Which statement about shielding gas use for aluminum welding is correct?

• A. Oxygen can be used to improve weld quality
• B. Hydrogen can be used in trace amounts
• C. CO2 can be used in trace amounts
• D. Neither oxygen, hydrogen, nor CO2 should ever be used for welding aluminum with GMAW

Answer: (D)

When welding aluminum with GMAW, the shielding gas must protect the molten pool from reacting with air, and it should not introduce elements that cause oxide or gas porosity. Argon (or argon with helium blends) is used because these gases are inert and prevent oxidation without adding any reactive species to the weld. Gases that contain oxygen, CO2, or hydrogen will react with aluminum or create gas pores in the weld. Oxygen promotes oxide inclusions, CO2 can lead to oxidation and porosity, and hydrogen can form gas pockets or cause hydrogen-related cracking in aluminum. Because of these issues, none of those gases should be used for shielding aluminum in GMAW. The correct approach is to use an inert shielding gas such as argon (and possibly helium for certain applications).