Cracked right in the middle of the aluminum weld

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I was wondering if some of you guys could offer some advice on my set up. I made a custom aluminum plenum for my race car. Everything was TIG welded and I just used the filler rod that the guy at the LWS gave me (don't remember). Anyways, The plenum is very wide so it would bulge out under boost pressure and then suck back in from vacuum when the throttle plate was closed. This caused an "oil can" effect which eventually cracked my weld right down the middle of the bead. I have since reinforced the top of the intake manifold to keep it from flexing under boost and vacuum. However, I am wondering if the weld was just not as strong as it could be. Mainly because I watched the video online of the guy who OXY welded two aluminum sheets together using flux (obviously). He then proceeded to beat the piss out of it, shape it, smash it, stretch it and then shrink it. He abused this thing for a while and the weld never gave. So I am thinking my weld was inadequate since it cracked from just a little oil canning of the plenum.What do you guys think? Unfortunately I don't know the grade of aluminum that was used as the brake metal or the filler rod I used(I think 4043 rod). Maybe a particular filler rod would be better? I don't think it is a matter of penetration due to the fact that it split right in the middle of the weld right?I just don't know. Maybe the answer is simply reinforcing the top like I did to keep it from flexing. It has held up fine ever since then, but it is still something I think about. Here is the weld. Here is a picture of the plenum before I reinforced it. Lots of surface area allowing the top to flex a bunch.Last edited by DiabolicZ; 03-18-2011 at 03:17 PM.Lincoln Precisoin Tig 1851980's Miller plasma cutter.Used to own...Hobart Tig Mate.
Reply:Its very easy to make a poor weld on an aluminum corner joint, the most common problems seem to be either 1) not enough fusion of the base metal, just enough amps to puddle over the corners and make it pretty or 2) too much heat which causes excess oxidization of the inside of the joint and prevents it from flowing together, leaving a seam.Here's a piece I did a while back to make a point about aluminum corner joints. Notice I dont have much buildup or big bulges at the dip, and the weld doesn't sit high on the corners.  This eliminates stress concentrators and ensures that I get good penetration. Then after I back-bent it, you want something like this.  It failed in the HAZ like it should,  also the weld doesn't have a seam running through the middle.Have we all gone mad?
Reply:Hello DiabolicZ, since your plenum is likely a boxed construction it is very unlikely that you were able to gain "complete fusion" through the weld joint/seam. As you mentioned, the oil canning from the vacumn and boost caused an effect similar to grabbing hold of a single sided welded joint and working it back and forth until it failed. Aluminum, can be a different duck when it comes to single-side access, full-pen weld joints, there will almost always be a lack-of-fusion line on the backside of the weld seam/joint, this will cause a type of notch that will eventually bring about a crack as a result of the type of movement that was initially happening on your plenum. Welding of aluminum will also cause a reduction in tensile strength of the particular alloy, how much is generally based on grade of material and condition(anealed, heat-treated, etc.). Most of the time, however, this strength reduction will be predominant in the HAZ and not necessarily the weld metal or the parent metal outside of the HAZ. I believe the crack down the middle of your weld was a result of the shape of the penetration of the bead on the backside of your weld. The notch/crack that was left there after you completed the initial welding is what brought about the crack after all of the flexing over time from the vacumn, boost. Good luck and best regards, Allanaevald
Reply:why not build it out of 10 ga steel...?
Reply:Originally Posted by weldbeadwhy not build it out of 10 ga steel...?
Reply:Think Rojo and Sn0 have both given good advice.  Actually, all the advice has been good.Just a couple things I'll add.  Joint configuration for this type weld can be critical.  If you butted the vertical to the horizontal or butted the horizontal to the vertical, you inherently weakened the weld.  The best joint, to insure the best penetration, is an open joint where the edges of the horz and vert piece just meet.  Then you're filling the gap with filler when you run your bead.  Also allows for better penetration to the backside and results in a smaller haz.I also agree with the comment about closer dip spacing.May just be me, but it looks like the bead could have used a few more amps.  Not that it's "cold" but just not "flowed out right".If the weld bead is done correctly, I would expect to see the crack in the HAZ rather than in the filler.LOL.  After going back and rereading Rojo's post, I see we're saying basically the same thing about how to set up the joint for welding.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:I might of made that plenum box with heavier material knowing it was going to flex that much. Maybe even with some angle tying the sides together so you could get better welds......  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Scroll down to post number 17 of this thread (post by Kevin Morin).Click hereHe does an excellent job of showing (with photos) the "keyhole" you should have, which pretty well guarantees full penetration/moderate back bead.  You don't want much, as a blob on the back only shows too much heat imput (greater HAZ), but when the keyhole slightly opens up, it shows that you have wetted out the entire thickness of the parent metal, and the act of filling the keyhole does form a slight back bead, provided you are running with enough heat/fast enough.  If you have too little amperage, and thus have to linger, then you'll likely end up with the "butt crack."Who is John Galt?
Reply:A question now that I have seen BC's post: Would a backfire, even a mild one give the pressure to blow this seam on a one shot basis? I know a blower backfire can take a whole top end clean off. And on the old GSXR bikes, a backfire would blow the carbs off if they were Keihn flat slides that were closed. (Held on by rubber boots....)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:Thank you for all of the input guys. After I saw Sn0border88's weld, I thought, "Damn, now that looks good." Nice even blob on the back side of the weld. I am having a hard time getting that. I was out practicing some more today on some 1/8" aluminum (what the plenum is made of). Trying to get that solid bead on the back side of the weld like snoboarder's weld. It always looked like a seam right down the middle of it though with blobs on either side of the joint. Oh well, keep practicing.Making the intake manifold out of steel would be very difficult (not impossible). The sheet metal is welded to a lower intake which is obviously aluminum. If I wanted to make it out of steel, I would have to have custom steel flanges made, make the runners, plumb the water lines for the heads, and whole slew of other stuff. You can see what I mean in the pic below.Also, as I said in the initial post, I have already reinforced the intake manifold after this crack happened and repaired it. I used two pieces at 4"x4"x3/16" and welded them on the top of the plenum making it a total of 5/16" thick. This has eliminated flexing and it has not cracked since then. Here is a pic showing that the plenum is only welded to a ported OEM lower intake. This is why making the entire thing out of steel would be too much of a challenge that I don't want to undertake right now. Yes, a backfire would definitely turn my intake manifold into an aluminum balloon LOL. That hasn't happened yet though. When it does, then I will have to make another one.Last edited by DiabolicZ; 03-19-2011 at 01:03 AM.Lincoln Precisoin Tig 1851980's Miller plasma cutter.Used to own...Hobart Tig Mate.
Reply:Instead of welding corners, you could form them and butt weld the joints . . . control the flexing with the shape.Dynasty 300DXSmith He/Ar gas mixerMM350PHobart Handler 120Smith LW7, MW5, AW1A
Reply:This guy can weld..............http://www.marcellamanifolds.net/  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Yupv.
Reply:Originally Posted by RojodiabloA question now that I have seen BC's post: Would a backfire, even a mild one give the pressure to blow this seam on a one shot basis?
Reply:Originally Posted by zapsterYou can do a stitch there and double your strength on the outside only.....zap!
Reply:You can do what you do and I will do what I do.Really makes no difference to me..It's all about failure rate..Whatever works....zap!Last edited by zapster; 03-19-2011 at 06:20 PM.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:Originally Posted by zapsterNo question about it..Without proper penetration one hiccup and you get what you see here.....zap!
Reply:Good point, my 64 Nova Wagon had Nitrous and I left the tank on one night after running around town drag racing.......The next morning I went out to start the car and it blew up so hard that the hood flew off and intake came apart......  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:I don't know much about aluminum but I'll add my .02 about nitrous. I have seen a few nitrous back fires (small to large) with aluminum intake manifolds in my community and big ones have enough pressure to split the manifold up completely and smaller ones can do exactly what is pictured.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:What I'd do is take a rod or 3 down the center.  Still the OD of the rod through plenum top and bottom, then weld the rod to the plenum tops and bottoms from the outside.  This will hold the top sheet metal and bottom sheet metal together, keeping it from oil canning and based on the diameter of the rod obstruction can be controlled.  I'd do a like 3/8" rod in 3 places down the center of the plenum.
Reply:Originally Posted by DiabolicZYou did not read the entire first post.
Reply:The weld that cracked, was fairly decent, although perhaps the penetation was a little shallow as has been mentioned,Proper joint design and preheat is very important when faced with this type of flexing.Stiffening  has apparently solved the problem, and as long as you are satisfied with the overall appearance, then all is good. I would prefer to see the edges rolled, and then the seam welded down the sides rather than on the corners. Think of it as a pressure vessel.
Reply:Here is the intake manifold I had made for my car:Very large plenum but you can see how it was rolled and formed to prevent against expansion.
Reply:Originally Posted by GambleI don't know much about aluminum but I'll add my .02 about nitrous. I have seen a few nitrous back fires (small to large) with aluminum intake manifolds in my community and big ones have enough pressure to split the manifold up completely and smaller ones can do exactly what is pictured.
Reply:Originally Posted by zapsterWhatever works....zap!Hey Jon K,I just wanted to commend you on your work & the absolute superb workmanship you engaged with that manifold. I'm sure the level of "seat time" to attain that skill is really not comprehended by the youngsters/newbies who want to TIG aluminum. Those (2) pics should be a "sticky" with the title: "Aluminum TIG Goal...It Can Be Attained". We do have several members here also who post superb work to try to enlighten the TIG newbies that it takes time and a really dedicated mindset to get to that level. The other link pics were also superb..... love to see the "artform" of welding. Thanks.....DennyComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:Denny..He had it MADE for him...I don't know who did it....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:Originally Posted by sn0border88I agree, if it works for you then fine.  The part that irks me is you go making wild claims about making the weld two times a strong by adding a little weave when we both know damn well that's not true.
Reply:Hey Zap,I guess I misinterpreted the way his sentence was constructed. Many times I've said, "Here's something I had welded last year", meaning the word "had" was used in the "past tense". Yup, words can really be twisted into different meanings..... sorry for the misunderstanding...DennyComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:The outermost curve would be an ideal corner joint, smooth transition with no loss of cross section.The inner two curves show what would happen to the throat of the weld if the legs were increased by .065" and .125", respectively. I fail to see any possible scenario in which adding a wider weld could increase the strength, but I would like to hear any relevant input if you have it. Again, I have no problems with you welding in whatever way you desire as you have earned the right to do so.  I'm just trying to avoid spreading information to others that is misleading at best.Have we all gone mad?
Reply:Originally Posted by sn0border88The outermost curve would be an ideal corner joint, smooth transition with no loss of cross section.I fail to see any possible scenario in which adding a wider weld could increase the strength, but I would like to hear any relevant input if you have it.
Reply:Did I miss it, or did no one ask what type of aluminum was used?The OP did not know what filler he used, and apparently does not know what the base metal is.  This could very well be related to the cracking since some alumunim alloys are not weldable.  6061 is readily weldable using 4043 or 5356 filler, yet if it is welded without filler or with too little dilution of filler, it is prone to centerline hot cracking.
Reply:Originally Posted by 4sfedsn0border,Your analysis assumes there would be no change to the inside surface of the joint.  Starting with your ideal joint and just changing the outside radius without adding additional filler would look more like this . . .
Reply:Originally Posted by pulserDid I miss it, or did no one ask what type of aluminum was used?The OP did not know what filler he used, and apparently does not know what the base metal is.  This could very well be related to the cracking since some alumunim alloys are not weldable.  6061 is readily weldable using 4043 or 5356 filler, yet if it is welded without filler or with too little dilution of filler, it is prone to centerline hot cracking.
Reply:4043 or 5356 are the most common depending on whether the part is to anodized or not. 4043 cant be anodized 5356 can.
Reply:I wanted to thank all of you guys for posting up your thoughts and suggestions. I appreciate the help. However, I specifically wanted to thank Sn0border88 for posting up the picture of the front and back side of that weld. After I saw that, I've been out practicing. I couldn't get the back side to melt together like that. Then I finally turned it up to 130 amps and just cranked down on it. Finally got the back side to melt together. I'm gonna have to practice some more because my welds are not as pretty when I hit them with that much heat, but at least now I know that it should be melting together on the back side, and what the weld acts like WHEN it is melting together on the back side. I can see "The key hole" now.After seeing this, I am fairly certain that because it did not melt together on the back side of the weld, that is what ultimately caused it to crack. Yes, the oil canning was the cause, but the lack of penetration was the weak link. Thanks again guys.Last edited by DiabolicZ; 03-23-2011 at 10:46 PM.Lincoln Precisoin Tig 1851980's Miller plasma cutter.Used to own...Hobart Tig Mate.