Originally Posted by ultra-g
I think it's in terms of 6061 vs. 6066, it's just different strength ratios, meaning they can use less material... equaling lighter frame weight without losing frame strength.
Do a search of the forums, because there have been a ton of threads about frame materials.
the last two numbers of an alloy number indicated the percentage of alloying elements, ie 1076 steel is iron alloyed with 7.6% carbon. I'm not sure what your aluminum is alloyed with.