Identification of precipitates appearing in Al-Li-Cu-Zr alloy

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 degrees 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, delta', and T-1(+theta') phases. The heat evolution peak appearing in the temperature range over 36 similar to 78 degrees C is due to the formation of GP zone. Heat absorption peak appearing in 78 similar to 140 degrees C is associated with the dissolution of GP zone. Heat evolution peaking at 166 degrees C in the temperature range over 140 similar to 190 degrees C and next heat absorption peak are attributed to the formation and dissolution of delta' phase. Heat evolution peaking at 288 degrees C in the temperature range of 254 similar to 332 degrees C and heat absorption at high temperature are attributed to the formation and dissolution of T-1(+theta'). The hump in DSC curve at the temperature of 425 degrees C is considered as the formation of hexagonal structure T-2 phase.