www.dahon.com said:
Puro™ U6 Aluminum Alloy
Our proprietary ultra light Puro™ U6 aluminum alloy is 25% stronger and 20% more fatigue resistant than traditional 6061 aluminum alloy. We worked with the suppliers of this material to develop custom tubes for our high end frames and forks and we are the only manufacturer using this material for folding bicycle frames. Puro™ U6 aluminum allows us to use very thin tubing without sacrificing strength.
So, its significantly better than 6061... (7005 is about 5.5% 'stronger' (in terms of Tensile strength at yield) than 6061)
I think 'U6' is just a trade name (like 'Araldite' for example). Ive found an aluminium alloy that has very similar properties to those claimed by Echo and Dahon (Folding bikes). It is 'UltrAlloy® 6020-T9 Aluminum' (which is where the 'Ultra' bit comes from? And the '6' from the series of alloy? I dunno... just an informed guess)
www.MatWeb.com said:
Material Notes:
Weldability = B; Stress Corrosion Cracking Resistance = A; General Corrosion Resistance = B (A = best; E = worst). General 6020 characteristics and uses: Excellent machinability, high corrosion resistance, good joining characteristics, and excellent response to anodizing. The T8 temper offers excellent residual stress control for applications requiring tight dimensional control after machining.
All in all sounding pretty sweet for bike frames.
Anyway... i hope that can be of some help... id really like Deng to fill us in though, if he could
Adam