Experimental Investigation of Ternary Al-Si-Cu Alloy Solidified with Unsteady-State Heat Flow Conditions

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 (V L ) and cooling rate ( ) 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 (λ 3 ) 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 (V L ) influence is "built into" the effective partition coefficient (K ef_Cu and K ef_Si ) that has been determined for the range of V L 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 (K ef_Cu and K ef_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 V L on ternary Al-9.0wt%Si-4.0wt%Cu alloy.

Investigation of Thermal Parameters Effects on the Microstructure, Microhardness and Microsegregation of Cu-Sn alloy Directionally Solidified under Transient Heat Flow Conditions

“…The thermal parameters were calculated from the cooling curves experimentally measured, i.e., solidification speed (S S ) and cooling rate (C R ). The solidification speed (S S ) is experimentally calculated as S S = dP / dt, as suggested by Baptista et al 19 , while the cooling rate (C R ) at each thermocouples position is calculated as C R = dT/dt, as showed in the literature by Baptista et al 16 and Sales et al 31 . With the cooling curves, the solidification front position curve was determined as a function of time by regression of the experimental data, as shown in Figure 5.…”

“…In this present paper, a unidirectional solidification apparatus is adopted, which heat is extracted from bottom of mold by water cooling system. The apparatus is detailed in previous articles 7,19 . The upward solidification system gives more stability in liquid region since it does not induce convection currents during solidification process.…”

“…In addition to solid back-diffusion, there is another phenomenon denominated: solidification kinetics must be considered, as far as it can influence microsegregation profiles. Although the influence of thermal variables, such as temperature gradient and cooling rate on the dendritic arm spacings has been studied, the literature still is scarce on research about the effects of solidification speed on the microsegregation profiles, Ferreira et al 4 , Baptista et al 16 and Baptista et al 19 . An equation for effective partition coefficient (k ef ) as a function of the solidification speed (S S ), was proposed by Burton et al 27 , eq.…”

“…These models are widely considered in the literature to compared with experimental results. However, inaccuracies from these models were presented and discussed by Ferreira et al 11 and Baptista et al 19 and some corrections were implemented to achieve a better prediction with experimental data. The main correction included the consideration of solidification speed in calculations of partition coefficient.…”

Effect of Solidification Processing Parameters and Silicon Content on the Dendritic Spacing and Hardness in Hypoeutectic Al-Si Alloys

“…99.9 wt% Al, 99.7 %wt %Si. The casting assembly used in the directional solidification experiments is showed in details by Baptista et al 21 , which consists of water-cooled mold with heat being extracted only from the bottom, promoting vertical upward directional solidification. Solidification experiments were performed with two hypoeutectic alloys (Al-Si) under thermally and solutally stable directional solidification conditions, i.e., natural convection due to density variations is not caused by temperature differences since the vertical casting is cooled from the bottom.…”