Two Metals, One Problem
When dissimilar metals contact each other in a conductive environment, an electrochemical cell forms spontaneously. The more active metal (lower electrode potential) becomes the anode and dissolves, while the nobler metal acts as cathode and is protected. This galvanic corrosion was first described by Luigi Galvani in 1780 and remains one of the most common corrosion failures in engineering — from automotive body panels to marine hardware.
The Galvanic Series
Metals can be ranked by their electrode potential in a given electrolyte, forming the galvanic series. In seawater, magnesium and zinc are most active (anodic), while platinum and graphite are most noble (cathodic). The potential difference between coupled metals directly drives the corrosion current. Coupling metals far apart in the series — such as copper plumbing to steel radiators — creates aggressive galvanic cells that can penetrate pipe walls in months.
Area Ratio: The Hidden Multiplier
Perhaps the most dangerous aspect of galvanic corrosion is the cathode-to-anode area ratio. The total galvanic current is determined by the cathode area, but this current concentrates on the anode surface. A large stainless steel structure with small carbon steel fasteners focuses all corrosion onto the bolts, causing rapid failure. The golden rule: always make the less noble metal the larger component, or better yet, use insulating barriers.
Engineering Prevention
Preventing galvanic corrosion requires breaking one element of the corrosion cell: use metals within 0.25V of each other in the galvanic series, apply insulating gaskets and coatings between dissimilar metals, reduce electrolyte conductivity where possible, or employ cathodic protection. This simulation lets you explore how each factor — potential difference, conductivity, area ratio, and temperature — influences the corrosion rate.