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

Abstract

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(Al 2 Cu), α(Al) and ξ(Ag 2 Al) 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 (Al 2 Cu) phase of the alloy grows into coarse dendrite. When 78 K≤ΔT≤171 K, its refined θ (Al 2 Cu) phase grows alternatively with α(Al) phase. Once ΔT≥171 K, its microstructure is characterized by the anomalous (θ+α+ξ) ternary eutectic.Al-Cu-Ag, free fall, nucleation, ternary eutectic, rapid solidification, high undercoolingRecently, there is an extensive study of the rapid solidification of undercooled metallic melt [1][2][3][4][5][6][7][8] . However, its solidification theory is not mature and limited to the solidification processes of pure metal or binary alloy. The precise theory of rapid solidification of multicomponent and multiphase alloy has not been established, and there is no way to precisely describe the crystal nucleation and microstructural evolution. The metallic materials in industrial use are usually multicomponent and multiphase alloys. As for Al-Cu-Ag ternary alloy, Ag and Cu present excellent electric conductivity and mechanical ductility, and Al is the matrix of lightweight metallic materials. The Al-Cu-Ag ternary alloy is an important component of industrial aluminum alloys [9,10] . There is a great deal of research on its conventional solidification and properties, but there is little research on the rapid solidification under high undercooling conditions. Under the equilibrium solidification condition, the Al-Cu-Ag ternary alloy has many varieties of liquid-solid phase transitions [11,12] . When T=774 K, the ternary eutectic transition L→α+θ+ξ happens to the Al-Cu-Ag ternary alloy. When T=871 K, the typical ternary peritectic transition L+ξ+ε→ξ 2 takes place. When T = 808 K, there is the typical ternary peri-eutectic transition L+η→θ+ξ. Therefore, the Al-Cu-Ag alloy is usually used to study the rapid solidification of the ternary alloy of various crystalline growth varieties. The temperature of these phase transitions falls within medium temperature range is therefore suitable for space experiments. In this way, we can compare the space experiments and ground experiments to reveal the rapid solidification mechanisms of the ternary alloy. Wilde et al. [13,14] explored the nucleation character of α(Al) and θ(Al 2 Cu) phases in the bulk Al-Cu-Ag alloy by using the spatial microgravity of the MAXUS rocket, but he did not obtain the experimental results under the high undercooling condition. In this paper, we study the rapid solidification of the Al-30%Cu-18%Ag ternary alloy, which lies in th...

Microstructural evolution and mechanical properties of rapidly solidified Ni-Ge alloys

“…近年来, 利用空间环境"微重力、无容器、超高真 空"等特征来探索具有优异力学性能的金属材料成为 材料科学领域的重要研究课题 [1,2] . 自由落体技术作为 地面模拟空间环境的一种有效手段, 通过将深过冷与 急冷有机结合实现微重力条件下合金快速凝固 [3,4] .…”