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priming mating surfaces of different aluminum alloys

KayS

Well Known Member
everybody please respect the cease fire in the primer wars...

my understanding is that 2024-T3 and 6061-T6 have different characteristics when it comes to corrosion, with 6061 being less prone to corrode that 2024 alclad. is it advisable to prime the contact surfaces of 2024-T3 and 6061-T6 for an aircraft that lives in a moderate climate, not close to the sea etc.? how big is the likelihood that especially these mating surfaces of different alloys will corrode?

background is that (after my RV-7 is flying) i started a new project, a hummel ultracruiser. the aircraft main structure is 6061-T6 but with a lot of parts in 2024-T3. i don't plan to prime or paint the aircraft due to weight restrictions and so on.

the question is not entirely related to RV's but i hope it's still ok to ask that here. And also RV's have some 6061 alloy in it, so the information could be also useful for RV's.

Thanks in advance
Kay
 
Last edited:
A couple things...(I'm primer OCD)

The Hummel is made from the same alloys as the RV. All the extrusion in the RV is 6061-T6 and all the ribs and skins are 2024-T3 ALCLAD The Alclad is pure aluminum coating that is the first line of defense against corrosion on the 2024. The 6061 by nature is less prone to corrosion on its own. No extrusion is Alclad other than roll form extrusion, which is not used on these aircraft. The most vulnerable area of the 2024 sheet is the edges, and the holes where the parent 2024 alloy is exposed. Generally speaking, if the plane is kept in a good environment, it will age like an old Cessna or Piper that had no primer. It will outlive you. If you want to go the extra mile (like I would because I'm in the business of aging aircraft), you could apply primer to the mating surface of the extrusion ,and "swab" the rivet holes with primer before assembly. My RV-4 has every hole swabbed and all structure primed in and out..more of my OCD corrosion prevention mind. In short, the 6061 and the 2024 play fairly well together, but any steel contact (bolts) should at least get a primer swabbed hole. I would not loose sleep over your choice to not prime the Hummel !
 
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