What is porosity in a MIG weld, and what is a common cause in collision repair work?

• A. Porosity are gas pockets within the weld caused by contamination or moisture; common causes include moisture on wire, damp shielding gas, oil/paint/solvents on the surface
• B. Porosity is a design feature that improves strength
• C. Porosity refers to the color of the weld
• D. Porosity is the same as undercut

Answer: (A)

Porosity in a MIG weld means there are gas pockets trapped in the weld metal, which weakens the joint. In GMAW welding, porosity usually comes from hydrogen entering the weld because shielding isn’t perfect or contaminants add gas.

Common causes in collision repair work include moisture on the welding wire, damp or contaminated shielding gas, and oil, paint, or solvents on the surface being welded. Moisture on the wire can vaporize into the weld pool, the shielding gas can be insufficient or contaminated and fail to protect the molten metal, and oils or solvents on the surface release gases as they burn, all creating bubbles in the weld.

Porosity shows up as small gas pockets inside the weld and compromises strength and corrosion resistance, unlike color changes or surface features like undercut, which are different issues.