Castability of aluminium alloys

Castability is the ability of an alloy to be cast without formation of defects such as cracks, segregations, pores or misruns. Alloy dependent phenomena that determine castability are fluidity, macrosegregation, hot tearing and porosity. These phenomena have been known for a long time but have only recently become well understood and work is underway to develop predictive castability models. These models require input of physical properties, such as solidification path, dendrite coherency, solidification shrinkage and interdendritic permeability. Some of these properties are difficult to determine experimentally but new experimental techniques are being developed to extract such data. This paper will review the phenomena that limit castability of aluminium alloys. The influence of alloy composition on fluidity, macrosegregation, hot tearing and porosity will be described. Models for castability prediction will be briefly reviewed and data on coherency, fluidity, permeability and shrinkage will be presented.