Retrogression characteristics of a novel Al-Cu-Li-X alloy

Zhi-shan Yuan1,2), Zheng Lu2), Xiu-liang Wu2), You-hua Xie2), Sheng-long Dai2), and Chang-sheng Liu3) 1) Grikin Advanced Materials Co. Ltd., General Research Institute for Non-Ferrous Metals, Beijing 100088, China 2) Beijing Institute of Aeronautical Materials, Beijing 100095, China 3) School of Materials & Metallurgy, Northeastern University, Shenyang 110004, China

摘 要：Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ’ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ’ and θ’ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ’ and θ’ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ’, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.

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