Self- and Interdiffusion in liquid Al-Fe and Al-Si-Fe

Kurzfassung

The solidification and microstructure formation of Al-Si–Fe alloys are of particular interest because iron, often retained as an impurity during the recycling process, can form intermetallic phases that degrade the properties of the desired alloy. To better understand the behavior of Fe in such systems in the liquid phase, we present measurements of the self-diffusion coefficients in Al-Fe alloys conducted with quasielastic neutron scattering. In the Fe concentration range between 10 and 75 at%, the measured Fe self-diffusion coefficient in the melt remains almost constant up to about 30 at% Fe, thereafter it decreases with increasing Fe concentration. This composition dependence differs from that observed for the Ni self-diffusion in Al-Ni melts, despite the chemical similarity of Fe and Ni. In the Al-Ni system, the Ni self-diffusion coefficients on the Ni-rich side are almost concentration-independent when the Ni content exceeds 40 at %, which correlates with the packing density of the alloys. We extended our investigation by performing both an interdiffusion and self-diffusion experiment of liquid Al-Si-Fe alloys on a satellite using a specially designed shear cell furnace, as well as interdiffusion measurements of Al-Fe alloys on ground using X-ray radiography. Both techniques allowed us to minimize the impact of convective flow. For the Fe concentration below 20 at%, the Al-Fe interdiffusion coefficient decreases with increasing Fe content, while alloying Si seems to accelerate the mass transport in the melt. Ab initio MD simulations are included to address the differences between Al-Fe and Al-Ni in the local order and provide important insights into the coordination numbers and interatomic distances. These transport coefficients also build the foundation for refining predictive models, as the experimental data can be used as training material for neural network potentials.