Shielding Gases

If air comes in contact with the molten or heated metal, the oxygen in the air will oxidise the metal, the nitrogen might cause porosity or brittleness in the weld metal, and moisture from the air may also cause porosity.

The shielding gas composition affects the material transition from the molten electrode to the weld pool, which in turn infuences the amount and size of the spatter created.

It also affects the appearance of the weld bead, the weld geometry, the possible welding speed and plays a key role in the possible burn-off of alloying elements (which affects material strength) or oxide formation on the bead surface.