Glossary

Galvanic corrosion is a form of electrochemical corrosion that occurs when two different metals are in electrical contact in the presence of an electrolyte, such as water that contains salts, acids, or other conductive impurities. This situation creates a galvanic cell, where one metal functions as the anode and the other as the cathode. The anode is the more active metal, meaning it has a greater tendency to give up electrons, and therefore it corrodes more quickly than it would on its own. The cathode, being the more noble metal, is protected from corrosion. A common example is seen when steel and copper are connected in a marine environment: the steel, acting as the anode, corrodes rapidly, while the copper, as the cathode, remains unharmed.

The severity of galvanic corrosion is influenced by several conditions. The greater the difference in electrochemical potential between the two metals, the faster corrosion will occur. The conductivity of the electrolyte also plays a major role, with saltwater being particularly aggressive in accelerating the process. Additionally, the relative size of the metals in contact affects the outcome; a small anode connected to a large cathode will corrode at a much faster rate due to the disproportionate distribution of current.

To prevent or reduce galvanic corrosion, engineers employ several strategies. Metals that are close to each other in the galvanic series are often chosen to minimize potential differences. Coatings, insulators, or paints can be applied to separate the metals electrically. Protective measures such as galvanization or the use of sacrificial anodes, like zinc on ship hulls, can redirect corrosion to a controlled, replaceable material. Designers may also consider the ratio of exposed metal areas to reduce the imbalance between anodic and cathodic surfaces.

In fasteners and construction, galvanic corrosion is especially important to address because it can compromise the integrity of joints and assemblies. A classic example is the use of stainless steel bolts in aluminum structures. Without proper insulation or coatings, the aluminum can corrode quickly in a moist environment, weakening the structure and leading to premature failure. This makes galvanic corrosion a critical factor in selecting and designing fastening systems for long-term durability.