Influence of Solidification Thermal Parameters on the Columnar-to-Equiaxed Transition of Aluminum-Zinc and Zinc-Aluminum Alloys

ALICIA ESTHER ARES; SERGIO F. GUEIJMAN; ARIANE BONCZOK; ADRIANA CANDIA; MIGUEL ANGEL ALTERACH; RUBENS CARAM; CARLOS ENRIQUE SCHVEZOV

San Antonio, Texas - USA.

Congreso; SOLIDIFICATION, MODELLING AND MICROSTRUCTURE FORMATION: A SYMPOSIUM IN HONOR OF PROF. JHON HUNT; 2006

The Minerals, Metals and Materials Society (TMS).

Understanding the interaction between the parameters involved in the columnar-to-equiaxedtransition (CET) has gained considerable attention over the last two decades in the study of thestructure of ingot castings. The present investigation was undertaken to investigate experimentally the directional solidification of Al-Zn and Zn-Al (ZA) alloys under different conditionsof superheat and heat-transfer efficiencies at the metal/mold interface. The CET is observed;grain sizes are measured and the observations are related to the solidification thermal parameters: cooling rates, growth rates, thermal gradients, and recalescence determined from thetemperature vs time curves. The temperature gradient in the melt, measured during the transition, is between ?0.338 °C/mm and 0.167 °C/mm. In addition, there is an increase in thevelocity of the liquidus front faster than the solidus front, which increases the size of the mushyzone. The size of the equiaxed grains increases with distance from the transition, an observationthat was independent of alloy composition. The observations indicate that the transition is theresult of a competition between coarse columnar dendrites and finer equiaxed dendrites. Theresults are compared with those previously obtained in lead-tin alloys.