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Anodizing for Prototyping
and Production
Applicable Materials
Colors
Texture
Thickness
Black
Clear
Gold
Red
Blue
Anodizing is an electrolytic passivation process that grows the natural oxide layer on aluminum parts for protection from wear and corrosion, as well as for cosmetic effects. It is a conversion coating, similar to Alodine, meaning that the surface of the aluminum recedes dimensionally before the protective oxide layer is built up. After the process is complete, the oxide layer is integral to the aluminum substrate below, which means it won’t chip or flake.
The name anodizing comes from the fact that the treated part forms an anode (positive electrode) in an electrical circuit. During this process, the part to be anodized is hung on a conductive rack and submerged in an electrolytic solution, where a direct current of electricity is introduced. While the acidity of the solution dissolves the oxide layer of the part, the electric current releases oxygen at its surface, which builds up a protective layer of aluminum oxide. By balancing dissolve rate with build-up rate, the oxide layer forms with nanopores, allowing continued growth of the coating beyond what is naturally possible.
The final steps of the anodizing process involve sealing the nanopores. Otherwise, they are the perfect passageways for corrosion initiation! Just before sealing, however, they are sometimes filled with other corrosion inhibitors or colored dyes for cosmetic purposes. After the process is complete, the coating will be 0.0002-0.0012” in thickness, in accordance with the common engineering spec MIL-A-8625 Type II.
Applicable Materials
Colors
Texture
Thickness
Type III Anodizing (commonly specified with MIL-A-8625 Type III in North America) is the same general process as Type II and provides similar benefits of increased resistance to wear, corrosion, and other general environmental effects. However, this type is also known as hard or hardcoat anodizing, as the protective oxide layer must be thicker than >= 0.0005”, with coatings up to 0.004” sometimes applied.
While the thicker coating of Type III offers greater physical protection to a part, it comes with some tradeoffs:
Increased Cost
Growing the oxide layer to a consistent and specified thickness requires far more process control than with Type II. This, in addition to the lower temperatures and much higher voltages needed to run the process, causes the cost of this process to be higher than Type II Anodizing.
Impact on Tolerances
A second tradeoff of Type III is the increased care that must be taken to ensure parts stay within specified tolerance. Type II thickness is minimal enough that most dimensions should remain similar after the process, but even the thinnest Type III can impact a tight tolerance on a reamed bore, render a threaded hole non-functional, etc. Therefore, plugging holes and masking sensitive surfaces is almost always employed with this type of anodizing.
Applicable Materials
Colors
Texture
Can be applied with
*Type in Parenthesis
MIl-PRF-8625 (IA)
MIl-PRF-8625 (IB)
MIl-PRF-8625 (IC)
MIl-PRF-8625(II)
MIl-PRF-8625(III)
ASTM D1730
ASTM B580
SAE AMS2469J
AAMA 611-98 (A4)
AAMA 611-98(A3)
ASTM D3933-98
ASTM B580
Self-Serve Options on Platform
| Standard | Type | Composition | Application Examples |
|---|---|---|---|
| MIL-PRF-8625 | Type II | Sulfuric Acid | Good for hardness and resistance to abrasion, such as optical components and hydraulic valve bodies |
| MIL-PRF-8625 | Type III (w/ PTFE available) |
Sulfuric Acid (Hard Coat) | Cookware; Good thermal resistance, electrical insulation, abrasion/wear resistance, and strong finish |
| Class Designations apply to Sealing: Class 1, non dyed; Class 2, dyed, color to be specified. | |||
Available Through RFQ Only
| Standard | Type | Composition | Application Examples |
|---|---|---|---|
| ASTM D1730 | Type 2, Method 1 (MIL-A-8625 equiv.)Zn |
Sulfuric Acid | Anodized finishes requiring dyeing, saltwater resistance, kitchen appliances |
| ASTM B580, type A equiv to hard coat |
AKA Type III | Sulfuric Acid (Hard Coat) | Cookware; Good thermal resistance, electrical insulation, abrasion/wear resistance, and strong finish |
| SAE AMS2469J equiv to hard coat |
AKA Type III | Sulfuric Acid (Hard Coat) | Cookware; Good thermal resistance, electrical insulation, abrasion/wear resistance, and strong finish |
| AAMA 611-98 | Class I (A4) | Sulfuric Acid | Aerospace parts requiring high performance architectural aluminum anodic coating; kitchen applicances |
| AAMA 611-98 | Class II (A3) | Sulfuric Acid | General use commercial architectural anodic coating |
| ASTM D3933-98 | N/A | Phosphoric Acid | Structural adhesive bonding; aerospace parts |
| ASTM B580 | Type G (MIL-A-8625 Type I equiv.) |
Chromic Acid | Provides a good surface for paint and adhesive bonding |
| MIL-PRF-8625 | Type IA | Conventional Chromic Acid | Paint primer for aerospace parts |
| MIL-PRF-8625 | Type IB | Low Voltage Chromic Acid | Modified Type I used for 7XXX series aluminum alloys |
| MIL-PRF-8625 | Type IC | Non-Chromic Acid Electrolyete | Improves paint adhesion and fatigue resistance |
| *May increase quote time, lead times, and costs | |||
*Custom colors available, upon request
Anodizing is a conversion coating process that involves immersing aluminum into an acid electrolyte bath and passing an electric current through it. This creates a robust and fully integrated coating of aluminum oxide on the surface of the aluminum, replacing the naturally occurring oxide layer and penetrating through to the base metal. Unlike paint, anodizing doesn’t chip or flake.
Durability (wear resistance)
Abrasion resistance
Increased hardness
Corrosion protection
Cost-effective
Longevity
Desirable electrical properties
95.4%
Perfect order success rate (on-time, in-full delivery)
Get Instant QuotePart of the anodizing process is to remove the naturally occurring oxide layer, in a process called deoxidizing, by immersing the parts in an acidic solution. The electrochemically formed oxide layer is thicker than the naturally occurring oxide layer. Therefore, the build-up is actually less than the coating thickness, or the actual dimensional growth is less than the thickness of the anodized oxide layer. Here are the terms commonly utilized in anodizing and you can see these in more detail in the image below:
Your parts may require masking, if you have tight tolerances on your threads or holes. This may even be applicable for a thinner, Type II MIl-PRF-8625 coating. Masking may be accomplished with plastic plugs, tape, or even painted-on liquid plastics. Masking should be called out on a drawing with notes. If you have questions about masking or plugging, contact one of our experts today.
Fictiv also offers other finishes for your machined parts, including:
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