In bonding dissimilar materials, which component is used to localize corrosion to that component?

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

Answer: (A)

When dissimilar metals are joined in the presence of an electrolyte, a galvanic cell forms and the more anodic metal tends to corrode. Using a suitable washer between the metals creates a controlled, sacrificial area that will preferentially corrode, localizing the corrosion to that washer. This keeps the rest of the joint protected and makes corrosion easier to monitor and replace. A rubber gasket or plastic spacer would insulate the metals and prevent galvanic action, and an adhesive sealant often acts as a sealant barrier, also reducing or blocking galvanic current. Therefore, the washer is the component chosen to direct corrosion to itself.