hello, my names paul I have been welding for 7 + years,but I still would to ask for advice. So I wanted to ask if anyone has experience with 6061 t6 aluminum (aircraft grade) pre welding tensile strength of 45,000 psi now I have done a little research on welding this and warned about overheating and the tensile strength reduced up to half after welding,but also it being stronger tensile wise after welding and the mention of preheating 250F before welding. I'm looking at 1/4 wall 1 1/2x 1 1/2 inch and a half tubing or 2x2 inch tubing to make a tow bar for a 49' cessna. weights 2 tons any suggestions on either tubing size being stronger and also welding. rod for tig and mig spool wire? and preheating and stronger/ weaker in tensile strength. and lastly have to ask.....has anyone made a frame for a hotrod or cross members out of aluminum? I greatly appreciate your help thank u
Do yourself a favor and do a Google search on "Endurance Limit" and "Fatigue Limit" with regards to aluminum in high vibration applications. It doesn't matter how strong or huge you make it, it will eventually fail, even at near zero load. Aluminum is just a poor choice for an automotive frame. Race cars and super cars may use it to save weight, but they get poured over on a very regular basis (and with very short terms between) to keep an eye out for fatigue cracks. It can be done, but your maintenance schedule will be murder and the cost of fabrication will be very high. Unless it's an application where every pound is worth $1500, you're better off to go back and start looking at thinner walled 1018 steel tube. If weight is really a problem, consider using very thin walled 4130 steel tube. It still has a higher probability of developing fatigue cracks than mild steel (1018), but no where near as bad as aluminum. Welding 4130 is more involved than 1018, and the whole chassis may need to be normalized afterwards, but it will still likely be less trouble than doing a full chassis out of heat treated alum tubing. EDIT: Missed the part about it being a tow bar for parking a plane. My old man had a 172, and we had a tow bar made of rectangular aluminum tube, with the fork to hook over the nose gear machined right into the end. In this case, alum will be fine, even without reheat treating, as failure will only result in the plane stopping where it is, or coasting a very short distance to a stop. Have at it.
Welded aluminum generally requires a heat treat operation to bring it up to full hardness after welding. It will "age harden" in time, but it really should be checked (not something that you can do at home!) on a certified hardness tester. I'd also be suspect of using aluminum to tow anything close to 2 tons even as a yard designated aid. Unless you have a proven design to copy in aluminum, I'd go with mild steel. You can use a thinner wall than with aluminum so the weight difference might be less than you think. Bob
The few Al structures I've been part of, in design, had a "wet-noodle" characteristic that meant far more deflection when loading was cycled in addition to the above mentioned concerns. Frames would be a bit on the flexible side.
The question of application is important to your question. What are the stresses applied during application. Most important is the use of proper gussets in areas of stress, and this applies to any type of metal. I have welded a bunch of this type of aluminum, but never in a situation where there was stress or vibration, so I can't help much, other than these things I have mentioned. Preheating is always a good idea.
What is tow bar being used for, to move around the hanger. If it fails in that case I don't see a big danger. If used for flight somehow, well hmm. With the proper size material it can be done and work. Welding store can guide you on the filler, 5052 I believe is 1 good choice. I would tig it myself. Properly designed for the right application it will be fine. Bad design, wrong app well.... it won't matter what material you use.
Without additional heat treatment, Aluminum is softer after welding. The tensile strength of T6 takes a serious nose dive. --- Chrysler used an Aluminum frame for the Prowler, some of the high end Corvettes use an Aluminum frame, and Aluminum is commonly used for frames on Japanese motorcycles. Done with the correct engineering, and heat treating, no problem.
I want to say thank you guys for your advice and time stopping by I appreciate it and all the knowledge. Sounds like the car frame is more trouble than it's worth. But as far as the tow bar for the cessna, the tow bar would only be used around the hanger and as far as the heat treatment process after welding,take it would have to be done by a heat treating shop not an at home thing as bobss396 mentioned? and steel tubing over 1/4 wall inch and a half by inch and one half sq tubing and possbile wall thickness on the steel.... thank u again for your help
heat tret. will be done in a controlled oven with temps at a stagerd degree for a time table for the final t-grade ask your local FBO they should have the specs. if not get back to me in an e-mail, will dig out my old aircraft maintence books and see what i can come up with....
The temper of the welds and the area around it will be way off after you do this, maybe be higher or lower tensile strength depending on how fast you introduce heat and how fast it cools, preheating impacts this as well. When making anything structural out of Aluminum it should be annealed to a uniform level before you put any load on it, especially a repeated load. The size, thickness, form of the material as well as the speed of heating, final temperature, time at temperature and cool down speed and time all have an impact, not something to play around with. You may be able to find a local aluminum extrusion company to help you, they should have an oven to harden their final products and you may be able to slip your project in. I used to design these ovens for an extruder, this is an actual science on how to get it right, but the work was in another language and 16 year ago so some of my terms may be off a little bit.
Check out Panoz aluminum frame. They use diferent angle extruded couplings to assemble thier frames. You can google some good articles.
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