Abstract
Ternary Al-9.0wt%Si-4.0wt%Cu alloy was solidified in a vertical directional solidification system under unsteady-state heat flow conditions. The resulting dendritic morphology and microsegregation were investigated. A more detailed analysis was dedicated to the microsegregation phenomena where a multielement interaction was observed. The solidification parameters such as: solidification speed (VL) and cooling rate (T˙) were determined from the cooling curves obtained during the solidification process. The thermal variables effect on the dendritic morphology is presented. The measurements of tertiary dendrite arm spacing (λ3) and microsegregation were performed for different positions along the casting. The experimental curves for microsegregation were obtained for Si and Cu from the center of dendritic tertiary arm to the next nearest tertiary arm. The solidification speed (VL) influence is built the effective partition coefficient (Kef_Cu and Kef_Si) that has been determined for the range of VL and microsegregation curves are calculated by Scheil's equation for comparison with experimental data. Good agreements of the Scheil's equation with experimental data on microsegregation curves of the Si and Cuwere obtained when effective partition coefficient (Kef_Cu and Kef_Si) is taken into consideration. The multielement interaction effect on the Si microsegregation is investigated. Experimental results show that, Cu-rich dendrites were accompanied by minute amounts of Si. The concentration profiles obtained experimentally point to a strong negative correlation between Si and VL on ternary Al-9.0wt%Si-4.0wt%Cu alloy.
Highlights
During casting process of alloys a large variety of microstructures can be observed
The present experimental paper is based on the research line of previous references, highlighting the correlation between the thermal parameters and tertiary dendrite arm spacing (λ3) and microsegregation during solidification of a ternary Al-9.0wt%Si-4.0wt%Cu alloy under unsteady-state heat flow conditions
The δ depends on the solidification speed (VL), the liquid viscosity and the agitation condition ahead the solid/ liquid interface, and its value can vary from 10-6 to 10-3m, according to the Chalmers cited by Meza et al.[16]
Summary
During casting process of alloys a large variety of microstructures can be observed. The most commonly found ones are known as cell, dendrite and eutectic morphology. The solidification thermal parameters have influence on the microstructure and microsegregation andthese, in turn, are key featuresin inducing non-uniformity on the as-cast material mechanical properties. Spinelli et al.[12] proposed a theoretical and experimental work to investigate the thermal parameters during solidification process of binary Sn-Pb alloys. The authors have adopted an experimental equation for solute concentration (Cu and Fe) which shows a good agreement to the experimental data They have shown that solidification speed has significant effect on the resulting microsegregation curves. The present experimental paper is based on the research line of previous references, highlighting the correlation between the thermal parameters and tertiary dendrite arm spacing (λ3) and microsegregation during solidification of a ternary Al-9.0wt%Si-4.0wt%Cu alloy under unsteady-state heat flow conditions. The δ depends on the solidification speed (VL), the liquid viscosity and the agitation condition ahead the solid/ liquid interface, and its value can vary from 10-6 to 10-3m, according to the Chalmers cited by Meza et al.[16]
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