Contact corrosion can occur when metals of different grades are in close contact with one another: for example, if a stainless steel screw is screwed to a zinc-plated steel sheet. The higher-grade metal then promotes corrosion (rusting). This results in what is known as “contact corrosion”. Prerequisite for this process is a corrosive medium between the two metals, such as water or quite simply normal humidity.
The table below shows various combinations of materials and their compatibility with respect to contact corrosion: