Abstract: Studies were carried out on the precipitation in two sets of binary Al-Li alloys by means of hardness tests,DSC analyses and TEM observations.When the alloys were aged for constant time,a peak appeared on the plot of temperature dependence upon their hardness in the range of low temperatures,and the endothermic dissolution peak was quite distinct on the DSC curve also at low temperatures.These are believed that an Li-rich GP zone formed in the al- loys aged at low temperatures,but no more GP zone if aging at elevated temperatures.The hardness of the alloys raises rapidly with coarsening of δ′-phase grains.The two endothermic peaks of δ′ dissolution on the DSC curve relate to the structural adjustment at twice of the δ′ precipitation.The equilibrium δ-phase,being of higher thermal stability,nucleates and grows directly from the supersaturated solid solution with the aid of the gram boundary.

Key words: binary Al-Li alloy, precipitation, dissolution, endothermic peak, aging