Hardness-based precipitation kinetics and mechanical response of cast Al-Li-Cu-Mg-Zr alloy during artificial aging

Abstract The precipitation behavior of Al–Li–Cu–Mg–Zr alloys plays a critical role in determining their mechanical performance, particularly under artificial aging treatments that are widely employed in aerospace and structural applications. Conventional investigations into these transformations typically depend on advanced microstructural probes such as transmission electron microscopy (TEM), which are not always accessible in industrial or rapid-screening contexts. This study presents a practical, TEM-free framework to evaluate precipitation kinetics and mechanical response of a cast Al–Li–Cu–Mg–Zr alloy aged at 150 and 175 °C. Microhardness–time data at 175 °C were fitted with a Johnson–Mehl–Avrami–Kolmogorov (JMAK) model over the monotonic hardening interval (0–28 h), yielding an early stage kinetic description, subsequent hardness measurements reveal a narrow peak-aged plateau. Refinement around the maximum shows a stable hardness of ≈180 Vickers hardness (HV) between 65–72 h (≈+210% versus the solution-treated 58 HV), along with the highest ultimate tensile strength (UTS) ≈350 MPa (≈+40% versus ∼250 MPa in solution-treated). The peak strength is accompanied by reduced ductility, whereas slight over-aging (∼98 h) trades a small loss in UTS for recovery in elongation. Fractography of tensile fracture surfaces documents the expected evolution from ductile dimpling (0 h) to mixed mode (28–46 h) and predominantly intergranular facets (≥ 65 h). Taken together, the results identify a practical ±5 h processing window centered near 65 h at 175 °C and provide an industry-oriented route for screening aging schedules.