Chem film and alodine coating per MIL-DTL-5541.
Argent partners with U.S. finishers qualified to MIL-DTL-5541 for chemical conversion coating of aluminum aerospace parts. Class 1A (maximum corrosion resistance) and Class 3 (electrical conductivity) chromate conversion coatings, plus RoHS-compliant trivalent chromium alternatives where hexavalent chromium is being phased out.
What chem film does and where it's used.
Chem film (chemical film, also called alodine coating, iridite, or chromate conversion coating) is a thin chemical coating applied to aluminum to prevent corrosion and provide a paint-ready surface. The aluminum part is dipped in or sprayed with a chromate-containing solution that reacts with the surface to form an integral coating typically 0.00001 to 0.00004 inches thick — far thinner than anodizing.
The governing specification is MIL-DTL-5541F (Chemical Conversion Coatings on Aluminum and Aluminum Alloys), which superseded the older MIL-C-5541. Chem film is referenced on essentially every aerospace aluminum drawing where corrosion protection is needed but anodizing isn't appropriate.
The two classes of MIL-DTL-5541
- Class 1A — Maximum corrosion protection. Used where the part will be painted afterward or where corrosion resistance is the primary concern. Gold-yellow color (hexavalent chromium) or nearly clear (trivalent chromium alternative).
- Class 3 — Electrical conductivity. Used where the part must maintain electrical bonding (grounding straps, EMI shielding, electrical chassis). Thinner coating, lower resistance across the surface. Same material as Class 1A but applied with shorter immersion time.
Where chem film beats anodizing
- Electrical conductivity matters. Anodizing is electrically insulating. Class 3 chem film is conductive. Required on grounding surfaces, EMI/RFI joints, and electrical chassis.
- Dimensional change must be minimized. Anodize adds 0.0002–0.001 inches of coating thickness. Chem film adds essentially nothing — under 0.00004 in. Required on parts with tight assembly tolerances.
- Selective coating is needed. Chem film can be touched up by hand on specific zones — anodize cannot. Common on assemblies with masking requirements.
- Cost matters and Class A protection isn't needed. Chem film is significantly less expensive than Type II anodize and provides excellent paint adhesion. Common on internal aluminum parts that will be painted.
- Touch-up after machining. Chem film can be applied locally to repair anodized parts that have been machined post-anodizing, restoring corrosion protection at the new surface.
Chem film and alodine specifications.
Aluminum alloys we chem film
- 2024 — high-strength aerospace structural; chem film commonly spec'd on machined details and internal parts
- 6061 — general-purpose aerospace machined parts
- 7050 / 7075 — high-strength aerospace structural; chem film alternative to Type I chromic anodize in certain applications
- 2219 — cryogenic propellant tank structural
- 5052 / 5083 / 5086 — marine and defense applications
- 6063 / 6005 — extruded structural shapes
Typical aerospace applications
- Aerospace electronic chassis and housings — Class 3 conductivity required for EMI/RFI compliance
- Avionics enclosures with grounding requirements — Class 3 on mating surfaces, Class 1A on external surfaces
- Internal aluminum brackets and structural details — Class 1A under aerospace primer and topcoat
- Aerospace primer base coat — MIL-PRF-23377 epoxy primer applied over Class 1A
- Spot repair of anodized assemblies — chem film touch-up after secondary machining
- Defense electronic equipment — chassis and shields with conductive coating requirements
The hexavalent chromium transition in aerospace.
If you've been working with aerospace finishing for the past five years, you've encountered the hexavalent chromium reduction effort. Traditional MIL-DTL-5541 chem film uses hexavalent chromium (Cr+6), which is a known carcinogen and is regulated under OSHA, EPA, REACH, and RoHS. The aerospace industry has been transitioning toward trivalent chromium (Cr+3) alternatives that provide comparable corrosion protection without the toxicity.
Where each is still used
- Hexavalent chromium (traditional alodine 1200, iridite 14-2) remains spec'd on most legacy aerospace and defense programs. Existing prime contractor drawings, qualification testing, and supply chain agreements were built around hex Cr and changing them requires program-level requalification.
- Trivalent chromium alternatives (Surtec 650, Bonderite T 5900, alodine 5200) are increasingly required on new aerospace programs, in California (Prop 65 driven), and on programs exporting to Europe where REACH applies. Trivalent chem film has been qualified to MIL-DTL-5541 since the 2009 revision and is fully approved by Boeing, Lockheed, and most major primes.
Argent works with U.S. finishers qualified for both chemistries. We don't push you toward one or the other — tell us what your drawing specifies and we route to the right partner. For new program work where you have a choice, we can advise on which chemistry typically performs better for your specific corrosion environment.
Pairs well with.
Argent customers typically combine multiple capabilities on the same program. These are the most common pairings with this work.