The effects of an electric field appl ied du ring solution treatment on the precipitation kinetics in Al-Li all oy 2090h ave been studied using differential scanning calorimetry(DSC).It is found tha t electric field decreases the peak temperatures of?' and T 1 phases precipitation,bringing their curves forward.It le ssens the enthalp y of T 1 precipitation,while keeping that of?' precipitation unchanged.At the sa m e time,the electric field increases the rates of?' and T 1 precipitation in the first stages,while decreases those in the last stages .An electric field also reduces the activation energies of?' and T 1 phases precipitations.It is though t that the electric field increases t he concentration of vacancies and the hence solubility of alloying elements,there by decreasing the activation energies of these two precipitation mechanisms.