Modelled heat transfer coefficients for Al-7 wt-%Si alloy castings unidirectionally solidified horizontally and vertically downwards

A model is described for the calculation of the interfacial heat transfer c oefficient during the unidirectional solidification of Al-7 wt-%Si alloy ca stings against a water cooled copper chill. The model includes the deformat ion of the initial solidified skin of the casting into a convex shape withi n the first seconds of solidification. Thereafter, heat transfer from the c asting to the chill takes place through a central contact area and an outer annulus where local separation has occurred. Modelled heat transfer coeffi cients for solidification horizontally and vertically downwards are compare d with experimentally determined values and show broad agreement. Some limi tations of the model which prevent better agreement with the experimental v alues are discussed. MST/4308. (C) 2000 IoM Communications Ltd.