Which best describes lack of fusion in a weld, and a typical corrective action?

• A. The weld metal did not fuse with the base metal or previous pass; fix by increasing heat, adjusting travel speed, and ensuring proper contact.
• B. The weld metal did not penetrate through the joint thickness; fix by reducing heat and decreasing travel speed.
• C. Surface porosity due to moisture; fix by cooling quickly.
• D. The weld bead is too wide; fix by moving electrode away.

Answer: (A)

Lack of fusion happens when the weld metal fails to bond to the base metal or to a previous weld pass, so there’s no metallurgical link between the layers and a visible gap or seam remains. This usually comes from not enough heat input, improper contact between the electrode and work, or moving too fast for the molten metal to fuse properly. The best corrective action is to increase heat input, adjust travel speed so the arc spends more time heating and melting at the joint, and ensure proper contact and alignment so the molten metal actually fuses to the base metal or prior weld.

The other descriptions refer to different defects: a lack of penetration means the weld doesn’t extend through the joint thickness and would be addressed by changes that increase fusion, not reduce heat; surface porosity from moisture is a cleanliness/material issue and is fixed by drying the parts; a bead that is too wide is a heat/feeed angle issue and would be corrected by adjusting electrode distance or travel speed.