July 2011 Archives

#089 Anodic Oxidation Process

| No Comments | No TrackBacks

(1) Basic process of Anodic Oxidation

Basic process of Anodic Oxidation is as follows.

Preliminary processes -> Pretreatments -> Anodic Oxidation process -> Post treatments

1. Preliminary process
A processes that effect the final finish of the coating such as buffing, brushed finishing, satin finish, and pattern marking that are generally performed outside of the actual anodizing process.

2. Preliminary treatment
These are: degreasing, etching, and desmut, etc that are cleaning and dissolving of the base surfaces. Inappropriate pretreatment causes stains and uneven finishes.

3. Anodic Oxidation process
This is a process to create the anodized coating. In order to obtain satisfactory coating quality, appropriate electrolyte bath, power supply waveform, bath temp., agitation, and process time are selected.

4. Post treatments
After the electrolytic process (anodic oxidation) the surface pore sealing is always performed. Before the surface is sealed, dying, secondary electrolytic coloring, and electrostatic coating are applied as need.

(2) Anodize process steps for various applications

The following are anodizing steps based on various applications. (Water cleaning omitted)

Construction Material (sash, spandrel, partition, door, fence, etc)

Construction Material (sash, spandrel, partition, door, fence, etc)

Industrial Products (Home appliance parts, heat exchangers, machine parts, etc.)

Industrial Products (Home appliance parts, heat exchangers, machine parts, etc.)

Cooking utensils (pots, kettles, warmers, etc.)

Cooking utensils (pots, kettles, warmers, etc.)

Ornamental products (automotive decoration parts, general decorative items, mirrors, name plates, camera parts, etc.)

Ornamental products (automotive decoration parts, general decorative items, mirrors, name plates, camera parts, etc.)

#088 Natural Colorization of Anodizing

| No Comments | No TrackBacks

The color of anodize coatings vary depending on the electrolytic process conditions such as aluminum alloy type, electrolyte bath, and power supply waveform. The [Table 1] and [Table 2] show electrolytic colorization under a DC power supply, and these colors will vary further by the coating thickness. Thicker coatings will have darker colors.

[Table 1] Natural Colorization of Anodize Coatings (Rolled material)
Alloy Group Representative
Color Tone of Anodize Coating
Hydrochloric Acid Bath Oxalic Acid Bath
Pure AL
1050, 1100 Silver White Color Gold - Yellow Tan
AL - Cu
2017, 2024 Gray White Light tan - Gray Red
AL - Mn
3003, 3004 Silver White -
Light Yellow
Yellow Tan
AL - Si
4043 Gray - Gray Black Gray Yellow -
Gray Yellow Black
AL - Mg
5005, 5052 Silver White -
Light Yellow
AL - Mg - Si
6061, 6063 Silver White -
Light Yellow
AL - Zn - Mg
7072 Silver White Gold
[Table 2] Natural Colorization of Anodize Coatings (Cast / Die-cast)
Alloy Type Contained
Color Tone of Anodize Coating
Acid Bath
Oxalic Acid
Acid Bath
Cast AC1A, 1B, 5A High Cu with
low Si
Light Red Light Red Tan Red Gray
AC2A, 2B, 3A4A, 4B, 4C, 4D, 8A, 8B, 8C With Si 5% or more Gray ->
Dark Gray
Gray ->
Dark Gray
Gray ->
Dark Gray
AC7A High Mg with
low Si
White Silver Tan Gray White
Die - cast ADC1, 3, 10, 12, 14 High Si
Gray ->
Black Tan Gray Black
ADC5, 6 High Mg with
low Si
Clear ->
White Silver
Gold Gray White

Therefore, the following must be considered when designing products with anodizing.

1. When selecting an aluminum alloy material, confirm that a desired color can be obtained by anodizing process.

2. When useable aluminum alloy is limited due to manufacturing method and strength for usage, and such alloy has its distinctive anodized color, use dying or electrolytic coloring to obtain the desired color.

3. When dark colorization is unavoidable due to specific condition such as applying a hard anodizing on some specific alloys, have the clients understand that the colors cannot be changed in order to preserve the wear resistant property of the coating.

#087 Structure of Anodizing Layer

| No Comments | No TrackBacks

Fig.1 shows a cross section schematic illustration of an anodizing layer.


(1) Barrier Layer

An electro-conductive coating film that forms during the early stage of the electrolytic process. This layer supports the growth of a porous layer that forms on the top. This is where a porous film is formed by a reaction of electrolytically dissolved aluminum and oxygen at the bottom of the barrier layer. As the porous layer film grows, the bottom portion of the barrier layer migrates lower while the thickness remaining the same. The thickness is approximately 20nm.

(2) Porous Layer

The anodizing layer is an aggregation of this porous layer. It is a collection of hexagonal layer cells with a centrally located micropore, viewed from the top. The diameter of the cells is 100~300nm and the diameter of the micropores is 10~20nm, depending on the condition of the electrolytic process.
Dye Colored Anodizing is accomplished by applying the coloring dye at the top portion of the micropores, and Electrolytically Colored Anodizing is accomplished by depositing metal or metal oxides at the bottom portion of the micropores.


#086 What is Anodizing (Anodic Oxidization Process)?

| No Comments | No TrackBacks

Anodizing is also called Alumite processing for the name was a registered trade name for the process by Riken Chemical Labs a long time ago. Anodizing process and layer properties will be discussed below.

(1) Process

Refer to [Fig.1] below. The process uses the subject aluminum object as the anode (+ pole) and a carbon electrode as the opposing pole, and performs an electrolysis (applies a DC current) submerged in electrolyte baths. The surface aluminum of the subject dissolves and binds with oxygen to create a aluminum oxide surface layer. This layer is called anodic oxide layer (anodized layer).

[Fig.1] Anodize Process Diagram

(2) Layer Structure

When a acid solution is electrolysis processed, the anode normally emits oxygen but not in a case of aluminum anodes. The oxygen from the aluminum anode immediately binds before gasifying with dissolved surface layer metal and forms an aluminum oxide. The layer forming process is shown in [Fig.2] below.

A barrier layer forms during the initial phase of the electrolysis advancing to a formation of porous layer. As the process progresses, this porous layer grows to a certain thickness. As can be seen on the diagram, an anodized layer is made up of a electrically conductive but non-growing barrier layer, and isolating but growing porous layer.

[Fig.2] Layer Formation Model Diagram

#085 Aluminum Alloy Types and Characteristics

| No Comments | No TrackBacks

Aluminum alloy materials can be classified into wrought alloys such as plates, bars, rods, and wire, and cast/die-cast alloys for sand/mold casting. They all have various characteristics and are designated by four digit JIS numbers*. The alloys are assigned 1000 class numbers and the lower two digits denote the associated information. For example, 99.7% aluminum is A1070 and AL-Mg alloy is A5052.

(1) Wrought Material

[Table 1] Wrought Aluminum Alloys and Characteristics
AlloyCharacteristicsPurposeAlloy Number*
(Pure aluminum)
Excellent corrosion resistance, machinability, electrical/thermal conductivity. Good surface treatability.Various containers, electrical appliances, reflector plates1070
(AL-Cu Alloys)
Duralmin alloys, high strength, cuts well. Corrosion resistance and surface treatability is inferior.Aircrafts, transfer equipment, machine parts2017
(AL-Mn Alloys)
High strength with corrosion resistance. Press forms well, surface treats wellGeneral objects, cans, construction material3003
(AL-Si Alloys)
Low melting points. Naturally anodize coloring alloyBrazing/welding fillers, construction material4043
(AL-Mg Alloys)
Wide alloy variety based on Mg content variations. High strength/corrosion resistance. Surface treats well.Construction, structural, ship vessels, can lids, optical5005
(AL-Mg-Si Alloys)
Good corrosion resistance, increase in strength by heat treating. Extrudes and surface treats well.door framing, structural6061
(AL-Zn-Mg Alloys)
Highest strength aluminum alloy. Good weldability.Aircraft, sporting equipment, railway vehicles, welded structural material7075

(2) Cast Aluminum Alloys

[Table 2] Types of Cast Aluminum Alloys
AlloysCharacteristicsRepresentative Alloys*
AL-Si AlloysGood castabilityAC4A、AC4C、AC9A
AL-Mg AlloysGood corrosion resistanceAC7A、AC7B
AL-Cu AlloysIncreases in strengths by heat treatingAC1A、AC2A、AC5A

(3) Die-casting Aluminum Alloys

[Table 3] Die-casting Aluminum Alloys
AlloysCharacteristicsRepresentative Alloys*
AL-Si AlloysGood castabilityADC1、ADC7
AL-Mg AlloysGood corrosion resistanceADC5、ADC6
AL-Si-Cu AlloysHigh cast strengthADC10、ADC12

月別 Archives


Powered by Movable Type 6.0.3

About this Archive

This page is an archive of entries from July 2011 listed from newest to oldest.

June 2011 is the previous archive.

August 2011 is the next archive.

Find recent content on the main index or look in the archives to find all content.