fastening aluminum to mild steel or stainless steel

Where will this materials combination reside ? Inside or outside exposed to the atmosphere ?

The APIGUY....

if the stainless is in contact with the aluminium in air then the aluminium will corrode even if the carbon steel is painted

This will be outside exposed to the atmosphere.

Aybee, I'm not sure I understand your statement. "if the stainless is in contact with the aluminium in air then the aluminium will corrode even if the carbon steel is painted" We are looking at either fastening mild steel to the aluminum, or stainless to aluminum, providing it would have corrosion advantages.

thanks
rustang

My guess is that this probably some sort of HVAC system ? The aluminum will oxidize over and corrode slightly if biological growths are permitted to remain on the duct work causing hole type pitting. The stainless fasteners are fine in direct contact with the aluminum if you use some sort of silicone sealant to protect from moisture ingress.

Remember: For galvanic corrosion to happen you need two dissimilar metals in the presence of an electrolyte. Eliminate one of these, almost no corrosion happens. If you eliminate the moisture path, chances are you will eliminate the corrosion also.

We use this same combination to insulate pressure vessels quite frequently.

The APIGUY....