Thermal Stability of Precipitates in Al-2.8 wt%Cu-1.4 wt%Li Alloy

The microstructures and mechanical properties of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy after thermal exposure at 125, 150 and 175 °C were measured and characterized by universal testing machine, scanning electron microscope and transmission electron microscope. The thermal stability of microstructures and mechanical properties of T87 heat-treated Al-2.8 wt%Cu-1.4 wt%Li alloy was investigated. The results show that the tensile strength of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy increased first and then decreased with the increase of thermal exposure temperature, which is due to the change of the number and size of precipitates. After thermal exposure at 125 °C, the alloy exhibited higher strength due to further precipitation of θ′ phase and stable size of T₁ phase. After thermal exposure at 175 °C, the mechanical properties of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy decreased obviously, which was related to the dissolution of θ' phase and thickening of T₁ phase.