Influence of Cu Content on Precipitation Behavior and Mechanical Properties Under Aging Treatment of Al-Cu-Li Alloys

The influence of Cu content (3.10, 3.50, and 3.80 wt.%) on the precipitation behavior and mechanical properties of Al-Cu-Li alloys under two aging conditions (direct aging at 175 °C vs. 3.5% pre-stretching followed by aging at 155 °C) was systematically investigated. The alloys were characterized using hardness testing, tensile property evaluation, and transmission electron microscopy (TEM) to correlate microstructural evolution with performance. The results revealed that increased Cu content accelerated early-stage hardening kinetics and elevated peak hardness and strength. Aging at 175 °C/36 h produced T₁ phase-dominated microstructures with θ' phases. With the increase of Cu content, the enhancement effect on the precipitation of T₁ and θ' phases becomes more pronounced, gradually overshadowing the initial promotion effect on precipitate growth. Pre-deformation prior to 155 °C/36 h aging induced significant T₁ phase refinement and proliferation, with increasing Cu content continuously reducing T₁ phase sizes while moderately enlarging θ' precipitates. Precipitation-strengthening analysis revealed a transition in T₁ strengthening from bypass to shearing dominance under 155 °C/36 h aging after pre-deformation, enhanced by Cu-promoted T₁ refinement, which collectively drove superior strength in high-Cu alloys. These findings provide valuable insights for the composition design and mechanical property optimization of Al-Cu-Li alloys.