A new generation of metal chillers to control the solidification structure of Al-4.5 wt%Cu alloy

Abstract

This paper introduces and examines a new generation of chillers for judicious control of the solidification structure of cast metals and alloys. This innovative chiller makes use of the absorption of the latent heat of melting of a Phase Change Material (PCM) incorporated in the chiller. In this work, Al-4.5 wt%Cu melt was cast in sand molds fitted with a traditional solid steel chiller as well as this new type of chiller consisted of a steel container filled with a given amount of pure zinc as PCM. Effects of the PCM fitted chiller on the thermal history, solidification and structure of the castings were studied by experimental and computer simulation investigations. The optimum casting parameters and mold and chillers dimensions were selected using ProCast simulation software. Use of the PCM fitted chiller resulted in faster columnar-equiaxed transition, 27 %, 54 % and 40 % reduction in the length of the columnar zone and the primary and the secondary dendrite arm spacings, respectively, and about 30 % improvement in the hardness. Thermal gradients and cooling rates at different points of the PCM fitted casting were generally more than those in the traditionally chilled casting. Use of the PCM fitted chiller eliminated the formation of the feathery grains and reduced the formation of the undesired Fe-rich phases close to the chiller due to different thermal history of the castings. Segregation pattern and change of Growth Restriction Factor (GRF) along the castings were studied and related to the cooling and growth conditions experienced by each casting.

Keywords

• Solidification structure
• Phase change material (PCM)
• PCM fitted chiller
• Directional solidification
• Columnar to equiaxed transition (CET)
• Feathery grains