Active Welding Shielding Gas Based on CO2
Pure carbon dioxide or argon-dominated mixed gas that chemically interacts with the weld pool to increase arc stability and control droplet transfer.
CO2 in shielding gas is not a noble gas; it reacts in the arc. That stuff breaks down in the heat and releases oxygen that oxidizes the weld pool. That's why you need filler wire with enough deoxidizers like manganese and silicon, otherwise you get porosity.
A high CO2 content makes the arc more aggressive and spattery, but the gas is cheap. Pure CO2 works for some jobs, but the bead looks rougher. A mixed gas with less CO2 and more argon burns more stable and cleaner, which is the better choice for thinner sheets and visible welds.
Also, watch out that no draft hits the weld pool, otherwise the gas gets blown away and you pull in air. Then you get porosity in the weld right away. And the gas flow has to be right – too little gas does nothing for you, too much also sucks in air again.