same as that for test material A1, except that boiling water is used as the sealing agent.

[0065]

[0066] As shown in Table 2, when the sealing test was performed, the mass loss per unit area of ​​test material A1 and test material A10 was 0.3 g / dm 2 In contrast, the mass loss per unit area of ​​the test material C1, which was not subjected to the sealing treatment, was 0.3 g / dm 2 Therefore, by comparing the test material A1 and the test material A10 with the test material C1, it can be understood that the pores in the oxide layer of the test material A1 and the test material A10 are sufficiently closed. Furthermore, since the test materials A2 to A9 and A11 to A12 were subjected to a pore sealing treatment under the same conditions as the test material A1 and the test material A10, it can be assumed that the pores in the oxide layer of these test materials are also sufficiently closed.

[0067] In addition, the ratio A in the test material A1 and the test material A10 Ni / A H The value of the ratio A is in the range of 0.1 to 5.0. Ni / A HThe value of is 0. Therefore, from the comparison of test material A1 and test material A10 with test material C2, it can be understood that a protective coating containing the metal element can be formed by bringing a sealing agent containing the metal element into contact with an oxide layer.

[0068] Example 2 This example describes an example in which heat resistance was evaluated when heated at a higher temperature than in Example 1. In this example, test materials A1-A2 and B1-B2 were prepared using the same method as in Example 1, and these test materials were heated in an oven set at a temperature of 250°C for 4 hours. Thereafter, cathodic polarization measurements were performed using the same method as in Example 1, and the current density ratio J1 / J2 was calculated. Table 3 shows the current density ratios J1 / J2 for test materials A1-A2 and B1-B2.

[0069]

[0070] As shown in Table 3, the current density ratio J1 / J2 of test materials A1 and A2, in which sealing treatment was performed after heating the oxide layer, was lower than the current density ratio J1 / J2 of test materials B1 and B2, in which heating of the oxide layer was not performed, even when heated at a temperature of 250° C. Therefore, it can be seen from these results that the heat resistance of the aluminum material can be improved by performing sealing treatment after heating the oxide layer.

[0071] (Reference Example) In this example, an example of measuring the amount of strain in an aluminum material having a protective coating on the base material will be described. Note that, among the symbols used in this example, the same symbols as those used in the previous examples represent the same components as those in the previous examples unless otherwise specified.

[0072] The test material used in this example was prepared as follows. First, an aluminum plate having a thickness of 1.1 mm and a chemical composition represented by alloy number AA6016 was prepared as base material 2. This base material 2 was subjected to a pretreatment for anodizing in the same manner as in the examples, and then to anodizing. After anodizing, base material 2 was heated in a heating furnace to relieve the internal stress of oxide layer 31. The set temperature of the heating furnace was the value shown in the "Heating Temperature" column in Table 4, and the residence time of the base material in the furnace, i.e., the time from the start of heating to the end of heating, was the value shown in the "Heating Time" column in Table 4.

[0073] Thereafter, the base material 2 having the oxide layer 31 thereon is immersed in boiling water as a sealing agent for 60 minutes to form a hydrated oxide layer 32 on the oxide layer 31 and seal the pores 311 in the oxide layer 31 with the hydrated oxide layer 32. In this manner, the test material D1 shown in Table 1 can be obtained.

[0074] Test material E1 shown in Table 4 is a test material for comparison with test material D1. The method for producing test material E1 is the same as the method for producing test material D1, except that after forming oxide layer 31 on base material 2, oxide layer 31 is brought into contact with a sealing agent without heating. The base material shown in Table 4 is obtained by subjecting a plate made of an aluminum alloy having a chemical composition represented by alloy number AA6016 to pretreatment with anodizing by the method described above.

[0075] When measuring the amount of strain in the aluminum material 1 having the test material D1 and the test material E1, the base material 2 is exposed on the back side of the surface of the aluminum material 1 that has the protective coating 3, as shown in Figure 5. Then, a strain gauge 4 is attached to the exposed base material 2. By heating the aluminum material 1 with the strain gauge 4 attached in this way, it is possible to measure the strain of the base material 2 and the protective coating 3 during heating. Note that, for convenience, the structure of the protective coating 3 is depicted in a simplified form in Figure 5.

[0076] Although not shown in the figure, the amount of strain in the base material 2 can be measured by attaching a strain gauge to one surface of the base material 2 in the thickness direction, and then heating the base material 2.

[0077] Figure 6 shows the change in strain when test material D1, test material E1, and the base material are heated for 30 minutes in a heating furnace set at 200°C. The vertical axis in Figure 6 represents strain, and the horizontal axis represents the elapsed time from the start of heating. Immediately after the start of heating, the test material and the base material thermally expand as the temperature rises, so as shown in Figure 6, the strain increases rapidly for several minutes after the start of the test. After that, when the temperatures of the test material and the base material reach a substantially constant temperature, the strain of the test material and the base material becomes a substantially constant value.

[0078] Table 4 shows the maximum strain values ​​during heating of the test material and base material. Table 4 also shows the value ε1 - ε2 obtained by subtracting the maximum strain value ε2 of the base material from the maximum strain value ε1 of the test material. The difference ε1 - ε2 between the strain value ε1 of the test material and the strain value ε2 of the base material indicates the magnitude of the internal stress of the protective coating that was released by heating during the test; the smaller the difference in strain ε1 - ε2, the smaller the internal stress of the protective coating.

[0079]

[0080] As shown in Table 4, the strain of test material D1, which forms a hydrated oxide layer after heating the oxide layer during the manufacturing process of the test material, is smaller than the strain of test material E1, which forms a hydrated oxide layer without heating the oxide layer. This is thought to be because the internal stress of the oxide layer is relieved by heating the oxide layer. Furthermore, it is thought that the internal stress of the protective coating is hardly changed in the sealing treatment performed after heating the oxide layer. Therefore, from these results, it is presumed that the difference ε1 - ε2 between the strain amount ε1 of the test material and the strain amount ε2 of the base material is within the specified range for test materials A1 to A12 in Example 1, and the internal stress of the protective coating is relieved.

[0081] The above has described aspects of the surface-treated aluminum material and the method for manufacturing the same according to the present invention based on the examples, but the specific aspects of the surface-treated aluminum material and the method for manufacturing the same according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not impair the intent of the present invention.

[0082] For example, the surface-treated aluminum material according to the present invention can take the following aspects [1] to [4].

[0083] [1] A surface-treated aluminum material having a base material made of aluminum or an aluminum alloy and a protective coating formed on the base material, wherein the protective coating is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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, A measurement solution was prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid at a volume ratio of 1000:1. The base material and the surface-treated aluminum material were heated at 200°C for 4 hours to carry out cathodic polarization measurement. The current density was measured at a central potential in a potential region showing the diffusion limiting current of hydrogen ions in the base material. The ratio J1 / J2 of the current density J1 of the surface-treated aluminum material to the current density J2 of the base material was 90×10 -5 The surface-treated aluminum material is as follows:

[0084] [2] A surface-treated aluminum material having a base material made of aluminum or an aluminum alloy and a protective coating formed on the base material, wherein the protective coating is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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, wherein a sample having the protective coating on one side of the base material is prepared from the surface-treated aluminum material, and a strain gauge is attached to the back side of the protective coating of the sample, and the difference ε1 - ε2 between the amount of strain ε1 of the sample at a temperature of 200°C and the amount of strain ε2 of the base material at a temperature of 200°C is 100 x 10-6 The surface-treated aluminum material is as follows:

[0085] [3] When a sealing test was performed according to the method specified in JIS H8683-2:2013, the mass loss per unit area was 0.3 g / dm 2 [4] The surface-treated aluminum material according to [1] or [2], wherein the integrated value A of the hydrogen emission intensity in the range from the surface of the surface-treated aluminum material to a depth of 500 nm is: H The integrated value A of the luminescence intensity of the metal element M Ratio A M / A H [4] The surface-treated aluminum material according to any one of [1] to [3], wherein the value is 0.1 or more and 5.0 or less.

[0086] The metal housing according to the present invention can take the following form according to [5]: [5] A metal housing made of the surface-treated aluminum material according to any one of [1] to [4].

[0087] The kitchen appliance according to the present invention may take the following form according to [6]: [6] A kitchen appliance having the metal casing according to [5].

[0088] The method for producing a surface-treated aluminum material according to the present invention can take the following aspects [7] to

[10] .

[0089] [7] A method for producing a surface-treated aluminum material according to any one of [1] to [4], comprising the steps of: anodizing the base material to form the oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 200°C or higher and 400°C or lower; and bringing the oxide layer into contact with a sealing agent containing the metal element to form the hydrated oxide layer on the oxide layer and seal the pores.

[0090] [8] The method for producing a surface-treated aluminum material according to [7], wherein the heating time from the start of heating the oxide layer to the end of heating is 3 minutes or more and less than 12 hours. [9] The method for producing a surface-treated aluminum material according to [7] or [8], wherein the electrolytic solution used in the anodizing treatment contains an inorganic electrolyte consisting of inorganic cations and one or more anions selected from the group consisting of sulfate ions, phosphate ions, and borate ions.

[10] The method for producing a surface-treated aluminum material according to any one of [7] to [9], wherein the sealing agent is an aqueous solution containing ions of the metal element.

Claims

1. A surface-treated aluminum material having a base material made of aluminum or an aluminum alloy and a protective coating formed on the base material, wherein the protective coating is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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, A measurement solution was prepared by mixing a 5% by mass NaCl solution and a 99.7% by mass acetic acid in a volume ratio of 1000:

1. The base material and the surface-treated aluminum material were heated at a temperature of 200° C. for 4 hours to perform cathodic polarization measurement. The current density was measured at a central potential in a potential region showing the diffusion limiting current of hydrogen ions in the base material. When 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 90×10 -5 The surface-treated aluminum material is as follows.

2. 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, wherein the protective film is made of an oxide of aluminum and has an oxide layer covering the base material and a hydrated oxide layer covering the oxide layer, wherein the hydrated oxide layer contains a hydrated oxide of aluminum and a metal oxide and / or metal hydroxide containing 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, wherein a sample having the protective film on one side of the base material is prepared from the surface-treated aluminum material, and a strain gauge is attached to the back side of the protective film of the sample, and the difference ε1 - ε2 between the amount of strain ε1 of the sample at a temperature of 200°C and the amount of strain ε2 of the base material at a temperature of 200°C is 100 x 10 -6 The surface-treated aluminum material is as follows.

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

4. The integrated value A of the hydrogen emission intensity in the range from the surface of the surface-treated aluminum material to a depth of 500 nm, as measured by glow discharge optical emission spectrometry. H The integrated value A of the emission intensity of the metal element M Ratio A M / A H The surface-treated aluminum material according to any one of claims 1 to 3, wherein the surface-treated aluminum material is 0.1 or more and 5.0 or less.

5. A metal housing made of the surface-treated aluminum material according to any one of claims 1 to 4.

6. A kitchen appliance equipped with the metal housing according to claim 5.

7. A method for producing a surface-treated aluminum material according to any one of claims 1 to 4, comprising the steps of: anodizing the base material to form the oxide layer having pores on the base material; heating the base material and the oxide layer at a temperature of 200°C or higher and 400°C or lower; and contacting the oxide layer with a sealing agent containing the metal element to form the hydrated oxide layer on the oxide layer and seal the pores.

8. The method for producing a surface-treated aluminum material according to claim 7, wherein the heating time from the start of heating the oxide layer to the end of heating is 3 minutes or more and less than 12 hours.

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

10. A method for producing a surface-treated aluminum material according to any one of claims 7 to 9, wherein the sealing agent is an aqueous solution containing ions of the metal element.

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