tig welding aluminum with a DC only tig

[jakeru]

Wouldn't in Theory if you have aluminum with no oxidation or contaminants in an inert atmosphere you could weld it DCEN?

For whatever reason (I don't know, maybe no one has really proved it, I'm sure there are some theories out there...) the aluminum seems to form oxides on the surface at high temperature, even in an inert atmosphere. Maybe the oxygen is being transferred through the metal somehow? I don't know. I hate to say it, but it "just does."

For probably the same reason that oxides form on the front side of the weld (without flux, and without EP), shielding the back side of an aluminum weld joint with an inert gas (like argon) doesn't seem to work to allow full penetration. You can't just backpurge aluminum, like you can, say, stainless steel. Some oxides invariably will form on the back side of the aluminum weld joint, even in an inert/backpurged environment, and impede the flow of the metal on the back side (usually preventing the "weld bead penetration" from going all the way through to the back surface or beyond, like you can effortlessly easily achieve with steels and stainless steels.)

If you had a DC TIG and wanted to weld aluminum, and could clean the back side, I'd look into using some flux. Like, an aluminum stick welding electrode, which is covered in flux. Or alternately, apply some oxy-fuel welding flux to the aluminum before striking your DC arc. Although you won't have the finesse in controlling the front surface of the puddle like you can with AC TIG (since you'll have a layer of molten flux on the surface), and so you wont get the same aesthetic to your weld bead, you sure can make some very solid, and strong welds that won't have oxide inclusions underneath the surface if you use some flux... Even with DC TIG.

The flux does need to be removed! It's basically kind of like a really strong salt. If you leave it on there, it will absorb water right from the atmosphere, and, even over a short period of time, you will see your work getting pretty severely corroded. (If not removed.) Removal typically requires pretty vigorous mechanical scrubbing with preferably pretty hot water. Got a laundry tub and a metal brush? Hot water in there and a metal brush should do the trick. (Or really strong acids like hydrofluoric, that I have not tried, and probably never will. I believe they are strong enough to be able to eat away at glass!)

I used to oxy-fuel weld aluminum, with mixed results. I am so happy I don't need to use flux anymore, due to the availability of the AC TIG welding process that I currently enjoy.

If you had DC TIG however, and wanted to make it weld aluminum though, and could access the back side of the joint for mechanically removing flux (in addition to the front which since you're able to strike an arc, you should likely be able to access well enough for flux removal) , look into using a stick welding electrode with the flux covering it, for the DC TIG process with should allow much better heat control (and less oxidation so you flux will stay cleaner) than stick welding aluminum. Or, look into some kind of separate flux (such as for oxy-fuel aluminum welding) to add to the weld joint before striking the DC TIG arc, to make the aluminum puddle underneath the flux flow.

cheers

[jp2code]

Good stuff, Jake.

I used to have some aluminum arc rods that I used at a welding shop. There were no directions, though, and I noticed after we welded with it ...and did NOT remove the slag! ...that moisture would quickly form beneath the slag and the aluminum bead. I would have described that moisture as very salty. I don't know if I tasted it or some managed to get on my lips or something while trying to remove the slag.

[welderdude]

I remember a guy on WW claiming that he used UHP lab grade helium and DCEN to weld aluminum. Whether or not its really doable or not, I don't know.