Why should you avoid cross-contamination with carbon steel during cleaning aluminum surfaces before TIG welding?

• A. It can rust and stain
• B. It can introduce carbon steel particles that cause porosity in aluminum welds
• C. It improves weld quality
• D. It has no effect

Answer: (B)

Contaminating an aluminum surface with carbon steel introduces iron particles into the weld area that don’t dissolve in the aluminum melt. Those steel particles become inclusions or oxide sites in the weld pool, which disrupt proper bonding and act as nucleation points for gas porosity. In aluminum TIG welding, porosity is a common defect, and iron contamination makes it much more likely. That’s why keeping cleaning tools and methods free of carbon steel is important. The other ideas don’t fit because the issue isn’t simply cosmetic rust or staining, it’s the impurity causing porosity and weakening the weld.