What effect does adding oxygen or CO2 to shield gas have in GMAW?

Adding oxygen or carbon dioxide to the shield gas in Gas Metal Arc Welding (GMAW) primarily has the effect of increasing the risk of porosity and potential oxidation in the weld. Oxygen and CO2 can react with the molten metal and the underlying materials, leading to the formation of oxides or gas inclusions within the weld pool. This interaction can compromise the integrity of the weld, resulting in weaknesses or pinholes in the final weld, which are indicative of porosity.

Furthermore, while these gases can influence the arc characteristics and metal transfer modes, their presence ultimately poses risks that can negatively impact weld quality. Therefore, while there might be some benefits to using these gases for certain applications or processes, the primary concern is the potential for introducing defects, making this the correct understanding in the context of GMAW practices.