MIL-DTL-5541
Chemical Conversion Coatings on Aluminum and Aluminum Alloys
Covers chemical conversion coatings formed by reaction of qualified materials with aluminum and aluminum-alloy surfaces.
What MIL-DTL-5541 specifies
MIL-DTL-5541 defines applied conversion coatings by chemistry and service class. Type I materials contain hexavalent chromium; Type II materials contain no hexavalent chromium. Class 1A is for maximum corrosion protection, painted or unpainted, while Class 3 is for corrosion protection where low electrical contact resistance is required. Both classes are verified by 168-hour ASTM B117 salt spray on process-control panels, and painted systems are subject to wet-tape adhesion. The drawing or order should state type and class, color if controlled, contact-resistance requirements, paint system, masking, and whether touch-up is allowed. The specification superseded MIL-C-5541E.
MIL-DTL-5541 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
Type I Class 1A | Hexavalent-chromium conversion coating for maximum corrosion protection and paint adhesion. | ASTM B117, 5% salt spray, 168 h; wet-tape adhesion when painted. |
Type I Class 3 | Thin hexavalent-chromium conversion coating for low electrical contact resistance. | ASTM B117, 5% salt spray, 168 h; contact resistance not over 5000 µΩ/in² as supplied and 10000 µΩ/in² after exposure when tested at 200 psi. |
Type II Class 1A | Non-hexavalent conversion coating for maximum corrosion protection and paint adhesion. | ASTM B117, 5% salt spray, 168 h; wet-tape adhesion when painted. |
Type II Class 3 | Thin non-hexavalent conversion coating for corrosion protection with low electrical contact resistance. | ASTM B117, 5% salt spray, 168 h; contact resistance requirements apply when specified. |
Tests and the drawing call-out
Tests the document imposes
- ASTM B117 5% salt spray for 168 h
- No more than 5 isolated pits per panel and 15 across five panels; no pit larger than 0.031 in
- Wet-tape adhesion per FED-STD-141 Method 6301
- Class 3 electrical contact resistance at 200 psi
- Visual examination for continuous coating and objectionable powder
How to cite it
Drawing call-out
CHEMICAL CONVERSION COAT PER MIL-DTL-5541 TYPE <I|II>, CLASS <1A|3>, [COLOR], [MASKING]Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to MIL-DTL-5541
MIL-DTL-5541 — frequently asked
Is MIL-C-5541 the same as MIL-DTL-5541?
MIL-DTL-5541 superseded MIL-C-5541E. Legacy notes using MIL-C-5541 should be reviewed against the current revision because Type II non-hexavalent chemistry and later qualification requirements may not appear in the older drawing basis.
What is MIL-DTL-5541 Class 1A versus Class 3?
Class 1A prioritizes maximum corrosion protection and paint adhesion. Class 3 uses a thinner film where low electrical contact resistance is required.
What are Type I and Type II?
Type I materials contain hexavalent chromium. Type II materials contain no hexavalent chromium; the type does not replace the need to state Class 1A or Class 3.
Does MIL-DTL-5541 specify coating thickness?
It controls conversion-coating performance rather than a dimensional thickness range. Process time affects film weight and electrical resistance, especially for Class 3.
MIL-DTL-5541 is a work of the US Government and not subject to copyright. The authoritative copy is the DLA ASSIST database; check it for amendments issued after this page was updated. Official source ↗