7075-T6 Weld or JB Weld?

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I have some 7075-T6, .090" thick that is cut out for a small 1 gallon gas tank that's needed for a formula SAE car and I barely found out that you can't really weld 7075 so I would like to know what would be the best way to hold the panels togther?The gas tank is just a rectangle, no complex geometry but I'm stuck as to how to hold these sheets together. Any ideas?
Reply:Hello duffman 1278, can you use another grade instead? The 7075 T-6 is considered to be heat-treated tooling plate, is very hard, and not considered weldable or formable due to it's specific alloying components. I believe that you would be better served by finding some 5052 and re-making this tank. 5052 is readily formable and weldable, corrosion resistant and would better serve your intended purpose. Just my $.02 worth. Good luck and best regards, Allanaevald
Reply:Since plan A-welding 7075 won't work in conventional welding,it looks like your plan B--JB weld ---is up to bat.Show us with some pics--when plan B strikes out, please......then your intentions with plan C---using weldable AL.(I see a scattering of items coming into my shop-repairs andstumbling fabrication attempts---where JB weld was usedto 'FIX' things---unsuccessfully.)Last edited by dave powelson; 04-16-2011 at 01:27 AM.Reason: correctionBlackbird
Reply:I agree.  Toss it and start over.My name's not Jim....
Reply:Yea I think i'll start over. Would it be fine to use steel instead of aluminum for a gas tank? That thing that scares me though is the corrosion, plus steels cheaper.
Reply:Does the steel tank under your car scare you?  Or on your lawnmower? Or motorcycle?  Those tanks are all thinner than you might think.My name's not Jim....
Reply:Well not the safety part, I'm more concerned that the fuel would corrode the steel and might put that corrosion into the fuel injectors or fuel pump and clog it since I'm unaware of any off the shelf products that could be used to coat the inside of the gas tank to prevent the corrosion.
Reply:The fuel won't corrode the tank, but the air will if the tank sets empty for a long time.  The bike your donor motor came out of had a steel tank....My name's not Jim....
Reply:Yea I know, but they're usually coated from the manufacture. Plus that tank won't fit in the vehicles frame that I'm working with. I guess steel it is. Thanks for the help
Reply:Originally Posted by duffman1278Yea I know, but they're usually coated from the manufacture.
Reply:If I remember correctly, 1 gallon af gasoline has the same explosive power as 16 sticks of dynamite. Do you really want to trust that to JB Weld? I wouldn't, IMHO.
Reply:I don't know what a Formula SAE car is, or how large a gas tank it uses, but I really prefer stainless for performance and longevity.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:I don't think the JB weld will adhere reliably to aluminum when also exposed to gasoline.Aluminum soldering/brazing your 7075 pieces together comes to mind.  There are Zinc-aluminum rods available that can join your 7075 aluminum, that melt at around 800F-900F, which you can apply with an oxy-acetylene welding tip.  You "tin" the edges to be joined first with the braizing rod, scrubbing it into the surface (scratching the aluminum oxide layer) with a wire brush.  Then you set the "tinned" pieces together and re-apply heat to get them back up to melting temperature, and add material to flow the tinned surfaces together in a nice fillet.  No flux or post-joining cleanup is necessary.Either that, or go to a weldable alloy (such as 3003, 5052, or 6061) and TIG weld them.If you try to TIG weld 7075, expect it to be extremely prone to "hot cracking" (hairline cracks forming upon weld bead solidification).  It is generally referred to as a "nonweldable" alloy for this reason.
Reply:Just to give you an idea of what it is and the limited space I'm working with. Also, the rules for the competition restrict us from running more than 1 gallon which is why I need such a small amount.
Reply:Not to hijack, but I have seen reweld m-16's for sale and they are, generally speaking, all made of 7075. There are several gunsmiths out there that have very successfully repaired, via welding, m16/ar15 receivers.  I am curious how they are "successfully" accomplishing welds on a non-weldable alloy.Thanks,Rene
Reply:Originally Posted by duffman1278Well not the safety part, I'm more concerned that the fuel would corrode the steel and might put that corrosion into the fuel injectors or fuel pump and clog it since I'm unaware of any off the shelf products that could be used to coat the inside of the gas tank to prevent the corrosion.
Reply:I would guess competition  rules will regulate what you can or can not use as far as the fuel tank. I doubt epoxy would be an acceptable material for this. I'd agree you would be best starting over and use a welddable alloy. The only other thought I'd have would be angle supports and rivits. They made liquid tight tanks and containers for years with rivits. Not an easy task by any stretch, but better than JB weld..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:In the end I just went to a local metal yard and got a thin walled steel tube and sheet metal to cap the ends. Took some time to make but still much easier and less worries now. Thanks a lot everyone for the help