en گروه سرامیک Ceramic Materials and Engineering Research Paper Research Paper Abstract: Guinier-Preston (GP) zone formation and precipitation behavior of T1 (Al2CuLi) phase during the ageingof an Al-Cu-Li-Zr alloy was studied by differential scanning calorimetry (DSC) technique and electrical resistancemeasurement of the samples. Results show that endothermic effects in the thermograms of the alloy between 180°Cand 240°C can be related to the enthalpy of GPzones dissolution. Formation of GPzones in the structure increasedhardness, tensile strength and electrical resistance of the Al-Cu-Li-Zr alloy. Furthermore, precipitation of T1 phaseoccurred in temperature range of 250ºC to 300ºC whereas its dissolution occurred within the temperature of 450-530ºC. Activation energies for precipitation and dissolution of T1 phase which were determined for the first time inthis research, were 122.1(kJ/mol) and 130.3(kJ/mol) respectively. Results of electrical resistance measurementsshowed that an increase in the aging time resulted in the reduction of electrical resistance of the aged samples. Keywords: aluminum- lithium alloys, DSC; activation energy, natural aging, Al-Cu-Li-Zr alloy, T1 phase, dissolutionenergies 15 20 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-3-98&slc_lang=en&sid=1 A. Shokuhfar 180031947532846003 180031947532846003 No S. Ahmadi sh.ahmadi@modares.ac.ir 18003194753284600821 18003194753284600821 Yes H. Arabi 18003194753284600850 18003194753284600850 No S. Nouri 18003194753284600851 18003194753284600851 No