Screwing aluminum extrusions to steel

[YukonOne]

Anyone have any advise on when the dissimilarity of steel and aluminum becomes a problem.

I'm looking at a high end residential steel interior stair stringer that wants to have an aluminum extrusion anchored to it. The extrusion is what anchors a glass railing to the stringer. A typical detail shows screws into the element supporting the extrusion.

At what point is the dissimilarity of the metals a problem?

 

[JAE]

Steel and aluminum - we've always separated them. Use a neoprene or rubber gasket at all interfaces.

 

[JAE]

Here's another similar thread:

thread507-129229

 

[apsix]

But if it is inside (and dry) there shouldn't be a problem.

 

[Deutero]

In the thread JAE referred to, rmw explained that, "For galvanic action to occur, the two dis-similar metals have to be in the presence of an electrolytic fluid." Though this may be inside, will this high-end residential structure have a humidifier installed in its furnace? Will moisture be in the air? I am not a corrosion expert, therefore, is a potential high-humidity/moisture content enough to transfer an electrolytic reaction?

Will the high-end residential client be understanding if corrosion does occur?

Be safe! Separate the metals per JAE.

 

[Ron]

YukonOne....even though inside, isolate them and use stainless steel fasteners.

If you look at corrosion charts, steel should cause aluminum to corrode. Well....it does, but the initial corrosion on the aluminum creates a passivation layer, the aluminum is then protected, and then the steel starts to corrode without anything to prevent it. That's why you commonly see carbon steel fasteners corroding when used to fasten aluminum.

The materials don't have to be drowned in an electrolyte in order to corrode. Vapor collection/condensation at crevices can do it.

Being inside only makes it take a bit longer.