Product Information (Chromic Acid Alumite)

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Chromic Acid Anodic Oxide Coating(Chromic Acid Alumite)
ANODIZE(Anodic Coatings for Aluminum and Aluminum Alloys)

Chromic acid alumite is a coating produced by anodizing of aluminum in an aqueous solution ofchromic anhydride. Chromic acid alumite provides excellent corrosion resistance particularly for highstrength aluminum alloys with a high copper content. As a crack-free coating having resistances
against heat, rapid temperature changes and cyclic fatigue, chromic acid alumite has been applied toaircraft structures and functional components. The chromic acid used for electrolysis solution proveseffective as a corrosion inhibitor. Even if remaining on a product, chromic acid is harmless to theproduct. Chromic acid alumite is therefore applicable to assembling components.

For pore-sealing treatment, we offer hot water, dichromate, and nickel acetate sealings. (Other typesof sealing besides the above-mentioned sealings are also available upon your request. Please contact
us for more information.)

Chromic acid alumite has been also
applied to the International Space
Station (ISS). (The picture shows
the airlock part of the ISS.)

図中語句
日本語英語皮膜Coating

A：バリアー層厚さ

A: Barrier layer thickness

500Å

500Å

B：孔壁厚さ 440Å

B: Pore wall thickness440Å

C：孔径 240Å

C: Pore size 240Å

Riken Alumite Industry Co., LTD.

Product Information (Chromic Acid Alumite)

2 / 4Features◎Appearance: The coating gives an opaque gray white or gray-colored appearance. (Depending on
the type of alloy, some alloys may develop a yellowish or yellow-greenish color, and other alloys may
develop no color.)◎ Adhesion property: The coating allows high adhesion of paint and adhesive agents, proving
effective when applied to surface preparation treatment for painting and adhesive coating. (Dependingon the paint or adhesive agent, the coating treated with relatively cold deionized water sealing or
without sealing may allow strong adhesion of paint and adhesive agents.)◎Fatigue strength: The coating hardly reduces fatigue strength of aluminum alloys.
◎Application to assembling components: Any residual electrolyte is harmless to the product.
◎Crack-free coating: Since the coating is soft and flexible, coating breakdown does not occur evenunder high-temperature and ultralow-temperature environments. The features prevent reduction incorrosion resistance due to cracking. (This does not guarantee any use under such extremely hightemperatures as affecting the base metal.)◎Precision level: Product size change after coating is negligible. As one of its features, the coating
provides hardly any size change for products regardless of whether dyed or undyed.
◎Pureness: The unsealed chromic acid anodic oxide coating is reported to have a pure γ-alumina
structure. Compared with other treatment methods, the coating treated with chromic acid is stable andcontains extremely small amount of residual electrolyte anions, causing hardly any anion elution.

Standard performance and quality assurance - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ◎ Meets the performance requirements of the U.S. military specification MIL-A-8625 Type I(Guaranteed by salt spray test (ASTM B117) for 336 hours using materials 2024-T3 and 7075T6/coating mass 200mg or greater/ft2 (2.15g or greater/m2))

Applicable standards - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - MIL-A-8625 Type I Classes 1 and 2 (the latest version: F Amendment 1)
SAE-AMS 2470 and other aeronautical standards

Sealing・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・

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Product Information (Chromic Acid Alumite)

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Hot water sealing and steam sealing are pore-sealing treatments utilizing hydration reactions of anodic
oxide coating. With the hydration reactions, microscopic pores of anodic oxide coating are sealed off,
while the coating becomes chemically inactivated. The sealing treatment improves corrosion
resistance and stain resistance of coating, which is also applied to dye fixing for dyed products. Innickel acetate sealing, orifices of microscopic pores are filled with deposits, thus preventing dye
bleeding and providing excellent corrosion resistance and surface smoothness. The MIL-A-8625
specifies that pores of non-dyed coating should be completely sealed off in 5% sodium dichromate,potassium dichromate, acetate, or other suitable solutions. The high-pressure steam sealing developedby the Institute of Physical and Chemical Research (RIKEN) allows the maximum-level hydration
sealing treatment and provides outstanding corrosion resistance. At the Riken Alumite Industry, weoffer nickel acetate sealing treatment, dichromate sealing treatment, deionized water (hot water)
sealing treatment, and pressurized steam sealing treatment.

Design Information◎Size change: Depending on the product and the coating thickness, the coating causes hardly any
product size change. (Note that in some cases, reduction in size may be observed during pretreatment.)◎Products with complex shapes and assembled products: Chromic acid alumite is produced by using
chromic acid which is a corrosion inhibitor as the electrolytic solution. Chromic acid alumite istherefore safely applicable to objects where electrolytic solution is highly likely to remain such as
products with complex shapes, components with deep blind holes, and products assembled by using
welding, riveting and other methods. To perfectly eliminate the residual chromic acid or prevent
discoloration caused by the residual chromic acid, post-processing, coating applied separately forindividual components, masking of any gaps and other methods would prove effective.
◎Electrical insulation: The anodic oxide coating has electrical insulation properties. For the sites
requiring electrical contacts, electrical contacts can be secured by removing the coating through postprocessing or leaving the conductive substrate uncoated with prior masking.
◎Precautions pertaining to chemical substances: The residual electrolyte Cr (VI) in the coating is
extremely small in quantity, complying with the regulations on chemical substances contained inproducts. (Not applicable to products subject to the regulations on substances prohibited from inprocess use.)◎Application of MIL-A-8625: Type I coating method is inapplicable to alloys with a Cu content of
5% or higher or an Si content of 7% or higher, or alloys with a total alloy content exceeding 7.5%. (InRiken Alumite Industry Co., LTD.

Product Information (Chromic Acid Alumite)4 / 4these alloys, anodic dissolution may occur.) For the above-mentioned alloys, Type IB coating method
using a low voltage chromic acid anodizing process is applicable. In these cases, please specify thatType IB coating method was applied instead of Type I in the drawing instruction.

Examples of alloys with a Cu content of 5% or higher: 2001, 2004, 2011, 2111, 2219, 2319, 2419,2519, 2021

Examples of alloys with an Si content of 7% or higher: 4004, 4104, 4032, 4343, 4045, 4147

Examples of alloys with an alloy content of 7.5% or higher: 7000 series, and castings and die castings
with some exceptions

Riken Alumite Industry Co., LTD.