The influence of Mg and Ag on the precipitation kinetics and the formation of the T1 phase in Al-Cu-Li alloys

Al-Cu-Li alloys are extensively used for aerospace applications. The main hardening phase is the T-1 phase that precipitates as thin platelets on {111}(Al) planes. To facilitate its nucleation, different minor alloying elements are added and dislocations are introduced by cold deformation before the ageing treatment. The impact of these additions in combination with the presence of dislocations on precipitate nucleation and growth needs a deeper understanding. In this work, we investigated the precipitation kinetics of the T-1 phase in alloys containing a common content of Cu and Li and different contents of minor solutes (Mg, Ag) where these elements are present either together or independently. A general overview on the precipitation kinetics was achieved by in-situ small-angle X-ray scattering and hardness measurements. The evaluation of precipitation kinetics reveals that magnesium plays an important role during precipitation by enhancing nucleation kinetics. Additionally, a smaller yet measureable effect of Ag, both in the presence and absence of Mg has been evidenced.