sounds like an interesting idea, but why would you want to bond alu to steel anyway? i would think you would want the frame stiff so how would you match a thicker alu end to a slimmer steel end? that would mean the lug would have to be 2 different sizes at each end and i'd assume you would have to either make it yourself or buy a big lug and trim it down for the steel side. so to make things easier, go all steel.