Galvanic corrosion is best prevented by pairing metals that sit close together in galvanic potential. Where that is not possible, isolate the metals with gaskets or coatings, add a sacrificial third metal that corrodes preferentially, or reduce the environment's corrosivity with corrosion inhibitors. Between aluminium and stainless steel specifically, the aluminium is the anode and corrodes preferentially.
Why do aluminium and stainless steel corrode when joined?
Aluminium and stainless steels - austenitic, duplex and super duplex - sit far enough apart in galvanic potential that coupling them can drive galvanic corrosion. In this pair the aluminium becomes the anode in the electrochemical cell and is preferentially attacked, while the stainless steel is protected.
How do you prevent galvanic corrosion?
There are several practical options:
- Pair compatible metals. Use metals that are close in galvanic potential so little or no galvanic corrosion occurs.
- Isolate the metals. Separate them with gaskets or coatings - though this can create crevices, which bring their own corrosion risk.
- Add a sacrificial anode. Introduce a third metal that corrodes in preference to the other two.
- Treat the environment. Reduce its corrosiveness with corrosion inhibitors in the solution.
For a related surface-corrosion topic, see what is fretting corrosion?