How does brazing differ from welding in terms of metallurgical bonds?

• A. Brazing forms a metallurgical bond by capillary flow of filler metal without melting base metals; welding fuses base metals together.
• B. Brazing fuses base metals together; welding relies on capillary action of filler metal.
• C. Both involve melting base metals; the difference is only filler material.
• D. Brazing never forms bonds.

Answer: (A)

In brazing, the base metals stay solid. A filler metal with a lower melting point is heated until it becomes molten and flows into the joint by capillary action, wetting the surfaces. As the filler cools, it bonds to the base metals, forming a metallurgical bond at the interfaces. There is no melting of the workpieces themselves, so the strength and integrity come from the solidified filler metal bridging the joint.

In welding, the heat is high enough to melt the base metals, and they fuse together as the molten material solidifies. This creates a weld pool that coalesces the pieces into a single piece, with a bond formed by the fusion of the base metals (and any filler) rather than by a separate filler layer between solid pieces.

So, the correct concept is that brazing bonds through the capillary flow of a filler metal without melting the base metals, whereas welding fuses the base metals themselves to form the joint. The idea that brazing fuses base metals, that both processes melt base metals, or that brazing never forms bonds isn’t accurate.