Originally Posted by
Tritium
Usually if an aluminum object is not initially assembled by welding (it is joined by riveting or some other method) then the aluminum alloy used is NOT weldable. Paraphrase from Jody of WeldingTipsandTricks.com
Thurmond
Or they actually need to have some strength in the part, or couldn't weld for corrosion reasons. The reduction in strength of non post weld heat treated aluminum for most common weldable alloys is quite high, especially with heat treatable alloys. Most 5000 series alloys don't lose a great deal of ultimate strength (yield still suffers) from welding, but then again, most 5000 series alloys aren't as strong as say heat treated 6061 to start with. Weldable 7000 series alloy (usually 7005) is pretty much only available in tube form, and is easier to get in Europe. It is used on bicycle frames.
I have welded "unweldable" 7000 and 2000 series alloys, including Aluminum Lithium alloys....but that was with Friction Stir Welding, not conventional fusion welding.
Either way, keep an eye on the welded areas as they may crack again, or could corrode quite fast as compared to the base metal.
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