Iron is a common impurity element in both primary and secondary aluminum-silicon-based foundry alloys. During solidification, iron segregates to form various intermetallic phases, and little is known about their influence on the castability of these alloys. Previous researchers have identified a propensity for the formation of interconnected shrinkage porosity in the presence of #beta#-Al_5FeSi platelets. This relationship has been confirmed by experimental data, and explanations for the mechanisms involved have been offered as a combination of altered alloy solidification sequence, altered eutectic nucleation and growth, and decreased permeability arising from physical obstruction of interdendritic feeding paths. The development of iron-related shrinkage porosity seems to be strongly influenced by marginal casting conditions. Shrinkage porosity defects of this origin can result in the loss of pressure tightness in commercial castings. In order to assist in the reduction of casting reject rates, the effect of iron content (from 0.1 to 1.3 wt percent) on the castability of an AlSi9Cu3 alloy has been studied. It was found that the total average porosity of the castings increased approximately 30 percent across the range of iron content studied, and that there was an increased propensity to farm interconnected shrinkage porosity at high iron levels.
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