Galvanic corrosion

When different materials are used together and there is direct contact between them, we have to allow for the possibility of a very specific form of corrosion: galvanic corrosion. Examples: aluminium sheets anchored using stainless steel fasteners, use of copper and metal, etc. There are hardly any problems with some combinations of materials, while combinations of others can create a risky situation (e.g. if part of a load-bearing structure) and cause serious problems.

Materials such as stainless steel and aluminium, both of which are corrosion resistant when separate from each other, should not be combined. It is preferable to combine the same materials in a workpiece, and use fasteners of the same material.

What exactly happens with galvanic corrosion? A potential difference between the two metals causes the weaker metal to corrode. And of course some environmental conditions or substances just accelerate this effect. It is therefore best to use the same materials together. If that is not possible, there are two options: we can ensure that the two metals do not come into contact by inserting a synthetic insulator, for example, or look in the tables to see which materials combine well and which do not.

Two kinds of tables are commonly used. You can find the first via this link to the English version of Wikipedia, where you can determine which materials can or cannot be combined by checking the potential differences. A second table works using codes (A to E). Combination A is not a problem but combination E is to be avoided, except for a couple of variations. You can download the table from this page: