Welding Aluminum: MIG welding options

Welder at The WDC
03/10/2021 - by Jack Miller

Aluminum material has very specific properties which need to be considered during welding to prevent excessive distortion and grain growth. They are:

  1. High coefficient of thermal expansion (approx. twice that of steel) and,
  2. High Thermal conductivity.

It must therefore seem logical for any fabricator of aluminum to select a low heat input process, and for MIG welding this is often short circuiting and pulse transfer.

Short circuiting MIG welding is a process related to low voltages and amperage in comparison to other transfer modes (Spray). The wire feed rate just exceeds the burn off rate and a short circuiting of the wire on to the parent material is witnessed.

Pulse MIG welding is a transfer mode which can operate at a moderately low amperage. The droplets created tend to be smaller than the diameter of the electrode and no contact is required, "free flight". A background and peak current are applied at a controllable frequency. During times for peak current the weld pool penetrates the material creating conditions for good fusion.

Short circuiting pros and cons.

  • Pros:
    1. Low heat input relative to spray
    2. Great for positional welding
    3. Good on thin materials
    4. Low distortion
    5. DCEP has good oxide cleaning effect
  • Cons:
    1. Low heat input can lead to lack of fusion defects
    2. Low heat input and rapid cooling can create conditions for porosity (wormhole and cluster)
    3. Stop start defects are common

Pulse welding pros and cons.

  • Pros:
    1. Lower average heat input
    2. Good for positional welding
    3. Good on thick and thin materials
    4. Low distortion index
    5. DCEP has good oxide cleaning properties
    6. Helps to lower porosity
    7. Creates good penetration
    8. Wider operating window
  • Cons:
    1. Increased capital investment
    2. Marginally more difficult to set-up

It should be noted that most welding equipment like Lincoln electric power MIG 360MP have a start and crater function. These controls help to provide amperage control at the start and finish of a weld run. This will help to prevent stop start defects.