Revealing the substantial impact of trace Mg addition on the microstructural configuration of a cast Al-Li-Cu-Zr alloy under various conditions

Abstract

In this study, the impact of 0.2 wt% Mg addition on the microstructural configuration of a cast Al-2.5Li-2.5Cu-0.15Zr alloy under different heat treatment conditions was investigated using multiscale characterization. Results indicate that in the as-cast state, trace Mg forms the low-melting-point Al₂CuMg eutectic phases and promotes grain refinement. In the natural aging state, trace Mg promotes the precipitation of fine Guinier-Preston (GP) zones independent of pre-existing δ′-Al₃Li phases. In the artificial aging state, trace Mg mainly leads to the inducing of GP zones, suppression of θ′-Al₂Cu phases, and promotion of T₁-Al₂CuLi phases. δ′ phases with slight diameter reduction and minimal S′-Al₂CuMg phases with two variants are also observed. Atomic-level analysis of the two newly formed composite precipitates indicates that L1₂ structure phases on both sides of the GP zone have an anti-phase relationship. This study is expected to provide theoretical insights into the microstructural origins underlying the beneficial effects of Mg microalloying in cast Al-Li-Cu alloys.