Dissimilar metal corrosion is most likely to occur in which situation?

• A. Where two components of the same alloy are joined.
• B. Only when aluminum contacts steel in dry conditions.
• C. Anywhere different types of metal come in contact with each other, especially where moisture is present.
• D. In sealed, isolated aluminum joints.

Answer: (C)

Dissimilar metal corrosion happens when two different metals are in electrical contact and an electrolyte is present. In that situation, the more active metal (the anode) tends to corrode, while the more noble metal (the cathode) is protected. Moisture provides the electrolyte that allows ions to move and current to flow, so corrosion occurs most readily when different metals touch and moisture is around. Dry conditions or joining identical metals don’t set up a galvanic couple, so corrosion is much less likely.

So the best scenario is any situation where different metals come into contact and moisture is present.