A fabrication shop is welding aluminum tanks for a chemical processing plant. The welding procedure requires Gas Metal Arc Welding (GMAW) with argon shielding gas. After welding, visual inspection reveals numerous wormhole-like indications on the weld surface and grinding exposes more internal porosity. If the shielding gas regulator is confirmed to be set correctly, what is a highly probable cause of this severe porosity in the aluminum weld, given the process?

Question: A fabrication shop is welding aluminum tanks for a chemical processing plant. The welding procedure requires Gas Metal Arc Welding (GMAW) with argon shielding gas. After welding, visual inspection reveals numerous wormhole-like indications on the weld surface and grinding exposes more internal porosity. If the shielding gas regulator is confirmed to be set correctly, what is a highly probable cause of this severe porosity in the aluminum weld, given the process?

Answer options:

• Excessively high welding speed. ✅ Contaminated filler wire or base material.
• Insufficient welding current.
• Incorrect tungsten electrode type (for GMAW).

Correct answer: Contaminated filler wire or base material.

Explanation: In GMAW of aluminum, severe porosity (including wormhole porosity) is strongly associated with hydrogen contamination, which can come from moisture or hydrocarbons on the filler wire or base material. Aluminum readily absorbs hydrogen at welding temperatures and expels it as gas upon solidification, forming pores. While welding speed and current can influence porosity, gross contamination is often the primary cause of severe and widespread porosity.