Incomplete fusion occurs when

Incomplete fusion occurs when

• A. Weld pool fuses completely with base metal.
• B. Weld pool flows onto unwelded base metal without fusing.
• C. Weld pool contracts and leaves voids.
• D. Weld pool fails to reach the weld root.

Answer: (B)

Incomplete fusion happens when the weld metal doesn’t actually bond to the base metal, even though molten metal is present. In this case, the weld pool flows onto unwelded base metal but fails to fuse with it, so there’s a lack of metallurgical connection at the interface. That’s why this option best describes lack of fusion: the metal is there, but the bond isn’t formed. Other situations aren’t the same defect: welding that fuses completely with the base metal is proper fusion; weld metal contracting and leaving voids points to shrinkage or porosity issues rather than a failure to fuse; and the weld pool not reaching the weld root describes incomplete penetration, which is a different defect from incomplete fusion.

Incomplete fusion happens when the weld metal doesn’t actually bond to the base metal, even though molten metal is present. In this case, the weld pool flows onto unwelded base metal but fails to fuse with it, so there’s a lack of metallurgical connection at the interface. That’s why this option best describes lack of fusion: the metal is there, but the bond isn’t formed.

Other situations aren’t the same defect: welding that fuses completely with the base metal is proper fusion; weld metal contracting and leaving voids points to shrinkage or porosity issues rather than a failure to fuse; and the weld pool not reaching the weld root describes incomplete penetration, which is a different defect from incomplete fusion.