why are my welds cracking?

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My tig alum welds are cracking right away. See picture.  It's 1/8" thick aluminum box channel.  The outside temp was 40F.   It cracks with and without using filler rod.  Any tips?Thanks,Adam Attached Images
Reply:Using filler such as 4043 will end that problem fast..Can't fuse aluminum like you can stainless.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Okay Adam, Let's try get you set. How many amps, and what style of welding are you doing. ( I understand it is tig) Are you pedaling a lot, or just putting the pedal down, and adding filler? How many base amps is the machine set at? It looks though the outer material is pulling the heat out of the bead, and that is causing the cracking. Other obvious question- you're cleaning with SS brush, and a quick acetone wipe, correct? Also, if you do a second pass over it, does that one crack also?? I would bet not, as there would be more heat in the part. Your cleaning balance looks OK, so I don't think that is the problem. Maybe just not quite enough heat to keep the weld warm long enough to cool without cracking. For an easy test, try to go a little hotter. If that is a no go, try to preheat the part a little bit with a propane torch for 10 seconds. I can't really tell from the pic, as it is a little blurry.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Are you leaving a crater at the end of the weld? That would be one thing, when you get to the end of the bead back of the pedal slowly, and add a little filler, make it convex at the end
Reply:Originally Posted by adamb113My tig alum welds are cracking right away. See picture.  It's 1/8" thick aluminum box channel.  The outside temp was 40F.   It cracks with and without using filler rod.  Any tips?Thanks,Adam
Reply:Back off on your heat. Your getting solidification cracking, (hot shor cracking). Use filler. More than likely that is a t6061t6 and that alloy needs filler or it will crack almost everytime. --Gol'
Reply:im with Zap on this one ues fillerChuckASME Pressure Vessel welder
Reply:I think Zap nailed it.
Reply:The first question to ask is, what alloy are you welding?Some Al alloys are unweldable, can't remember off hand but I seem to recall some 2000 and 7000 alloys.I do know for sure, 6061 must be welded with filler metal, or it will crack. Use 5356 for best strength if the welded part will not be heat treated.  Use 4043 if the welded part will be heat treated and you want the weld to respond to the heat treatment (strengthen).  4043 will give a dark grey weld if anodized, so if that's a problem, use 5356.
Reply:Sorry for the delayed response.  New baby in the house.  I don't know what alloy the material is.  But it is very weldable.  It is scrap and there are some very beautiful welds on it.  I don't know what filler rod I have. ( I know I'm not making it easy to help me!!!)  It's rod that was given to me.  It seems to work nicely in other areas.  I agree that it is probably a cool down crack.  the picture you see is with filler.  Could I be using the wrond diameter filler rod?  I think your preheating suggestion is a good idea.  I will also try the tack suggestion.  That should also help.  I will try to get a better picture of that weld and another that cracked.  Was the suggestion about the energy (pedal and setting) to put more in quicker or ease into it?Thanks,Adam
Reply:Another guess:The weld may be way too hot and wide for the thickness of material.That coupled with a crater crack at the stop, could cause the crater crack to carry back through the weld.