MECHANISMS OFPRECIPITATES FORMATION IN AN Al- Cu- Li-ZrALLOYUSINGDSC TECHNIQUE AND ELECTRICALRESISTANCE MEASUREMENTS

Abstract: Guinier-Preston (GP) zone formation and precipitation behavior of T۱ (Al۲CuLi) 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 ۱۸۰°Cand ۲۴۰°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 T۱ phaseoccurred in temperature range of ۲۵۰ºC to ۳۰۰ºC whereas its dissolution occurred within the temperature of ۴۵۰-۵۳۰ºC. Activation energies for precipitation and dissolution of T۱ phase which were determined for the first time inthis research, were ۱۲۲.۱(kJ/mol) and ۱۳۰.۳(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:

Keywords: aluminum- lithium alloys , DSC , activation energy , natural aging , Al-Cu-Li-Zr alloy , T۱ phase , dissolutionenergies