Iron-related porosity in Al–Si–(Cu) foundry alloys

An experimental program has been undertaken to explore the effect of iron concentration on porosity levels in Al–Si alloy sand castings. The effect of iron concentrations above, below and equal to the critical iron content for alloys with either 5 or 9% Si and either 0, 1 or 3% Cu has been determined. Increasing iron concentrations were found to increase porosity in all alloys except the copper-containing Al–5% Si alloys which displayed a porosity minimum at the critical iron content. Porosity was observed to be higher in the Al–9% Si castings than the Al–5% Si castings. Differences in the primary phase volume fraction and morphology may explain this observation. The results of this experimental work do not support the existing published theories that have been proposed to explain the effect the iron on porosity. An alternative theory is therefore developed.