Cleaning base metal prevents which defects?

• A. Cracking.
• B. Warping.
• C. No effect.
• D. Porosity, inclusions, and poor fusion.

Answer: (D)

Contaminants on the base metal—oil, dirt, rust, moisture, or oxide films—block proper surface wetting and can trap gases in the weld pool. Cleaning removes these impurities, allowing the filler metal to fuse properly with the base metal and giving shielding gas a clean path to protect the molten metal. With a clean surface, the weld is less likely to have gas porosity, debris inclusions, and weak bonding between base metal and filler. Cracking and warping depend more on heat input, joint design, and restraint, so cleaning isn’t the primary factor for preventing those. So cleaning base metal most directly prevents porosity, inclusions, and poor fusion.