Creep-aging behaviors of Al-Cu-Li alloy with different grain sizes

Abstract

The Al-Cu-Li alloys with different grain sizes were manufactured through different routes and treated with T34 before the creep aging process. Their creep-aging behaviors at 160 °C under 175 MPa were investigated and their corresponding mechanical properties were tested. Their microstructure was characterized by EBSD and HAADF-STEM. The results show that the total creep strains increase with increasing grain size. The creep strain of specimens with an average grain size of 53.4 µm is twice as that with an average grain size of 12.2 µm. However, their yield and tensile strengths are grain size independent. This appearance could be explained by the large creep strain achieved before the secondary primary creep stage, which is contributed by dislocation motion and increases with increasing grain size. When strengthening precipitates start to nucleate and grow, the creep resistance of dislocations sharply increases and Harper-Dorn creep becomes the main creep mechanism. The alloys with different grain sizes have similar precipitates and substructures in their peak-creep-aged state, leading to their similar yield and tensile strengths at room temperature. • A new thermomechanical treatment was used to fabricate sheets with fine grains. • The creep mechanism of the complex four-stage creep age test in the Al-Cu-Li alloy has been clarified. • Grain refinement was proven to have a negative influence on the total creep strain in this work. • GND densities was used to characterize the distribution evolution of dislocations during creep age test.