Grain size and porosity of cast hypoeutectic aluminium-silicon alloys in hexachloroethane coated mould

This paper examined the effect of concentration of hexachloroethane (C2Cl6) in alumina mould wash on the grain size and apparent porosity of cast hypoeutectic aluminium silicon alloy. A hypoeutectic aluminium-silicon alloy was prepared and cast in metal mould coated with alumina slurry to which varied concentrations (0–40 wt %) of volatile organic compound, C2Cl6, have been added. The effects of the amount of the hexachloroethane in the mould coating on the grain size and apparent porosity of cast hypoeutectic aluminium-silicon alloy were assessed. There was an observed initial decrease and subsequent increase in the grain size as the concentration of C2Cl6 in the mould wash increased while there was no significant change in the apparent porosity of the cast alloy. It was concluded that coating metal mould with alumina mould wash containing approximately 15 wt % C2Cl6 produces optima grain size. The study also revealed that the use of such volatile mould coating does not introduce any noticeable gas porosity in the cast hypoeutectic aluminium-silicon ingots but rather aids the expulsion of possible trapped gases.