What is the configuration of the aluminum and stainless parts? The amount of anode (aluminum) vs cathode (stainless) will help determine how much of a problem you have.What is the environment?
This is a building, in the Midwest (northern climates, not near any sea water or salt spray). Handrail is alumimum connected to building with stainless steel.
Should another type of material be used or isolate them from each other? The parts would be connected together with stainless screws.
Midwest, like where they salt roads and walks in the winter.
You should try to design a joint that will electrically isolate the two metals from each other. There are such connections commercially available mostly made from plastics (special washers and such). Otherwise you run the risk of rapid corrosion of the Al.
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Corrosion, every where, all the time.
Manage it or it will manage you.
EdStainless: I would doubt that those connections would be exposed to road salt since this is 35 feet above grade. The handrails are decorative only and there are no adjacent deck where people could potentially salt.
Do you have a website or a company name for commercially available connections?
If that is the case then just make sure that no water gets trapped or allowed to stand at the joints.
I recall seeing such washers on a web site for a company that builds stainless hand rails. I can't find it right now. They are similar to the hardware that you use when connecting system that have cathotic protection and you need to isolate some parts.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
There are various paints and gels that can be used to electrically isolate the two metals. The one I'm currently using is called Tef-gel and should be available world wide under that name. Another product is called duralic, it's a yellow zinc chromate paint, but it might be known under a different name outside Australia.
Because the area of aluminum greatly exceeds the area of stainless, I would not hesitate to use SS bolts in your situation. While they are far apart on the galvanic series, this situation should not be a problem because the galvanic cell won't have the "battery" to activate - the electic potential just won't exist. If you are serious about isolating the bolt from the aluminum, you will need to sleeve the hole also, not just under the bolt head. Teflon sleeves are probably available from McMaster or such.
Check any big marine supply store or catalogue for a dielectric paste for use with SS fasteners on Al fittings. I can't remember a name but the stuff I've used comes in a small tube.
Recommend you consider LOCTITE® Zinc Anti-Seize (39901) for SST fasteners in contact with AL, it is a smooth homogenous mixture of zinc dust and petrolatum.
Graphite based material may cause pitting of the AL.
Guys don't forget that the ss far away from the bolts could still cause a galv cell. Don't just consider the bolts when looking at surface area. Is this system being bolted to the building frame or an isolated structure.
You should try to isolate them if easily done so. However, it seems that individuals here forgot the first rule of corrosion engineering. You have to consider the materials in the environment they will be used in.
Since SS and AL will pasivate in the given environment you will likely see a reaction that is completely different than that listed on the tables. You will end up with a dull finish on both materials with little corrosion of either. It is doubtfull that you will have enough of a cell to "burn through" the passivating mechanisms of either metal.
