Divorced eutectic growth in a ternary Al-Mn-Si alloy under microgravity

We report on first experiments dedicated to understanding a particular form of divorced eutectic growth that develops along the univariant eutectic reaction: Liquid --> a-Al + a(AlMnSi)+ Liquid ' during unidirectional solidification of the hypoeutectic ternary alloy AI-Mn I wt%-Si 3wt%. We show that this growth mode is not oscillatory, though it leads to a banded distribution of alpha (AlMnSi)-particles. An experiment in microgravity, performed during the Spacehab mission STS-95 in November 1998, shows that particle size and distribution is velocity dependent, a fact that on earth is masked by gravity. The microgravity experiment was performed in ESA's Advanced Gradient Heating Facility, AGHF.