Dependence of Eutectic Fraction on Inclination Angle of Columnar Dendrite Structures in Al-3 mass% Cu Alloy Analyzed by Phase-field Simulation

The effect of the inclination angle of the columnar dendrite on the microsegregation during directional solidification of a model alloy, i.e., Al-3 mass% Cu alloy, was investigated using two-dimensional quantitative phase-field simulation. The extent of the microsegregation was characterized by the fraction of the eutectic region in the as-cast microstructure. It was found that the microsegregation significantly decreases as the average value of the primary arm spacing increases for each inclination angle. In addition, the microsegregation decreases as the inclination angle increases. These behaviors are mainly ascribed to the change of shape of last-solidified liquid related to contribution of back diffusion for different values of the primary arm spacing and inclination angle. Furthermore, the degree of microsegregation was well-predicted from the inclination angles and primary dendrite arm spacings. This suggests the possibility that the microsegregation can be simply predicted from inclination angles and primary dendrite arm spacings.