You can read the paper by J.O McCaldin and H.Sankur "Diffusivity and solubility
of Si in the Al metallization of integrated circuits Appl Phys Lett 19(1971)
524..

 according to the paper the diffusivity of Si in Al @ 400 deg C is approx
10um*2/min

Rakesh

Bill Moffat  wrote:
I do not know the eutectic point. I do know that in at least 5
different semiconductor manufacturers I worked in we alloyed aluminum to
silicon at about 435 degree C in a reducing atmosphere. It led to the
manufacture of our 450 degree C oven with reducing gas control.