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Re: Al-yoo-minium

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Weld procedures, welders qualifications and NDT are a must. Inclusions and porosity can be big problems at the welded joints. Burn through by the welder is also a problem - sometimes you think it's like solder. Also check this out:

Review AWS D1.2 - Structural Welding Code - Aluminum. A good reference is "Aluminum Structures - A Guide to Their Specifications and Design" by Kissell and Ferry published by Wiley.

Once as the resident engineer on the seismic strengthening of an aluminum nuclear rocket test stand: There had been a piece of the original tower cut out and replaced and the original piece had been thrown on the ground. As I walked by this piece, I kicked it with my boot and it came apart! This started an investigation of all the existing connections in the tower that had been deemed adequate. Using NDT, almost all of the existing connections showed problems of porosity. Ultimately, most of the connections were strengthened with additional plates, etc.

Neil Moore, S.E.
neil moore and associates

At 07:14 AM 8/12/2005, you wrote:
As many, including Chris, have mentioned, Aluminum is definitely a different beast from steel.

Get the Aluminum manual. It will set you back about $350 and take a week to arrive. Mine did, and I'm the next state over from their printing shop (in MD, if you're curious). It will have not just the formulas and factors your looking for, but the stress allowables (ult, yield, shear) for the common Al alloys and tempers.

E is about 10E6 psi for design (~1/3 steel, as mentioned).   Many welds
must use near-annealed values, as the resulting weld cannot be restrengthed. This is, obviously true of all the H (work/strain hardened) "tempers". 1, 3, 4, and 5 series are not heat-treatable, only work hardened. 2, 6, and 7 are heat treatable.

Welds are typically bad ideas in aluminum for anything stress critical due to the ease in which inclusions appear in the welds, though some alloys will take welds well. For spaceflight, welding is a last resort for pieces which cannot be joined any other way. Also, don't forget that there is no fatigue limit for aluminum like there is for steel - as cycles increase, it just gets weaker and weaker.

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