Galvanic Table

Dissimilar metals and alloys have different electrode potentials.  When two or more dissimilar metals come into contact in an electrolyte, such as water, one metal acts as and anode, the other a cathode. The electro-potential difference between the dissimilar metals is what causes galvanic corrosion on the anodic member of the pair or group. The anode metal dissolves into the electrolyte, and deposit collects on the cathodic metal.

The electrolyte provides a means for metallic ions to move from the anode to the cathode. This leads to the anodic meta corroding more quickly than it would otherwise, and corrosion at the cathode is inhibited. The presence of an electrolyte and an electrical conducting path between the metals is essential for galvanic corrosion to occur.

In some cases, this type of reaction is intentionally encouraged. One example is the cathodic protection of buried or submerged structures and objects. In this case, sacrificial metals work as part of a galvanic coupling, promoting corrosion of the sacrificial anode, while protecting the cathode metal.

In other cases, such as mixed metals in molds (for example, aluminum and steel), galvanic corrosion will accelerate corrosion of parts of the system.  Choose metals are closer together in the galvanic table, when used in water cooled areas of the mold.  They have less difference in electrical potential, and therefore are less likely to corrode.

Acidity or alkalinity (pH) is also a major consideration with regard to mold cooling systems. Should the pH balance and corrosion protection design be incorrect, galvanic corrosion will be accelerated.