What causes aluminum cracks?

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I was reading on another forum and saw this pic. What could cause all 4 runners to crack at once? Something like this would you want to use a 5356 over a 4043 to prevent cracking ? Or is 5356 more prone to cracking?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:I am going to guess the customer used wrong alloy for the base material like 2024. The copper diluted into the weld and crack ensued. 5356 is more ductile, but would not have prevented the crack the way I see it.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Al can crack for any number of reasons but that right there is just downright special. Unless that manifold has two foot runners and a lead pipe for the plenum. Even then it would crack at the top and unhinge there before the bottom even started to crack. That has definitely got to be either wrong parent metal, wrong filler or a combination of the two.  Either that or bad welding. It looks like enough heat was used and doesn't appear to be contaminated but who knows. Most piping and usually most flanges like that are made out of 6061 and 4043 will do a great job in that application. This is my intake manifold. It has a built in water to air intercooler and holds probably a half gallon of water or more. I should really put some bracing on it but haven't had a problem yet and have about 10k miles on it. Full and with the lines attached I'm sure there's at least 15 lbs hanging on my welds and with some decent leverage too. If I ever had a failure I would also expect it to be where the tubing meets the weld, not in the middle of the weld. 6061 flange and tubing, 4043 filler. Lincoln precision TIG 275Millermatic 140 MIG
Reply:Jakeru had an interesting post on aluminum cracking here:http://weldingweb.com/showpost.php?p...31&postcount=9
Reply:Poor prep, & lack of penetration.The ends of those pipes were never sanded.  Acetone will not clean oxidation off.They cracked exactly in the center, & the welds do not look stressed at all besides the one crack in the center.Also note the little "waves" in the crack in the few spots that he penetrated a little more.I'd also be willing to bet that the flange was never re-machined to flat once welded.The cracks are slightly more open in line with the bolts leading me to believe there was more stress there.If 5356 was the cause I think that the cracks would be lower, toward the flange.No matter what kind of filler metal that you use it needs to penetrate into the base metal or you may as well use glue.Buy American, or don't whine when you end up on the bread line.
Reply:Stress cracks maybe from cooling contraction?  How thick is that base plate?I had a similar thing happen to something I was building using 1" steel plate and 3" sched 40 pipe.  I didnt use preheat and I had the pipe clamped tight to the plate.  A more experienced welder I knew told me to preheat the plate a little and not clamp the pipe down tight to allow for some expansion and contraction.  Sure enough it worked.
Reply:If those flanges have ridges/stops on the inside, then butting the pipe up to the ridges can do it. The aluminum expands as you weld and starts to push against the stop and pulls against your new weld. Many times it will start a crack before you even finished the bead. One that can surface later...
Reply:Originally Posted by ZmechanicIf those flanges have ridges/stops on the inside, then butting the pipe up to the ridges can do it. The aluminum expands as you weld and starts to push against the stop and pulls against your new weld. Many times it will start a crack before you even finished the bead. One that can surface later...
Reply:Are we all sure that those are not titanium or stainless instead of aluminum?I find it hard to believe there are aluminum headers on anything...They do exist but I don't believe it is what we are looking at......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:It's an aluminum intake manifold.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Originally Posted by GambleIt's an aluminum intake manifold.
Reply:I've seen the manifolds plenum damn near blow apart with a nitrous backfire, but this one had no nitrous in it.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:the flange looks machined. it should have been machined with a step to allow the tubes to slip into and bottom out onto the step, then all that is needed is a nice small weld around the pipe to flange to hold it in place. i would also perhaps web the tubes for a tad more stability.
Reply:Originally Posted by welding_kidthe flange looks machined. it should have been machined with a step to allow the tubes to slip into and bottom out onto the step, then all that is needed is a nice small weld around the pipe to flange to hold it in place. i would also perhaps web the tubes for a tad more stability.
Reply:What causes aluminum cracks?   Well technically speaking, stress causes cracks.  It's mostly prevalent with heat in some way shape or form.  Sorry, I couldn't resist.