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

Abstract

Hypereutectic Al–x%Si–0.8Sc alloys (x=13, 16, 19 and 22wt%) were produced by spray forming. The microstructures of all the alloys exhibited very fine silicon phase with average size of about 5–10µm 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 (1.34GPa) in contrast to 1.04GPa 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 10µm 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.