If the AL6 is a manufactured part from a known manufacturer I wouldn't worry about it. If you intend to free issue the material to a weld shop I wouldn't,t go that route
unless they had a weld procedure and the qualification record
This isn't the forum to get into the technicalities of welding but the AL6 is temperature critical as it is usually welded with alloy 625( very expensive) filler metal and the 2 alloys have different melting points No. Problem for those who have developed a procedure.
Also note that AL6 should not be cut with traditional oxy fuel
systems. Plasma or saw cut is recomended.
Duplex is much more readily available in Europe
and the welding of it more commonly understood but less so in the US.