| The precipitation behaviors including the precipitation sequence, the varieties of precipitates, and interrelation between δ` and third precipitates in Al-2.35%Li-1.45%Cu alloy were investigated by employing adiabatic calorimeter, transmission electron microscopy and hardness tester. The results obtained were as follows. The precipitation sequence was as follows : Supersaturated solid solution →(δ` + T₁,)→T₁. The endothermic reactions corresponding to δ` or T₁ phase were appeared on the S-T curves obtained from as-quenched specimens, the difference in specific heat between exothermic and endothermic concerned with the formation and dissolution of δ` was 42J/mole, which was caused by the precipitation of δ` phase formed during quenching. Another mechanisms to form platelike. δ precipitates by T₁/δ` interrelations were found. In the peak hardness conditions aged at 190℃ for 24 hours, the high densities δ` and T₁ phases coexisted, and the average diameter of δ` phases were 160Å. |
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