Abstract
To clarify the solidification mechanisms of an eutectic system alloy under microgravity conditions, Al-Cu alloys containing 32.4 mass%Cu and 33.5 mass%Cu have been remelted and resolidified on orbit aboard the Space Shuttle, Endeavour. Both primary crystals of α aluminum dendrite in the hypoeutectic and CuAl_2 in the hypereutectic alloys grew continously from the surface of the samples inwards. Neither primary crystals moved during solidification because of the absence of fluid flow. The matrix of the samples showed irregular eutectic lameller structures. Small gas bubbles, which could not move in the molten metal in space, appeared near the surface of the samples.
