Ageing response of a Al-Cu-Li 2198 alloy

The effects of different ageing treatments on microstructure evolution, properties and fracture are investigated in the present study. 2198 alloy exhibits strong ageing response during ageing. It is found that tensile properties, hardness and conductivity of 2198 alloy are very sensitive to ageing temperatures, which corresponds to different microstructures. In the naturally-aged condition (T3), only δ' (Al₃Li) was detected. After artificial ageing (T8), large amounts of precipitates emerged and major precipitates that were detected turned to be δ', θ' (Al₂Cu) and T₁ (Al₂CuLi) phase. Exposure to higher temperature caused greater amounts of the precipitation. The constitution and morphology of precipitates varies with different ageing temperature; the major precipitates are δ', θ' when ageing below 160°C, while above 160°C, T₁ phase comes out in large numbers, becoming dominate strengthening phases gradually. Fracture transforms from a typical dimple type to a dimple-intergranular mixed type with the rise of ageing temperature.