How to Mig Weld Aluminum

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Metal inert gas (MIG) welding uses a consumable wire electrode and shielding gas, which is continuously fed through a welding gun. Aluminum requires some specific changes for welders who are accustomed to welding steel. It is a much softer metal so the feed wire must be larger. Aluminum is also a better conductor of heat, so welding aluminum requires more control over the power supply and the feed rate of the electrode.

Steps

Choose Equipment and Materials

  1. Select more powerful welding machines for thicker metal. A 115-volt welder can handle aluminum up to an eighth of an inch thick (3 mm) with adequate preheating, and a 230-volt machine can weld aluminum thats up to a quarter of an inch thick (6 mm). Consider a machine with an output greater than 200 amps if you will be welding aluminum daily.
  2. Choose the correct shielding gas. Aluminum requires a shielding gas of pure argon in contrast with steel, which typically uses a blend of argon and carbon dioxide (CO2). This should not require any new hoses, although you may need to replace regulators that were designed specifically for CO2.
  3. Use aluminum electrodes. Electrode thickness is especially critical with aluminum and there is an extremely narrow range to consider. Thinner wire is more difficult to feed, while thicker wire requires greater current to melt. The electrodes for welding aluminum should be 35,000ths of an inch in diameter (less than 1 mm). One of the best choices is 4043 aluminum. A harder alloy like 5356 aluminum is easier to feed, but will require more current.

Use Correct Technique

  1. Feed the electrodes with an aluminum feeding kit. These kits are commercially available and will will allow you to feed softer aluminum wire with the following features:
    • Larger holes on the contact tips. Aluminum expands more than steel as its heated. This means the contact tips will need larger holes than the ones used for steel wire of the same size. However, the holes should still be small enough to provide good electrical contact.
    • U-shaped drive rolls. Aluminum feeders should use drive rolls that wont shave aluminum wire. The inlet and outlet guides for these feeders shouldnt shave the softer aluminum wire. In contrast, steel feeders use V-shaped drive rolls, which are specifically designed to shave the wire.
    • Non-metallic liners, which will further reduce the friction on the wire as it goes through the feeder.
  2. Keep the gun cable as straight as possible so the wire feeds properly. Softer wire is more prone to kinks due to feeding restrictions.

Tips

  • The most weldable aluminum alloys also tend to be the weakest alloys. Many aluminum alloys are simply not weldable.
  • An aluminum weld will rarely be as strong as the base material.
  • Use heat treatment after the weld has been made to improve the strength of heat treatable alloys.

Warnings

  • Always wear a face plate when welding. You should never look directly at the arc, even while wearing a face plate.
  • Wear clothing that completely covers your arms and legs while welding, including gloves. Flying sparks and embers are a constant hazard.

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Sources and Citations

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