[ekbmuts]

Today I'm welding 1" square aluminum tubing. 6061, 1/8" wall. I'm welding a bunch of rectangles that are about 18" x 8". So my main members are 18" and the intersecting members are 6". I'll get some pictures but in the meantime, hopefully this paints a picture.

I'm tacking with 4043, 1/16" and finally welding with 5356, 3/32".

Some of (most of) my tacks are cracking, even though I am adding a good amount of filler.

And some of the ENDS of my final welds are cracking.

Hmmm...

My argon flow is about 20CFH. I'm welding with a 3/32" LaYZr tungsten. My workhorse Lincoln PT185 is supplying the current. I have the machine set at 185 amps but that's just so that I can get a good punchy start and increase the heat if needed. I'm using no pulse and about 75% penetration/25% cleaning (estimate).

I am only welding flat; no fillets. I am not grooving my aluminum but just penetrating as much as I can and I do feel I am getting decent penetration.

Maybe because the 18" piece is a bigger heat sink than the 6' pieces, I'm getting differing rates of expansion? Perhaps because I don't have the pieces firmly clamped? Sadly I don't have a welding table, just a 3' x 6' slab of 3/8" steel so I'm a bit limited in terms of tools for fitting up securely.

cj737, tweake - you guys there?

[cj737]

It is not uncommon for tacks to crack. Aluminum tacks are fragile and they usually are on the surface and not deeply penetrating.

5356 as a filler is known to crack when it cools if it’s under stress. It’s called “hot short cracking”. I’m guessing you are using differing fillers due to sizes you have on hand? 5356 to 6061 is not a great marriage in my opinion. I’d stuff 1/16 4043 in and stick with it.

Aluminum frames expand quickly while welding, then shrink when cooling. If the cracks occur after welding while the work is cooling, it’s stress induced. Keep everything clamped up, the quench it or wait it out. In general, welding aluminum tubing is full of patience-testing diabolical tricks. I hammer it with heat and filler and clamp it up so Thor can’t break it out. But in general, you probably need 3-4 dips for decent tacks that will hold during fit up.

[ekbmuts]

That helps. Thanks very much. You're right - 5356 @ 3/32" is what I have to hand. But I also have plenty of 4043 @ 1/16" so I'll just stick with that. With my machine set at 185 amps, I'm not close to full penetration on this 1/8" wall material interestingly enough but my welds are holding.

When you say to quench it, are you literally talking about dipping the hot piece in water?

As always, thanks for responding. Appreciated.

[tweake]

And some of the ENDS of my final welds are cracking.

check how your terminating the welds. ie crater fill. ends of welds will crack if you don't get it right.

the other is mechanical, distortion as the welds cool and that can certainly break tacks and put enough stress on beads to crack them, especially when hot. check your order of operations.

[Timmy_Tiggs]

adding text on Monday

[Timmy_Tiggs]

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[Timmy_Tiggs]

I think at agricultural college they only specified that you had to drop a tack on the notch at the end of the weld but we didn't address the little crater on the tack. I usually spiral the tungsten away while decreasing the pedal (what I did here). This is much easier to learn from a video and I'm pretty sure this is demonstrated on at least one of the WT&T videos.

[Timmy_Tiggs]

I uploaded this picture directly from my phone. If I could do this from home, I would have cropped it and enlarged it (and made it right side up. I was trying to demonstrate what a weld looks like with a notch at the end vs. adding a tack at the end. Maybe I can find a way of doing this without giving Google access to my pictures.