Aluminum Chromate Conversion Coating
Chromate coating is a conversion coating that improves corrosion protection on aluminum and aluminum alloy surfaces while preserving electrical conductivity. By improving the adhesion properties of the surface, it creates a suitable surface for primer and paint applications. It is also known as Alodine coating. The coating forms as an extremely thin film with negligible thickness. Chromate (Alodine) coating, which can be applied under paint, helps powder and wet paint adhere to aluminum. It is generally applied to parts used in the aerospace and defense industries.
In accordance with MIL-C-5541 (MIL-DTL-5541) and ASTM B449-93, we apply two types of chromate (Alodine) conversion coating: with Cr+6 and without Cr+6.
Chromate Coating Process
- Degreasing and cleaning: machining oils and contaminants are removed.
- Etching / deoxidizing: the natural oxide layer on the aluminum surface is removed.
- Chromate bath: a thin conversion film is formed on the surface.
- Rinsing and drying: the film is dried without being damaged.
Type and Class Selection
The MIL-DTL-5541 standard defines Type I coatings containing hexavalent chromium (Cr+6) and Type II coatings free of Cr+6. Class 1A is used for maximum corrosion protection, and Class 3 for surfaces requiring low electrical resistance. Type I coatings are usually yellow (iridite) in tone, while Type II coatings are clear or light-colored.
Where Is It Used?
- Electronic enclosures, chassis and contact surfaces requiring grounding/EMI shielding
- Surface preparation under primer before powder or wet painting
- Parts with tight dimensional tolerances where a thick coating cannot be applied
It is enough to specify the standard, type and class in your technical drawing (e.g. MIL-DTL-5541 Type II Class 3). For details, see our articles (in Turkish) What is Alodine coating? and Coating notes on technical drawings . For the difference between Cr6 and Cr3 and RoHS, read RoHS in chromate coating .
Related services: At our facility in Ankara İvedik OSB we also offer anodizing, electrostatic powder coating and wet painting services. You can send the technical drawing of your part via our quote form .
Guide (in Turkish): What is Alodine (chromate conversion) coating? MIL-DTL-5541 types and classes
Yellow Chromate Conversion Coating (contains Cr+6)
MIL-DTL-5541 Type 1.
Clear (Transparent) Chromate Conversion Coating (Cr+6 free)
MIL-DTL-5541 Type 2.
