Question

Which ONE of the following is FALSE with respect to filler material used in brazing?

• A. Melting temperature of the filler material must be less than the base metal.
• B. Wettability of the base metal by the filler material must be low.
• C. Viscosity of the filler material must be low for penetration into the interface.
• D. Chemical reactivity between the filler material and the base metal must be low.

Hint:

Brazing depends on capillary action, which needs HIGH wettability and low viscosity to pull filler into the joint gap.

Answer 1

The Correct Option is B

Step 1: Recall why brazing works.
Brazing joins two metal parts using a filler metal that melts and flows into the gap between them, while the base metal itself stays solid.
The joint forms mainly through capillary action, the same effect that pulls water up a thin tube.

Step 2: Check option (A).
The filler must melt at a lower temperature than the base metal, since only the filler is meant to melt while the base parts stay solid.
This matches the real rule for brazing, so option (A) is a true statement, not the answer.

Step 3: Check option (B).
Wettability means how well a liquid spreads over a solid surface.
For capillary action to pull the molten filler deep into the joint gap, the filler needs high wettability on the base metal, not low.
So the claim that wettability must be low is wrong, which makes option (B) the false statement.

Step 4: Check option (C).
Low viscosity means the molten filler flows easily, which helps it get pulled into narrow gaps by capillary action.
This is a correct requirement, so option (C) is true.

Step 5: Check option (D).
Some reaction between filler and base metal is needed for a bond, but too much reaction forms brittle compounds and eats away the base metal.
So reactivity should stay low, and this statement is also true.

Final Answer:
The false statement is that wettability must be low; it must actually be high for good capillary flow. \[ \boxed{\text{Option (B)}} \]