In bonding dissimilar materials, what is the purpose of using a washer?

• A. To localize corrosion to the washer
• B. To prevent corrosion entirely
• C. To provide electrical insulation
• D. To increase corrosion at the bond interface

Answer: (A)

When two different metals are bonded and exposed to moisture, a galvanic cell can form. The idea behind using a washer is to create a sacrificial corrosion site that takes the hit for the joint. The washer is chosen so that it is more anodic than the metals being joined, so corrosion preferentially occurs on the washer rather than at the bond interface. This localizes the corrosion to the washer, helping protect the actual bond from accelerated deterioration while maintaining the electrical connection. It’s not about preventing all corrosion or insulating the joint—both would defeat the purpose of the bond; it’s about directing the corrosion to a sacrificial element to preserve the bond’s integrity.