What is Galvanic Corrosion?
Galvanic Corrosion is a electrochemical process where one material corrodes if comes in contact with another material. It is also known as Dissimilar Metal Corrosion.
Prior conditions for galvanic corrosion:
- Electrochemically dissimilar metals with different anodic index must be in contact.
- Electrically conductive path between metals for the movement of metal ions from higher anodic metal to higher cathodic metal.
How to prevent Galvanic Corrosion ?
Straight a way answer is : Do not bring dissimilar metals in contact. But In design scenario it is not feasible option.
One of the way is to control the galvanic compatibility of a metal by finish operations such-as plating. Plating can facilitates in bringing dissimilar materials in contact and protecting the base materials from corrosion.
Design Recommendations :
- For harsh environments (high humidity and salt concentration), difference in materials anodic index value shall be less than 0.15 V .
- For environments with varying temperature and humidity, difference in materials anodic index value shall be less than 0.25 V.
- In worst conditions, difference in materials anodic index value shall be not more than 0.5 V.
Anodic Index Table
|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|