Black scale on TIG weld bead...why???

by eric
(Atlanta, GA)

I am learning to TIG weld aluminum with a Miller 180 SD machine. The plate in the picture is 1/4 inch plate, rod is 4043 3/32, electrode is 100% tungsten and the gas is 100% argon. I brushed the plate really well with a dedicated stainless steel brush and I cleaned the rod with acetone and then took oxidation off with a scrotchbrite pad.

However, after I try to create the famous stack of dimes I get a black crusty scale that develops on top of the beads and I don't know why this is happening. I thought it was a dirty tungsten or dirty aluminum but I cleaned this stuff really well without contamination. I then thought it was because I didn't have a tight arc but I've been very deliberate in trying to keep the arc tight at about 1/8 inch above the plate and also avoiding getting the rod into the arc at all.

Maybe you guys can see where I'm slacking in my technique or something. I've already burned through a pound of aluminum rod and I'm going back this week to get some more...practice makes perfect as they say.

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Eric, you are getting contamination in your shielding gas.

you either have a bad cylinder of argon, a leak, a faulty collet body, or something else causing your shielding gas to be crappy at the puddle,

is your tungsten bright and silver after running a bead? if not, then that cinches it.

i wouldnt use the scotchbrite either until you figure this out.

i will email you directly so you wont have to wait for these to be posted going back and forth.

good luck,

jody