I used to work for a Tier 1 brake supplier and we played around with the Duralcan cast material, which was 356 base alloy with 20% SiC loading. Our friction materials division made up pads formulated to work with the Duralcan. The project never went anywhere with our customer; I think Porsche or BMW used it for rear discs on one model. The Chrysler street rod (I forget the name of the car) may also have used it. One thing to keep in mind is that the heat capacity of aluminum, being 1/3 that of cast iron, results in less heat sink capacity being available and thus the potential for brake fade with multiple high energy stops. This is why it was only looked at for rear disc applications. As for fly ash--this is a wet dream idea to simulate the Duralcan material on the cheap.