Microsegregation during solidification of an Al-Cu binary alloy at largely different cooling rates (0.01 to 20,000 k/s): Modeling and experimental study

Microsegregation in the Al 4 wt pct Cu alloy was investigated experimentally in a large range of cooling rates from 0.01 to 20,000 K/s using different solidification techniques. The microstructure was modeled using two-dimensional (2-D) pseudo-front tracking (PFT) developed by Jacot and co-workers. The experimentally determined amount of nonequilibrium eutectics increases with the cooling rate in the range 0.01 to 3 K/s and then decreases in the range 20 to 20,000 K/s. The fraction of eutectic calculated from the 2-D PFT model shows not only the same tendency, but also agrees quantitatively very well with the experiments over the range of cooling rates. It can also be explained qualitatively how the observed in terms of coarsening of the secondary dendrite arms and the back diffusion in the way both depend on the local solidification time.