Formation mechanism of precipitate T1 in AlCuLi alloys

The formation mechanism of the plate-like strengthening T1-phase in an Al-4.15Cu-1.15Li (wt.%) alloy has been revealed by means of advanced imaging techniques and the first-principle calculations. It is shown that T1-precipitates nucleate directly from their own GPT1 zones and grow thicker in two possible paths. One is regular by repeating T1-cells, and the other is abnormal via T1-variants. Structural model of GPT1 zones has been suggested, and refined by image simulation. A possible structural evolution from GPT1 zones to precipitate T1 at atomic level is suggested and proved to be energetically reasonable.