The role of the bimodal distribution of ultra-fine silicon phase and nano-scale V-phase (AlSi<inf>2</inf>Sc<inf>2</inf>) on spark plasma sintered hypereutectic Al-Si-Sc alloys

Hypereutectic Al-Si and Al-Si-Sc alloys were spark plasma sintered from corresponding gas-atomized powders. The microstructures of the Al-Si and Al-Si-Sc alloys possessed remarkably refined silicon particles in the size range of 0.38-3.5μm and 0.35-1.16μm respectively in contrast to the silicon particles of size greater than 100μm typically found in conventionally cast alloys. All the sintered alloys exhibited significant ductility of as high as 85% compressive strain without failure even with the presence of relatively higher weight fraction of the brittle silicon phase. Moreover, the Al-Si-Sc alloys have shown appreciable improvement in the compressive strength over their binary counterparts due to the presence of intermetallic compound AlSi2Sc2 of size 10-20nm distributed uniformly in the matrix of those alloys. The dry sliding pin-on-disc wear tests showed improvement in the wear performance of the sintered alloys with increase in silicon content in the alloys. Further, the Al-Si-Sc ternary alloys with relatively lesser silicon content exhibited appreciable improvement in the wear resistance over their binary counterparts. The Al-Si-Sc alloys with bimodal distribution of the strengthening phases consisting of ultra-fine (sub-micron size) silicon particles and the nano-scale AlSi2Sc2 improved the strength and wear properties of the alloys while retaining significant amount of ductility.