ON LIQUID-FILM MIGRATION IN ALUMINUM-COPPER ALLOYS

Experimental and numerical modelling results are presented for the mig ration of liquid lenses, formed on melting of grain-boundary theta pre cipitates in Al-3.4 wt% Cu alloys, which had been previously equilibra ted at 400 degrees C. Liquid films of comparable thickness. formed upo n the melting of intragranular Widmanstatten precipitates, were found not to migrate. The modelling studies are based on the hypothesis that the leading and trailing solid-liquid interfaces are each characteriz ed by a constrained local equilibrium, as determined by chemical, cohe rency and capillary terms, and that the process is driven by the liqui d concentration gradient resulting from different equilibrium concentr ations at the two interfaces. The model is utilized to explore the sen sitivity of the process to variations in physico-chemical parameters, and ultimately as an aid in the understanding of the migration of the liquid lenses and its cessation. It is concluded that the capillary te rm has a strong influence on thr migration process, even for liquid po ol dimensions of several microns. (C) 1998 Acta Metallurgica Inc.