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

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 (h_i), growth and cooling rates (V_L and T_R, 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 h_i values given by the general expression h_i=at^-n . The V_L and T_R 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 (λ_HD) as a function of h_i, V_L and T_R have been proposed. The halo microstructure has been observed when h_i, V_L and T_R values reach 3,608.00 Wm^oC⁻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.

KEYWORDS:

• Unsteady-state upward solidification
• numerical solidification model
• transient heat flow parameters
• halos dendrites

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors acknowledge the financial support provided by IFPA – Federal Institute of Education, Science and Technology of Pará (Instituto Federal de Educação, Ciência e Tecnologia do Pará), UFPA – Federal University of Pará (Universidade Federal do Pará), and CNPq – The Brazilian Research Council (Conselho Nacional de Desenvolvimento Científico e Tecnológico) grants 302846/2017-4 and CAPES – Coordination of Superior Level Staff Improvement, Brazil (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) (Teaching Initiation Program).