Galvanic Series Chart
In the galvanic series chart below, any element to the left of the alloy you want to protect is anodic to it and can protect its sacrificially, while any element to the right is cathodic to it and can cause it to corrode galvanically. This is the problem that our Computational Galvanic Corrosion Prediction technology solves.
A word of warning: The table below is for flowing seawater, and it was measured perhaps half a century ago for the purposes of determining which naval alloys can be used in seawater. While it is widely used, it does not include the alloys, composites, coatings, and other materials and surface treatments that are found in modern aircraft, vehicles and other equipment, and it is not correct for stationary (quiescent) liquids, which are found in most non-naval applications. Work is underway at Boeing to develop a complete replacement for this table that will include galvanic potentials, polarization curves, and galvanic currents – data that will be used for Computational Galvanic Prediction.
Notice that Cd is to the left of (i.e. anodic to) steels and so is used as a way of protecting them from corrosion since, like Zn, it sacrifices itself in place of the steel it protects. Notice also that Cd is close to the Al alloys in galvanic potential, whereas the stainless steels and nickel alloys are far to the right. This is why it is a very bad idea to mix aluminum alloys and stainless steels in any piece of equipment that may get wet; the result is rapid corrosion of the aluminum alloy. Where this must be done (as is often the case for aircraft) we frequently cadmium plate the stainless so that its galvanic potential more or less matches aluminum.