In brazing, what indicates that the temperature target has been reached during the cycle?

• A. Base metals have begun to melt.
• B. Flux begins to vaporize.
• C. Joint shows excessive oxidation.
• D. Filler metal melting and complete flow into the joint.

Answer: (D)

The main idea is that brazing reaches the target temperature when the filler metal itself melts and flows into the joint. This happens because the filler is chosen to melt at a lower temperature than the base metals, so once you hit the braze temperature, the filler becomes molten and is drawn into the joint by capillary action, filling the gap and wetting the surfaces. This flow into the joint is what lets the braze bond form properly, creating a continuous, leak‑tight joint without melting the base metals. Other signs aren’t what you want to rely on: base metals starting to melt means you’ve overheated and could ruin the joint; flux vaporizing or excessive oxidation point to heat control issues or cleaning problems. So the reliable indication of having reached the brazing temperature is the filler metal melting and completely flowing into the joint.