Hello moltinmaster, short of taking a sample and sending it off to a lab for testing there is no easy precise method for identification. Tensile testing would probably give you an idea as to strength, but it is most likely a heat-treated frame so this wouldn't necessarily help you identify it as to composition. A number of the different bike frame builders use annealed aluminum alloys for the initial fabrication of their products and then they straighten and heat-treat them upon completion. If you are looking for a really good reference for aluminum materials and their weldability there is a book called " Welding Alcoa Aluminum", it was first copyrighted in 1954 and the latest copyright that I am aware of is listed as 1972. Check on the internet with Amazon.com for it or there is a technical book store in Portland, Ore. that sells new and used books called Powell Technical Book Store that may have a copy of it. I believe they also have an internet site that you could look for it on. Short of knowing the alloy specifically and being able to match the filler specifically I would consider repairing it with 5356 alloy. Just my 2 cents. Best of luck and regards, aevald
Thanks guys. I got some info frome one of the people at Trek. They said that it is not recomended to perform the repair because of the heat treatment, but that if I absolutley had to repair the frame they would send a piece of rod. I told him yes just to see what it was like.
P.S. It has to be welded in a inert atmosphere(must have Mag in it or something) Thanks for all of the replies.___