Influence of upward and horizontal growth direction on microstructure and microhardness of an unsteady-state directionally solidified Al-Cu-Si alloy

Raimundo Lucivaldo Marães de Araújo, Rafael Hideo Lopes Kikuchi, André Santos Barros, Laércio Gouvea Gomes, Daniel Joaquim da Conceição Moutinho, Fernando de Almeida Gonçalves, Antonio Luciano Seabra Moreira, Otávio Fernandes Lima da Rocha


In order to analyze the effect of the growth direction on dendrite arm spacing (ï¬1) and microhardness (HV)
during horizontal directional solidification (HDS), experiments were carried out with the Al-3wt.%Cu-
5.5wt.%Si alloy and the results compared with others from the literature elaborated for upward directional
solidification (UDS). For this purpose, a water-cooled directional solidification experimental device was
developed, and the alloy investigated was solidified under unsteady-state heat flow conditions. Thermal
parameters such as growth rate (VL) and cooling rate (TR) were determined experimentally and correlations
among VL, TR, ï¬1 and HV has been performed. It is observed that experimental power laws characterize ï¬1
with a function of VL and TR given by: ï¬1=constant(VL)-1.1 and ï¬1=constant(TR)-0.55. The horizontal
solidification direction has not affected the power growth law of ï¬1 found for the upward solidification.
However, higher values of ï¬1 have been observed when the solidification is developed in the horizontal
direction. The interrelation of HV as function of VL, TR and ï¬1 has been represented by power and Hall-Petch
laws. A comparison with the Al-3wt.%Cu alloy from literature was also performed and the results show the
Si element affecting significativaly the HV values.

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