Military Specification MIL-A-8625
This specification is the gold standard for military, aerospace, and defense anodizing. It establishes the foundational requirements for six types and two classes of non-architectural aluminum anodizing.
Because of its rigor, MIL-A-8625 serves as the blueprint for countless proprietary company specifications across the manufacturing industry, almost all of which reference its core requirements.
The anodic coating types and classes are:
Types I and IB are used when outstanding corrosion resistance, paint adhesion, and fatigue resistance are required.Types IC and IIB are used for these same attributes. An example of Type IC would be the Boeing Boric-Sulfuric Anodizing process. Type IIB is a thin film sulfuric acid anodize.The specification states that anodic coating thickness should be specifically called out by the purchase documents and/or the part drawing.An example of a hard anodized and black dyed finish designated by this specification would be: MIL-A-8625(latest version), Type III, Class 2 black, 2.0 mil coating thickness
| Designation | Anodizing Type / Process | Primary Application & Attributes |
|---|---|---|
| Type I | Chromic Acid Anodizing (Conventional) |
Used when outstanding corrosion resistance, paint adhesion, and fatigue resistance are required. Ideal for critical aerospace structural components. |
| Type IB | Chromic Acid Anodizing (Low Voltage Method) |
Utilizes a low-voltage process method while retaining the core protective attributes of conventional Type I coatings. |
| Type IC | Non-Chromic Acid Anodizing (e.g., Boric-Sulfuric Anodizing) |
Serves as an environmentally friendly, non-chromate alternative to Type I and IB coatings while matching identical performance attributes. |
| Type II | Sulfuric Acid Anodizing (Conventional) |
The most common industrial finish. Provides an optimal, cost-effective blend of corrosion resistance, structural durability, and baseline wear resistance. |
| Type IIB | Sulfuric Acid Anodizing (Thin-Film Sulfuric Method) |
A thin-film variant designed explicitly to serve as a non-chromate alternative to legacy Type I and IB military specs. |
| Type III | Hardcoat Anodizing (Hard Anodize) |
Produces a thick, exceptionally dense coating engineered specifically for extreme wear, high-friction, and harsh abrasion-resistant applications. |
| Class 1 | Non-Dyed Finish | Natural, uncolored protective finish. Keeps the original metallic tint intact. |
| Class 2 | Dyed Finish | Dyed post-anodizing to achieve colored finishes (e.g., black, red, blue, gold) for aesthetic purposes or industrial color-coding. |
