Solidification microstructure selection in the Al-rich Al–La, Al–Ce and Al–Nd systems

Abstract

The effect on solidification and microstructure of solidification conditions in wedge chill casting and Bridgman growth have been investigated for Al 5.7 to 19 wt% X (X=La, Ce, or Nd) alloys. The systems are shown to exhibit an asymmetrical zone of coupled eutectic growth on a plot of front velocity versus alloy composition. Only the equilibrium phases αAl and Al 11X 3 form under the conditions studied and the results are consistent with a eutectic composition of ∼12 wt% X for all three systems, as proposed in 1990 by Kononenko and Golubev. Both primary αAl and primary Al 11X 3 underwent significant morphological changes as the boundaries of the coupled zone were approached. The positions of these boundaries at high velocities yielded values of the growth parameters for primary Al 11X 3 and the αAl–Al 11X 3 eutectic similar in magnitude to recent measurements for corresponding primary phases and eutectics in the related Al–Fe and Al–Ni systems.