micro cracks in HAZ, 6061T6, weld joint

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is the micro crack a norm in HAZ of 6061T6 weld joint? Attached Images
Reply:Not usually..Where exactly is the weld?...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:I second zapster's comment.  Not normal at all.  Can you polish the sample to a smoother finish (<10um), and then etch to show the microstructure?  It would be helpful to know if the cracks are intergranular(along grain boundaries), or transgranular(through the centers of the grains)?
Reply:thanks for the help.i do not think i can do any better and we have only a 40X microscope witha nikon coolpix digital camera.let's assume it is folow the grain boundaries, then what?the upper left is the molten pool. the lower right is the parent metal.
Reply:dho,sorry for the delay in responding.  I didn't notice your last reply until now.  I don't want to draw any conclusions about why it's cracking without knowing what the base metal is, what the filler metal is, and how it was welded.  There are too many possibilities to just pick one and assume it's the root cause.  Im' not even comfortable with assuming the cracks are intergranular.  Not without some visual evidence to support this conclusion.
Reply:Base metal could be old. Aluminum gets brittle as it ages.Bend in the metal could get cracks from work hardening.Poor fit up can cause cracks.Filler material incorrect.Heat input excessive.Post flow of shielding gas not long enough.Was the crack near a stop or start?Do you know dor certain it was 6061-T6?Was it anodized?We could go on but more facts are needed.Usually cracks in micro structure are looked at with 100 power magnification.What was the magnification?
Reply:it could possibly be the wrong filler.  maybe in need of heat treatment6G zirconium 702 GTAW 2" xxheavy6G P.E.D. carbon steel GTAW 2" xxheavy3G titanium Gr. 2 - Gr. 7 GTAW up to 3/4" 3G 316L stainless GTAW up to 1" 3G carbon steel GTAW up to 1" 3G Hastalloy GTAW up to 3/4"1G tantalum GTAW up to .060"
Reply:At the risk of a pounch in the nose, if the micro cracking is occouring in the hax and the weld it should be no suprise since the 6061T6 is quite heat treated and most filler 4043/5356 are non heat treatable the micro is a result of the lack of  homogenous filler and base metal. When I have to deal with this problem I've found lower heat input and more filler material will generally allow for more dilution/mixing of the base metal and that of the filler rod resulting in no more micro cracking. This is just my opinion and as stated before my reply, you would need to elaborate a bit more on size, filler, joint type pre heat or no preheat would all allow for a better diagnosis.ric