Thermal analysis via horizontal solidification of Al3Cu2Si (mass%) alloy: thermal and microstructural parameters, intermetallic compounds and microhardness

Abstract

A transient horizontal solidification experiment was performed to investigate the role of the thermal parameters, such as growth and cooling rates (GR and CR, respectively), on the microstructure and microhardness (HV) of the Al2Si3Cu (mass%) alloy. Thermal data were generated using a water-cooled solidification device. This allowed to determine a large range of GR and CR. As-cast samples from the cooled surface were characterized by optical microscopy and scanning electron microscopy (MO and SEM). The resulting microstructure was characterized by an Al-rich dendritic primary phase (Alα) and by an interdendritic eutectic mixture composed of Alαeutectic + Si particle + (Al2Cu and Fe) intermetallic compounds. The Alα phase was characterized by primary, secondary and tertiary dendrite arm spacings (λ1, λ2 and λ3, respectively). The λ1, λ2 e λ3 dependence on GR and CR was characterized by power-type mathematical equations. It was evidenced the tertiary branches occurrence for GR > 0.95 mm s−1 and CR > 6.5 °C s−1. Microhardness (HV) was measured at the center of the dendritic primary phase and within the interdendritic regions. Higher HV values were observed in the eutectic mixture. Experimental power and Hall–Petch mathematical equations were proposed to characterize HV variation within the interdendritic region as a function of λ1, λ2 and λ3. A parametric factor given by the expression $$\varepsilon = \frac{\text{CR}}{{\left( {\mathop \sum \nolimits_{1}^{\text{n}} C_{\text{on}} } \right)/n}}$$ that allows to predict the appearance of tertiary dendritic arms for the assumed solidification conditions was proposed by the present work, for future predictions. A comparison with the literature was conducted.