The solidification and mechanical properties of chill-cast AI-AI3IMi and AI-AI2Cu eutectic alloys

Abstract

This paper describes the effect of chill-casting on the solidification behaviour and mechanical properties of the AI-AI3Ni and AI-AI2Cu eutectic alloys. Cellular microstructures were obtained by casting the eutectic alloys into preheated split-steel moulds mounted on either a water-cooled or plain copper chill, to promote growth along the length of the ingot and not radially from the mould wall. This produced the required cellular microstructure with good alignment of AI3Ni fibres or AI2Cu lamellae within the cells, with an interfibre/interlamellar spacing of ∼ 1 μm. The experimental solidification results showed an increase in solidification rate with increasing distance from the chill associated with a decrease in interfibre/interlamellar spacing along the length of the solidifying ingot. There were no significant variations in the room-temperature tensile properties of the two chill-cast aluminium based eutectic alloys for the various casting conditions. Variations in solidification rate along the ingots for the different chill-casting conditions were not sufficient to affect the stress-strain behaviour of the chill-cast alloys. The room-temperature tensile behaviour of the chill-cast AI-AI3Ni eutectic alloy was very similar to, and that of the AI-AI2Cu eutectic alloy significantly different from, those obtained by Lawson and Kerr. The ultimate tensile strengths of the chill-cast eutectic alloys were not as high as those of the corresponding unidirectionally-solidified eutectic alloys prepared at a slow and constant solidification rate although the reasons for this were different for the two alloys. The ultimate tensile strength of the chill-cast AI-AI3Ni eutectic alloy was found to be in reasonable agreement with that expected from the rule of mixtures for discontinuous fibre reinforcement.