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

摘要

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 △Tmax=171 K (0.20T,). 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 △T<78 K, the primary θ(Al2Cu) phase of the alloy grows into coarse dendrite. When 78 K≤△T≤171 K, its refined θ(Al2Cu) phase grows alternatively with α(Al) phase. Once △T≥171 K, its microstructure is characterized by the anomalous (θ+αξ) ternary eutectic.