Hypoeutectic Al-11wt.%Si alloy: interfacial heat transfer coefficient, thermal variables, microstructural parameters and microhardness

ABSTRACT

This paper presents a theoretical-experimental study aiming to determine the interfacial heat transfer coefficient and solidification thermal parameters from experimentally obtained data correlating these with the primary and secondary dendritic spacings as well as microhardness during the horizontal solidification of the Al-11wt.%Si alloy under transient heat flow conditions. For the experimental procedure, a water-cooled solidification device was used which allows the horizontal directional solidification and the monitoring of the temperature profiles in different positions from the metal-mold interface considering the center line corresponding to the longitudinal axis of the ingot. A numerical technique which compares theoretical and experimental thermal profiles has permitted the evaluation of the variation of metal-mold heat transfer coefficient along the solidification. The interfacial heat transfer coefficient of studied alloy is represented by a equation which show the time dependence during the process. The experimental and calculated values have shown a very good agreement. Experimental techniques were applied to calculate the following solidification thermal variables: solidification front displacement, growth rate and cooling rate. The experimental results allowed establishing a quantitative correlation between such thermal variables and the studied structural parameters by means of power type equations represented by characteristic exponents. Finally, correlation between the values of both primary and secondary dendritic spacings found with Vickers microhardness behavior for the studied alloy is also presented.

Keywords
Horizontal solidification; Heat transfer coefficient; Thermal parameters; Microstructure; Microhardness