A study of fluidity, flow stoppage and silicon modification in lost foam casting of hypereutectic aluminum-silicon alloys

Hypereutectic Al-Si alloys were cast by the lost foam casting (LFC) process to study the effect of silicon level and superheat on the alloy fluidity and silicon morphology. Three alloys with 14% Si, 18% Si and 22%Si were cast at three superheats 60°C, 115°C and 170°C. Expendable poly styrene (EPS) foam spirals, 12.50 mm wide and with two different thicknesses, 6.25 mm and 12.50 mm were used.;Significant PSC floatation was observed for Al-22%Si alloy. The size of the silicon depleted zone increased with an increase in superheat. However, this trend was reduced by the addition of phosphorus, which modified the shape and reduced the size of PSC.;Increasing the ceramic master alloy (CMA) content in the alloy resulted in a progressive modification of the eutectic silicon from needle-like to lamellar and finally to fibrous shape. Further, the addition of CMA induced precipitation of Mg rich phases.;There was an increase in the surface hardness of the alloys due to addition of CMA as well as phosphorus.;It was observed that metal fluidity increased with increases in silicon level and superheat. The investigation revealed that the interlocked primary silicon crystals (PSC) agglomerated behind the flow tip, which contained the eutectic silicon. The distance between the flow tip and the PSC agglomerated zone increased with an increase in silicon level.