The Galvanic Series Chart
Magnesium Magnesium alloys	POSITIVE CHARGE Anode (+) least noble
Zinc
Aluminum 1100
Cadmium
Aluminum 2024-T4
Steel or Iron Cast Iron	LESSENING POSITIVE CHARGE
Ni-Resist
Type 304 Stainless (active) Type 316 Stainless (active)
Hastelloy "C"
Lead Tin Soldiers Lead, Tin
Nickel (active) Inconel	ELECTRIC CURRENT FLOWS FROM POSITIVE TO NEGATIVE
Hastelloy "B"
Brasses, Copper, Bronzes Copper-nickel alloys Monel
Silver Solder
Nickel (passive) Inconel (passive)	INCREASING NEGATIVE CHARGE
Chromium-iron (passive)
Type 304 Stainless (passive) Type 316 Stainless (passive)
Silver
Titanium
Graphite, Gold Platinum	NEGATIVE CHARGE Cathode (-) most noble

The loss to the world economy due to corrosion is in the billions per year. This loss is due to, galvanic corrosion, direct attack corrosion, and other types of corrosion. A rusty bolt on a machine could shut down a production line for hours, or even days. Its the old age problem of corrosion. There are steps you can take to minimize the problem. Assess the environment where your investment will be, and use the proper corrosion-resistant fastener accordingly. At Clark Craft, we supply fasteners in corrosion-resistant metals. In the long run, when you consider the labor, maintenance, and replacement cost of a failed fastener, the cost would have been far less if the proper fastener had been used.

What is corrosion? Corrosion is the wearing away, or alteration of a metal by galvanic reaction, or by direct chemical atttack. An example is the rusting of iron, or steel.

Direct Attack Corrosion. Atmospheric corrosion is an example of direct chemical attack. Present in the atmosphere are oxygen, carbon dioxide, water vapor, sulfur, and chlorine compounds. The severity of the attack is directly related to the amount of water vapor, sulfur and chlorine compounds present.

Galvanic Corrosion (Electrochemical). All metals have specific relative electrical potential. When metals of different electrical potenial such as steel and copper are in contact in the presence of moisture, a low energy electric current flows from the metal having the higher position in the galvanic series.This is called "galvanic action."

To help prevent direct attack corrosion. Select the material most likey to resist the corrosive environment to which the fastener will be subjected.

To help prevent galvanic corrosion. If possible use the same, or similar metals in an assembly, especially where an electrolyte may be present. ( One example of an electrolyte would be water). When dissimilar metals are used together in the presence of an electrolyte, separate them with a dialectric material such as insulation, paint or coating. Avoid combinations where the area of the less noble material is relatively small. The current density is greater when the current flows from the small area to the large rather than in the reverse situation. Typically, the fastener will be small compared to the rest of the assembly. The fasteners alloy, if not the same as the material being joined, should be lower in the galvanic series. The galvanic process can be used to your advantage by coupling the part to be protected to pieces of less noble metal which are not functional and can thus corrode sacrificially. An example of this would be a zinc fastened to the strut on a yacht in sea water.