Effect of Zn on precipitation evolution and mechanical properties of a high strength cast Al-Li-Cu alloy

Abstract

The influence of Zn addition on microstructure evolution and mechanical performance of a novel cast Al-Li-Cu-Mg alloy is studied in detail. The results reveal that Zn modifies the precipitation behaviors and improves the tensile strength effectively. As Zn content increases to 1 wt%, the precipitation of T1 (Al2CuLi) phase is greatly enhanced at the expense of S′ (Al2CuMg) phase. Zn atoms are observed to enrich in T1 phase by using high-angle annular dark field-scanning transmission electron microscope (HADDF-STEM), possibly attributed to some Cu atoms being substituted by Zn atoms. The precipitation of δ′ (Al3Li) is increased as Zn addition, suppressing the widening of δ′-precipitation-free zones. A more uniformly distribution of S'is also observed in the Zn-containing alloys. With the collaborative effect of both T1 and δ′ precipitates, the optimal ultimate tensile strength of 504 MPa is obtained in 1 wt% Zn-containing alloy aged at 175 °C for 64 h, which is the highest value in cast Al-Li alloy field at present.