EFFECT OF COOLING RATE AND GRAIN REFINEMENT ON THE MICROSEGREGATION IN Al-4.8 wt.% CuALLO

Microsegregation is one of the most important phenomena occurs during solidification. It usually results in formation of some unexpected second phases which generally affect the mechanical properties and specially reduce the workability of casting products. The aim of this research is to study the effect of cooling rate and grain refinement on the microsegregation in Al-4.8 wt.% Cu. For this purpose two series of experiments were designed. In the first set of experiments, the alloy was melted and cooled in three different rates, i.e. 0.04, 0.42, and 1.08 K/s in a DTA furnace. In the second series of experiments, the effect of grain refinement on the microsegregation at a constant cooling rate of 0.19 K/s was investigated. Al-5Ti-1B master alloy was used as grain refiner. Results showed that by increasing the cooling rate the amount of non-equilibrium eutectic phase increases from 5.1 to 7.4 wt.%, and the minimum concentration of solute element in primary phase decreases from 1.51 to 1.05 wt.% Cu. By grain refinement of the alloy, the amount of non-equilibrium eutectic phase decreases from 5.5 to 4.7 wt.%, and the minimum concentration of solute element in the primary phase increases from 0.98 to 1.07 wt.% Cu. So it is concluded that increasing cooling rate in the range of 0.04 to 1.08 K/s, increases and grain refinement reduces the microsegregation.