Rapid Solidification and Subsequent Analysis of Some Hypereutectic Aluminum-Based Alloys

Abstract

A number of hypereutectic aluminum-based alloys have been prepared using rapid solidification processing. Two types of studies have been made, each involving a different set of alloy compositions. The first experiment was concerned with determination of the change in microstructural morphology of rapidly solidified Al-Ni alloys as a function of solute concentration. The results obtained for both laser surface melting and melt spinning were essentially identical in that there is a marked variation in microstructure for nickel concentrations in the range of 4.5 to 8.0% (atomic percent). The occurrence of these various microstructural morphologies has been interpreted on the basis of local interface undercooling and an asymmetrically disposed region of coupled growth. The second experimental approach involved a comparison of the responses of Al-4.1Fe-0.6X (indicated in atomic percent), where X was either molybdenum or cerium. The microstructure of the rapidly solidified molybdenum-containing alloy was found to be identical to that of the binary Al-4.7Fe and consisted of a cellular morphology with randomly distributed refined intercellular particles. The cerium-containing alloy also exhibited a cellular morphology, but the intercellular regions seemed to contain two phases, the first being the same as that found in the binary and molybdenum-containing alloys and the second tentatively identified as an oxide based on cerium. The microstructural changes and hardness variations have been determined as a function of aging at temperatures up to 773 K.