front upright suspension arm/knuckle

[niall_wallace]

Looking at the suspension upright on the b5 s4 ( the one that all the balljoints/arms/tre connects to) it looks like its cast steel/iron whatever.

I noticed on a 02 plate a4/a6 ( or thereabouts) , the upright, which looks the same at least, looks as though it is made of some kind of alloy, and as a result, would be considerably lighter?

Does anyone know if this is the case and would one fit the other?
just a thought

Niall.