1	Aluminum Anodizing by AACOA, Inc.
2	What is Anodizing? Aluminum is “rusted” artificially and uniformly Electricity and Chemicals required electrical current passes through aluminum immersed in an acid solution
3	Anodic Coating Properties Abrasion Resistance only diamond is harder Corrosion Resistance withstands salt spray and CASS testing Thermal Resistance aluminum substrate will melt before the coating Electrical Resistance 800 V required to pass a current through 1 mil of coating Porous allows for the coloring and sealing of the coating
4	Common Process Steps
5	Racking 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
6	Clean, Etch, and Desmut Cleaning - heated, nonetching alkaline cleaner (10 min) removal of most shop residues and fabrication oils no removal of adhesives, greases, or buffing compounds Etching - heated sodium hydroxide (0-20 min) 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 Desmutting - ambient acid bath (1-5 min) removes etch smut resulting from alloying constituents
7	Anodizing Immersion in chilled 10% (v/v) sulfuric acid bath DC current applied at densities of 8-20 amps/ft² 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 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
8	Cross Sectional View of a Dyed and Sealed Anodic Film
9	Types of Anodic Finish Clear Hardcoat Absorptive dye Uptake of organic or inorganic molecules Electrolytic Two-step Tin Deposition Cobalt Deposition Other Integral Color Overdye
10	Clear Anodic Finish
11	Hardcoat Anodic Finish
12	Dyed Anodic Finish
13	Electrolytic (2-Step) Color
14	Sealing Unsealed - Excellent base for paint and adhesives Hydrothermal Seal - 200-205 F (15-60 min) Temperature drives coating hydration causing coating expansion to squeeze shut the pores at the surface Mid-Temperature Seal with Metal Salts - 180 F (15 min) Deposition of metal salts in pores and some sealing by hydration Room Temperature Seal - 90 F (15 min) Creation of a “super molecule” at the surface consisting of coating, metal salts, and fluoride Prone to causing green tints or a fuzzy surface
15	Unracking and Packing Unracking - First Inspection Point Appearance Coating Thickness Seal Quality Packing - Second Inspection Point and Packaging Type Size Materials
16	Laboratory Testing 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
17	Advantages of Anodizing Highly durable Inexpensive to produce and maintain Won’t chip, flake, peel or chalk Maintains metallic appearance of aluminum Environmentally friendly No VOC’s No heavy metals Byproducts aid municipal wastewater treatment facilities to separate solids and neutralize pH
18	Maintenance Anodizing: The Renewable Finish Accumulated dirt and stains can be removed with a mild detergent applied with an abrasive cleaning technique AAMA 609.1 Voluntary Guide for Cleaning and Maintenance of Architectural Anodized Aluminum
19	Metallurgical Factors Alloy and temper selections Mixed alloys - various products Extrusion, sheet, forming, casting Extrusion defects Hot spots, corrosion, die lines, bearing marks
20	Specifying Anodizing 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
21	AACOA, Inc.