Which shielding gas is best for welding aluminum?

• A. CO2
• B. Helium
• C. Air
• D. Pure Argon

Answer: (D)

Aluminum welds need an inert shielding gas to keep oxygen from reacting with the molten metal, which would form oxides and cause porosity. Pure argon is the best choice because it is inert and provides stable arc and good coverage for non-ferrous metals like aluminum. Other options introduce reactive elements or contaminants: CO2 and air bring oxygen and moisture that promote oxidation and porosity, while helium can increase heat input but is more expensive and not as universally recommended for typical aluminum welding. Hence, pure argon gives the most reliable protection and weld quality for aluminum.