LASER RAPID SOLIDIFICATION OF AL-CU ALLOYS - BANDED AND PLANE FRONT GROWTH

Laser rapid solidification experiments have been performed on Al-Cu alloys with compositions of up to 44 wt.% Cu. By taking thin foils from the surface of the laser traces it has been possible to study the resulting growth morphologies using transmission electron microscopy, and because the microstructural orientation follows the direction of heat nux the morphologies can be related to their local growth velocities. Transitions to banded and plane front growth have been observed at the highest growth velocities (approximately 2.0 m s(-1)) that are attainable with the particular experimental arrangement. These transitions are consistent with current solidification models, which do, however, require a knowledge of metastable phase equilibria. The metastable azeotrope predicted by the phase diagram calculation is shown to explain the important experimental observations.