Galvanic Corrosion

Aluminum in contact with a dissimilar metal in the presence of an electrolyte tends to corrode more rapidly than if exposed by itself to the same environment; this is referred to as galvanic corrosion. The tendency of one metal to cause galvanic corrosion of another can be predicted from a ‘‘galvanic series,’’ which depends on environments. Such a series is listed below; the anodic metal is usually corroded by contact with a more cathodic one:

Anodic Magnesium and zinc Protect aluminum
Aluminum, cadmium, and
chromium
Neutral and safe in most environments
Steel and iron Cause slow action on aluminum
except in marine environments
Lead Safe except for severe marine or
industrial atmospheres
Copper and nickel Tend to corrode aluminum
Cathodic Stainless steel Safe in most atmospheres and fresh
water; tends to corrode aluminum in
severe marine atmospheres

Since galvanic corrosion is akin to a battery and depends on current flow, several factors determine the severity of attack:

Electrolyte Conductivity. The higher the electrical conductivity, the greater the corrosive effect.

Polarization. Some couples polarize strongly to reduce the current flow appreciably. For example, stainless steel is highly cathodic to aluminum, but because of polarization, the two can safely be used together in many environments.

Anode–Cathode Area Ratios. A high ratio minimizes galvanic attack; a low ratio tends to cause severe galvanic corrosion.

J. G. Kaufman

Kaufman Associates

Columbus, Ohio

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

Copyright  2006 by John Wiley & Sons, Inc.

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