Research of dendrite/cellular interfacial transitional velocity in directionally solidified Al-4%Cu alloy

The transition from cellular to dendrite was obtained at the spindle of tip radius by comparing experimental and theoretical study on Al-4%Cu alloy during directional solidification. It was found that the tip radius fell quickly in cellular stage but fell slowly in dendrite stage. The KGT (W. Kurz, B. Giovanola and R. Trivedi) model and non-equilibrium effect were applied to research the tip radius and interface temperature in order to obtain the transitional characteristic from dendrite to cellular. The results indicated that the tip radius and interface temperature were both decreased with increasing withdrawal rate, after reached the critical points, finally turned to rise sharply. It was eventually obtained that the transition from dendrite to cellular was occurred at the spindle of tip radius and temperature, that was the tip radius and tip temperature reached minimum, V_Rmin and V_Tmin. Moreover, solute trapping became obvious during the transition, which led to decrease of microsegregation.