Formation mechanisms of precipitates in an Al–Cu–Li–Zr alloy and their effects on strength and electrical resistance of the alloy

Guinier–Preston (GP) zone formation and precipitation behavior of T1 (Al2CuLi) phase during the aging of an Al–Cu–Li–Zr alloy was studied by differential scanning calorimetry (DSC) technique and electrical resistance measurement of the samples. Results show that precipitation of T1 phase occurred in temperature range of 250–300 °C whereas its dissolution occurred within the temperature of 450–530 °C. Activation energies for precipitation and dissolution of T1 phase which were determined for the first time in this research, were 122.1 kJ/mol and 130.3 kJ/mol respectively. Results of electrical resistance measurements showed that an increase in the age hardening time resulted in the reduction of electrical resistance of the samples. In addition, TEM observation showed that T1 phase has plate shape morphology and its crystal structure is in the form of hexagonal close-packed. The lattice parameters were found to be: a = 0.4672 nm and c = 0.8785 nm.