Definition
A pair of dissimilar metals placed in electrical contact in the presence of an electrolyte (such as moisture or salt water), which causes an electric current to flow between them and accelerates corrosion of the more chemically active metal.
Plain English
When two different metals touch and get wet, one of them starts to corrode faster than it normally would. The pairing of those two metals is called a galvanic couple.
Context Anchor
Seen in aircraft corrosion control, structural inspections, and maintenance around dissimilar metals such as steel fasteners in aluminum structure.
Derivation
Named after Luigi Galvani, an 18th-century Italian scientist who discovered that electricity can flow between dissimilar metals in contact with a moist conductor. 'Couple' simply means a pair — the two metals working together as an electrical pair.
Why Pilots Care
Unchecked galvanic corrosion weakens airframe components and fittings, potentially leading to structural failure if protective coatings or isolation methods are not used.
Analogy
A galvanic couple is like a tiny unwanted battery forming on the airplane. The two different metals are the battery parts, and moisture helps the electrical action start.
Grounding Statement
Picture a steel screw in an aluminum panel with salty moisture trapped around it; that small contact area can become a place where corrosion starts.
Intuition Check
A galvanic couple is not just any two parts touching. The usual concern is two different metals with moisture or contamination present, creating a path for electrical action and corrosion.
Example Sentence 1
The mechanic noted that the steel bolt and aluminum bracket formed a galvanic couple, and he applied a sealant to prevent moisture from reaching the joint.
Example Sentence 2
Insulating gaskets were installed to break the galvanic couple between the stainless steel fitting and the aluminum skin.