JP-7855194-B2 - Aluminum alloy material having an anodized coating and method for manufacturing the same

Inventors

• 永井 達夫
• 柳 洋介
• 山本 建次

Assignees

• ミクロエース株式会社
• 宮崎県

Dates

Publication Date

20260508

Application Date

20220324

Claims (4)

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 method for manufacturing an aluminum alloy material according to claim 3, characterized in that the current density of the anodizing treatment is 0.8 to 1.5 A/ dm² .

Description

This invention relates to an aluminum alloy material having an anodized coating and a method for producing the same. Aluminum alloys are widely used in our daily lives. However, while they form a dense and stable natural oxide film in air, this film is very thin (around 2 nm) and easily corrodes depending on the environment. Therefore, to improve corrosion resistance, an oxide film is formed through artificial oxidation treatment (anodic oxidation). After anodizing, countless pores are formed in the anodic oxide film on the material surface. These pores are chemically active and readily react with oxygen and other chemical substances. Therefore, sealing treatment is commonly performed to prevent these reactions (improving corrosion resistance). Known sealing methods include boiling water sealing, pressurized steam sealing, room temperature nickel sealing, and high-temperature nickel sealing. In surface treatment methods involving anodizing and sealing aluminum alloys, various revisions to the sealing process are being undertaken to improve corrosion resistance. Japanese Patent Publication No. 50-117648 (Patent Document 1) presents an invention relating to room-temperature nickel sealing that improves corrosion resistance by containing a polar solvent and a metal fluoride. Japanese Patent Publication No. 56-062991 (Patent Document 2) provides a two-stage sealing method to improve corrosion resistance by first forming an anodic oxide film, then immersing the film in an aqueous solution at 5-80°C containing one or more commonly used sealing agents such as metal salts, ammonium derivatives, amine compounds, alkali hydroxides, or boron compounds in a concentration range of 0.1 g/L to saturation, and then immersing the film in water heated to 60-100°C as a second sealing treatment. Furthermore, regarding domestic standards for anodized aluminum alloy coatings, JIS H8601-1968 specifies hydration sealing as the sealing method, while JIS H9500-1971 and JIS H9501-1971 specify the processing conditions for pressurized steam sealing or boiling water sealing, and permit the addition of sealing aids in the case of boiling water sealing. The sealing treatment involves forming hydrates of aluminum oxides such as boehmite ( Boehmite Al₂O₃ · H₂O ) or bayerite (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. Japanese Unexamined Patent Publication No. 117648/1983Japanese Unexamined Patent Publication No. 56-062991Patent No. 6667191 Takeshi Tsujita et al., Proceedings of the 45th Joint Conference on Vacuum, Vol. 48, No. 3, pp. 217-219 (2005).Koda, Mitsuru et al., Metal Surface Technology, Vol. 33, No. 5, pp. 242-248 (1982)Sachiko Ono et al., Surface Technology, Vol. 66, No. 8, pp. 364-371 (2015) This diagram compares the corrosion resistance of various sealing methods based on a simplified acid resistance test.This is a representative photograph showing the bleaching phenomenon.These are FE-SEM images of the bleached surface and cross-section.This is a photograph illustrating how to determine the length of a microcrack.This diagram shows the relationship between gloss and surface roughness before and after alkali resistance testing. Below, an aluminum alloy material having an anodic oxide coating according to one embodiment of the present invention will be described in detail. 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 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 less than 5 nm in width 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 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 square micrometer, 0.6 micrometers is set as the lower limit. 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. Furthermore, the A5000 series as defined by JIS includes materials containing Mg such as A5052, A5056, and A5083, while the A6000 series as 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. In this embodiment,