7075 vs 2024 vs 6061 aluminum vs 1018 steel, which one is more rigid and stiff?

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I am building a kiosk basically a box on a 4x4" aluminum pole that is attached to a 18x24" base plate. I've used 1/8" thick carbon steel mostly because it's cheap and stiff. I've also used 1/4" aluminum plate 6061 T6 which is more rigid than 1/8" carbon steel but about the same weight since it's twice as thick!even tried 1/8" thick carbon fiber but it was not rigid at all, flexed a lot.since this product is moved around a lot. I want a stiff light base that wont' break the bank, so no titanium . I supposed I just need to  buy some scraps off ebay and do some testing???But I will ask any ways, which material is most rigid or stiff? 7075 vs 2024? are they just as stiff as carbon steel or even better?ironically none of the regular aluminum supplers that I use have this as a stock item special order only. alro the steel supplier I use has it . the 2024 t3 sheet is almost twice the price of the 60615x10' x 1/8" sheet 88 lbs of 6061 is $290 a sheet4x12' x 1/8" sheet  86.5 lbs of 2024 is $480 a sheet!ps did a search , hardly any threads about this, probably because 2024 and 7075 can't be welded!
Reply:You forgot 7005 alum, and magnesium.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:those are even more rare to find, I'm just talking about the more easily to buy grades. dont' want to spend a fortune just shipping heavy metals across country because they are so rare they are not available locally.
Reply:Design also has a lot to do with stiffness. Take a plain piece of paper and try to stand it up on edge, it simply falls over. Now fold it in half, and it stands up. Do multiple corrugations and that sheet can now hold something up.Thinking about it, you might want to look at that corrugated plastic that they use for lawn signs and so on. It's stiff and light weight, and I believe you can order it in any number of colors and finishes. It's often used for light weight large signs..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:K@ AluminumWelder - All aluminums have a Young's Modulus (E) of ~ 10x10^6 psi.  Irrespective of Grade. Stiffness is related to shape/geometry for a given element, material, or alloy. You could build a shape out of paper mache & bailing wire that would rival the "stiffness" of an ill designed weldment of aluminum sheet.Recommend you think through your requirements. You say light & stiff.  That's a relatiive description.  How many translational/ rotational DOFs (degrees of freedom) does your support need to resist?  5lbs tension/compressions or 1k lbf? What you consider light may differ from someone else's interpretation.People often say that aluminum is good to use over steel because for a given unit weight a product can be made "stiffer" with aluminum.  Aah, but here's the rub.  The "Figure of Merit", or stiffness per unit $cost of material, is ~ 3.5 times greater for aluminum than steel.You want strong, light, stiff, extensible, and cheap?  Select steel.Last edited by ManoKai; 08-04-2015 at 08:55 PM.Reason: spelling"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:I have tons of coroplast very flimsy for base plate, but good for other stuff, also have alumalite which is coroplast with aluminum skins too weak as well. I'm talking about a 50 lb kiosk box on a 4 foot tall torque arm that people press all day long with 5 to 10 lbs of force, that's a lot of torque on the plate and I don't want it wobbling back and forth. see example photo, but box will be twice as big! I'm talking about the base on the floor I really want something light and strong, but in my google searches have next to zero information on people that use high strength aluminum plate. , also have tried HAP, or hexagon hollow aluminum 1/2" plate with .040 skins, skin tends to get dinged up so solid is best. Also tried 1/8" aluminum with 1/2x1" aluminum tube welded under it, works well, but a lot of labor.Honestly steel has been the best so far, but would love to switch to high strength aluminum for weight savings!as far as design goes, it's a base plate, there are no design tolerances that allow me to fold, bend or otherwise make it stronger through mechanical means, it's either stiff enough or not
Reply:Skip any aluminum.  Portability a key requirement?  What a about a heavy duty, circular, base with embedded wheels so when you tip the column 30deg, say, the wheels engage and off you go?  Would expand the x-y dimms of thre base.  You say ~ 40ft-lb of torque.  What about when someone applies 2x in force, or worse, falls into the product by accident?You def want heft/mass in the base to resist all DOFs.  If you are unable to bond the item permanently on site, then consider a smart/strong alternative. What's the floor material the product's base will rest on?  What about supplemental support via suction cups?Last edited by ManoKai; 08-04-2015 at 08:30 PM."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:the carbon steel base I'm using now is about 20 lbs  so less than that would be greatas far as deflection I think less than 5 degrees would be good, collum is bolted to base from under neat with 4 stainless steel 3/8" boltsif a person falls on top of it, that's gonna hurt, no way am I gonna make the kiosk so heavy that it can withstand a 200 lbs individual falling over, I want it portable and strong, not tank proof and heavy.
Reply:I'd go with a heavy steel plate and then just move with a two wheel cart.  With camera and stuff on top, you don't want it tipping over.2nd choice would be a base made out of square tubing, covered with sheet, and big enough that the operator has to stand on it.My name's not Jim....
Reply:already have a heavy 20 lb  steel plate, just looking for alternatives on a metal alloy that no one seems to have experience with?
Reply:Originally Posted by DSW        look at that corrugated plastic that they use for lawn signs and so on. It's stiff and light weight, and I believe you can order it in any number of colors and finishes. It's often used for light weight large signs.
Reply:Well, I'm admittedly an idiot  when it comes to this stuff, but...Were it I, I would go with steel; and if stiffness was an issue I would weld on some reenforcing gussets going from that center post out to the four corners of the plate.I would do like ManoKai said and also add wheels that only engage when tipped up at an angle. Actually, ditto everything he said.
Reply:What about putting the base down with thin set? Problem solved. Might be a devil to move/remove.... If it were me I'd bevel a piece of half inch steel plate and put anti-skid on the bottom. Maybe 3M has something designed to keep kiosks in place that's easy to remove... like their command hangers. Might be worth calling them.Last edited by forhire; 08-05-2015 at 04:46 AM.
Reply:All good ideas but honestly i am also just curious how strong these hard to come by aluminum alloys are? Gonna buy some off ebay and find out
Reply:Steel is three times the density of aluminum.  Steel is three times the stiffness of aluminum.  High strength steel is over three times the tensile strength of high strength aluminum.  In a properly designed part where deflection is the limiting factor, steel and aluminum parts will have very similar weights.Now before you start jumping on me about steel airplanes, airplane parts are generally designed so strength is the limiting factor.  That favors aluminum.  But airplane parts are not welded aluminum parts.  High strength aluminum parts are fastened together by bolts, screws, rivets, and glue.It appears to me your biggest concern should be stability of the part.  Think of a couple of teenage boys screwing around and one pushes the other.  You don't want the whole thing to fall over when somebody is knocked against it.  That suggests as heavy of base as practical, favoring steel or iron.Last edited by bent; 08-05-2015 at 08:02 AM.
Reply:Originally Posted by AluminumWelderalready have a heavy 20 lb  steel plate, just looking for alternatives on a metal alloy that no one seems to have experience with?
Reply:so regardless of aluminum alloy 3003 5052, 6061 2024 7075, they will all deflect the same amount because youngs modulus is the same among all alloys?Unfortunately if I made the base 100 lbs or 5/8" thick steel 24x18" in size it would not sell. People that buy these things I make want them to be easy to move. anything more than 30 lbs is probably not sellable.
Reply:i guess what I dont' understand is how can the 2000 and 7000 series aluminum be considered stronger alloys, but have the same youngs modulous? doesn't a stronger metal bend less?https://books.google.com/books?id=Ls...alloys&f=falsestarted reading this , but it is a bit over my head.
Reply:Originally Posted by AluminumWelderi guess what I dont' understand is how can the 2000 and 7000 series aluminum be considered stronger alloys, but have the same youngs modulous? doesn't a stronger metal bend less?https://books.google.com/books?id=Ls...alloys&f=falsestarted reading this , but it is a bit over my head.
Reply:E is inversely proportional to ambient temperature a given element/alloy is subjected to.  QED.   E -vs- Temperature"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Why not build the post and yoke from alum, and bolt a base made from steel to keep bottom heavy? I see they are bolted in your image.Alum is not really more expensive than steel, because you get 3 times the amount per pound. Alum could be potentially cheaper in the long run. Get alum extruded tube and weld threaded plated inside.Last edited by shovelon; 08-05-2015 at 09:48 AM.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:Thats what im doing now all aluminum with steel baseSteel is about half the price per equivalent need However by the time i factor in cleaning by hand and prime and paint the labor makes it more expensive
Reply:Originally Posted by AluminumWelderThats what im doing now all aluminum with steel baseSteel is about half the price per equivalent need However by the time i factor in cleaning by hand and prime and paint the labor makes it more expensive
Reply:Originally Posted by AluminumWelderi guess what I dont' understand is how can the 2000 and 7000 series aluminum be considered stronger alloys, but have the same youngs modulous? doesn't a stronger metal bend less?...
Reply:^ Ashby Plot.  Perfect context! :cool"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyiso these high strength aluminum allows will bend just as easy as the cheap alloysThe only benefit is if you are building somethign that will have pull streteching forces on it and then it won't break as easily?Kind of useless to me, most things I build dont' get pulled apart, they have side loads that cause bending. and if they do get pulled apart it is typically at a joint that is riveted or bolted together since these high stregth alloys can't be welded. , even if you could weld them the temper is near zero at a welding joint. Love to know what applicaitons this aluminum is needed in? I know in aerospace, but where? on a plane wing? ON a rudder? my guess is they are nich product and therefore expensive due to low manufacturing volumes.
Reply:tha'ts a cool graph, gotta look for a higher resolution link, becuase it's hard to read.
Reply:IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal.  Main alloying element is Cu.IF you desired excellent strength, stress/strain resistance, and anti-corrosion properties, THEN 7075 would be a solid candidate.  Main alloying ingredient is Zn.Your application/design needs none of those properties.Aerospace Aluminum Alloy DevelopmentLast edited by ManoKai; 08-05-2015 at 06:28 PM."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Originally Posted by AluminumWelderso these high strength aluminum allows will bend just as easy as the cheap alloys
Reply:Commercially available, Kiosk Stands.  Note the dimensions and tare WEIGHT of these stands. The carrying handle is convenient."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:"IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu. IF you desired excellent strength, stress/strain resistance,................. then 7075....."When I read this those two sentences mean the EXACT same thing to me. looked up fatigue is the weakening of a material caused by repeatedly applied loadsstress strain is applying a load and measuring the deformation.Not trying to be dense, but obviously there are reasons to choose one over the other that can be explained more simply? 7075 springs back to it's orginal shape better? is that the main difference you are trying to convey?
Reply:I got a headache from this thread   here you go !  http://www.ebay.com/itm/New-PSPADLK5...item51b41d3640
Reply:Unless the aluminum is tempered (and if you weld it, that usually requires heat-treating it after you weld it), in general, pound-for-pound, steel is slightly stiffer and stronger than aluminum.
Reply:Originally Posted by AluminumWeldertha'ts a cool graph, gotta look for a higher resolution link, because it's hard to read.
Reply:Originally Posted by ManoKai^ Ashby Plot.  Perfect context! :cool
Reply:@ A_DAB_will do - check out the high-rez Dick Ashby plots in the Metallurgy sticky (post #22). "Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Originally Posted by AluminumWelder"IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu. IF you desired excellent strength, stress/strain resistance,................. then 7075....."When I read this those two sentences mean the EXACT same thing to me. looked up fatigue is the weakening of a material caused by repeatedly applied loadsstress strain is applying a load and measuring the deformation.Not trying to be dense, but obviously there are reasons to choose one over the other that can be explained more simply? 7075 springs back to it's orginal shape better? is that the main difference you are trying to convey?