Aluminum member and method for producing same

Abstract

To provide an aluminum member capable of achieving iridescence development with a simple structure in which recesses are provided on the surface of an aluminum substrate.SOLUTION: There is provided an aluminum member 1 comprising a substrate 10 formed from a 7000 series aluminum alloy, wherein the surface of the substrate 10 is provided with a plurality of recesses 11 arranged without gaps, the plurality of recesses 11 comprises a plurality of hexagonal recesses 11, the average diameter of the plurality of hexagonal recesses 11 is 380 nm to 1200 nm and the ratio of the total area of the plurality of hexagonal recesses 11 per unit area on the surface of the substrate 10 is 47% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an aluminum component and a method for manufacturing the same. [Background technology]

[0002] It has been known that structural colors can be achieved by forming a microstructure on the surface of a metal component and using the interference of light through the microstructure. This technology makes it possible to obtain a metal component that changes color when viewed from different angles without using paint.

[0003] Patent Document 1 discloses a coloring structure comprising a light-reflecting layer and a light-transmitting layer having nanoholes in that order, with the light-transmitting layer having a light-absorbing layer on the inner surface of the nanoholes. According to the coloring structure of Patent Document 1, light transmitted through the light-transmitting layer is totally reflected on the surface of the light-reflecting layer, and incident light is reflected on the outer surface of the light-transmitting layer. This provides a coloring structure that appears to be colored even without a coating. Patent Document 2 also discloses an aluminum material having a copper concentration of 30 ppm or less. Patent Document 2 uses an aluminum material having a copper concentration of 30 ppm or less, and specifies an upper limit for the Cu content that hinders regular pore arrangement, thereby providing porous alumina that is regularly arranged by anodizing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-9650 [Patent Document 2] Japanese Patent Application Publication No. 2018-3048 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the coloring structure of Patent Document 1 forms a complex multilayer film on the surface of a substrate, and the structure of the multilayer film may need to be carefully adjusted. The production of such a coloring structure may require complex and advanced technology. Furthermore, Patent Document 2 discloses forming an ordered arrangement in high-purity aluminum, but does not disclose forming an ordered arrangement in an aluminum alloy.

[0006] The present disclosure has been made in view of the problems inherent in the prior art, and an object of the present disclosure is to provide an aluminum member and a method for manufacturing the same that can achieve rainbow coloring with a simple structure in which recesses are provided on the surface of an aluminum base made of an aluminum alloy. [Means for solving the problem]

[0007] The aluminum member according to a first aspect of the present disclosure includes a substrate made of a 7000 series aluminum alloy. A plurality of recesses are provided on the surface of the substrate, and the recesses include a plurality of hexagonal recesses. The average diameter of the plurality of hexagonal recesses is 380 nm to 1200 nm. The ratio of the total area of ​​the plurality of hexagonal recesses per unit area on the surface of the substrate is 47% or more.

[0008] A method for producing an aluminum component according to a second aspect of the present disclosure includes the steps of anodizing an aluminum alloy substrate in an electrolytic solution to form an anodized film on the surface of the substrate, and removing the anodized film from the surface of the substrate. The anodization is performed by increasing the voltage from 0 V to an electrolysis voltage at a rate of 50 V / sec or more. The electrolysis voltage is 120 V or more and 500 V or less. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide an aluminum member and a method for manufacturing the same that can achieve rainbow coloring with a simple structure in which recesses are provided on the surface of an aluminum base material made of an aluminum alloy. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of an aluminum member according to an embodiment. [Figure 2] FIG. 1 is a plan view illustrating an example of an aluminum member according to an embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a substrate prepared by a preparation step. [Figure 4] FIG. 2 is a cross-sectional view showing an example of a state after the surface of the substrate has been smoothed by a surface conditioning step. [Figure 5] FIG. 2 is a cross-sectional view showing an example of a state after an anodized film is formed by an anodizing process. [Figure 6] FIG. 2 is a cross-sectional view showing an example of an aluminum member obtained by the anodized film removal step. [Figure 7] 1 is a spectrum obtained by measuring the spectral intensity on the surface of the aluminum member according to Example 1 using a goniospectrophotometric colorimetry system. [Figure 8] 1 is a spectrum obtained by measuring the spectral intensity on the surface of the aluminum member according to Comparative Example 1 using a goniospectrophotometric colorimetry system. [Figure 9] 1 is a spectrum obtained by measuring the spectral intensity on the surface of the aluminum member according to Reference Example 1 using a goniospectrophotometric colorimetry system. [Figure 10] 10 is a spectrum obtained by measuring the spectral intensity on the surface of the aluminum member according to Reference Example 2 using a goniospectrophotometric colorimetry system. DETAILED DESCRIPTION OF THE INVENTION

[0011] The aluminum member and the method for manufacturing the aluminum member according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0012] [Aluminum components] First, an aluminum member 1 according to this embodiment will be described. As shown in Fig. 1, the aluminum member 1 includes a substrate 10. The shape and thickness of the substrate 10 are not particularly limited and can be changed appropriately depending on the application. The shape of the aluminum member 1 may be, for example, a plate, a column, a prismatic column, a cylinder, a foil, a rectangular tube, or a combination thereof.

[0013] The substrate 10 of this embodiment is made of an aluminum alloy. Specifically, the substrate 10 is made of a 7000-series aluminum alloy. Conventionally, unlike high-purity aluminum, aluminum alloys contain elements other than aluminum, making it difficult to achieve rainbow color development. However, in this embodiment, it has been found that by performing hard-start anodization as described below, it is possible to form a plurality of regularly arranged recesses 11 on the surface of the substrate 10, even with an aluminum alloy. The aluminum member 1 described in this embodiment can achieve rainbow color development. Note that, in this specification, high-purity aluminum refers to aluminum with an aluminum content of 99.95% by mass or more. The aluminum member 1 according to this embodiment will be described in detail below.

[0014] As described above, the substrate 10 is formed of a 7000-series aluminum alloy. 7000-series aluminum is specified by JIS (e.g., JIS H4000). The 7000-series aluminum alloy may be an aluminum alloy containing 0.5% by mass or more and 3.1% by mass or less of magnesium, 0.5% by mass or less of iron, 0.4% by mass or less of silicon, 2.6% by mass or less of copper, 0.7% by mass or less of manganese, 0.8% by mass or more and 7.3% by mass or less of zinc, 0.3% by mass or less of chromium, and 0.20% by mass or less of titanium, with the remainder being aluminum and unavoidable impurities. Alloys with such compositions have particularly excellent strength. Specifically, the substrate 10 is formed of a 7000-series alloy. Examples of 7000-series alloys include A7204 (A7N01), A7010, A7050, A7075, A7475, and A7178 as specified in the JIS standard.

[0015] By including 0.5% by mass or more and 3.1% by mass or less of magnesium in the substrate 10, it is possible to improve the strength of the substrate 10 while suppressing a decrease in the corrosion resistance of the substrate 10. The magnesium content may be 0.8% by mass or more, 1.1% by mass or more, 1.4% by mass or more, or 1.7% by mass or more. The magnesium content may be 3.0% by mass or less, 2.8% by mass or less, 2.6% by mass or less, 2.4% by mass or less, or 2.2% by mass or less.

[0016] The iron content may be greater than 0.05% by mass, greater than or equal to 0.06% by mass, or greater than or equal to 0.07% by mass.The iron content may be less than or equal to 0.4% by mass, less than or equal to 0.3% by mass, less than or equal to 0.2% by mass, or less than or equal to 0.1% by mass.

[0017] The silicon content may be greater than 0.05% by weight, or 0.06% by weight or greater. The silicon content may be 0.3% by weight or less, 0.2% by weight or less, or 0.1% by weight or less.

[0018] The copper content may be more than 0.05% by mass, 0.1% by mass or more, or 0.15% by mass or more, and may be 2% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.15% by mass or less, or 0.1% by mass or less.

[0019] The manganese content may be more than 0.05% by mass, or may be 0.5% by mass or less, 0.3% by mass or less, 0.1% by mass or less, 0.07% by mass or less, or 0.05% by mass or less.

[0020] By including 0.8% by mass or more and 7.3% by mass or less of zinc in the substrate 10, it is possible to improve the strength of the substrate 10 while suppressing a decrease in the corrosion resistance of the substrate 10. The zinc content may be 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more. The zinc content may be 7% by mass or less, 6.5% by mass or less, 6% by mass or less, or 5.5% by mass or less.

[0021] The chromium content may be greater than 0.05%, greater than or equal to 0.1%, or greater than or equal to 0.2% by mass. The chromium content may be less than or equal to 0.2%, or less than or equal to 0.1% by mass. The titanium content may be greater than 0.05%, greater than or equal to 0.1%, or greater than or equal to 0.1% by mass. The titanium content may be less than or equal to 0.1% by mass.

[0022] The substrate 10 may contain unavoidable impurities. In this embodiment, unavoidable impurities refer to those present in raw materials or unavoidably mixed in during the manufacturing process. Although unavoidable impurities are essentially unnecessary, they are tolerated because they are present in trace amounts and do not affect the properties of the aluminum alloy. The unavoidable impurities that may be contained in the aluminum alloy are elements other than aluminum, magnesium, iron, silicon, copper, manganese, chromium, zinc, and titanium. Examples of unavoidable impurities that may be contained in the aluminum alloy include gallium, boron, vanadium, zirconium, lead, calcium, and cobalt. The total amount of unavoidable impurities in the aluminum alloy is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, even more preferably 0.15% by mass or less, and particularly preferably 0.10% by mass or less. Furthermore, the content of each element contained as an unavoidable impurity is preferably 0.05% by mass or less, more preferably 0.03% by mass or less, and even more preferably 0.01% by mass or less.

[0023] As shown in FIG. 2, a plurality of recesses 11 are provided on the surface of the substrate 10 and are arranged without gaps. The recesses 11 form a honeycomb pattern on the surface of the aluminum member 1. The recesses 11 include a plurality of hexagonal recesses 11. Note that a hexagon refers to a polygon having six sides and six vertices. The hexagon is a convex hexagon in which all interior angles are smaller than 180° and the sum of the interior angles is 720°. As shown in FIG. 1, the bottom of each recess 11 has a shape close to a semicircle in cross section.

[0024] The average diameter of the plurality of recesses 11 may be 380 nm to 1200 nm. By setting the average diameter of the plurality of recesses 11 within the above range, light reflected from each recess 11 interferes based on the equation for the bright line condition of the diffraction grating (d sinθ = mλ, d: diameter of recess 11, λ: wavelength, m = 0, 1, 2...), and specific wavelengths reinforce each other depending on the viewing angle, resulting in rainbow colors. The average diameter of the recesses 11 may be 400 nm or more, or 500 nm or more. The average diameter of the hexagonal recesses 11 may be 1100 nm or less, 1000 nm or less, 900 nm or less, 800 nm or less, or 700 nm or less. The average diameter of the recesses 11 can be obtained by observing the surface of the aluminum member 1 with an SEM and calculating the average diameter converted from the area of ​​the recesses 11.

[0025] The average diameter of the plurality of hexagonal recesses 11 is 380 nm to 1200 nm. By setting the average diameter of the hexagonal recesses 11 to be 380 nm or more and 1200 nm or less, it is possible to provide an aluminum member 1 that can realize rainbow color development. The average diameter of the hexagonal recesses 11 may be 400 nm or more, or may be 500 nm or more. The average diameter of the hexagonal recesses 11 may also be 1100 nm or less, 1000 nm or less, 900 nm or less, 800 nm or less, or 700 nm or less. The average diameter of the hexagonal recesses 11 can be obtained by observing the surface of the aluminum member 1 with an SEM and calculating the average value of the longest diameter D1 of the diagonal lines of the opposing corners of the hexagonal recesses 11.

[0026] The average depth of the plurality of recesses 11 may be 50 nm to 500 nm. When the average depth of the recesses 11 is 50 nm or more, it is easily recognized as a wavelength in the visible light region. Furthermore, when the average depth of the recesses 11 is 500 nm or less, incident light is less likely to be scattered or absorbed within the recesses 11, making it easier to confirm clear color development. The average depth of the plurality of recesses 11 may be 100 nm or more. Furthermore, the average depth of the plurality of recesses 11 may be 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less. The average depth of the plurality of recesses 11 can be obtained by observing the cross section of the aluminum member 1 with an SEM and calculating the average value of the depth L1 of each recess 11. The average depth of the plurality of hexagonal recesses 11 may be within the above-mentioned range.

[0027] The ratio of the total area of ​​the hexagonal recesses 11 per unit area on the surface of the substrate 10 is 47% or more. When the ratio of the hexagonal recesses 11 is 47% or more, it is possible to provide an aluminum member 1 that can achieve rainbow color development. The ratio of the hexagonal recesses 11 may be 50% or more, 55% or more, or 60% or more. There is no particular upper limit to the ratio of the hexagonal recesses 11, and it may be 100% or less, 90% or less, 80% or less, or 70% or less. The ratio of the hexagonal recesses 11 can be obtained by the method described in the examples.

[0028] The proportion of the total area of ​​the hexagonal recesses 11 among the plurality of recesses 11 may be 47% or more. When the proportion of hexagonal recesses 11 is 47% or more, rainbow colors can be more reliably achieved. The proportion of hexagonal recesses 11 may be 50% or more, 55% or more, or 60% or more. There is no particular upper limit to the proportion of hexagonal recesses 11, and it may be 100% or less, 90% or less, 80% or less, or 70% or less.

[0029] The spectral intensity in the wavelength range of 390 nm to 730 nm may be measured at acceptance angles of -70°, -60°, -50°, -40°, -30°, -20°, and 0°, and the number of acceptance angles at which the intensity ratio of the maximum intensity to the minimum intensity at each acceptance angle is 1.5 or greater may be between three and seven. This configuration more reliably achieves rainbow color development. The number of acceptance angles at which the intensity ratio is 1.5 or greater may be four or more, five or more, six or more, or seven. The number of acceptance angles at which the intensity ratio is 1.5 or greater may be six or less, five or less, four or less, or three.

[0030] The spectral intensity in the wavelength range from 390 nm to 730 nm is measured at seven light-receiving angles: -70°, -60°, -50°, -40°, -30°, -20°, and 0°. The maximum wavelength at which the spectral intensity is maximized for each light-receiving angle is identified, and the difference between the largest and smallest wavelengths among the seven maximum wavelengths is calculated. The wavelength difference may be 100 nm or more. This configuration more reliably achieves rainbow color development. The wavelength difference may be 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, or 150 nm or more. The wavelength difference may be 250 nm or less, 240 nm or less, 230 nm or less, 220 nm or less, or 210 nm or less.

[0031] The surface of the aluminum member 1 may be provided with at least one of a porous anodic oxide film, a barrier anodic oxide film, and a coating film containing an organic material, an inorganic material, or a composite material thereof. This configuration can improve the corrosion resistance, scratch resistance, and stain resistance of the aluminum member 1. For example, providing a coating film on the surface of the aluminum member 1 can prevent fingerprints from adhering to the aluminum member 1. However, since the anodic oxide film and the coating film are not essential, the aluminum member 1 does not necessarily have to have either the anodic oxide film or the coating film. The thickness of the porous anodic oxide film may be, for example, 30 nm or more and 5,000 nm or less. The thickness of the barrier anodic oxide film may be, for example, 30 nm or more and 500 nm or less. The thickness of the coating film may be, for example, 20 nm or more and 50,000 nm or less.

[0032] Examples of organic coating films include resin coating films such as acrylic resin, urethane resin, and fluororesin. Examples of inorganic coating films include sputtered films of DLC (Diamond-like Carbon), silicon, and other metals, and inorganic coating films containing inorganic components, such as those coated with the Permeate (registered trademark) series manufactured by D&D Corporation. Examples of composite coating films include coating films containing resin and inorganic substances.

[0033] The aluminum member 1 can achieve rainbow color development with a simple structure of recesses provided on the surface of the aluminum base material 10. Therefore, the aluminum member 1 does not need to contain pigments or dyes. However, the aluminum member 1 may contain pigments and dyes as long as rainbow color development can be achieved.

[0034] [Method of manufacturing aluminum components] Next, a method for manufacturing the aluminum member 1 according to this embodiment will be described. The method for manufacturing the aluminum member 1 includes a preparation step, a surface adjustment step of the base material 10, an anodization step, an anodized film removal step, and a clear coating step.

[0035] (preparation process) As shown in FIG. 3 , in the preparation step, a substrate 10 for forming the aluminum member 1 is prepared. The substrate 10 may be produced, for example, by preparing a molten metal containing predetermined elements, casting, extrusion, rolling, heat treatment, or the like. The substrate 10 is made of a 7000 series aluminum alloy. In the method for producing the aluminum member 1 according to this embodiment, the anodized coating 20 is formed by hard starting, as will be described later. Therefore, even if the substrate 10 is made of an aluminum alloy rather than high-purity aluminum, a plurality of recesses 11 can be formed on the surface of the substrate 10, with the recesses 11 being closely spaced from one another.

[0036] (Substrate surface conditioning process) As shown in FIG. 4 , the surface conditioning step for the substrate 10 involves, for example, smoothing the surface of the substrate 10. While the smoothing step is not necessarily required as a surface conditioning step for the substrate 10, it can result in a color with a strong specular reflection component. The smoothing step can smooth the surface of the substrate 10 by removing the corners of the irregularities on the surface of the substrate 10. The smoothing method is not particularly limited as long as it can smooth the surface of the substrate 10. The smoothing step may include, for example, at least one polishing method selected from the group consisting of a chemical dissolution treatment such as chemical polishing using chemicals, physical processing, and electrolytic polishing. Furthermore, as a surface conditioning step for the substrate 10, in addition to the smoothing step, the substrate 10 may be subjected to an anodizing treatment while the rolling or extrusion pattern remains, or physical unevenness may be formed by blasting or the like.

[0037] Chemical dissolution treatments such as chemical polishing chemically dissolve the surface of the substrate 10 to smooth the surface layer of the material. Chemical dissolution treatments such as chemical polishing can smooth the surface of the substrate 10 by dissolving it with at least one of an acidic solution and an alkaline solution. The acidic solution may be, for example, an aqueous solution such as a phosphoric acid aqueous solution, a nitric acid aqueous solution, a sulfuric acid aqueous solution, or a mixture thereof. The alkaline solution may be, for example, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, or a sodium carbonate aqueous solution. The concentrations of the acidic and alkaline solutions are not particularly limited. When a sodium hydroxide aqueous solution is used, the sodium hydroxide concentration in the sodium hydroxide aqueous solution may be, for example, 10 g / L to 300 g / L. The etching time and etching temperature are also not particularly limited and can be adjusted appropriately depending on the condition of the substrate 10 and the etching solution. For example, the etching time is 5 to 180 seconds, and the etching temperature is 40 to 80°C.

[0038] Physical processing involves using a machine to physically process the surface of the substrate 10. Methods for mechanically processing the substrate 10 include, for example, grinding with a milling machine, as well as physically processing the surface with emery paper, buffing, barrel polishing, and hairline finishing.

[0039] Electrolytic polishing is a method of polishing the surface of the substrate 10 by electrolysis. Electrolytic polishing can be performed by immersing the substrate 10 in an electrolytic solution and passing an electric current through the substrate 10 to dissolve the surface of the substrate 10.

[0040] The arithmetic mean height Sa of the surface of the substrate 10 smoothed in the surface conditioning step may be less than approximately 300 nm. The arithmetic mean height Sa can be measured in accordance with ISO 25178. The arithmetic mean height Sa of the surface of the substrate 10 may be 200 nm or less, 100 nm or less, 80 nm or less, or 60 nm or less. The lower limit of the arithmetic mean height Sa of the surface of the substrate 10 is not particularly limited, and the arithmetic mean height Sa may be 0 nm or more. Note that if the surface of the substrate 10 is already smooth, the substrate 10 may be anodized without performing the smoothing step. For example, the arithmetic mean height Sa of the surface of the substrate 10 obtained by hairline processing may be less than approximately 600 nm. Furthermore, the arithmetic mean height Sa of the surface of the substrate 10 obtained by blasting may be less than approximately 2500 nm.

[0041] (Anodizing process) As shown in FIG. 5, in the anodizing step, the substrate 10 is anodized in an electrolytic solution to form an anodized film 20 on the surface of the substrate 10.

[0042] The electrolyte may be, for example, an aqueous solution containing at least one selected from the group consisting of phosphoric acid, phosphonoacetic acid, sodium tetraborate decahydrate, malonic acid, citric acid, malic acid, and etidronic acid (1-hydroxyethane-1,1-diphosphonic acid). For example, using these electrolytes has a higher pKa than sulfuric acid, oxalic acid, or the like, and is weaker in acidity than sulfuric acid and oxalic acid. Acids with a high pKa are less likely to dissolve the coating, allowing for a higher electrolysis voltage, which in turn increases the voltage rise rate. Furthermore, increasing the electrolysis voltage increases the diameter of the recesses 11, resulting in a more distinct color development. The electrolyte preferably contains etidronic acid or sodium tetraborate decahydrate. It is also preferable that the electrolyte contain at least one of etidronic acid and citric acid. The concentration of the etidronic acid aqueous solution may be, for example, 0.01 mol / L or more and 1.0 mol / L or less.

[0043] Anodization is performed by a hard start, in which the voltage is increased to a set voltage immediately after the start of electrolysis. Specifically, the voltage is increased from 0 V to the electrolysis voltage at a voltage increase rate of 50 V / sec or more. By increasing the voltage increase rate to 50 V / sec or more, an aluminum member 1 can be obtained in which the ratio of the total area of ​​the hexagonal recesses 11 per unit area is 47% or more. The voltage increase rate may be 50 V / sec or more, 80 V / sec or more, 100 V / sec or more, or 120 V / sec or more. There is no particular upper limit to the voltage increase rate, but the voltage increase rate may be, for example, 260 V / sec or less.

[0044] The reason why the ratio of the total area of ​​the hexagonal recesses 11 per unit area is 47% or more by using the hard start is that, with the hard start, the voltage rises to its maximum immediately after the start of electrolysis, and a high voltage is applied all at once. The anodic oxide film 20 first forms a barrier film that corresponds to the voltage. The diameter of the recesses 11 depends on the voltage. Therefore, recesses are formed in the anodic oxide film 20 by dissolution of the anodic oxide film 20 by an acidic or alkaline electrolyte. Here, the high voltage is applied all at once, resulting in the formation of recesses with a large diameter, rather than a small diameter. Therefore, the structure tends to become most stable at that high voltage, and the recesses 11 tend to become regularized when their diameters are large.

[0045] On the other hand, in a soft start, in which anodization is started at a slower voltage increase rate than a hard start, electrolysis begins at a low voltage. As mentioned above, the diameter of the recesses 11 depends on the voltage. Because the formation of the recesses 11 begins at a low voltage, the most stable structure is achieved at low voltage. Therefore, regularization is likely to occur when the recesses 11 have a small diameter. When a stable structure is achieved when the recesses 11 have a small diameter, the ratio of the total area of ​​the recesses 11 per unit area tends to be large. However, as the voltage increases, the diameter of the holes increases, and adjacent recesses 11 merge with each other and grow to a size commensurate with the final voltage. Therefore, it is thought that the shape of the recesses 11 is less likely to become hexagonal compared to when one recess 11 grows without merging with adjacent recesses 11.

[0046] The electrolysis voltage after boosting in the anodization step is preferably 120 V or more and 500 V or less. When the electrolysis voltage is in this range, the average diameter of the plurality of recesses 11 can be set within the predetermined range as described above. The electrolysis voltage after boosting may be 140 V or more, 150 V or more, 160 V or more, or 170 V or more. The electrolysis voltage after boosting may also be 440 V or less, 380 V or less, 320 V or less, or 260 V or less.

[0047] The electrolysis time after pressure increase in the anodization step is preferably 1 minute or more and 180 minutes or less. By setting the electrolysis time to 1 minute or more, the ratio of the total area of ​​the hexagonal recesses 11 per unit area can be increased. Furthermore, by setting the electrolysis time after pressure increase to 180 minutes or less, the manufacturing time of the aluminum member 1 can be shortened. The electrolysis time after pressure increase may be 5 minutes or more, 10 minutes or more, or 15 minutes or more. The electrolysis time after pressure increase may be 150 minutes or less, 120 minutes or less, 90 minutes or less, or 60 minutes or less.

[0048] The current density after boosting in the anodizing process was 150mA / cm 2 More than 350mA / cm 2 By setting the current density after the voltage increase within the above range, the ratio of the total area of ​​the hexagonal recesses 11 per unit area can be increased. The current density after the voltage increase is 160 mA / cm 2 More than 170mA / cm 2 More than 180mA / cm 2 or more, or 190mA / cm 2 The current density after the voltage increase may be 340 mA / cm or more. 2 Below, 300mA / cm 2 Below, 270mA / cm 2 Below, 240mA / cm 2 or less, or 210mA / cm 2 It may be the following:

[0049] The amount of electricity per unit area after the pressure increase in the anodizing process is 5 C / cm 2 More than 3780C / cm 2The amount of electricity after the voltage increase may be 5 C / cm or less. 2 By setting the value to 3780 C / cm or more, the ratio of the total area of ​​the hexagonal recesses 11 per unit area can be increased. 2 By setting the voltage to 10 C / cm or less, it is possible to reduce the consumption of electricity and processing time, increase production volume, and reduce electricity costs, thereby lowering costs. 2 Above, 50C / cm 2 Above, 100C / cm 2 or more than 200C / cm 2 The quantity of electricity after the voltage increase may be 2520 C / cm 2 Below, 1260C / cm 2 Below, 630C / cm 2 or less, or 500C / cm 2 It may be the following:

[0050] The electrolysis temperature after the pressure increase in the anodization step is not particularly limited and may be, for example, 0° C. to 95° C. The electrolysis temperature after the pressure increase may be 10° C. or higher, 20° C. or higher, 30° C. or higher, or 40° C. or higher. The electrolysis temperature after the pressure increase may also be 90° C. or lower, 80° C. or lower, or 70° C. or lower.

[0051] (anodic oxide film removal process) 6, in the anodized film removal step, the anodized film 20 formed in the anodized film step is removed from the surface of the substrate 10. By removing the anodized film 20 on the substrate 10, the bottoms of the multiple holes in the anodized film 20 are exposed to the surface, and multiple recesses 11 are formed on the surface of the substrate 10, lined up without gaps.

[0052] The method for removing the anodic oxide film 20 is not particularly limited as long as it can selectively remove the anodic oxide film 20 formed on the substrate 10. The anodic oxide film 20 may be removed by, for example, dissolving the anodic oxide film 20 by immersion in a chromic acid-phosphoric acid mixed solution containing chromic acid and phosphoric acid. The chromic acid-phosphoric acid mixed solution preferably contains 0.05 mol / L to 0.5 mol / L of chromic acid, more preferably 0.1 mol / L to 0.4 mol / L, and even more preferably 0.2 mol / L to 0.3 mol / L. Furthermore, the chromic acid-phosphoric acid mixed solution preferably contains 0.2 mol / L to 0.8 mol / L of phosphoric acid, preferably 0.3 mol / L to 0.7 mol / L, and preferably 0.4 mol / L to 0.6 mol / L. Such a chromic acid-phosphoric acid mixed solution has excellent solubility for the anodic oxide film 20.

[0053] The dissolution temperature of the anodic oxide coating 20 is preferably 40°C to 100°C. By setting the dissolution temperature within this range, the anodic oxide coating 20 can be effectively and selectively dissolved. The dissolution temperature may be 50°C or higher, 60°C or higher, or 70°C or higher. The dissolution temperature may also be 95°C or lower, 90°C or lower, or 85°C or lower.

[0054] (film formation process) Although the film formation step is not an essential step, the film formation step can provide at least one of a porous anodic oxide film, a barrier anodic oxide film, and a coating film containing an organic material, an inorganic material, or a composite material thereof on the surface of the aluminum member 1. This can improve the corrosion resistance, scratch resistance, and stain resistance of the aluminum member 1.

[0055] The porous anodic oxide film can be formed by anodizing the aluminum member 1 after removing the anodic oxide film. Examples of electrolytes for forming the porous anodic oxide film include acidic and alkaline electrolytes. The barrier anodic oxide film can be formed by anodizing the aluminum member 1 after removing the anodic oxide film. Examples of electrolytes for forming the barrier anodic oxide film include neutral electrolytes. The film formation step can be performed by a known coating method, such as painting, using a transparent coating material such as an organic material, an inorganic material, or a composite material. Furthermore, anodizing treatment can be combined with coating by a coating method such as painting.

[0056] As described above, the aluminum member 1 includes a substrate 10 made of a 7000 series aluminum alloy. The substrate 10 has a surface on which a plurality of recesses 11 are arranged without any gaps. The recesses 11 include a plurality of hexagonal recesses 11. The average diameter of the hexagonal recesses 11 is 380 nm to 1200 nm. The proportion of the total area of ​​the hexagonal recesses 11 per unit area on the surface of the substrate 10 is 47% or more.

[0057] The aluminum member 1 according to this embodiment has a regular arrangement with an average diameter. Therefore, light interference occurs on the surface of the aluminum member 1. As a result, the aluminum member 1 according to this embodiment can produce rainbow colors. Therefore, the aluminum member 1 according to this embodiment can produce rainbow colors with a simple structure in which recesses 11 are provided on the surface of the aluminum base material 10.

[0058] Conventionally, it has been difficult to form a large-diameter regularly-arranged structure like the aluminum member 1 according to this embodiment using an aluminum alloy containing 30 ppm or more of Cu, unlike high-purity aluminum. However, according to the method for manufacturing the aluminum member 1 according to this embodiment, by performing anodization with a hard start, it is possible to form a plurality of regularly-arranged recesses 11 on the surface of the substrate 10, even in an aluminum alloy. Therefore, according to the method for manufacturing the aluminum member 1 according to this embodiment, it is possible to manufacture the aluminum member 1 described above.

[0059] The method for producing the aluminum member 1 may include the steps of anodizing a substrate 10 made of an aluminum alloy in an electrolytic solution to form an anodized film on the surface of the substrate 10, and removing the anodized film 20 from the surface of the substrate 10. The anodization may be performed by increasing the voltage from 0 V to the electrolysis voltage at a rate of 50 V / second or more. The electrolysis voltage may be 120 V or more and 500 V or less. This method makes it possible to more reliably produce the aluminum member 1 described above. [Example]

[0060] Hereinafter, the present embodiment will be described in more detail with reference to examples, comparative examples and reference examples, but the present embodiment is not limited to these.

[0061] First, aluminum members according to the examples, comparative examples, and reference examples were produced.

[0062] (Preparation of substrate) A rolled and annealed aluminum plate having the following composition and a thickness of 3 mm was cut into a length of 50 mm and a width of 50 mm to be used as a substrate. High-purity aluminum High-purity aluminum 3N8 (aluminum content 99.98% by mass) 5000 series aluminum alloy (5000 series (1)) Contains 2.7% by mass of magnesium, 0.07% by mass of iron, 0.04% by mass of silicon, and 0.1% by mass of copper, with the remainder being aluminum and inevitable impurities. 5000 series aluminum alloy (5000 series (2)) Contains 0.4% by mass of magnesium, 0.05% by mass of iron, 0.05% by mass of silicon, and 0.15% by mass of copper, with the remainder being aluminum and inevitable impurities. 7000 series aluminum alloy (7000 series) Contains 2.00% by mass of magnesium, 0.07% by mass of iron, 0.06% by mass of silicon, 0.01% by mass of copper, and 5.10% by mass of zinc, with the remainder being aluminum and inevitable impurities.

[0063] (Material surface adjustment) The surface of the substrate was smoothed under the following conditions: The arithmetic mean height Sa of the smoothed substrate surface was set to less than 300 nm. Chemical dissolution treatment (etching) The substrate was etched by immersing it in a 50 g / L aqueous solution of sodium hydroxide at 50°C for 1 minute, and then immersed it in a 200 g / L aqueous solution of nitric acid at room temperature (approximately 20°C) for 2 minutes to remove smut. ·Electrolytic polishing The substrate was electropolished in a mixed solution of 13.6 mol / L CH3COOH and 2.56 mol / L HClO4 (a mixed solution of 78 vol% CH3COOH and 22 vol% 70%-HClO4) at a constant voltage of 28 V for 1 to 5 min.

[0064] (anodic oxidation) The substrate whose surface had been conditioned by the above method was immersed in a predetermined electrolytic solution as shown in Table 1, and the voltage was increased from 0 V to a predetermined electrolysis voltage at a predetermined rate, followed by electrolysis at a predetermined electrolysis voltage, electrolysis time, current density, amount of electricity, and electrolysis temperature to perform anodic oxidation. The electrolytic solutions used in the anodizing treatment are as follows:

[0065] Etidronic acid A 0.2 mol / L aqueous solution of etidronic acid (Sigma-Aldrich, USA) containing 60 wt % etidronic acid was prepared and used as the electrolyte. Citric acid A 0.1 mol / L aqueous citric acid solution was prepared using 98 wt % citric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) and used as the electrolyte. ·Sulfuric acid A 0.5 mol / L aqueous sulfuric acid solution was prepared using 95 wt % sulfuric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) and used as the electrolyte. Oxalic acid A 0.3 mol / L aqueous solution of oxalic acid was prepared using 98% oxalic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) and used as the electrolyte.

[0066] (anodic oxide film removal) The anodized substrate was immersed in a 0.20 mol / L CrO3 / 0.51 mol / L H3PO4 mixed solution at 80°C to selectively dissolve the anodized film on the aluminum substrate, thereby obtaining the aluminum member according to each example.

[0067] [evaluation] (area ratio) The area ratio was obtained by calculating the ratio of the total area of ​​hexagonal recesses per unit area on the surface of the aluminum part. The surface of the aluminum part was observed using a scanning electron microscope (SEM), and the resulting SEM image was binarized into black and white. The binarized SEM image was subjected to Voronoi tessellation using the Python library OpenCV to extract the boundaries between the recesses, and the ratio of the total area of ​​hexagonal recesses per unit area was calculated. Note that recesses that existed at the edge of the SEM image and were partially cut off and obscured from view were not counted as recesses.

[0068] (average diameter of recesses) The average diameter of the recesses was obtained by observing the surface of the aluminum member with an SEM and calculating the average value of the longest diameters of the diagonal lines of the opposite corners of the hexagonal recesses on the surface of the aluminum member.

[0069] (strength ratio) Spectral intensity was measured at reception angles of -70°, -60°, -50°, -40°, -30°, -20°, and 0°. The maximum and minimum intensities were identified for each reception angle, and the intensity ratio (maximum intensity / minimum intensity) was calculated for each reception angle. A sample with an intensity ratio of 1.5 or greater at three or more reception angles was judged "OK," while a sample with an intensity ratio of 1.5 or greater at two or fewer reception angles was judged "NG." Spectral intensity was measured using a Gonio-Spectrophotometer GSP-4, a goniospectrophotometric colorimeter manufactured by Murakami Color Research Laboratory Co., Ltd. The light source used for measurement was D65, with a tilt angle of 25° and an incident angle of 10°. Spectral intensity was measured from 390 nm to 730 nm at 10 nm intervals. 7 to 10 show spectra obtained by measuring the spectral intensities on the surfaces of the aluminum members according to Example 1, Comparative Example 1, and Reference Examples 1 and 2 using a goniospectrophotometric colorimetry system. Table 4 also shows the intensity ratio at each light-receiving angle, the number of times the intensity ratio was 1.5 or greater, and the evaluation results.

[0070] (wavelength difference) The spectral intensity was measured at seven receiving angles: -70°, -60°, -50°, -40°, -30°, -20°, and 0°. For each receiving angle, the maximum wavelength (unit: nm) at which the spectral intensity reached its maximum was identified, and the wavelength difference between the largest and smallest of the seven maximum wavelengths was calculated. A wavelength difference of 100 nm or more was judged as "OK," while a wavelength difference of less than 100 nm was judged as "NG." The spectral intensity was measured using a gonio-Spectrophotometer GSP-4 manufactured by Murakami Color Research Laboratory Co., Ltd. The light source used for the measurement was D65, with a tilt angle of 25° and an incident angle of 10°. The spectral intensity was measured from 390 nm to 730 nm at 10 nm intervals. The spectra obtained by measuring the spectral intensity on the surfaces of the aluminum members according to Example 1, Comparative Example 1, and Reference Examples 1 and 2 using the gonio-spectrophotometric colorimetric system are shown in Figures 7 to 10. Table 5 also shows the maximum wavelength, wavelength difference, and evaluation results for each light-receiving angle.

[0071] (Color development) The appearance of the aluminum member was evaluated visually. If the appearance of the aluminum member was rainbow-colored, it was judged as "OK," and if the appearance of the aluminum member was not rainbow-colored, it was judged as "NG."

[0072] [Table 1]

[0073] [Table 2]

[0074] [Table 3]

[0075] [Table 4]

[0076] [Table 5]

[0077] Conventionally, in aluminum members made of high-purity aluminum, strong iridescent coloring was confirmed even when soft-start anodizing was performed using etidronic acid. As shown in Table 3, in line with conventional knowledge, iridescent coloring was also confirmed in the aluminum members according to Reference Examples 1 and 2. Furthermore, in the aluminum member according to Reference Example 3, citric acid was used as the electrolyte, but iridescent coloring was confirmed as in Reference Examples 1 and 2. In the aluminum members according to Reference Examples 1 to 3, the average diameter of the hexagonal recesses was 380 nm to 1200 nm, and the proportion of the total area of ​​the hexagonal recesses was 47% or more.

[0078] However, as shown in Tables 1 and 2, in the aluminum members according to Comparative Examples 1 and 2, in which the Cu addition amount was 30 ppm or more, no strong iridescent coloring was observed even when the aluminum members were fabricated using etidronic acid with a soft start as in Reference Examples 1 and 2. Similarly, in the aluminum member according to Comparative Example 3, no strong iridescent coloring was observed even when the aluminum members were fabricated using citric acid with a soft start as in Reference Example 3. In the aluminum members according to Comparative Examples 1 to 3, the average diameter of the hexagonal recesses was 380 nm to 1200 nm, but the proportion of the total area of ​​the hexagonal recesses was less than 47%.

[0079] On the other hand, as shown in Table 1, for the aluminum member according to Example 1 having a Cu addition amount of 30 ppm or more, hard-start anodization was performed using etidronic acid. As a result, strong iridescent coloring was confirmed for the aluminum member according to Example 1. For the aluminum member according to Example 1, the average diameter of the hexagonal recesses was 380 nm to 1200 nm, and the ratio of the total area of ​​the hexagonal recesses was 47% or more.

[0080] Furthermore, as shown in Table 2, sulfuric acid was used as the anodizing electrolyte for the aluminum member according to Comparative Example 4, in which the Cu content was 30 ppm or more. Oxalic acid was used as the anodizing electrolyte for the aluminum member according to Comparative Example 5, in which the Cu content was 30 ppm or more. However, strong iridescent coloring was not observed for the aluminum members according to Comparative Examples 4 and 5. For the aluminum members according to Comparative Examples 4 and 5, the ratio of the total area of ​​the hexagonal recesses was 47% or more, but the average diameter of the hexagonal recesses was less than 380 nm. For the aluminum members according to Comparative Examples 4 and 5, the electrolysis voltage could not be increased, and therefore the pressure rise rate could not be increased either. This is thought to be why the ratio of the total area of ​​the hexagonal recesses 11 did not reach 47% or more, and the average diameter of the hexagonal recesses did not reach 380 nm or more.

[0081] 7 to 10, the aluminum members of Example 1 and Reference Examples 1 to 3, in which strong rainbow coloring was confirmed, had three or more light-receiving angles at which the intensity ratio was 1.5 or more. Furthermore, the aluminum members of Example 1 and Reference Examples 1 to 3 had wavelength differences of 100 nm or more.

[0082] These results show that strong rainbow coloring can be confirmed in aluminum members in which the average diameter of the hexagonal recesses is 380 nm to 1200 nm and the ratio of the total area of ​​the hexagonal recesses is 47% or more.

[0083] Next, for reference, aluminum members according to Reference Examples 4 to 12 were produced under the conditions shown in Tables 6 and 7, and the area ratios and average diameters of the recesses were measured in the same manner as above. The results are shown in Tables 6 and 7. The aluminum plates used as the substrates had the following compositions: 3000 series aluminum alloy (3000 series) Contains 1.5 mass% manganese, 0.7 mass% iron, 0.6 mass% silicon, and 0.2 mass% copper, with the remainder being aluminum and inevitable impurities. 5000 series aluminum alloy (5000 series (1)) Contains 2.7% by mass of magnesium, 0.07% by mass of iron, 0.04% by mass of silicon, and 0.1% by mass of copper, with the remainder being aluminum and inevitable impurities. 5000 series aluminum alloy (5000 series (2)) Contains 0.4% by mass of magnesium, 0.05% by mass of iron, 0.05% by mass of silicon, and 0.15% by mass of copper, with the remainder being aluminum and inevitable impurities. 5000 series aluminum alloy (5000 series (3)) Contains 1.1% by mass of magnesium, 0.7% by mass of iron, 0.3% by mass of silicon, and 0.20% by mass of copper, with the remainder being aluminum and inevitable impurities. 5000 series aluminum alloy (5000 series (4)) Contains 4.9% by mass of magnesium, 0.4% by mass of iron, 0.4% by mass of silicon, 1% by mass of manganese, and 0.1% by mass of copper, with the remainder being aluminum and inevitable impurities. 6000 series aluminum alloy (6000 series) Contains 0.69% by mass of magnesium, 0.14% by mass of iron, 0.43% by mass of silicon, 0.01% by mass of copper and 0.02% by mass of manganese, with the remainder being aluminum and inevitable impurities. 8000 series aluminum alloy (8000 series) Contains less than 0.01% by mass of magnesium, 1.0% by mass of iron, 0.08% by mass of silicon, and 0.01% by mass of copper, with the remainder being aluminum and unavoidable impurities.

[0084] [Table 6]

[0085] [Table 7]

[0086] As shown in Tables 6 and 7, the aluminum members according to Reference Examples 4 to 8 and Reference Examples 10 to 12 were anodized using etidronic acid with a hard start. As a result, similar to the aluminum member of Example 1, the aluminum members according to Reference Examples 4 to 8 and Reference Examples 10 to 12 also exhibited strong iridescent color development. Similarly, as shown in Table 7, the aluminum member according to Reference Example 9 was anodized using citric acid with a hard start. As a result, the aluminum member according to Reference Example 9 also exhibited strong iridescent color development. In the aluminum members according to Reference Examples 4 to 12, the average diameter of the hexagonal recesses was 380 nm to 1200 nm, and the proportion of the total area of ​​the hexagonal recesses was 47% or more. These results show that strong iridescent color development can be observed when the average diameter of the hexagonal recesses was 380 nm to 1200 nm and the proportion of the total area of ​​the hexagonal recesses was 47% or more. It is also found that such aluminum members can be manufactured by hard starting, in which the voltage is increased at a rate of 50 V / second or more.

[0087] Although the present embodiment has been described above using examples and comparative examples, the present embodiment is not limited to these examples and comparative examples, and various modifications are possible within the scope of the gist of the present embodiment. [Explanation of symbols]

[0088] 1. Aluminum components 10 Base material 11 Recess 20 Anodized film

Claims

1. A substrate made of a 7000 series aluminum alloy, a plurality of recesses arranged without gaps on the surface of the substrate; the plurality of recesses includes a plurality of hexagonal recesses; the average diameter of the plurality of hexagonal recesses is 380 nm to 1200 nm; An aluminum member, wherein the ratio of the total area of ​​the plurality of hexagonal recesses per unit area on the surface of the base material is 47% or more.

2. The spectral intensity in the wavelength range of 390 nm to 730 nm is measured for acceptance angles of -70 °, -60 °, -50 °, -40 °, -30 °, -20 °, and 0 °, and the acceptance angles at which the intensity ratio of the maximum intensity to the minimum intensity at each of the acceptance angles is 1.5 or more are 3 to 7. The aluminum member according to claim 1.

3. The aluminum member according to claim 1 or 2, wherein the surface of the aluminum member is provided with at least one of a porous anodized film, a barrier anodized film, and a coating film containing an organic material, an inorganic material, or a composite material thereof.

4. anodizing the substrate made of the aluminum alloy in an electrolytic solution to form an anodized film on the surface of the substrate; removing the anodic oxide coating from the surface of the substrate; Including, The anodization is performed by increasing the voltage from 0 V to the electrolysis voltage at a voltage increase rate of 50 V / second or more, The method for producing an aluminum member according to claim 1 or 2, wherein the electrolysis voltage is 120 V or more and 500 V or less.

5. The method for manufacturing an aluminum member according to claim 4 , wherein the electrolytic solution contains at least one of etidronic acid and citric acid.

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