Transient heat flow parameters and microstructure of the upward solidified eutectic Al–Si alloy: a theoretical and experimental study

Abstract

ABSTRACT In this work, a theoretical and experimental study has been carried out with the eutectic Al12.6Si alloy (wt.%) in order to determine and evaluate the transient heat flow parameters, such as metal/mold interfacial heat transfer coefficient (hi), growth and cooling rates (VL and TR, respectively), during upward solidification. The experimental thermal data were obtained via temperature mapping using a directional solidification device as well as via mathematical model to determine the time-varying hi values given by the general expression hi=at -n . The VL and TR values were determined from the generated simulated and experimental curves. The results showed a good agreement between the simulated and experimental values. The prediction of the microstructure has revealed the formation of irregular eutectic as well as the presence of non-faceted α-Al primary phase, like halos dendrites, and massive faceted primary Si crystals. Mathematical expressions that correlate halos dendrite spacing (λHD) as a function of hi, VL and TR have been proposed. The halo microstructure has been observed when hi, VL and TR values reach 3,608.00 WmoC−1, 0.36 mms−1 and 0.13 oCs−1, respectively. A comparative analysis with other works from literature has been conducted and the results have confirmed that the n exponent assumes values less than 0.5 for non-ferrous alloys (n < 0.5). For the particular case of binary Al–Si alloys it can be less than 0.35, that is, n < 0.35.