What describes lack of fusion in welding?

• A. Weld metal fails to fuse with the base metal or previous weld bead.
• B. Weld metal fuses excessively with the base metal.
• C. Weld bead appears with excessive reinforcement.
• D. The weld breaks under minor bending.

Answer: (A)

Lack of fusion happens when the weld metal does not melt and bond to the base metal or to a previously deposited weld bead, so the joint has an unbonded interface. This is a discontinuity because the metal never actually fused across that boundary, which weakens the joint and can cause failure under load. The option describing weld metal failing to fuse with the base metal or previous weld bead matches this defect precisely. The other descriptions refer to different problems: excessive fusion means too much melting and bonding, excessive reinforcement means too much weld material on top, and breaking under minor bending points to a general weakness that could arise from several issues, not specifically lack of fusion.