I am welding an aluminum (6061) part that is 8.75 long. I start with a tack weld at the ends on material that is 1"x.5"thick and then weld the center which is .050 thick. In the ..050 thick welding I have no problems ( I am purging the back with 100% burn through), however, when I butt weld the ends which are thicker (1 x .50) I see gas bubbles starting to escape. I try to slow down to let the bubbles dissipate but when the material is cleaned up the pin holes are still there. The material is being welded with 4043 rod the ends call out an .125 bevel , it is immaculately clean (it is cleaned with acid etch and stainless wire wheeled. The weld is not dirty it welds clean but no one seems to know why the pin holes keep forming or why the gas bubbles form.

The machine is a Miller 350 Lx with 10 PPS and 2% thoriated tungsten is 3/32 with a glass lens.

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