When bonding dissimilar materials, which component should be used so that corrosion occurs on that component rather than at the bond surfaces?

When bonding dissimilar materials, which component should be used so that corrosion occurs on that component rather than at the bond surfaces?

• A. A suitable washer
• B. An adhesive sealant
• C. A rubber gasket
• D. A copper gasket

Answer: (A)

When two different metals are bonded together and moisture is present, they form a galvanic cell. The more active metal (the anode) will corrode first, which is often the metal at the bond surfaces. To make sure corrosion happens on a sacrificial element instead of the bond, you place a component that will act as that sacrificial metal between the surfaces. A suitable washer made of a metal that is more anodic than the metals being joined serves this purpose, drawing the corrosion away from the bond surfaces and protecting the actual joints. Adhesive sealant and rubber gasket don’t provide this sacrificial protection, so they won’t direct corrosion away from the bond. A copper gasket is relatively noble and could shift where corrosion occurs in a way that doesn’t protect the bond surfaces. The key idea is using a sacrificial washer to absorb the corrosion.

When two different metals are bonded together and moisture is present, they form a galvanic cell. The more active metal (the anode) will corrode first, which is often the metal at the bond surfaces. To make sure corrosion happens on a sacrificial element instead of the bond, you place a component that will act as that sacrificial metal between the surfaces. A suitable washer made of a metal that is more anodic than the metals being joined serves this purpose, drawing the corrosion away from the bond surfaces and protecting the actual joints.

Adhesive sealant and rubber gasket don’t provide this sacrificial protection, so they won’t direct corrosion away from the bond. A copper gasket is relatively noble and could shift where corrosion occurs in a way that doesn’t protect the bond surfaces. The key idea is using a sacrificial washer to absorb the corrosion.