ALUMINUM/STAINLESS STEEL INTERFACE

[wynn]

We need to secure a flange made from 6061 Aluminum angle with 1/2 dia Grade 316 stainless steel bolts. The flange offers a flat surface exposed to weather with a 30 year service life in a mildly corrosive industrial environment. The nut and washer face into the weather.

Can anyone advise us what we can anticipate in terms of corrosion/deterioration for this connection.

 

[rustbuster1]

The aggressiveness of galvanic corrosion - corrosion of the aluminum will be accelerated- depends mostly on the length of time the two metals SHARE wetness. You can eliminate this relatively simply by coating or capping the SS fastener ends and/or by shaping the flange so water doesn't sit around. Occasional wetting will not be a problem, but close to constant wetting will, although that's true for the Al even without the ss galvanic effect.

Another way to prevent galvanic corrosion here is to electrically isolate the SS bolts from the Al flange with suitable bushings (Teflon is a common material).
You could have the Al flange anodized or coated with some other, rugged coating and keep it whole during the bolting.

 

[boo1]

You need to electrically isolate the aluminium. Sealants (like proseal) will work for 5 to 7 years. Isolation materials like teflon last longer, but check embedment and creep. At a minimiun seal the joint with paint, to prevent moisture pentetration.

 

[AlanD]

As for a suitable electrical isolating coating try zinc chromate paint, otherwise known as yellow gunk.

 

[SolarWeenie]

Hi,

Need some advice. We are specifying a racking system for PV modules (sheltered outdoor application). The basic construction is aluminum blocks (~1"x2"x2&quot bolted to a rail. The question is whether to use a HD galvanized rail or a stainless rail. The environment is rural but might have elevated SO2 levels because this is on the roof of a winery. The galvanized rail obviously will not last as long as the stainless (though the Zinc Coating Life Predictor indicates adequate life) but I am concerned about the galvanic couple. Also the aluminum block has two large (3/8&quot 18-8 bolts through it, the manufacturer claims this will not be a problem.

Thanks for the help!

 

[Metalguy]

SolarWeenie,

See reply in the other thread.