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Anodizing Reference Guide

 Anodic Oxide Detail

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




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.

 

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

  • Class 2

 

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