Rapid solidification of Al-Cu-Ag ternary alloy under the free fall condition

The rapid solidification of Al-30%Cu-18%Ag ternary alloy is investigated by using the free fall method. Its solidified microstructure is composed of θ(Al₂Cu), α(Al) and ξ(Ag₂Al) phases. The liquidus temperature and solidus temperature are determined as 778 and 827 K, respectively. The alloy melt undercooled amounts up to ΔT _Max=171 K (0.20T _L). Its microstructural evolution is investigated based on the theoretical analysis of undercooling behavior and nucleation mechanics. It is found that the undercooling increases with the decrease of the diameter of the alloy droplet. When ΔT<78 K, the primary θ(Al₂Cu) phase of the alloy grows into coarse dendrite. When 78 K≥ΔT≥171 K, its refined θ(Al₂Cu) phase grows alternatively with α(Al) phase. Once ΔT≤171 K, its microstructure is characterized by the anomalous (θ+α+ξ) ternary eutectic.