Attempts in TIG Alu - Newbie questions

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First of all, I am quite a newbie welder. I've finished few fabricator works already (mostly SMAW), but I am very far from calling myself experienced. I have a Jasic 200A AC/DC Pulse welder, which has arrived a week ago. On this weekend I tried to weld aluminium. I was never trained in alu welding, so it was just a jump into deep pool. I bought the welder with foot pedal. The first thing came out was that it is a great accessory, as I could adjust the current smoothly. I love it. On the other hand I have no idea about the level of current I was welding, thus I can not tell it now.The book I have got on my welder training is quite succinct in alu welding, so I have some questions. Why are there cracks? Some can come on flat-wide welds, some on narrow-high ones. How can I avoid them? What was wrong?Despite of that I used a heat sink (a 2kg cast-iron, I have no copper one), the piece of aluminium sheet (around 1.2 mm thin) bended during/after welding. How can I avoid this deformation?The tungsten (red, 1.6 mm dia) got blue colour (however it was 50-50% in clean area width), and when I ground it just broke exactly at the border of blueish part. Is it normal? Was it overheated? Would I choose 2.0 or 3.2mm diameter tungsten rather? I also have ceriated (grey) tungstens. Would it be better for aluminium?In every attempt I had problem with melting edges. Even if I took back the current as low as I could. Is there any trick to finishing the welds nicely? Or it will just com with practice?Thanks for answering. Attached Images
Reply:Welcome to Tivadar in Hungary Here's a quick answer, it's almost 2am here, I need to go to bed, sorry if I missed something.The blue tungsten is caused by too little post flow, turn it up. I get away with about 6 seconds. The plate will always warp, all welds shrink. When you weld a bunch of beads on a plate like that, every bead makes the plate hotter. Alum is really bad. I think thats why your beads got wider, hot, hotter, hottest. Try using 3 or 4 pieces for practice, weld one bead, lay that piece aside (preferably on a heat sink), weld on piece 2, set it aside, etc. As you near the edges there is a LOT of heat running that direction, less pedal, more filler. Also a piece clamped along the edge will dissipate the heat.I only get cracks if I don't add filler, you were, so I don't know.Red tung if fine. Did you start with a point on your tung? Red should hold a point, don't ball red. Once you loose the point, assuming you started with one; stop, regrind, try again. If you started with a point check your gas flow, we use 15 cfh. I don't know what that would be there. Good night. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Also, your welds look more like mig than tig, which would indicate to me that you need to increase your travel speed and decrease your heat. Seems to be a thin piece of aluminum. Try to find something thicker. You will have more room for error, and heat. The thin stuff takes to much finesse for a guy trying to learn on.Bill
Reply:Originally Posted by Craig in DenverRed tung if fine. Did you start with a point on your tung? Red should hold a point, don't ball red. Once you loose the point, assuming you started with one; stop, regrind, try again. If you started with a point check your gas flow, we use 15 cfh. I don't know what that would be there.
Reply:Originally Posted by EngloidRed tungsten, with a point, is reccomended for inverter machines only...and if you run your inverter at a low AC frequency, it will be welding the same as a transformer machine, so you might as well plan to ball the tungsten anyway.  I'm not familiar with his machine.
Reply:Cracks, when welding aluminum, are usually caused by one or more of three things:1)  Contamination-  It looks like you're often letting the arc get long, and allowing the puddle to lose gas shielding, and become contaminated.  It can also be from dirty material, but it isn't likely, looking at your pictures.2)  Too much heat-  When you get aluminum too hot, or have it at heat for too long, the manganese content is depleted.  This reduces the weld's ductility, making it more brittle and succeptible to cracking during...sometimes immediately after it cools.3)  Lack of filler-  Your filler material will have a higher manganese (and other chemicals) content, to help combat the loss of elements during the welding process.  This is why austentic (no filler) welding of aluminum is not a good choice.  You need the filler to mantain the proper mix of elements in the weld.  If you can get closeups of the cracs, I may be able to help narrow it down some more.
Reply:Originally Posted by Engloid...  This is why austentic (no filler) welding of aluminum is not a good choice.  You need the filler to mantain the proper mix of elements in the weld.  If you can get closeups of the cracs, I may be able to help narrow it down some more.
Reply:Guys, thanks for the answers and advices. Originally Posted by Craig in DenverThe blue tungsten is caused by too little post flow, turn it up. I get away with about 6 seconds.
Reply:Originally Posted by ZTFabDo you mean autogenous welding?
Reply:After looking at the bigger pics, I'd have to say the most likely cause of cracking is overheating the weld puddle.  The welds that cracked are very hot and wide.  The areas that have some black speckles all over it are areas that you let the arc get too long.  As a beginner, you'll be trying to look at several different things (puddle, arc, tunsten, filler) at one time, and it's difficult to do so.  With practice, watching all these areas will become second nature.  Just keep in mind that when you start seeing these black specks appear, it's your arc length that is getting long.  You're losing gas coverage and getting a bit of contamination because of it.
Reply:IMHO, the welds are cracking because, yes, you are getting them too hot, and so, as a result, you start running too fast and don't add enough filler metal.  Note how flat those welds are.  Cracks right down the middle of the weld like that are referred to as "hot short" cracks.  With the heat treatable grades of aluminum, and 6061 being one of the most used, during the solidification phase of the welding, MgSi and FeSi (Magnesium silicide and Iron Silicide) migrate toward the grain boundaries and act as interstitial point defects between the crystalline structure.  (Okay, imagine putting a rock between two pieces of glass, and them pressing them together)  CRACK.  The addition on 4043 filler metal, which contains nominally 7 percent silicon, causes a lower melting (eutectic) phase which allows the crystalline structure to stabilize with the interstitials in place and hence not crack the weld.  (Okay, imaging putting putty around the rock you put in between the pieces of glass, press together, the putty equalizes the stress so the glass doesn't crack).  That's not the exact mechanism, but it's close enough to give you an idea of what's going on.Not putting enough filler metal into the puddle decreases the percent silicon in the puddle to below 1.5 percent, which is the threshold where hot shortness occurs.  No matter how fast you move, keep driving that filler metal in there.I r 2 a perfessional
Reply:Originally Posted by Engloid  This is why austentic (no filler) welding of aluminum is not a good choice.  You need the filler to mantain the proper mix of elements in the weld.
Reply:More infohttp://www.afsa.org.za/welding-corne...ugust-2005.pdfEd Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Guys, thanks for your answers and advices.It was very useful. I hope I can show some better welds later.Have nice day.