Achieving high strength and ductility of Al-Cu-Li alloy via creep aging treatment with different pre-strain levels

A method of integrating creep aging and pre-strain has been developed to optimize the strength and promote the nano-precipitates in an Al-Cu-Li alloy. The creep deformation, mechanical properties, and microstructure evolution of the alloy in different states were systematically investigated. The results show that creep aging at 200 ℃ with 9% pre-strain for 7 h can significantly increase the yield tensile strength (YTS) and ultimate tensile strength (UTS) to 604 MPa and 614 MPa, respectively, while maintaining the elongation greater than 8%. Due to the synergetic effect of creep aging and pre-strain, the main strengthening phase in the aged alloy is T₁ phase. Pre-strains at5–9% accelerate the precipitation kinetics of T₁ phase and significantly inhibits the precipitation of θ′ phase which is usually composited by a thin layer of δ′ phase. The length of T₁ precipitate decreases with the pre-strain, but the thickness shows an opposite trend. The effects of pre-strain and dispersoid on promoting the heterogeneous nucleation of T₁ phase were discussed. The strengthening mechanisms after creep aging with pre-strains are mainly ascribed to the effects of strain strengthening and precipitation strengthening, which were further quantitatively analyzed.