Finish specification

MIL-DTL-5541 (MIL-C-5541)

The military specification for chemical conversion coatings on aluminum and aluminum alloys. It replaced MIL-C-5541 in 2006, and most catalog records still use the old name.

11,640 NSNs in DLA's catalog cite this spec. See the catalog data

What MIL-DTL-5541 covers

MIL-DTL-5541 covers chemical conversion coatings on aluminum and aluminum alloys: a thin film that protects aluminum against corrosion, painted or unpainted, and that can also be specified where the surface must stay electrically conductive.

The spec does not name a single chemistry. The coating material must be qualified under MIL-DTL-81706 and accepted for listing on the qualified products list, QPL-81706. Because coating thickness is controlled by immersion time, the same material can be listed for both classes.

Types and classes

Type I
Compositions containing hexavalent chromium.
Type II
Compositions containing no hexavalent chromium.
Class 1A
For maximum protection against corrosion, painted or unpainted.
Class 3
For protection against corrosion where low electrical resistance is required. The spec notes describe it as intended for electrical and electronic applications, and say that because Class 3 coatings are thinner they are more susceptible to corrosion than Class 1A.

Status and revisions

MIL-DTL-5541F is dated 11 July 2006 and superseded MIL-C-5541E, dated 30 November 1990. That revision changed the designation from MIL-C to MIL-DTL; the coating it describes did not get a new name, which is why both numbers are searched and why DLA's catalog still cites MIL-C-5541 on most records.

Revision F is the latest revision we found.

Typical applications

  • Corrosion protection for aluminum parts that will be painted or left bare (Class 1A).
  • Aluminum surfaces that must stay electrically conductive, such as grounding and bonding points and electronic enclosures (Class 3).
  • In DLA's catalog it is called out most often on solid and blind rivets, sleeve and plate spacers, flat washers, angle brackets and loop clamps, mostly made from 2024 and 6061 aluminum.

What a shop needs to supply to MIL-DTL-5541

  • Use a conversion coating material that is listed on QPL-81706 for the class the drawing calls for.
  • Know which type the order requires. Type I contains hexavalent chromium and Type II does not, so the type decides the chemistry you can run.
  • Coated test specimens must pass 168 hours of 5 percent salt spray per ASTM B117 for the class applied.
  • For Class 3, the acquisition activity specifies the electrical resistance values. Materials are qualified under MIL-DTL-81706 at not more than 5,000 microhms per square inch as supplied and 10,000 microhms per square inch after 168 hours of salt spray.

The purchase order, drawing and the revision of the spec it invokes govern. Always work from the revision your contract names.

MIL-DTL-5541 in the DLA catalog

From DLA's public PUB LOG catalog, release 2026-10-27, covering 16 hardware and mechanical supply groups (fasteners, bearings, fittings, valves, power transmission, engine components and more).

11,640
NSNs whose catalog record cites MIL-DTL-5541
43%
coded open to new sources (5,004 NSNs): at least one managing service codes it AMC 1 or 2 with AMSC G
28%
coded for existing or approved sources (3,212 NSNs)

Most common items

Rivet, solid1,942
Rivet, blind1,555
Spacer, sleeve1,238
Spacer, plate719
Washer, flat553
Bracket, angle507
Clamp, loop499
Cover, access396
Shim304
Bracket, mounting286

Federal supply classes

5320 Rivets3,718
5340 Hardware, commercial2,829
5365 Bushings, rings, shims, and spacers2,636
5310 Nuts and washers1,208
5306 Bolts210
3120 Bearings, plain, unmounted164
3020 Gears, pulleys, sprockets, and transmission chain131
5325 Fastening devices126

Can a new source win these parts?

DLA codes each part with an acquisition method (AMC) and a suffix (AMSC). We count an NSN as open when at least one managing service codes it AMC 1 or 2 (competitive) with suffix G (the government has the full technical data and the rights to use it). Otherwise we count it as restricted when a service codes it AMC 3, 4 or 5 (buy from the manufacturer or prime) or uses a suffix that limits or conditions who can supply it (AMSC B, C, D, H, K, L, P, Q, R, T, U or Y): missing data or rights, source-control drawings, source or QPL approval, controlled castings, uneconomical breakout, an unstable design, or low-value screening for known sources. These are catalog codes; the solicitation always governs.

Open: AMC 1 or 2 with AMSC G5,00443%
Restricted: AMC 3, 4 or 5, or a restrictive AMSC3,21228%
Other acquisition codes1,59314%
No acquisition method in the catalog1,83116%

As of PUB LOG release 2026-10-27. How to read the codes: AMC and AMSC codes explained.

How catalog records call it out

Characteristic records that cite MIL-C-5541 or MIL-DTL-5541, grouped by the type, class or condition they name. Counted across the most common callout spellings, so the totals are a floor.

Not specified6,382
Class 1A2,796
Class 3614

Materials these parts are made from

  • Aluminum alloy 2024 (overall) 1,425
  • Aluminum alloy 6061 1,166
  • Aluminum alloy 6061 (overall) 820
  • Aluminum alloy 2117 (overall) 699
  • Aluminum alloy (overall) 593
  • Aluminum alloy 5052 583
  • Aluminum alloy 2017 (overall) 434
  • Aluminum alloy 2024 335

Sample NSNs that cite MIL-DTL-5541

Frequently asked questions

Is MIL-C-5541 the same as MIL-DTL-5541?

Yes. MIL-DTL-5541F, dated 11 July 2006, superseded MIL-C-5541E. The designation changed from MIL-C to MIL-DTL with revision F. DLA's catalog still cites MIL-C-5541 on most of the records that call for this coating.

What is the difference between Class 1A and Class 3?

Class 1A is for maximum protection against corrosion, painted or unpainted. Class 3 is for corrosion protection where low electrical resistance is required. Class 3 coatings are thinner, so they protect less against corrosion than Class 1A.

What is the difference between Type I and Type II?

Type I compositions contain hexavalent chromium. Type II compositions contain no hexavalent chromium.

What salt spray test does MIL-DTL-5541 require?

Coated specimens are exposed to 5 percent salt spray per ASTM B117 for 168 hours, for both Class 1A and Class 3.

How many DLA parts call for MIL-C-5541 or MIL-DTL-5541?

11,640 NSNs in DLA's PUB LOG catalog (release 2026-10-27, 16 hardware and mechanical supply groups) cite the spec. Rivets, spacers, washers and brackets lead the list.

Related

Sources