**2. Fusion welding (arc welding)**

Fusion welding is known as non-pressure welding, in which edge samples to be joined with the filler metal are heated above the melting points to create a weld pool and allow solidifica‐ tion. Gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) are categorized under fusion welding. GTAW and GMAW are mostly used by the welder to weld both ferrous and non-ferrous metals. In fusion welding, inert gases, such as argon (Ar), helium (He), and carbon dioxide (CO2), are used for surrounding the electrode and molten metal from the welded metal. These inert gases will eliminate the formation of metal oxides and nitrides, which can lower the ductility and toughness of the welded metal.

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