Red Seal Metal Fabricator (Fitter) Practice Exam

Which gas is commonly used as a shielding gas in MIG welding?

1. Argon

2. Oxygen

3. Carbon Dioxide

4. Hydrogen

The correct answer is: Argon

Argon is commonly used as a shielding gas in Metal Inert Gas (MIG) welding due to its inert properties. Being a noble gas, argon does not react with the molten metal, providing a stable and contamination-free environment during the welding process. This is crucial because any reaction that occurs between the shielding gas and the molten metal can lead to defects in the weld, such as porosity or reduced strength. While oxygen, carbon dioxide, and hydrogen can be used in certain welding applications, they do not provide the same level of protection that argon does. Oxygen can cause oxidation of the weld, leading to weak joints and impurities. Carbon dioxide, though sometimes used in combination with argon to reduce costs, can also introduce challenges, such as increased spatter and a less stable arc. Hydrogen, being reactive, can cause hydrogen embrittlement in metals, which is undesirable in many welding scenarios. Therefore, the use of argon is essential for achieving high-quality, durable welds in MIG welding processes.