Microindentation Hardness-Secondary Dendritic Spacings Correlation with Casting Thermal Parameters in an Al-9wt.%Si Alloy

Abstract

Experiments were carried out to analyze the effect of growth rates (V_L) and cooling rates (T_R) on both secondary dendritic arm spacings (λ₂) and Vickers microhardness (HV) of an Al-9wt.%Si alloy during the horizontal directional solidification under transient heat flow conditions. A water-cooled solidification experimental apparatus was developed allowing a wide range of T_R (from 0.2 to 3.5 ºC/s) to be experienced. Five computer guided thermocouples were connected with the metal, and the time-temperature data were recorded automatically. The solidification path was also calculated by Scheil model in Thermo-Calc software. Casting samples were characterized by the combined analyses of optical microscopy (OM) and scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) revealing a complex arrangement of phases including binary (α-Al + Si) and ternary (α-Al + Si + β-AlFeSi) mixtures within interdendritic regions. It was observed that power law functions characterize the variation of λ₂ as a function of V_L and T_R with exponents of -2/3 and -1/3, respectively. Finally, experimental laws of power and Hall-Petch types are proposed relating the resulting HV to the λ₂. According to these results, it was found that, for increasing values of λ₂, the results of HV decrease.

DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17319