Effect of scandium addition on the microstructure, mechanical and wear properties of the spray formed hypereutectic aluminum-silicon alloys

Hypereutectic Al-x%Si-0.8Sc alloys (x=13, 16, 19 and 22 wt%) were produced by spray forming. The microstructures of all the alloys exhibited very fine silicon phase with average size of about 5-10 µm irrespective of the silicon content of the alloy. Transmission electron microscopy revealed the presence of a nano-scale scandium rich phase, identified as AlSi2Sc2 (V-phase) uniformly distributed in the alloy. The presence of V-phase resulted in higher matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al-Si alloys by nanoindentation. Isothermal heat treatment at 375 °C revealed insignificant coarsening of silicon phase in both binary and ternary alloys. The Al-x%Si-0.8Sc alloys exhibited higher flow stress and tensile strength in contrast to their binary alloy counterparts which was attributed to the bi-modal size distribution of the strengthening phases in the form of nano-scale V-phase and sub-micron to 10 µm size silicon particles. The pin-on-disk wear tests exhibited appreciable improvement in the wear performance of the relatively low-silicon content ternary alloys over their binary counterparts while the high-silicon content binary and ternary alloys exhibited no much difference in the wear performance.