A Study on the Aging Behavior of Al-Li-Cu-Zr Alloy

Aging behavior of Al-2.1Li-2.9Cu-0.12Zr(wt%) alloy has been studied as functions of aging time and temperature by using a differential scanning calorimetry(DSC) and transmission electron microscopy(TEM). The aged specimens at 130, 160, 190°Cwere compared with the as-quenched specimen in view of the aging behavior by observing the reaction enthalpy during the heating period of DSC experiments. DSC peak associated with the formation of GP zone is not observed at 130 and 160°C, but it does at 190°C, so it is found that the thermal stability of GP zone is changed at between 160 and 190°C. At the aging temperature of 130°C, the heat absorption corresponds to the formation of δ´ increases, while the heat evolution related with the formation of T1 reveals an opposite trend. In aging temperature of 160 and 190°C, aging time representing the drastic decrease of heat absorption of δ´ is coincident with the transition time showing the decreasing of heat evolution of T1. The micro-Vickers hardness of the specimens aged at 160°C and 190°C shows maximum values about 182 and 165 at aging times of about 72 hr and 25hr, respectively. From comparing reaction enthalpies for the dissolution of δ´ and the formation of T1 phases with the aging time showing the maximum hardness, it is found that δ´ phase rather than T1 phase markedly contributes to the hardening at an aging temperature of 160°C. In contrast, T1 phase plays an important role in hardening at an aging temperature of 190°C.