Galvanic or dissimilar metal Corrosion is a electrochemical process where one material corrodes if it comes in contact with another material. You can check Galvanic corrosion in details here.
Prevention of Galvanic Corrosion
1. Insulation in between dissimilar metals
Presence of conductive media between two metals is primary requirement for galvanic corrosion. Insulation in between dissimilar metals can stop galvanic corrosion.
2. Selection of materials closer in galvanic series
Material selection shall be done based on their anodic index value. Lower the difference in anodic index values, higher will be galvanic corrosion resistance. You can refer Anodic Index table here.
|Serial Number||Material||Anodic Index (V)|
|1||Gold, Gold-platinum alloy||0|
|2||Rhodium plated on silver-plated copper||0.05|
|3||Silver, monel metal, High nickel-copper alloys||0.15|
|4||Nickel, titanium alloys, monel||0.3|
|5||Copper, low brasses or bronzes, silver solder, German silvery high copper-nickel alloys, nickel-chromium alloys||0.35|
|6||Brass and bronzes||0.4|
|7||High brasses and bronzes||0.45|
|8||18% chromium type corrosion-resistant steels||0.5|
|9||Chromium plated, tin plated, 12% chromium type corrosion-resistant steels||0.6|
|10||Tin-plate, tin-lead solder||0.65|
|11||Lead, high lead alloys||0.7|
|12||Aluminium, wrought alloys 2000 Series||0.75|
|13||Iron, wrought, gray or malleable, plain carbon and low alloys steels||0.85|
|14||Aluminium (other than 2000 Series), cast alloys of silicon type||0.9|
|15||Aluminium, cast alloys other than silicon type, cadmium, plated and chromate||0.95|
|16||Hot-dip-zinc plate; galvanized steel||1.2|
|17||Zinc, wrought; zinc-base die-casting alloys; zinc plated||1.25|
|18||Magnesium & magnesium-base alloys, cast or wrought||1.75|
3. Sacrificial Metallic Coating
Anodic metallic coatings provides sacrificial galvanic corrosion protection to the base material. Metallic coating sacrifices itself to protect the base material.
Even damaged sacrificial coating protects the base material. For example even after removal of GI coating from sheet cutting edge. It continues to protect the base material cutting edge as well.
Extent of corrosion protection depends on coating material and thickness. For example, 12 micron zinc plating over steel will provide more corrosion resistance compared to 8 micron coating.
4. Size of Cathode and Anode in dissimilar Metals
5. Metallic and non metallic coating
Non-Sacrificial coatings such as powder-coating or paints works as a barrier and reduce galvanic corrosion. These Coatings are not as effective as sacrificial coatings.