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Anodizing Reference Guide

Anodic Oxide Detail

Anodized_Coating

Mil Spec 8625 F and Test Methods for Type II Anodized Aluminum

Aluminum Alloy Reference for Anodizing

Type I Chromic Acid     Type II Sulfuric Acid   Type III Hard Coating

 

Mil Spec 8625 F

Type I A
Conventional coatings produced from chromic acid bath

Thickness
 0.5µ-7.6µ (microns)

Type I B
Low voltage chromic acid anodizing (20 volts)
Used for 7xxx series alloys

 0.5µ-7.6µ

Type II
Conventional coatings produced from sulfuric acid bath

1.8µ-25.4µ

Type III
Hard coat (Uniform anodic coatings)

12.7µ-115µ

  • Class 1
    • Non dyed

  • Class 2
    • Dyed

Test Methods For Type II Anodized Aluminum

Oxide Coating Thickness
ASTM B 244-97 (2002)
ASTM B 487-85 (2007)
Min Thickness
Class I  18 Microns (µ)
Class II  10 Microns
Oxide Coating Weight and Apparent Density
ASTM B 137-95 (2004)
  Min Weight Min Density
Class I 4.18 mg/cm2 2.32 g/cm3
Class II  2.40 mg/cm2 2.32 g/cm3

Adopted from AMAA 611

 
Corrosion Resistance
ASTM B 117-07
Min Hours Max Spots
Class I  3000  15
Class II 1000 15
Seal Quality
ASTM B 136-84 (2003)
ASTM B 680-80 (2004)
ISO 3210
Max Weight Loss
Class I  40 mg/dm2
Class II 40 mg/dm2
 
 

 

Aluminum Alloy Reference for Anodizing

Series (AA)* Alloying Constituants Metal Properties Coating Properties Uses A.Q.** Types Non-A.Q.** Types
1xxx None soft
conductive
clear
bright
cans
architectural
none 1100, 1175
Finishing advice: care should be taken when racking this soft material; good for bright coatings; susceptible to etch staining

2xxx Copper very strong
hard low
elongation
yellow
poor protection
aircraft
mechanical
none 2011, 2017 2219, 2224
Finishing advice: since copper content is >2%, these produce yellow, poor weather-resistant coatings; don't mix with other alloys on load

3xxx Manganese strong
small grains
grayish-brown cans
architectural
lighting
none 3003, 3004
Finishing advice: difficult to match sheet-to-sheet (varying degrees of gray/brown); used extensively for lighting

4xxx Silicon strong
fluid
dark gray architectural
welding wire
none 4043, 4343
Finishing advice: produce heavy black smut which is hard to remove; 4043 & 4543 used for architectural dark gray finishes in past years

5xxx Magnesium strong
ductile
fluid
clear
good protection
architectural
welding wire
lighting
5005, 5657 5052, 5252
Finishing advice: for 5005-keep silicon<0.1% and magnesium between 0.7% and 0.9%; watch for oxide streaks; 5005 used extensively for architectural

6xxx Magnesium & Silicon strong
ductile
clear
good protection
architectural
structural
6063, 6463 6061, 6101
Finishing advice: matte-iron>0.2%; bright-iron<0.1%; 6063 best match for 5005; 6463 best for chemical brightening

7xxx Zinc very strong clear
good protection
automotive none 7029, 7046 7075
Finishing advice: zinc over 5% will produce brown tinted coating; watch zinc in effluent stream; good for bright coatings

* AA - Aluminum Association
** A.Q. - Anodizing Quality - material suitable for architectural anodizing applications

 

TYPE I "Chromic Acid"

Color will vary from clear to dark gray depending on alloy. Copper bearing alloys only yield gray colors. Not as readily dyed as sulfuric anodize due to thinness of coating.

New salt spray requirement is 336 hours (5% solution per method 811 or FED-STD-No. 151).

Type I Chromic acid anodized coating. This process is used principally for the treatment of aircraft parts. An example is the Bengough-Stewart process where a 30 - 50 g/l chromic acid bath is maintained at 100° F and the voltage is gradually raised to 50V. Adjustments are made for high copper, zinc, and silicon alloys. Coating weights must be greater than 200 mg/ft2. Criteria for corrosion resistance, paint adhesion, and paint adhesion testing must be specified.
Type IB Low voltage (22)2V) chromic acid anodized coating. Typically associated with higher temperature, more concentrated chromic acid electrolytes. Coating weights must be greater than 200 mg/ft2. Criteria for corrosion resistance, paint adhesion, and paint adhesion testing must be specified.
Type IC Anodized coating produced in a non-chromic acid electrolyte. As with other Type I coating processes, the treatment is designed to impart corrosion resistance, paint adhesion, and/or fatigue resistance to an aluminum part. Coating weights must fall between 200 - 700 mg/ft2. Criteria for corrosion resistance, paint adhesion, and paint adhesion testing must be specified.

 

TYPE II "Sulfuric Acid"

MECHANICAL FINISHING A.A. COMMON DESCRIPTION EXAMPLES OF FINISHING METHODS
As Fabricated M-10 Unspecified
M-12 Nonspecular as fabricated No particular reflectiveness.
Buffed M-21 Smooth specular Polished first with coarser than 320 grit, followed by 320 grit, then buffed with Alum oxide.
M-22 Specular Buffed with Alum oxide compound.
Directional
Textured
M-31 Fine satin Sanded with 320-400 grit Alum oxide.
M-32 Medium satin Sanded with 180-220 grit Alum oxide.
M-33 Coarse satin Sanded with 80-100 grit Alum oxide.
M-35 Brushed Brushed with stainless steel wire brush.
CHEMICAL FINISHING        
Nonetched Cleaning C-11 Degreased Organic solvent treated.
C-12 Inhibited chemical cleaned Soap cleaner only.
Etched C-22 R-1 Medium matte Sodium hydroxide (caustic soda) 30-45 gr/li @ 60°-65° C for 5 min.
Brightened C-31 R-5 Highly specular Chemical bright dip solution of the proprietary phosphoric-nitric acid type, or electropolishing.
C-32 Diffuse bright Etched finish C-22 followed by Brightened finish C-31.
ANODIC COATING
General A-11   Prep for other applied coatings 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 10 min. Sometimes not sealed.
Decorative A-21 Clear coating 2.5u-7.5u 15% Sulfuric acid @ 20° C, 12 amps/sq ft.
 Less than 10u
A-211 200 Clear coating min. 2.5u 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 10 min.
A-212 201 Clear coating min. 5u 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 15 min.
A-213 202 Clear coating min. 7.5u mil 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 20 min.
A-23 Coating with impregnated color 15% Sulfuric acid @ 20° C, 12 amps/sq ft. , followed by dyeing with organic or inorganic colors.
A-24 Coating with Electrolytically 15% Sulfuric acid @ 20° C, 12 amps/sq ft. , deposited color followed by deposition of inorganic metallic salts.
Architectural
Class 2
A-31 204 Clear coating 15% Sulfuric acid @ 20° C, 12 amps/sq ft.
 10u-18u
A-33 Coating with impregnated color 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 30 min., followed by dyeing withorganic or inorganic colors.
A-34 Coating with electrolytically 15% Sulfuric acid @ 20° C, 12 amps/sq ft. deposited color for 30 min., followed by deposition of inorganic metallic salts.
Architectural
Class 1
A-41 215 Clear coating 15% Sulfuric acid @ 20° C, 12 amps/sq ft.
 18u and more
A-43 Coating with impregnated color 15% Sulfuric acid @ 20° C, 12 amps/sq ft. for 60 min., followed by dyeing with organic or inorganic colors.
  A-44   Coating with electrolytically 15% Sulfuric acid @ 20° C, 12 amps/sq ft. deposited color for 60 min., followed by deposition of inorganic metallic salts.

Data derived from "Designation System for Aluminum Finishes" (DAF45), published by The Aluminum Association.

 

TYPE III "Hard Coating"

Color will vary from light tan to black depending on alloy and thickness. Color overtones listed below may vary with the use of additives and/or the process. Can be dyed in darker colors depending on thickness. Coating PENETRATES base metal as much as builds up on the surface. The term THICKNESS includes both the buildup and penetration. Provides very hard ceramic type coating. Abrasion resistance will vary with alloy and thickness of coating. Good dielectric properties. Corrosion resistance is good, but recommend sealing in 5% dichromate solution where increased corrosion resistance is required. Where extreme abrasion resistance is required do not seal as some softening is encountered.

Type III Anodize Thickness Guide

Alloy Major Constituent (in) Maximum Thickness* Color Overtones***
1100 99.5% pure Alum. .003 Gray/Green**
2011 Copper Not recommended Not recommended
2014  Copper .001 Bronze
2017 Copper .001 Bronze
2024 Copper .0015 Bronze
3003  Manganese .002 Gray
4032 Silicon  .0012  Gray
5005 Magnesium .0035 Gray/Brown
5052 Magnesium .0035 Gray/Brown
5083 Magnesium .0035 Gray/Brown
6061 Mag/Silicon .003 Dark Gray
6063 Mag/Silicon .004  Green
6105  Mag/Silicon .0035 Gray/Green

Alloy Major Constituent (in) Maximum Thickness* Color Overtones***
6262 Mag/Silicon .0025 Gray
6463 Mag/Silicon .003 Gray
7075 Zinc  .004  Bronze
355 Silicon .0035  Gray
356 Silicon .0035  Gray
357 Silicon .0035  Gray
360 Silicon .0005 Gray
380 Silicon .0005 Gray
319 Silicon .0025 Light Gray
MIC-6 Silicon .0035   Dark Gray

50% Penetration and 50% Buildup per Surface
* Generally Accepted
** Over .0025" Thick
*** May vary