NACE Resource Center

Corrosion - Aircraft

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Prevention of galvanic corrosion by design

Quality engineering and design requires an understanding of material compatibility. There are three conditions that must exist for galvanic corrosion to occur. First there must be two electrochemically dissimilar metals present. Second, there must be an electrically conductive path between the two metals. And third, there must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal. If any one of these three conditions does not exist, galvanic corrosion will not occur. Galvanic corrosion can be minimized in design. Corrosion engineers have found the following practical rules invaluable in this respect (reference)

Select combinations of metals which will be in electrical contact from groups as close together as possible in the galvanic series
Electrically insulate from each other metals from different groups, wherever practical. If complete insulation cannot be achieved, paint or plastic coating at joints will help
If you must use dissimilar materials well apart in the series, avoid joining them by threaded connections as the threads will probably deteriorate excessively. Brazed or thermal joints are preferred, using a brazing alloy more noble than at least one of the metals to be joined
Avoid making combinations where the area of the less noble, anodic metal is relatively small compared with the area of the more noble metal.
Apply coatings with judgment. Example: Do not paint the less noble metal without also painting the more noble; otherwise, greatly accelerated attack may be concentrated at imperfections in coatings on the less noble metal. Keep such coatings in good repair.
Consider use of cathodic protection