Normal mild steel or alloy steel is very close to alumnium on the galvanic
table (-0.7 cf -0.75 V) so galvanic corrosion is unlikely ... however you
need to make sure the steel is protected from surface corrosion which is a
separate issue.

To use stainless steel bolts in aluminium is risky. Stainless steel will
have a potential of approx -0.2 V and so you have a -0.5 V potential which
is on the limits of acceptability. Is the interface was protected with a
product such as the Duralac recommended by Stealth Pilot then you might get
away with it. Otherwise pitting of the the aluminium around the strainless
fasteners might occur if moisture is present.

Stainless bolts in aluminium structure are not as bad as putting aluminium
bolts in stainless but still risky business if outdoors. An absolute no no
if in a salt atmosphere.




"george" wrote in message
oups.com...

Front Office wrote:
I need to build a dozen outdoor canopies for an office building.
I want to use structural aluminum channel, bolted with steel bolts.

Where might expect corrosion to arise over the years, and would
it be mainly in the aluminum or in the steel bolts?

Thanks for any help.

Please post here or email me at grayscale[AT]verizon.net

Use only stainless steel.