[countryboy1127]

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I noticed after i welded it ,There looked to be a crack in the center of the root . Couldnt get a picture of it due to phones getting larger and not being able fit . Could this lead failure or a possilble leak . Its 3" schedule 40 aluminum . I was using a thermal arc pro wave 185 tsw , foot pedal 20 cfh argon 1/8 2% lanthated tungsten . #8 cup

[AndersK]

If you file very carefully on the "crack" I believe you will see its just visible on the surface, right?

I've been trying to beat that thing on thin sheet too. I think its the oxide layers from the both sides not blending together properly. You have nothing on the back side breaking up the oxides, I assume you didnt back-purge it.

Hopefully some of the others that know a lot more than me here will chime in, I'd like to know how to avoid it if possible.

[countryboy1127]

I will try that and see . And correct i didn't back purge it .

[exnailpounder]

Heck, the weld lokks good to me. No real need to back purge aluminum although I suppose it can't hurt anything. Did you pre-heat before you welded?

[countryboy1127]

Thanks . I didnt pre heat it cranked the machine up and made a few 1 inch tacks to heat it up .

[exnailpounder]

[quote="countryboy1127"]Thanks . I didnt pre heat it cranked the machine up and made a few 1 inch tacks to heat it up .[/quote]
It might have short cracked on you if you didn't preheat. I don't really know. Aluminum is about 10% of what I do even though I got back into tig just to do aluminum and stainless. One of the regular aluminum guys will be around to help you.

[Otto Nobedder]

I agree with AndersK, I don't think you have a problem. The root-side always looks a bit odd, with the way the oxides and crud want to settle in to a line.

To avoid cracking on open-root aluminum, make sure you button off properly on your tacks. The tail-off on your tacks require much addition of filler so you don't get a crater at all, as the tail-off on the tacks is the biggest source of cracking in aluminum.

Steve S

[countryboy1127]

I paid very close attention to tailing off to avoid the craters and cracks . I had that problem a few times before . A couple of the starts and stops were a PITA ,the arc wouldnt end in a crisp shut off , it wanted to wander around and kinda sputter out . Either way heres another pic with one complete. And thanks for all the advice guys.

[RocketSurgeon]

Al is all we work with. We have our prep down to an art due to the fact that we hate rework. So, I'm not quite sure this will help you due to the overkill methods we use:

IF you have access, clean (120 Scotchbrite or stainless wire wheel/brush then acetone and then IPA) both sides to get to new metal.
Back purge isn't necessary, like exnailpounder said, but it couldn't hurt.
When possible, and in budget, use Ar/He mix in your shield gas. The more He in the mix, the better. If at all feasible, pure He.

Again, I'm not sure this will help you, but it shouldn't hurt...too much.

[Otto Nobedder]

...
When possible, and in budget, use Ar/He mix in your shield gas. The more He in the mix, the better. If at all feasible, pure He.

I have to disagree slightly with this. For the average user with HFAC, 60% helium is about the maximum before one has arc-control issues.

DCEN with pure He is doable for anyone with transformer or inverter, but most aren't doing this.

Steve S

[RocketSurgeon]

I have to disagree slightly with this. For the average user with HFAC, 60% helium is about the maximum before one has arc-control issues.

DCEN with pure He is doable for anyone with transformer or inverter, but most aren't doing this.

Steve S

You are quite correct, sir.