Some Considerations of the Volume Shrinkage of Aluminium-Silicon Alloy Castings Produced in Full Moulds

Abstract

The effects of casting conditions and of varying amounts of silicon on volume shrinkage have been determined on the full mould cast AlSi binary alloys. The constitution of the AlSi alloys leads to two stages in which either shrinkage or expansion is occurring during their solidification. The behaviour of the associated volume changes leads to the occurrence of shrinkage defects. In these castings, the overall amount of volume shrinkage that occurs during solidification is associated with both volumetric contraction and the formation of macrocavities, surface sinks and internal porosity. The amount of silicon affects the contraction and soundness of casting by influencing the eutectic silicon amount. An important finding is that increasing the silicon content leads to a decrease of the overall volume shrinkage. This is a common foundry variable which can be measured, and is amenable to some control. The results are discussed with relation to the inherent behaviour of various alloy systems and foundry processes.