Observation of early melting stages of an Al – Cu alloy in a temperature gradient

Abstract

Abstract Homogeneous Al-3.7 wt.% Cu samples (Al solid solution) were (partially) melted by rapid heating in a steep temperature gradient and quenched immediately after the onset of melting. Traces of melting, particularly intragranular eutectic and θ-phase particles as well as intergranular eutectic and θ-phase layers, were observed in the quenched microstructure. The intragranular particles (mean diameter locally < 200 nm) represent former liquid droplets that nucleated as a consequence of some supersaturation of the Al solid solution. The intergranular layers represent former liquid films that nucleated at the grain boundaries. At temperatures slightly above the solidus temperature, segmentation of the film was observed. Concentration distributions measured using energy dispersive X-ray analysis indicate the migration direction of the film and the supersaturation as the driving force for migration.