Quasi-in-situ EBSD Study on the Influence of Precipitations on the Strength, Plasticity and Deformation Mechanism in Al-Cu-Li Alloys

The present study investigates the tensile properties, activation of slip, and grain boundary cracks in Al-Cu-Li ternary alloys with varying precipitations resulting from different aging treatments. The size and distribution of precipitations were ascertained using transmission electron microscopy. The slip activtiy with tensile strain was observed by the electron back-scatter diffraction and scanning electron microscopy. Furthermore, the influence of precipitated strengthening was quantitatively evaluated. The presence of precipitations hinders dislocation movement, increasing strength but reducing the appearance of deformation mechanisms like slip activity, slip transfer, intragranularly misoriented grain boundaries, and lattice rotation, ultimately resulting in reduced ductility. In the sample of T6 aging for 72 h, the coarsed theta ' phase promotes the formation of dislocation rings, resulting in a decrease in the percentage of grains activated with slip to 9.7%. The percentage of grain boundaries with crack initiation reaches 6.9%. On the contrary, in the sample dominated by the T1 phase, the percentage of grains that activate slip is 14.6%, and the percentage of grain boundaries that initiate cracks is only 1.4%. This is because the continuous shear of the T1 phases helps disperse coplanar slip, thereby avoiding cracking caused by excessive stress concentration. Hence, to enhance alloy strength while preserving a certain level of ductility, it is vital to promote the precipitation of the T1 phase and avoid the coarsening of the theta ' phase. This study provides a new insight into the influence of precipitations on the strength and plasticity of Al-Cu-Li alloys.