Aluminum Workshop: Clearing up oxide misconceptions

Q: My company welds 6063 tubing using AC gas tungsten arc welding (GTAW) with 4043 filler metal and pure argon shielding gas. Appearance is important. How can we eliminate, or at least minimize, the oxidized area on each side of the weld?

A: We need to first clear up a misconception. The area you describe, which is usually 1/16 to ¼ in. wide on each side of the weld, is not oxidized. It is the area where all the oxide has been removed from the surface of the aluminum by the AC arc. It is necessary that this area be present. If it isn’t, you would be doing something wrong, and the weld would most likely be unacceptable.

We all know that the most common way to GTAW aluminum is to use AC. Why? It is much easier to weld using AC because the direct current electrode positive (DCEP) part of the AC wave actually removes the oxide from the aluminum. So we sacrifice a bit of penetration to get the arc cleaning when we AC weld.

Can you do anything to minimize the width of the arc-cleaned stripes? Yes. Conventional sine wave AC is symmetrical—50 percent EN and 50 percent EP. However, you don’t really need this much EP to get good arc cleaning. So GTAW power supply manufacturers give you a balance control to vary the proportion of EP to EN. If you want to minimize the width of the cleaning stripes, all you need to do is turn the balance control to higher EN values.

Most manufacturers call this the penetration end of the scale. You can probably run with adequate arc cleaning around 30 percent to 35 percent EP (that is, 65 percent to 70 percent EN). Try ist and see how the width of the cleaning stripes changes.