RAPIDLY SOLIDIFIED AL-CU ALLOYS .1. EXPERIMENTAL-DETERMINATION OF THEMICROSTRUCTURE SELECTION MAP

Laser rapid solidification experiments have been performed on Al-Cu al loys of hypereutectic composition 36, 40 and 44 wt% Cu. By taking thin foils from the surface of the laser traces it has been possible to st udy the resulting growth morphologies using TEM; the microstructural o rientation allowing the morphologies to be correlated with their local growth velocities. Microstructural features in the velocity range 0.0 1-2.0 ms-1 have been studied, and eutectic (both with and without osci llatory instabilities), dendritic, cellular, banded and planar front g rowth have all been observed. By combining these results with earlier observations made on alloys with lower Cu concentrations, it has been possible to produce a microstructure selection map for Al-Cu alloys. T he map correlates microstructure to growth velocity and composition in the ranges 0.01-2.0 ms-1 and 0-44 wt% Cu, i.e. the major part of the binary Al-Al2Cu eutectic (0-54 wt% Cu). As well as providing an intere sting overview of solidification structures, several features of this map can be used to gain information on the Al-Cu phase diagram.