We tried water quenching some parts during our automated flame-brazing operation, and the joints don't look good. Some are weak, showing poor filler-metal solidification around the joint. We sprayed the water-quench onto the part immediately after it departed from the flames in order to get the maximum quench effect. Can you tell us why the filler metal looks so bad?

Brazing filler metals (BFMs) should never be quenched while they are still molten during any brazing operation (be it torch, induction or furnace brazing). Neither does the quenching medium make a difference. Rapid quenching of molten BFM with water, air or inert gas makes no difference. BFMs must simply never be quenched while they are still molten. Rapid impingement of water or gas on the molten BFM disturbs the solidification process, causing the BFM to move and shift while trying to solidify, resulting in excessive voiding, cracking, etc. in the joint being brazed.

Additionally, the BFM must be completely quiescent while solidifying in order to give good results. So, after the BFM leaves the flame station or immediately after the induction coil is turned off, the part being brazed must be allowed to remain perfectly still (don't move it while the BFM is molten). No quenchant should be used until the brazing operator can physically see that the BFM pool has solidified. After the joint has completely solidified, any desired quenchant can be applied and the part may also be moved (shifted) to another location.

KEY TO SUCCESS: Do not disturb the joint in any way while molten BFM is liquid and starting to cool down. Allow it to solidify completely before quenching it or moving it. Careful adherence to this principle will prevent a lot of potential problems in brazing.