Identification of Precipitates Appearing in Al-Li-Cu-Zr Alloy

Abstract

Identification of precipitates appearing during DSC scan of Al-2.1Li-2.9Cu-0.12Zr(wt. pct) alloy has been conducted as a function of temperature by using a differential scanning calorimetry (DSC) and transmission electron microscopy(TEM). In the as-quenched specimen from 540°C, three couples of heat evolution and absorption peaks are observed during the heating period of DSC experiments. It is found from TEM works that these peaks are associated with the formation and dissolution of GP zone, δ‘, and T1(+θ') phases. The heat evolution peak appearing in the temperature range over 36~78°C is due to the formation of GP zone. Heat absorption peak appearing in 78~140°C is associated with the dissolution of GP zone. Heat evolution peaking at 166°C in the temperature range over 140~190°C and next heat absorption peak are attributed to the formation and dissolution of δ‘ phase. Heat evolution peaking at 288°C in the temperature range of 254~332°C and heat absorption at high temperature are attributed to the formation and dissolution of T1(+θ'). The hump in DSC curve at the temperature of 425°C is considered as the formation of hexagonal structure T2 phase.