Morphology of β-AIFeSi intermetallic in AI-7Si alloy castings

Abstract

The morphology of β-AlFeSi phase was investigated in permanent mould castings of an Al-7Si (wt-%) base alloy at the three iron levels of 0.3, 0.6, and 1.0 wt-% and at two mould temperatures of 25 and 400°C. At high cooling rates and low iron levels, the β platelets were found to be at the interface between flake silicon and aluminium. Increasing the iron level and decreasing the cooling rate encouraged the β platelets to crystallise independently of silicon. The pre-eutectic β platelets which form at high iron levels were efficient nucleants for the eutectic silicon in unmodified and strontium modified alloys. The size of the β platelets increased with increase in iron level and with decrease in cooling rate. It is postulated that the silicon content of the alloy will also influence the size of β platelets at high iron levels; the platelet size in this case will increase with increase in silicon content.