On Sun, 10 Jul 2016 10:51:35 -0500, Jon Elson
wrote:

Ed Huntress wrote:


Galvanized fasteners are quite resistant to galvanic corrosion with
aluminum. And the steel underneath the zinc is also fairly benign with
aluminum. In fact, the aluminum will act like a sacrificial anode
against plain steel, but the activity will be very low. The zinc
barrier should hold up for a long time.

Depends on how acidic your rain is, of course. Some lightly galvanized
fittings are stripped down to the steel in a few years here.

Jon

Moral: Get good galvanized fittings. Or move out of the acid rain. g

Aluminum and stainless together is a CONSTANT problem here. I'm three
miles from tidewater, and five miles from a large bay. It shows up all
the time on boats and on architectural trim that's exposed to salt
air.

Galvanized does much better. (It's right next to aluminum on the
galvanic scale.) I've seen attempts to isolate stainless from
aluminum, but they usually fail. Salt will bridge the barrier and then
you're right back in trouble, although the corrosion goes much more
slowly without physical contact.

I haven't heard of a solution except that a friend tried some very
expensive Monel bolts on his boat. Against aluminum, they proved to be
worse than stainless. So much for that...

Good luck!

--
Ed Huntress