Inert shielding gas
Inert shielding gas like argon or helium does not react with the weld pool. It displaces air from the weld zone and prevents oxidation, porosity, and embrittlement. This keeps the weld metallurgically clean and tough.
Physical-Chemical Mechanism of Action
Argon and helium are noble gases. They do not form chemical compounds with the molten metal. During welding, the gas flows from the nozzle and forms a protective shield around the arc and weld pool. This shield displaces oxygen, nitrogen, and water vapor from the surrounding air. Argon is heavier than air and stays close over the pool. Helium is lighter and rises faster but provides more heat into the arc. Without this protection, the hot metal surface oxidizes immediately and picks up harmful gases.
Metallurgical Relevance & Risks in Welding
If the protection is missing or the gas amount is wrong, the weld pool reacts with air. Oxygen forms oxides and slag, nitrogen causes porosity and embrittlement, and hydrogen leads to cold or hydrogen-induced cracking. Especially with high-alloy steels, aluminum, and titanium, any air contact leads to immediate quality loss. Also, too high gas flow disturbs the shielding layer and sucks in air. The result is porosity, discoloration, cracking, or lack of strength.
Shop Practice & Action Instructions
Set the gas flow exactly: for TIG welding 8–12 L/min, for MIG welding of aluminum 12–18 L/min, depending on nozzle size and drafts. Use pre-flow time of 1–2 seconds and post-flow time of 5–10 seconds to keep the pool protected until solidification. Keep the torch perpendicular and the nozzle distance constant (5–10 mm for TIG). Check hoses and connections for leaks. Never work in strong wind without wind protection. For aluminum and titanium, use argon with at least 99.996% purity.