2. 2
Aluminum Anodizing
● Aluminum is “rusted”
Aluminum is “rusted”
− artificially and uniformly
artificially and uniformly
● Electricity and Chemicals required
Electricity and Chemicals required
− electrical current passes through
electrical current passes through
aluminum immersed in an acid solution
aluminum immersed in an acid solution
What is Anodizing?
What is Anodizing?
It is an electrochemical oxidation of the
aluminum surface to produce a stable film
of aluminum oxide (Al2O3).
3. 3
Aluminum Anodizing
● Abrasion Resistance
Abrasion Resistance
− only diamond is harder
only diamond is harder
● Corrosion Resistance
Corrosion Resistance
− withstands salt spray and CASS testing
withstands salt spray and CASS testing
● Thermal Resistance
Thermal Resistance
− aluminum substrate will melt before the coating
aluminum substrate will melt before the coating
● Electrical Resistance
Electrical Resistance
− 800 V required to pass a current through 1 mil of coating
800 V required to pass a current through 1 mil of coating
● Porous
Porous
− allows for the coloring and sealing of the coating
allows for the coloring and sealing of the coating
Anodic Coating Properties
Anodic Coating Properties
4. 4
Aluminum Anodizing
Common Process Steps
Common Process Steps
1. Racking
2. Cleaning
3. Etching
4. Desmutting
5. Anodizing
6. Coloring
7. Sealing
8. Unracking
9. Packing
10. Lab Testing
5. 5
Aluminum Anodizing
Racking
Racking
● Provides a secure connection for transportation
Provides a secure connection for transportation
of the parts through the various chemical
of the parts through the various chemical
solutions
solutions
● Provides a secure connection for the flow of
Provides a secure connection for the flow of
electricity through each individual part
electricity through each individual part
● Allows for uniformity and consistency of current
Allows for uniformity and consistency of current
flow from part to part
flow from part to part
6. 6
Aluminum Anodizing
Clean, Etch, and Desmut
Clean, Etch, and Desmut
Cleaning - heated, nonetching alkaline cleaner (10 min)
Cleaning - heated, nonetching alkaline cleaner (10 min)
● removal of most shop residues and fabrication oils
removal of most shop residues and fabrication oils
● no removal of adhesives, greases, or buffing compounds
no removal of adhesives, greases, or buffing compounds
Etching - heated sodium hydroxide (0-20 min)
Etching - heated sodium hydroxide (0-20 min)
● roughens the surface to provide a matte finish
roughens the surface to provide a matte finish
● limited success at obscuring scratches, die lines, and bearing
limited success at obscuring scratches, die lines, and bearing
marks
marks
● removal of aluminum 0-2.5 mil (0-65 microns) per side
removal of aluminum 0-2.5 mil (0-65 microns) per side
Desmutting - ambient acid bath (1-5 min)
Desmutting - ambient acid bath (1-5 min)
● removes etch smut resulting from alloying constituents
removes etch smut resulting from alloying constituents
7. 7
Aluminum Anodizing
Anodizing
Anodizing
● Immersion in chilled 10% (v/v) sulfuric acid bath
Immersion in chilled 10% (v/v) sulfuric acid bath
● DC current applied at densities of 8-20 amps/ft
DC current applied at densities of 8-20 amps/ft2
2
− Time varies based on coating thickness (10-60 minutes)
Time varies based on coating thickness (10-60 minutes)
● Barrier layer formed first to a 0.0005 mil thickness
Barrier layer formed first to a 0.0005 mil thickness
● Coating builds to a 1.0 mil (25.4
Coating builds to a 1.0 mil (25.4 µ
µm) max. thickness
m) max. thickness
● Pores develop as the acid solution dissolves the coating
Pores develop as the acid solution dissolves the coating
− 250 - 500 billion pores per square inch
250 - 500 billion pores per square inch
● Part dimensions increase as the coating is 40%
Part dimensions increase as the coating is 40%
penetration and 60% build-up from the pre-anodized
penetration and 60% build-up from the pre-anodized
surface
surface
8. 8
Aluminum Anodizing
Cross Sectional View of a Dyed
Cross Sectional View of a Dyed
and Sealed Anodic Film
and Sealed Anodic Film
Aluminum
substrate
Non-hydrated
anodic coating
Hydrated anodic
coating
Ni(OH)2 precipitate,
absorbed dye, &
hydrated coating
9. 9
Aluminum Anodizing
● Clear
Clear
● Hardcoat
Hardcoat
● Absorptive dye
Absorptive dye
− Uptake of organic or inorganic molecules
Uptake of organic or inorganic molecules
● Electrolytic Two-step
Electrolytic Two-step
− Tin Deposition
Tin Deposition
− Cobalt Deposition
Cobalt Deposition
● Other
Other
− Integral Color
Integral Color
− Overdye
Overdye
Types of Anodic Finish
Types of Anodic Finish
10. 10
Aluminum Anodizing
Clear Anodic Finish
Clear Anodic Finish
● Translucent film allows the aluminum substrate
surface to be visible
● Coating thickness varies based upon specification
Alum. Assoc. ALCOA
Specification Coating Thickness Specification
A21 <0.1 mil or <3 microns Flash
A211 0.1 mil or 3 microns 201
A212 0.2 mil or 5 microns 202
A31 0.4 mil or 10 microns 204
A41 0.7 mil or 18 microns 215
11. 11
Aluminum Anodizing
Hardcoat Anodic Finish
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
12. 12
Aluminum Anodizing
Dyed Anodic Finish
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
13. 13
Aluminum Anodizing
Electrolytic (2-Step) Color
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
14. 14
Aluminum Anodizing
Sealing
Sealing
● Unsealed - Excellent base for paint and adhesives
Unsealed - Excellent base for paint and adhesives
● Hydrothermal Seal - 200-205 F (15-60 min)
Hydrothermal Seal - 200-205 F (15-60 min)
− Temperature drives coating hydration causing coating
Temperature drives coating hydration causing coating
expansion to squeeze shut the pores at the surface
expansion to squeeze shut the pores at the surface
● Mid-Temperature Seal with Metal Salts - 180 F (15 min)
Mid-Temperature Seal with Metal Salts - 180 F (15 min)
− Deposition of metal salts in pores and some sealing by
Deposition of metal salts in pores and some sealing by
hydration
hydration
● Room Temperature Seal - 90 F (15 min)
Room Temperature Seal - 90 F (15 min)
− Creation of a “super molecule” at the surface consisting of
Creation of a “super molecule” at the surface consisting of
coating, metal salts, and fluoride
coating, metal salts, and fluoride
− Prone to causing green tints or a fuzzy surface
Prone to causing green tints or a fuzzy surface
15. 15
Aluminum Anodizing
Unracking and Packing
Unracking and Packing
● Unracking - First Inspection Point
Unracking - First Inspection Point
− Appearance
Appearance
− Coating Thickness
Coating Thickness
− Seal Quality
Seal Quality
● Packing - Second Inspection Point and
Packing - Second Inspection Point and
Packaging
Packaging
− Type
Type
− Size
Size
− Materials
Materials
17. 17
Aluminum Anodizing
Advantages of Anodizing
Advantages of Anodizing
● Highly durable
Highly durable
● Inexpensive to produce and maintain
Inexpensive to produce and maintain
● Won’t chip, flake, peel or chalk
Won’t chip, flake, peel or chalk
● Maintains metallic appearance of aluminum
Maintains metallic appearance of aluminum
● Environmentally friendly
Environmentally friendly
− No VOC’s
No VOC’s
− No heavy metals
No heavy metals
− Byproducts aid municipal wastewater treatment
Byproducts aid municipal wastewater treatment
facilities to separate solids and neutralize pH
facilities to separate solids and neutralize pH
18. 18
Aluminum Anodizing
Maintenance
Maintenance
Anodizing: The Renewable Finish
Anodizing: The Renewable Finish
● Accumulated dirt and stains can be
Accumulated dirt and stains can be
removed with a mild detergent
removed with a mild detergent
applied with an abrasive cleaning
applied with an abrasive cleaning
technique
technique
● AAMA 609.1 Voluntary Guide for
AAMA 609.1 Voluntary Guide for
Cleaning and Maintenance of
Cleaning and Maintenance of
Architectural Anodized Aluminum
Architectural Anodized Aluminum
19. 19
Aluminum Anodizing
Metallurgical Factors
Metallurgical Factors
● Alloy and temper selections
Alloy and temper selections
● Mixed alloys - various products
Mixed alloys - various products
− Extrusion, sheet, forming, casting
Extrusion, sheet, forming, casting
● Extrusion defects
Extrusion defects
− Hot spots, corrosion, die lines,
Hot spots, corrosion, die lines,
bearing marks
bearing marks
20. 20
Aluminum Anodizing
Specifying Anodizing
Specifying Anodizing
● Aluminum Association Designation
Aluminum Association Designation
System for Aluminum Finishes
System for Aluminum Finishes
− Example: AAM12C22A31
Example: AAM12C22A31
where AA = Aluminum Association
where AA = Aluminum Association
where M = Mechanical finish
where M = Mechanical finish
where C = Chemical pretreatment
where C = Chemical pretreatment
where A = Anodic coating process
where A = Anodic coating process
21. 21
Aluminum Anodizing
AACOA, Inc.
AACOA, Inc.
Anodizing Facility
2551 C.R. 10 W.
Elkhart, IN 46514
Phone: 574.262.4685
Fax: 574.262.3439
www.aacoa.com
Extrusion Facility
2005 Mayflower Road
Niles, MI 49120
Phone: 269.697.6063
Fax: 269.697.6061
