Microstructure Development and Control in Hypereutectic Cast Al-Si Alloys Evaluated by Metallurgical Analysis and Neutron Diffraction

Presented results show individual effect of key alloying elements, i.e., 2.8%Cu, 0.7%Mg and 0.01%P on the as-cast microstructure development in the hypereutectic Al-19%Si alloy evaluated using classical metallurgical analysis as well as in-situ neutron diffraction during alloy solidification process. Neutron diffraction revealed possible Si atoms clustering above liquidus temperature i.e., 677 °C and pre-mature nucleation of α-Al crystallites below liquidus temperature i.e., 667 and 625 °C in addition to liquid-to-solid phase transformation assessment during solidification. Mechanical strength i.e., hardness and ultimate tensile strength improvement due to Cu, Mg and P additions is evidenced and linked with microstructure evolution under non-equilibrium solidification conditions. Primary Si refinement was improved with subsequent addition of Cu and Mg, and P addition alone had insignificant effect on primary Si refinement.