Precipitation Behavior and Mechanical Properties of an Al-5Cu-1.6Mg-0.4Li-0.59Sc Alloy under Thermomechanical Treatment

This study focuses on the thermomechanically treated Al-5Cu-1.6Mg-0.4Li-0.59Sc alloy. Using characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the evolution of precipitation phases in the experimental alloy was systematically investigated, and its mechanical properties were tested.The results show that in the as-rolled state, the secondary phases mainly consist of multiscale precipitates including primaryAl₃Sc、AlCuSc、Al₂Cu and Al₂CuMg. After T6 heat treatment (400℃/12 h+490℃/2 h+535℃/1 h+170℃/24 h), the alloy exhibited a large amount of finely dispersed precipitates, such as strip-shaped and step-shaped S (Al₂CuMg) phases, spherical Al₃Sc phases, core-shell structured precipitates with a two-layer structure of (Al,Sc,Cu)/(Al₃Sc) and a three-layer structure of (Al₃Sc, Sc-riched Al₂Cu)/(Al₂CuMg). These core-shell precipitates are fully coherent with the matrix.Mechanical testing shows that the T6-treated alloy achieves a yield strength of 266 MPa and an ultimate tensile strength of 320 MPa, increased by 11.3% and 24.0% compared to the as-rolled condition. This research provides a theoretical basis for the development of high-performance Al-Cu-Mg alloys.