Aluminum Anodizing by AACOA, Inc.

Aluminum Anodizing

What is Anodizing?
It is an electrochemical oxidation of the aluminum surface to produce a stable film of aluminum oxide (Al2O3).
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Aluminum is rusted - artificially and uniformly Electricity and Chemicals required - electrical current passes through aluminum immersed in an acid solution
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Anodic Coating Properties

l Corrosion Resistance l Thermal Resistance

l Electrical Resistance l Porous

Common Process Steps

Aluminum Anodizing

Racking
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Provides a secure connection for transportation of the parts through the various chemical solutions Provides a secure connection for the flow of electricity through each individual part Allows for uniformity and consistency of current flow from part to part
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Clean, Etch, and Desmut

removal of most shop residues and fabrication oils no removal of adhesives, greases, or buffing compounds roughens the surface to provide a matte finish limited success at obscuring scratches, die lines, and bearing marks removal of aluminum 0-2.5 mil (0-65 microns) per side removes etch smut resulting from alloying constituents

Etching - heated sodium hydroxide (0-20 min)

Desmutting - ambient acid bath (1-5 min)

Aluminum Anodizing

Anodizing
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Immersion in chilled 10% (v/v) sulfuric acid bath DC current applied at densities of 8-20 amps/ft2
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Time varies based on coating thickness (10-60 minutes)

Barrier layer formed first to a 0.0005 mil thickness Coating builds to a 1.0 mil (25.4 mm) max. thickness Pores develop as the acid solution dissolves the coating
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250 - 500 billion pores per square inch

Part dimensions increase as the coating is 40% penetration and 60% build-up from the pre-anodized surface
Aluminum Anodizing

Cross Sectional View of a Dyed and Sealed Anodic Film

Hydrated anodic coating

Non-hydrated anodic coating Aluminum substrate Aluminum Anodizing

Types of Anodic Finish

Clear Hardcoat Absorptive dye

- Uptake of organic or inorganic molecules - Tin Deposition - Cobalt Deposition - Integral Color - Overdye
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Electrolytic Two-step Other

Clear Anodic Finish

Translucent film allows the aluminum substrate surface to be visible Coating thickness varies based upon specification
Alum. Assoc. Specification A21 A211 A212 A31 A41 Coating Thickness <0.1 mil or <3 microns 0.1 mil or 3 microns 0.2 mil or 5 microns 0.4 mil or 10 microns 0.7 mil or 18 microns
Aluminum Anodizing

ALCOA Specification Flash 201 202 204 215

Hardcoat Anodic Finish

Low temperature anodizing Coating (aluminum oxide) density greatly increased over standard anodizing High wear or abrasive applications

1) Aluminum substrate 2) Anodic Coating

Dyed Anodic Finish

Absorption of either organic or inorganic molecules into the pores of the coating (2-30 min) Limitless range of colors Typically less fade resistance than other colored anodic finishes

1) Aluminum substrate 2) Anodic Coating 3) Organic/Inorganic Dyestuffs

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Electrolytic (2-Step) Color

Step 1: Clear Anodize Step 2: Electrolytic Color - AC plating of metal in the base of the coating pores - Bronze colors ranging from Champagne to Black (2-25 min)

1) Aluminum substrate 2) Anodic Coating 3) Metal Deposit - either Tin or Cobalt

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Sealing
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Unsealed - Excellent base for paint and adhesives Hydrothermal Seal - 200-205 F (15-60 min)
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Temperature drives coating hydration causing coating expansion to squeeze shut the pores at the surface Deposition of metal salts in pores and some sealing by hydration Creation of a super molecule at the surface consisting of coating, metal salts, and fluoride Prone to causing green tints or a fuzzy surface

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Mid-Temperature Seal with Metal Salts - 180 F (15 min)

Room Temperature Seal - 90 F (15 min)

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Unracking and Packing

Unracking - First Inspection Point

Appearance Coating Thickness Seal Quality Type Size Materials

Packing - Second Inspection Point and Packaging

Laboratory Testing
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Coating Thickness - ASTM B244 - Eddy Current Coating Weight - ASTM B137 - Acid Dissolution Seal Quality - ASTM B136 - Modified Dye Stain - ASTM B680 - Acid Dissolution Abrasion Resistance - FED-STD-141 Method 6192.1 Gloss - ASTM D523 Corrosion Resistance - ASTM B117 - Salt Spray - ASTM B368 - CASS
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Advantages of Anodizing
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Highly durable Inexpensive to produce and maintain Wont chip, flake, peel or chalk Maintains metallic appearance of aluminum Environmentally friendly
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No VOCs No heavy metals Byproducts aid municipal wastewater treatment facilities to separate solids and neutralize pH
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Maintenance
Anodizing: The Renewable Finish
l Accumulated dirt and stains can be

removed with a mild detergent applied with an abrasive cleaning technique l AAMA 609.1 Voluntary Guide for Cleaning and Maintenance of Architectural Anodized Aluminum
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Metallurgical Factors
l Alloy and temper selections l Mixed alloys - various products
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Extrusion, sheet, forming, casting Hot spots, corrosion, die lines, bearing marks
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l Extrusion defects
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Specifying Anodizing
l Aluminum Association Designation

System for Aluminum Finishes

Example: AAM12C22A31 where AA = Aluminum Association where M = Mechanical finish where C = Chemical pretreatment where A = Anodic coating process
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AACOA, Inc.
www.aacoa.com
Anodizing Facility 2551 C.R. 10 W. Elkhart, IN 46514 Phone: 574.262.4685 Fax: 574.262.3439 Extrusion Facility 2005 Mayflower Road Niles, MI 49120 Phone: 269.697.6063 Fax: 269.697.6061
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Aluminum Anodizing