Steel VS Al for A Frame

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Im building a tracked off road vehicle driven by hydraulics its more  or less a tank.I wanted to do AL for the frame to save weight. I understand once i weld 6061-t6 it looses the annealing in the HAZ. But through heat and work dont i gain some additional work hardening.In the case above am i better off going with Steel?Also what size should i be looking at?Total weight of the vehicle will be about 2k lbs. Loaded.Darwin admission- I fully aware that when welding frames etc etc i could be seriously hurt and or kill myself due to faulting welding or bad material selection... blah blah blah...
Reply:Your not one of the Howe brothers????? By the time you use thick enough alum., you might not be saving as much weight as you think. Others will chime in with more experience. I think the steel would be more impact resistant too. Plus if something does bend, you can take a French Wrench to it.200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:French Wrench LOL6061 is about 18Ksi in the annealed condition, in the T6 condition (solution heated near 1000F and quenched, then aged at 350F) it gets to 45Ksi and is commonly called "Jig Plate". Welding changes the solution ratio in the immediate area that gets above 1000F causing a regression in properties.Welded with 4043 the joint section must meet 24Ksi min and with 5554 it bumps up to 28Ksi (AWS D1.2 Structural Code).Sooooo... Unless you plan to re-heat treat the weldment you have to design the welded joint. This means the design of a welded joint with 4043 needs approx 2 times the mass and surface area of the parent part. Total heat input must be kept as low as possible (high power really fast travel) as the longer the heat dwells, the more the parent material softens.Considering weight/strength alone, 6061-t6 aluminum weldments work at less than 1/2 the weight of mild steel. When impact and fatigue are in the mix the weight goes up. From the high cost standpoint, aluminum is used long term (fuel usage) or short term for weight (go fast).You can end up with some very strange looking joint designs (other than fillet) to test well.NOW FOR SOMETHING REALLY DIFFERENT![ame]http://www.youtube.com/watch?v=m16t8wnMTwI&feature=related[/ame]Matt
Reply:[QUOTE=Matt_Maguire;384549]French Wrench LOL6061 is about 18Ksi in the annealed condition, in the T6 condition (solution heated near 1000F and quenched, then aged at 350F) it gets to 45Ksi and is commonly called "Jig Plate". Welding changes the solution ratio in the immediate area that gets above 1000F causing a regression in properties.Welded with 4043 the joint section must meet 24Ksi min and with 5554 it bumps up to 28Ksi (AWS D1.2 Structural Code).Sooooo... Unless you plan to re-heat treat the weldment you have to design the welded joint. This means the design of a welded joint with 4043 needs approx 2 times the mass and surface area of the parent part. Total heat input must be kept as low as possible (high power really fast travel) as the longer the heat dwells, the more the parent material softens.Considering weight/strength alone, 6061-t6 aluminum weldments work at less than 1/2 the weight of mild steel. When impact and fatigue are in the mix the weight goes up. From the high cost standpoint, aluminum is used long term (fuel usage) or short term for weight (go fast).You can end up with some very strange looking joint designs (other than fillet) to test well.""This is why I stick to sculpture! You lost me at "LOL" 200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:[quote=bert the welder;384696] Originally Posted by Matt_MaguireFrench Wrench LOL6061 is about 18Ksi ....(snip)This is why I stick to sculpture! You lost me at "LOL"
Reply:To me, it would make the most sense to build the frame of 4130 tubing, using the same standards that would apply to building a roll cage.  You could make the roll cage part of the frame at the same time, use it to help stiffen the frame, etc.To the best of my knowledge, home built aircraft use 4130 tubing, TIG or gas welded.  Obviously safety and weight are critical for aircraft.http://www.jumprunenterprises.com/JR...echniques.htmlUnless you are a highly skilled welder, I would discourage using MIG for any critical welds, which would include most of the frame.  It is too easy for a weak MIG weld to look good.My two cents.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:well if i was you i would just use steel because if you want to compare 6061 to steel it is about 1/3 of the weight but it is also 1/3 of the strength so that being said in a place you would use 1/8" steel you would need to use 3/8 aluminum and the fact that aluminum costs ALOT more
Reply:Yep Richard, 4130 can drop a bunch of weight with equal strength, but the difficulty of joining goes up. some of this, some of that...I'm still not sure why socoj2 would really want to lighten a tracked vehicle, but in my neck of the woods there is a "Cardboard Boat Regatta" every year???? Some go pretty far before sinking, after being worked on all winter!Yep, 03dodgeoffroad,  but we're not sure what in the "wide - wide world of sports" socoj2 is up to...Matt