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Service temperature for MIL-DTL-81706B Type II Class 3A

What is the recommended usable temperature range for MIL-DTL-81706B Type II Class 3A on aluminum sheet, for corrosion protection and low electrical resistance? What is the source of the recommendation.

Chris Hoinsky
aircraft - Stratford, Connecticut, USA
2005

2005

OK! Here we go!.
It is my understanding the specification MIL-DTL-81706 is not a process specification but a detail of procedures for allowable products to be added to the QPL-81706.

See MIL-DTL-81706 6.1.3 where it refers to processing under MIL-C-5541.

Unfortunately at this time, no non-hexavalent products are listed on QPL-81706, and as result cannot be used if plating per MIL-C-5541.

Now, to answer your question, when these products do get listed, their characteristics, such as heat resistance will be unique to that particular product.

We are using a Trivalent TCP coating and I do believe it is a bit more heat resistant than the old standard Hex coatings.
Please correct me if I'm wrong, I'd love a MIL-SPEC to plate by, but for now we are using ASTM B921

Bill Grayson
metal finishing - San Jose, California, USA

We too are using a trivalent chrome conversion coating (a.k.a. TCP) on aluminum, however, the coating while containing chrome contains another protective species which results in a tighter less porous structure (one that doesn't accept yellow dyes), is more abrasion resistant (i.e. tougher coating) and doesn't degrade corrosion wise upon exposure to temperatures over 140F (point at which conventional chromates begin to dehydrate and lose salt spray resistance). While not listed yet on the QPL-81706, at least one of these products is close to being so. In order to qualify the formulation must prove to be stable for 12-months so anyone submitting samples for Naval qualification is bound to waiting at least that long. I've heard that no such products will meet that criteria until early 2006 so don't hold your breath waiting for a non-chrome product to be QPL listed!

Milt Stevenson, Jr.
Syracuse, New York
2005

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