Where the
world gathers for metal finishing
Q&As since 1989


-----

MIL-C-5541 CL 1A Expected Lifetime

2002

I have an application where I would like to use a chemical conversion coating in accordance with MIL-C-5541 Class 1A on a 6061-T6 Al machined part and a 7075-T73 Al forging. Both parts will be located in-doors on a ship. What is the expected lifetime of the coating in a salt air and minor salt water environment?

Giuseppe DiGiallonardo
- Hudson, Massachusetts

---

168 hours in a 5% salt spray cabinet. How much wet salt is going to blow indoors on the ship? Interpolate.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2002

---

Robert,

Have you a reference for these figures? I would like to use them.

John Logan
- Brisbane, Queensland, Australia
2002

---

2002

For 6061 alloy, 168 hours is probably reasonable number since it is the standard value found in all chromate conversion coating specs for aluminum including the former MIL-C-5541.

For 7075 alloy, I'd expect somewhat less protection from just chromating. This is a highly alloyed aluminum that in our humid shop must remain wrapped in shipping until we're ready to process it or it will start to corrode overnight. This doesn't even happen with 2024.

Milt Stevenson, Jr.
Syracuse, New York