Galvanic Corrosion

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:

  1. Electrochemically dissimilar metals with different anodic index must be in contact.
  2. 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.

Check out in detail how we can protect Galvanic corrosion.

Design Recommendations :

  1. For harsh environments (high humidity and salt concentration), difference in materials anodic index value shall be less than 0.15 V .
  2. For environments  with varying temperature and humidity, difference in materials anodic index value shall be less than 0.25 V.
  3. In worst conditions, difference in materials anodic index value shall be not more than 0.5 V.
Note : Values given here are for indicative purpose only. Final decision on material and finish selection shall be done based on tests. 

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
19 Beryllium 1.85
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