[TheForge] Electrolysis

[Bruce .]

Dave,
The simple answer is that you risk corrosion anytime you connect disparate
metals.  There are some other conditions needed, like moisture and a
circuit, but those are so easily achieved as to be almost irrelevant.  The
sure way to avoid this is NOT to connect the metals -- i.e., use a
dielectric (an insulator) between them -- one that will not absorb water,
which would defeat the purpose.  So, not only would the metals not touch,
the connecting means (bolt, rivet, collar) must not bring them into
electrical contact.
Passivated SS is inert but aluminum is very active -- easily oxidized.
Unpassivated SS has iron on its surface (and will display surface rust) so
is also active.  (And remember that iron rust and aluminum are the
ingredients for thermite -- kinda high energy.)
That said, both aluminum and SS have protective oxides that might just
prevent corrosion in any event -- I can't say for sure.  If it were my
project, I'd make a test piece and check for electrical conductivity from
SS to aluminum.  If they conduct (after ensuring the meter probes penetrate
the oxide layers) I'd conclude that corrosion is a risk.
Caveat:  This is theoretical knowledge -- book larnin' -- not practical.
In chemistry, one can find many examples of thermodynamically favorable
reactions (like thermite) that just don't occur (e.g. without a catalyst or
ignition of a magnesium flame).  Which is to say that thermodynamically,
corrosion is likely to occur, but the kinetics oppose it.  (The reasons why
involve another lecture.)
Here's another take:
https://www.albanycountyfasteners.com/blog/2017/09/15/stainless-steel-and-aluminum/
Bruce
NJ


On Mon, Apr 13, 2020 at 9:37 AM Dave Mudge <davemudge1 at gmail.com> wrote:

> Good morning metalheads,
> Question: If I made an aluminum frame for something that is going to be
> used outdoors, could I use stainless steel fasteners (lag screws or bolts)
> or would the combination of metals cause electrolysis (corrosion) at the
> point of contact of the dissimilar metals?
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