Chemical Conversion Coatings on Aluminum Plating per MIL-DTL-5541 and MIL-C-5541
MIL-DTL-5541 Military Specifications
Aluminum alloys and coatings benefit from additional protective features of conversion coatings. These coatings can modify the surface of the aluminum material for improved corrosion resistance, electrical conductivity, and paint adhesion.
MIL-DTL-5514 governs the requirements for chemical conversion coatings applied to aluminum alloys.
The previous version (MIL-C-5541) is obsolete and only allowed compositions with hexavalent chromate Cr(VI).
The most current version (revision “F”) covers conversion coatings that are environmentally friendly and compliant with Reduction of Hazardous Materials (RoHS) initiatives. Hexavalent chromate is identified as Type I. Trivalent chromates and non-chromates were added as Type II.
AlumiPlate® electroplated aluminum coatings are also enhanced by conversion coatings. It is possible to apply hexavalent chromate on the typically greater than 99.99% pure aluminum coating. For a fully RoHS compliant solution, a trivalent chromate or non-chromate conversion should be applied.
MIL-DTL-5541
| Specification Requirement | AlumiPlate, Inc. | |
|---|---|---|
| Materials | Type I: hexavalent chromate compounds Type II: non-hexavalent chromate compounds | Type I: Hexavalent chromate bath available Type II: Trivalent Chromate and Non-Chromate Conversion baths are available |
| Corrosion Resistance | 168 hours exposure to 5% salt spray | Verified with in-house salt spray test per ASTM B-117 |
| Paint Adhesion | No intercoat separation between paint system and conversion coating | Test results on file for FED-STD-141 wet tape adhesion testing |
| Electrical Contact Resistance for Class 3 Coatings | As specified in the contract or order | Bath chemistry sourced from QPL-81706 approved source. Additional testing done as per contract or order. |
| Chemical Analysis | Concentration, pH and temperature within manufacturer’s recommendation | Bath chemistry sourced from QPL-81706 approved source. Concentration and pH tested by third party and bath operated at manufacturer’s recommendations. |
| Workmanship | Treatments and processes must meet specification guidelines | Bath chemistry sourced from QPL-81706 approved source |
Classes and Types
To order or call-out a conversion coating, the Type and Class should be included in the purchase contract or the drawing note.
Type I: used for applications where hexavalent chromate is acceptable
Type II: used for applications where a non-hazardous alternative is desired, such as trivalent chromate or non-chromate coatings
Both types must meet the same performance guidelines.
Class 1A: used for optimum corrosion resistance
Class 3: used for corrosion protection where low electrical resistance is desired
Both classes must meet the same minimum corrosion resistance requirements, but it is expected that Class 1A coatings exhibit increased corrosion resistance.
Qualification of conversion coatings that meet this specification are governed by MIL-DTL-81706 “Detail Specification: Chemical Conversion Materials For Coating Aluminum and Aluminum Alloys.”
Products that are qualified are listed in the Qualified Products List QPL-81706. Approved manufacturers must verify by certification that their product complies with the requirements every two years. No alterations to the qualified products formulation, raw materials, methods of manufacturing and production equipment are allowed without prior consent of the government certifying authority (Naval Air Warcraft Center, Materials Division).
AlumiPlate only uses certified chemical compounds from the options listed in QPL-81706.
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