Aluminum alloy material having an anodized coating and method for manufacturing the same

Abstract

To provide an aluminum alloy material having excellent corrosion resistance and reduced whitening, and a method for producing the same.SOLUTION: An aluminum alloy material includes an anodized film having undergone a hole-sealing treatment, in which a total length of microcracks with a width of 5 nm or more observed on a surface of the anodized film is 0.6 micrometers or more and 3.3 micrometers or less per unit area of 1 square micrometer on a surface of the alloy material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aluminum alloy material having an anodic oxide film and a method for producing the same.

Background Art

[0002] Aluminum alloys are widely used around us. However, although a dense and stable natural oxide film is formed in the air, its film thickness is very thin, about 2 nm, and it is easily corroded depending on the use environment. Therefore, in order to improve the corrosion resistance, an artificial oxidation treatment (anodic oxidation treatment) is performed to form an oxide film.

[0003] Numerous pores are formed in the anodic oxide film on the surface of the material after anodic oxidation treatment. Since these pores are chemically active and are in a state where they easily react with oxygen and other chemical substances, it is common to perform a sealing treatment to prevent those reactions (improve the corrosion resistance). As this sealing treatment method, boiling water sealing, pressurized steam sealing, normal temperature nickel sealing, high temperature nickel sealing, etc. are known.

[0004] In the surface treatment method of anodic oxidizing an aluminum alloy and further performing a sealing treatment, various reviews of the sealing treatment have been carried out in order to improve the corrosion resistance.

[0005] In Japanese Patent Laid-Open No. 50-117648 (Patent Document 1), an invention regarding normal temperature nickel sealing that contains a polar solvent and a metal fluoride to improve the corrosion resistance was announced. In Japanese Patent Laid-Open No. 56-062991 (Patent Document 2), after forming an anodic oxide film, as a first sealing treatment, it is immersed in an aqueous solution at 5 to 80 °C containing one or more of the commonly used sealing agents such as metal salts, ammonium derivatives, amine compounds, alkali hydroxides or boron compounds in the range of 0.1 g / L to the saturated concentration, and then, as a second sealing treatment, it is immersed in water heated to 60 to 100 °C to provide a two-step sealing treatment method for improving the corrosion resistance.

[0006] Furthermore, in domestic standards concerning anodic oxide coatings of aluminum alloys, JIS H8601-1968 specifies hydration sealing as the sealing method, and JIS H9500-1971 and JIS H9501-1971 specify the processing conditions for pressurized steam sealing or boiling water sealing, and in the case of boiling water sealing, the addition of sealing aids is permitted.

[0007] The sealing treatment involves forming hydrates of aluminum oxides such as boehmite (Al2O3·H2O) or bayerite (Al2O3·3H2O) or nickel hydroxide, and sealing the porous structure through volume expansion. Non-patent document 1 reports that pressurized steam sealing treatment exhibits approximately 1.5 times the corrosion resistance of boiling water sealing treatment. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 117648 / 1983 [Patent Document 2] Japanese Patent Application Publication No. 56-062991 [Patent Document 3] Patent No. 6667191 [Non-patent literature]

[0009] [Non-Patent Document 1] Takeshi Tsujita et al., Proceedings of the 45th Joint Conference on Vacuum, Vol. 48, No. 3, pp. 217-219 (2005). [Non-Patent Document 2] Koda, Mitsuru et al., Metal Surface Technology, Vol. 33, No. 5, pp. 242-248 (1982) [Non-Patent Document 3] Sachiko Ono et al., Surface Technology, Vol. 66, No. 8, pp. 364-371 (2015) [Overview of the project] [Problems that the invention aims to solve]

[0010] Figure 1 shows the results of a simple acid resistance test conducted by the inventors on aluminum alloy samples sealed using various sealing methods. Specifically, the test involved immersing the samples in 10 N hydrochloric acid at 35°C and measuring the time until hydrogen was generated. As is clear from Figure 1, the pressurized steam sealing method is currently the most reliable single sealing method, but even then, hydrogen is generated in approximately 500 minutes.

[0011] This indicates that, as reported in Non-Patent Document 2, the hydrates formed during sealing are more easily soluble in acidic solutions than the oxides formed by anodic oxidation, and even with the most highly effective pressurized steam sealing treatment, the corrosion resistance is insufficient for applications such as automotive exterior parts.

[0012] Japanese Patent Publication No. 6667191 (Patent Document 3) describes a first sealing treatment which involves immersion in a low-temperature nickel salt aqueous solution, followed by a second sealing treatment which involves pressurized steam sealing using water vapor, and then a third sealing treatment which involves forming a silicate film by the sol-gel method.

[0013] However, with conventionally manufactured aluminum alloy products, a problem exists in that white spots (whitening) appear, as shown in Figure 2, within a short period of time, such as one year, when used outdoors, and this problem has not yet been resolved.

[0014] Meanwhile, the inventors used a field emission scanning electron microscope (FE-SEM) to observe the area around the whitened region in detail and found that the whitening was caused by erosion of the very surface of the material, specifically the thin sealing layer formed above the pores of the anodic oxide film, which roughened the surface and caused light to scatter (Figure 3).

[0015] Furthermore, the inventors have observed through FE-SEM that the surface of conventional aluminum alloy products with an anodized coating has numerous microcracks with a width of 5 nm or more, and have also revealed that reducing these microcracks leads to improved corrosion resistance (suppression of whitening) of the material surface.

[0016] The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an aluminum alloy material in which the corrosion resistance of an anodic oxide film is improved by reviewing the pressurized steam sealing treatment conditions and a method for producing the same.

Means for Solving the Problems

[0017] The inventors repeatedly studied countermeasures against whitening (improvement of corrosion resistance) from both the surface morphology of the anodic oxide film and the corrosion resistance test, not only from the conventional corrosion resistance test. As a result, the optimum sealing treatment conditions were found, leading to the completion of the present invention.

[0018] That is, in the aluminum alloy material of the present invention, the first form is an aluminum alloy material having an anodic oxide film subjected to a sealing treatment, The total length of the microcracks having a width of 5 nm or more observed on the surface of the anodic oxide film is 0.6 micrometers or more and 3.3 micrometers or less per square micrometer of the unit area of the alloy material surface.

[0019] Another form of the aluminum alloy material uses an alloy of the A5000 series or A6000 series defined by JIS for the aluminum alloy material in the invention of the above form.

[0020] The method for producing the aluminum alloy material of the present invention is a pressurized steam sealing treatment performed after an anodic oxidation treatment of, 105°C or higher and 125°C or lower The process is carried out within the specified temperature range for a processing time of 60 to 120 minutes. .

[0021] Further, the conditions for the anodic oxidation treatment are a current density of 0.8 to 1.5 A / dm 2 .

Effects of the Invention

[0022] According to the present invention, in an aluminum alloy material having an anodic oxide film of an aluminum alloy, by reducing the length of the microcracks, the whitening phenomenon of the aluminum alloy material can be suppressed. [Brief explanation of the drawing]

[0023] [Figure 1] This diagram compares the corrosion resistance of various sealing methods based on a simplified acid resistance test. [Figure 2] This is a representative photograph showing the bleaching phenomenon. [Figure 3] These are FE-SEM images of the bleached surface and cross-section. [Figure 4] This is a photograph illustrating how to determine the length of a microcrack. [Figure 5] This diagram shows the relationship between gloss and surface roughness before and after alkali resistance testing. [Modes for carrying out the invention]

[0024] Below, an aluminum alloy material having an anodic oxide coating according to one embodiment of the present invention will be described in detail.

[0025] The aluminum alloy material of this embodiment is an aluminum alloy material having an anodic oxide film that has undergone sealing treatment, characterized in that the total length of the minute cracks with a width of 5 nm or more observed on the surface of the anodic oxide film is 0.6 micrometers or more and 3.3 micrometers or less per unit area of ​​1 square micrometer on the surface of the alloy material. Microcracks with a width of less than 5 nm are excluded because they are unlikely to cause whitening. For cracks with a width of 5 nm or more, whitening can be suppressed if the length per unit area of ​​1 square micrometer is 3.3 micrometers or less; therefore, 3.3 micrometers is set as the upper limit. Furthermore, since it is difficult to manufacture cracks with a length of less than 0.6 micrometers per unit area, 0.6 micrometers is set as the lower limit.

[0026] The type of alloy used in the aluminum alloy material of this embodiment is not limited to a specific type, but for example, alloys in the A5000 series or A6000 series as defined by JIS can be suitably used, and the material can be selected according to the application and other factors. The A5000 series defined by JIS includes materials containing Mg such as A5052, A5056, and A5083, while the A6000 series defined by JIS includes materials containing Mg and Si such as A6061 and A6063. Both are known as materials with excellent corrosion resistance and strength.

[0027] In this embodiment, an aluminum alloy material that has undergone anodizing treatment is used. Anodizing can be performed by conventional methods, and the conditions are not particularly limited in this embodiment. For example, a sulfuric acid bath (aqueous sulfuric acid solution) or an electrolytic sulfuric acid bath (aqueous sulfuric acid solution) can be used for anodizing, and the current density is not particularly limited, but is generally 0.8 to 1.5 A / dm 2 It is preferable that this be the case. In anodic oxidation, the process is carried out in such a way that the dissolution rate and oxidation rate of Al are balanced. The preferred range of current density is defined above from this perspective.

[0028] Aluminum alloy materials are subjected to a sealing treatment after anodizing. The sealing treatment is performed by at least a pressurized steam sealing method. The inventors have found that the length of the aforementioned microcracks can be shortened by lowering the temperature of the pressurized steam sealing treatment during the sealing process. The conditions for the pressurized steam sealing treatment are not particularly limited, but a treatment temperature of 105 to 125°C and a treatment time of 60 to 120 minutes are preferred, and a treatment temperature of 115°C and a treatment time of 75 minutes are more preferred. The pressure inside the apparatus is determined by the saturated water vapor pressure, and therefore the pressure differs depending on the treatment temperature.

[0029] Furthermore, the sealing process can be carried out in multiple stages, and as a pretreatment for the pressurized steam sealing process, room temperature nickel sealing, high-temperature nickel sealing, etc., can be appropriately selected. If sealing treatment other than pressurized steam sealing is to be performed, it can be done using known methods. In sealing treatment, the cracks formed are generally less than 20 nm in width. Therefore, when observing the distribution of cracks, it is acceptable to focus on microcracks less than 20 nm in width.

[0030] In the aluminum alloy material of the present invention, the total length of microcracks with a width of 5 nm or more on the alloy surface is suppressed to 0.6 micrometers or more and 3.3 micrometers or less per unit area of ​​1 square micrometer, exhibiting good corrosion resistance.

[0031] Furthermore, the aluminum alloy material of the present invention has a corrosion resistance rating of 170 or more cycles before whitening occurs in corrosion resistance tests, indicating excellent corrosion resistance. On the other hand, conventional aluminum alloy products have a corrosion resistance rating of 75 or fewer cycles before whitening occurs in corrosion resistance tests, meaning their corrosion resistance is insufficient. [Examples]

[0032] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited in any way by these descriptions.

[0033] The length of microcracks on the surface of the aluminum alloy materials obtained in each example and comparative example was measured, and corrosion resistance tests were performed using the following methods.

[0034] [Measurement of the length of micro-cracks on the surface] Using a field emission scanning electron microscope (Hitachi High-Technologies Corporation, S-4800), an image of the material surface at 100,000x magnification was acquired. The length of each microcrack with a width of 5 nm or more observed within the field of view was then determined by measuring the distance between two points, and the sum of these lengths, the "total length of microcracks per unit area," was defined as the microcrack length (Figure 4).

[0035] [Corrosion resistance test] As a corrosion resistance test simulating outdoor conditions, we diligently studied and developed our own test method, referencing the simplified acid resistance test shown in Figure 1. Specifically, the sample surface was heated to 65°C, one drop of 10 N hydrochloric acid was dropped onto the surface using a dropper (2 mm in diameter), and the process of natural drying (e.g., 5 to 10 minutes) and immediate drop-off after drying was repeated. The corrosion resistance was evaluated based on the number of drops until the surface turned white by visual inspection. In this corrosion resistance test, when we evaluated a product actually installed in an automobile, its surface turned white after 40 cycles. Next, when we evaluated multiple samples of the present invention, all of them lasted more than 170 cycles. This means that it can be evaluated as "not whitening (corrosion resistant)" more than four times longer than conventional products.

[0036] [Example 1] For JIS A6063 aluminum-magnesium-silicon alloy plates, anodizing treatment was performed using a sulfuric acid bath (sulfuric acid aqueous solution) under the following conditions, followed by room temperature nickel sealing treatment and pressurized steam sealing. The length of microcracks on the surface was then measured, and corrosion resistance tests were conducted. <Anodizing treatment in a sulfuric acid bath> • Processing tank volume: 3,300L Dimensions of JIS A6063 sheet: 2,000mm x 50mm x 20mm thickness • Cathode material: JIS A1050 (industrial grade pure aluminum) • Distance between JIS A6063 plate and cathode: 20 mm ·Current density: 1.5A / dm 2 ·Sulfuric acid concentration: 18% by mass ·Bath temperature: 20℃ Processing time: 25 minutes <Conditions for sealing nickel at room temperature> • Nickel concentration in sealing solution: 5g / L Processing temperature: 20°C Processing time: 20 minutes pH: 5.7 <Pressurized steam sealing conditions> • Pressure: 0.18 MPa Processing temperature: 115℃ Processing time: 75 minutes <Evaluation test results> Table 1 shows the total length of microcracks and the results of the corrosion resistance test.

[0037] [Example 2] For JIS A6063 aluminum-magnesium-silicon alloy plates, anodizing treatment was performed using a sulfuric acid bath (sulfuric acid aqueous solution) under the following conditions, followed by room temperature nickel sealing treatment and pressurized steam sealing. The length of microcracks on the surface was then measured, and corrosion resistance tests were conducted. <Anodizing treatment in a sulfuric acid bath> The processing conditions are as follows: • Processing tank volume: 25L Dimensions of JIS A6063 sheet: 150mm x 50mm x 20mm thickness • Cathode material: JIS A1050 (industrial grade pure aluminum) • Distance between JIS A6063 plate and cathode: 20 mm ·Current density: 0.8A / dm 2 ·Sulfuric acid concentration: 18% by mass ·Bath temperature: 20℃ Processing time: 30 minutes <Conditions for sealing nickel at room temperature> • Nickel concentration in sealing solution: 5g / L Processing temperature: 20°C Processing time: 20 minutes pH: 5.7 <Pressurized steam sealing conditions> • Pressure: 0.18 MPa Processing temperature: 115℃ Processing time: 75 minutes <Evaluation test results> Table 1 shows the total length of microcracks and the results of the corrosion resistance test.

[0038] For Examples 3 to 7, using the same treatment tank as in Example 2, samples were prepared with variations in alloy type, anodizing current density, and pressurized steam sealing conditions, as shown in Table 1. Surface microcrack length measurements and corrosion resistance tests were then performed.

[0039] [Comparative Example 1] For comparison, JIS A6063 aluminum-magnesium-silicon alloy plates were subjected to anodizing treatment using a sulfuric acid bath (sulfuric acid aqueous solution) under the following conditions, followed by room temperature nickel sealing and pressurized steam sealing. The length of microcracks on the surface was then measured, and corrosion resistance tests were conducted. <Anodizing treatment in a sulfuric acid bath> • Processing tank volume: 3,300L Dimensions of JIS A6063 sheet: 2,000mm x 50mm x 20mm thickness • Cathode material: JIS A1050 (industrial grade pure aluminum) • Distance between JIS A6063 plate and cathode: 20 mm ·Current density: 1.5A / dm 2 ·Sulfuric acid concentration: 18% by mass ·Bath temperature: 20℃ Processing time: 25 minutes <Conditions for sealing nickel at room temperature> • Nickel concentration in sealing solution: 5g / L Processing temperature: 20°C Processing time: 20 minutes pH: 5.7 <Pressurized steam sealing conditions> • Pressure: 0.45 MPa Processing temperature: 145℃ Processing time: 20 minutes <Evaluation test results> Table 1 shows the total length of microcracks and the results of the corrosion resistance test.

[0040] For [Comparative Example 2], samples were prepared using the same processing tank as in [Comparative Example 1], but with different pressurized steam sealing conditions. The length of microcracks on the surface was measured, and corrosion resistance tests were conducted.

[0041] [Table 1]

[0042] As is clear from Table 1, the aluminum alloy materials with anodized coatings prepared in Examples 1 to 7 showed suppressed cracking and higher corrosion resistance compared to the conventional product, Comparative Example 1. [Industrial applicability]

[0043] The aluminum alloy material of the present invention exhibits excellent corrosion resistance even in outdoor, exposed conditions, and can therefore be used in a variety of applications. For example, it can be suitably used as a material for automobile carrier rails and moldings.

Claims

1. An aluminum alloy material having an anodized coating that has undergone sealing treatment, characterized in that the total length of the microcracks with a width of 5 nm or more observed on the surface of the anodized coating is 0.6 micrometers or more and 3.3 micrometers or less per unit area of ​​1 square micrometer on the surface of the alloy material.

2. The aluminum alloy material according to claim 1, characterized in that the alloy type of the aforementioned aluminum alloy material is in the A5000 series or A6000 series as defined by JIS.

3. A method for manufacturing an aluminum alloy material according to claim 1 or 2, characterized in that the pressurized steam sealing treatment performed after anodizing is carried out within a processing temperature range of 105°C to 125°C for a processing time of 60 to 120 minutes.

4. The current density of the aforementioned anodizing treatment is 0.8 to 1.5 A / dm ２ The method for manufacturing an aluminum alloy material according to claim 3, characterized in that it is such.

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