DIRECTIONAL SOLIDIFICATION OF ALUMINIUM–COPPER ALLOYS IN A MAGNETIC FIELD

Abstract

The degree of normal segregation, occurring during directional (normal) freezing in a transverse magnetic field of 34 000 oersteds, has been determined for aluminium–copper alloys solidified for rates of [Formula: see text] to 4 inches per hour. For ingots in the composition range 0.5% < %Cu < 4.5%, solidified at rates exceeding [Formula: see text] inch per hour, the magnetic field increased normal segregation, corresponding to a maximum decrease in the effective distribution coefficient ke of approximately 13%. It is shown that the decrease in ke can occur only through a rise in the liquidus of the alloy system, which is in agreement with the theory developed to account for the inverse segregation results obtained for aluminium–copper ingots chill-cast in a magnetic field (previously reported). An increase in ke due to the field was found for 0.5% Cu ingots and also for the 4.5% Cu and 7% Cu ingots. The concentration dependence of ke is related to the concentration gradients and diffusion zone lengths, and is shown to be compatible with the thermodynamic constraints on the system undergoing the irreversible process of solidification in a magnetic field.