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 k e of approximately 13%. It is shown that the decrease in k e 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 k e 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 k e 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.