What challenge do dissimilar metals pose in brazing, and how is it mitigated?

• A. Similar melting points and diffusion rates; mitigated by using the same filler metal and high heat.
• B. Different melting points and diffusion rates; mitigated by selecting appropriate filler metal and controlled heating to avoid brittle intermetallics.
• C. Oxide formation; mitigated by rapid cooling.
• D. Color mismatch; mitigated by polishing.

Answer: (B)

Dissimilar metals in brazing bring the risk of brittle intermetallic compounds forming in the joint because the two bases have different melting points and diffusion rates. If one metal diffuses into the other too quickly or too far, hard, brittle phases can develop along the interface, weakening the joint. The way to mitigate this is to choose a filler metal whose alloy system is compatible with both base metals and has a suitable melting range, so it can bond without driving excessive diffusion. Coupled with controlled heating—keeping the joint within the filler’s melt window and limiting time at elevated temperature—you reduce the formation and growth of brittle intermetallics, yielding a tougher, more reliable joint.