Unraveling the elevated-temperature mechanical properties of a cast Al-Li-Cu-Mg-Sc-Zr alloy: A comprehensive investigation of precipitation evolution

Cast Al-Li alloys with high Li content demonstrate exceptional weight reduction and stiffness enhancement effects, showing significant potential for aerospace structural components. However, their application is often constrained by service temperature limitations. In this study, the mechanical behavior and microstructural evolution of a cast Al-Li-Cu-Mg-Sc-Zr alloy were systematically investigated over a temperature range from room temperature to 300 °C. The results indicate that the Al 3 (Sc, Zr, Li) particles exhibit superior thermal stability, and their significant strengthening effect is crucial in maintaining yield strength exceeding 300 MPa even at 200 °C. At 100 °C, no significant alterations in alloy properties were observed compared to room temperature performance. The θ′ phase demonstrates poor coarsening resistance and undergoes extensive coarsening at 200 °C. The internal stresses generated by rapid coarsening and stress concentration during tension leads to microcrack formation at intersecting θ′ phases, resulting in a sharp decrease in elongation. Additionally, dislocation bands form within some grains, featuring dynamically precipitated fine S′ phases, which dominate transgranular fracture. The T 1 phase does not exhibit significant coarsening until 300 °C, while the θ′ and S′ phases are nearly completely dissolved at this temperature, resulting in significant strength reduction and exhibiting ductile fracture characteristics. This study provides valuable insights for the compositional design of cast Al-Li alloys and the enhancement of their mechanical properties at elevated temperatures.