Understanding galvanic corrosion
Corrosion is the breakdownof metal(through chemical or electrochemical reactions) into oxide, hydroxide, or sulfide.
We commonly associate corrosion with rust which is just one form of localized corrosion.
There are several different types including galvanic corrosion which is of special interest for those involved in sheet metal fabrication finishes.
Galvanic corrosionis a result of two dissimilarmetals with electrical or physical contact in a corrosive electrolyte – commonly water, salt, soluble acids, or bases.
In these conditions, one of the metals becomes an anode and the other a cathode. The anode will corrode faster than it would have alone while corrosion to the cathode is slowed.
The anode is often referred to as the “sacrificial” metal.
Galvanic corrosion creates a significant risk for metal fabricated products where multiple metals are used.
Fasteners are a good example. Using metal bolts that act as a cathode to a frame will result in faster corrosion to the frame than you would normally expect from the metal used to make it.
Preventing galvanic corrosion involves three key things: choosing compatible metals whenever possible, prevent contact between incompatible metals through insulation or coating, or provide a coating to the connection to prevent exposure to the corrosion environment.
Some metal coatings take advantage of galvanic corrosion to enhance the corrosion resistant properties of a metal.
Zinc plated and galvanized dipped metals,for example, use these principals to enhance the corrosion resistance of different types of steel.
Zinc will take on the sacrificial anode role and corrode first, protecting the steel it is coating.
Other finishes can help prevent galvanic corrosion without acting as a sacrificial anode.
Ecoating, powder coating, Dacromet, and anodizing finishes can also provide protection by helping prevent contact between the two dissimilar metals or eliminating exposure to the corrosive environment.