Primer stringers?

[Zzz]

Is it common practice/best practice to primer aluminum stringers? Mine have sat apparently for years and show a little black oxidation in places. I suspect it's where they have abraded against each other in storage or transport. Although not a critical structural member, it seems like it would be nice to have them protected. What are you guys doing? Seems like etch/alodine would be a good solution but it's a difficult object to dip.

[N942VT]

Light coat of primer is always a good idea. Clean, etch, prime.

[Mark Goldberg]

The extruded stringers we supply with the kits are 5052 which is considered the "marine" aluminum. If you have these you could leave them bare. But primering is not a bad idea. Mark

[Battson]

I didn't bother because I have the QB kit stringers, they stay so dry and clean inside the skin.

I had a quick look around and found this:
5052-H32 is a non-heat treatable strain hardening alloy. It has good toughness at cryogenic temperatures, but it does tend to suffer from stress corrosion above about 150F, though not as badly as other 5000 series aluminum alloys that have more Magnesium. It is used in structural applications requiring moderate strength and where forming or welding are required.

6061-T6 is a solution-heat treated and aged alloy with similar strength to the 5052-H32. It also has good toughness at low temperatures and is used for light structure, but doesn't suffer from stress corrosion cracking to the extent that 5052-H32 does.

Both are used in marine applications and are weldable but the 6061 returns to a near-annealed state in the heat effected zone around the weld. Probably for this reason more than any other 5052-H32 is preferred over 6061-T6 in marine applications (so as to avoid a heat-treat after weld requirement). Neither are particularly strong compared to other aluminum alloys (compare 7075, 7050, 2024 series).

I didn't find any evidence of just how corrosion resistant it is... other than "a lot in sea water". So it will corrode and pit eventually. Alloyed Aluminium doesn't become passivated so it's just a question of how long it takes.