"Aluminium" is the British spelling and pronunciation of what American's call "aluminum", see
http://en.wikipedia.org/wiki/Aluminium. But they use "tin foil" to call what American's call "aluminum foil".
I can't really say I've heard bicycle people using "alloy" to refer generically to aluminum alloy. Car people seem to do that with "alloy wheels". But bicycle ad's always seem to specify the material.