MIG Wire Types


Versatility and efficiency have made metal inert gas (MIG) the most common form of welding used in metal fabrication and production. MIG welding uses wire, fed from a spool, to control the amount of filler metal added to the weld puddle. MIG wire is categorized by diameter, alloy and type.

MIG Wire Designations

  • The alloy of the MIG wire must match the base metal being welded to ensure a strong weld that will not crack or weaken when cooled. Welders have the option of welding carbon steel, stainless steel and aluminum thanks to the wide variety of wire alloys available for MIG welders.

    A MIG wire spool has the alloy, diameter and type of wire marked on a label. The label is located on the side of the wire spool that is visible while attached to the welding machine. For example: A carbon steel alloy can have the marking ER70S-6, which designates the carbon alloy. The diameter is marked either next to or under the alloy and would read as 0.035, which is a common diameter wire for metal fabrication.

    The wire type will also be marked on the label, but each manufacture has a different way of marking wire type. There are two distinct types of MIG wire, solid core and flux core.

Solid Core MIG Wire

  • Solid core MIG wire is a solid strand of the designated alloy. Welding with solid wire requires that an inert shielding gas be used to eliminate weld contamination. For carbon steel, 75 percent argon/25 percent carbon dioxide is commonly used to shield the weld puddle. Stainless steel and aluminum alloys use either argon, helium or a three gas mixture to shield the weld.

Solid Core Wire Disadvantages

  • Shielding gas can easily be disrupted while welding. If the shielding gas does not fully shield the weld, porosity can form. Porosity reduces the structural integrity of the weld and in the case of X-ray welds this can result in costly time consuming repairs. Gas bottles are heavy and hard to transport. This limits the portability of welding machines using solid core wire.

Flux Core MIG Wire

  • Flux core MIG welding wire has a flux paste inner core that is surrounded by the filler metal. When the flux core wire is fed into the weld puddle, the flux heats up and burns, this creates the shielding gas for the weld. Flux core does not require a bottle of gas to be attached to the welding machine, this reduces the amount of bulk required to weld in tight spaces outside of a shop.

Flux Core Wire Disadvantages

  • Welding with flux core wire has a tendency of producing more splatter than shielded solid wire. This increases the risk of fire in the area of the welder and welder burns increase when the welds are performed overhead. Another disadvantage of flux core wire is heat control. With no shielding gas to adjust, heat builds up rapidly and as a result, maintaining a proper weld setting becomes difficult.


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