Effect of Sc addition on evolution of microstructure, texture and strength of high-pressure torsion-processed AA2195 Al–Li alloy

The effect of Sc addition to AA2195 (NoSc) alloy by 0.025 wt% (LoSc) and 0.25 wt% (HiSc) on the evolution of microstructure, texture and mechanical property in AA2195 alloy during room temperature HPT processing was studied by electron microscopy, X-ray diffraction and Vicker’s microhardness test, respectively. Higher amount of Sc addition increased the volume fraction of precipitates formed after HPT processing by 5 rotations, as inferred from both STEM-HAADF imaging and high-resolution X-rays diffraction pattern analysis. This was primarily attributed to the size, distribution and morphology of the precipitates. Increased Sc content resulted in the decrease in solid solubility of Cu in the Al matrix, thereby causing higher precipitation of Cu containing precipitates. The increase in Sc content resulted in decreased intensities of the A₁^∗ and A₂^∗ ideal shear texture components and an increase in the intensity of the C components ({100} < 011 >), resulting from the easier dynamic recovery and recrystallization that occurs with the presence of larger precipitates. As a result, the highest microhardness was achieved in the LoSc alloy due to the formation of a nanocrystalline microstructure along with a homogeneous distribution of nanoscaled precipitates. This fine distribution of precipitates in LoSc alloy retained the smallest crystallite size and highest dislocation density at the disk periphery around a strain of 30. These enhanced properties in LoSc were attributed to the nearly homogeneous formation of fine precipitates ranging between 15 and 25 nm within the grains and < 100 nm at the grain boundaries during HPT processing.