Aluminum TIG bead cracking

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I am starting to try to learn how to TIG weld aluminum.  I am using the following:Lincoln 175amp square wave TIG3/32" plain tungsten100% argon110 amps5356 fillerHome Depot aluminum 1/8" thickThe beads look ok with good penetration, but every few bead cracks for the first 1/2" or so.  I have been able to reduce the cracking by slowing depressing the pedal before I start adding filler (maybe 3 seconds to full pedal)  I have done a bend test and while most of the bead cracks right outside of the weld (I guess the HAZ) the cracked portion cracks right on the crack (duh I guess)What is the solution?  I don't think I need to preheat 1/8" aluminum, is slowing increasing the heat the way to avoid cracking?
Reply:Is that a piece of angle? It sure looks like it's thicker than 1/8" in the pic.Are you welding joints, or just running beads on the metal?Rex
Reply:Are you complementing the correct filler to base material?
Reply:4043 is much more forgiving of hot-short cracks. 5356 is a bit more "technical" in nature and requires tacking sequences to prevent cracks. 5356 however is much more ductile when cool and is typically the filler of choice for fuel tanks, panels, and the like in sheet work.
Reply:I am using Home Depot aluminum which I am ASSuming to be 6061.  I think the 4043 and 5356 are both general purpose fine fillers for this alloy.   I did stop by my metal shop and bought some 6061 to try out.  It is 1/8th thick material.  I have tried both beads across the metal and a few joints with the same results.Back to my original question, how do you guys start you puddle?  Fast or build up current with the pedal for a few seconds before the aluminum liquefies?Chris
Reply:Originally Posted by *chris*Back to my original question, how do you guys start you puddle?  Fast or build up current with the pedal for a few seconds before the aluminum liquefies?Chris
Reply:I do the same thing that Craig in Denver dose to establish a puddle.keith The older the boys, the more expensive the TOYS!!Previous owned;Linde 300 Amp welderMiller Gas drv welder, Tumbstone,Dayton Miller ac to dc converter,High frequency unitLongevity LS60PCurrrently owned;Longevity WeldAll 200PI
Reply:Here is a quote from my Procedure Handbook of Arc Welding in the GTAW aluminum section, in regards to aluminum cracking with tig welding."Such causes of porosity as temp, welding time and solidification may also be contributing causes of cracking. Other causes may be discontinuous welds, welds that intersect, repair welds, cold-working either before or after welding, and weld-metal composition. In general, crack sensitive alloys include those containing 0.4 to 0.6% Si, or 1.5 to 3% Mg or 1% Cu."JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Originally Posted by *chris*I am using Home Depot aluminum which I am ASSuming to be 6061.  I think the 4043 and 5356 are both general purpose fine fillers for this alloy.   I did stop by my metal shop and bought some 6061 to try out.  It is 1/8th thick material.  I have tried both beads across the metal and a few joints with the same results.Back to my original question, how do you guys start you puddle?  Fast or build up current with the pedal for a few seconds before the aluminum liquefies?Chris
Reply:Originally Posted by makoman1860Chris, Read what I wrote on fillers.....dont argue. Remember, you asked a question, that makes you a student.
Reply:Chris, Hot-Short. Basicly means the solidifying pool has no strength while it cools/shrinks, and actually tears the semi solid aluminum. 4043 having 5% silicon melts at a lower temperature than the base metal ( and 5356 ), and therefore solidifys last as everything cools. So this means that things can cool down and shrink while the molten pool is still fluid enough to give and not tear. So how can we avoid hot-short cracks. Well for one, never start at the end of a part and weld accross it, thats a fundamental NO-NO right there as we have nothing to tie the leading edge of the weld together. Try running a bead from the center out in both directions. There are no "universal" fillers, period.