Galvanic corrosion (sometimes called dissimilar metal corrosion) is the technical name for what happens when different types of metals are coupled in an environment that contains electrolytes - generally speaking, water. One of the metals becomes a positively charged electrode, an anode, while the other becomes the negatively charged cathode. The anode then corrodes more quickly than it normally would, while the cathode corrodes more slowly than normal.

All metals are assigned a value on the Anodic Index (Volts) Scale. These values generally range from 0.00 - 1.85. For example, 18-8 stainless steel has an anodic value of 0.50, while aluminum has a value of around 0.90.

When variations in temperature and exposure to humidity are present, the coupled parts should have anodic values within 0.15 of each other in order to not experience galvanic corrosion. When temperature range and humidity value are tightly controlled, ranges up to 0.50 are likely to be tolerated.

In the example of stainless steel and aluminum, the value difference of 0.40 indicates that the metals will probably not experience serious galvanic corrosion in a temperature or humidity controlled environment, but will likely experience it in an outdoor, wet or more volatile environment.

Fortunately Fastener SuperStore carries parts in a wide variety of materials and finishes. It's always best to match or couple parts with parts of the same metallic makeup. Steel / Zinc with Steel / Zinc; 18-8 Stainless with 18-8 Stainless; etc....

If you must mix parts made from different materials, we recommend checking the Anodic Index values to see if galvanic corrosion should be a concern. Once you have that info you can make a more informed decision regarding what materials to utilize.