Al spiking of Si would not be a problem if the Si diffusion in Al were small and little Si diffused into the Al, leaving voids in the Si for the Al to fill.
Just how much does the Si diffuse into the AI?
If the diffusivity of St in Al at 450°C is about 40 µm2 min-1, calculate how far the Si will diffuse into the Al after 60 minutes at 450°C?
(Calculate the distance in which the Si concentration falls to 50% of the surface concentration.)