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

Resumo

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.