Q & A details - Can you weld Schedule 10 aluminum to Schedule 40?
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Can you weld Schedule 10 aluminum to Schedule 40?

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Is it possible to weld schedule 10 aluminum to schedule 40? The schedule 40 has a wall thickness of about 1 inch and the schedule 10 is about .16 inches. We are building a rocket and the body tube is made of the lighter schedule 10, while the end caps of the oxidizer tank are schedule 40. The end caps are circular and will be inside the tube and will have to be welded all along the edges. We have never tried to use two different schedules so we aren't even sure if they will hold well.
Update: Yeah we are planning on beveling the edges on Monday. To tell you the truth, we didn't even think we were going to make the body tube out of schedule 10. We were just going to do the whole thing out of 40 because it's damn near impossible to find 20 feet of schedule 10 for a decent price! However, we did, and ordered the pipe after we already received the caps, so we're just stuck with them now. I'm not in the ox tank group...but I believe we are going to have around 675 psi working on the caps and then we're going to a safety factor of 2. We are pressure testing the tank in a pool this coming week. And yes. Every part is made from 6061. 

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  • 0861788249

    0861788249 2017-01-20 09:47:46

    Shouldn't be a problem. One thing I'd advise is to bevel the edges of the caps so you get a full-penetration groove weld, instead of a simple fillet weld. Groove welds have more structural integrity since there's guaranteed fusion through the entire thickness of the material. Also groove welds require less heat input for fusion which will reduce the potential for distortion and burn-through. This is obviously a failure-critical weld. Have it done by someone with lots of experience TIG welding aluminum. Don't do it yourselves since you obviously don't know what you're doing. What is the oxidizer? Compressed N2O? Sch 40 seems a bit excessive to me, if the walls are only going to be sch 10. Have you done tank stress calculations? It would also be wise to pressure test your tanks with water to check for leaks, before fielding them. Also, the type of alloy you use comes into play with regard to weldability. AA 6061 is very common for applications like this. However 6061 is a precipitation strengthened alloy. Heat causes the weld + heat-affected zone to be in the solutionized condition- which means they will lose about 70% of their ultimate strength..... only slightly stronger than pure aluminum. The best procedure in this case would be to purchase materials in the all-solutionized condition, weld the parts, then have them be precipitation heat-treated *after* welding.

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