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View Full Version : post heat treatment tensile strength for alum. alloys



atomic_duck
05-14-2008, 04:01 PM
First of all hello.
I'm not a frequent english speaker so the spelling can be wrong sometimes.
I am designing a bicycle frame and I don't really have any good documentations on alum. alloys so I have to ask:
If I'm welding a frame made of tubes (Al 7005-T4) with a 5356 filler and heat treat the whole structure to 500+ deg. Celsius, quench and age at 200+ deg. Celsius is the weld as strong as the base metal?
From what I read on the internet it seems to be true, but, because I can't really crosscheck this with any technical literature I'm not sure how to approach this issue.

hotrodder
05-14-2008, 08:34 PM
5356 (and 4043 FWIW) will not respond to heat treatment. Given sufficient dilution with the base material enough alloying elements may be picked up to allow some response to PWHT- not gonna happen with a fillet welded bike frame though. Alloys containing more than 3% Mg (5356 is 5%) may suffer stress corrosion cracking at elevated temperatures (150F maximum service temperature is commonly quoted)

While there's several filler alloys that will work, 5180 was designed specifically for 7xxx series- a little less mag (than 5356) + a bit of zinc. 5183 has slightly better mechanical properties than 5356 as welded and is more commonly available than 5180

One of the nice things about 7xxx series (for this application) is that they take a long time to anneal (thus are 'damaged' less during welding) and make a better (and fast) recovery compared to, say, 6xxx series

Common practice in the bike industry is (or at least was until recently) NOT to fully heat treat frames fabricated from 7005. Some manufacturers would simply set the finished frame aside to naturally age, others (usually higher end, lighter frames) use artificial aging. Either way, if cold setting is required it needs doing ASAP upon completion of welding- 7005 age hardens rapidly

Your artificial aging temps sound a little high- 320F (160C) is the temp that come to mind (DON'T take my word for it though!)

Google 'easton + bicycle' they (used to at least) have a lot of free info on the commonly used alloys in the bicycle industry including framebuilding techinques. 'Columbus + bicycle' is probably worth a try too

atomic_duck
05-15-2008, 05:08 AM
Thank you for the answer
It helped me a lot.
I found the 5180 specifications and some heat treatment indications
Thanks again