Synergistic enhancement effect of cryo-pre-straining and precipitation in mechanical properties of an Al–Cu–Li alloy by pre-ACR and ageing

Although face-centered cubic (FCC) Al-Cu-Li alloys have received considerable attention due to their excellent light-weight and high-strength performance, its undesired strength–ductility balance still hinders the industrial application. The present work proposed a synergistic approach which combines cryo-pre-straining with subsequent precipitations for improving the mechanical properties of Al-Cu-Li alloys. Thermo-mechanical processing of Al-Cu-Li alloy sheets were carried out by pre-rolling at different temperatures (83 K, 298 K and 673 K) with large applied strains (the rolling reduction, 60% and 80%) and subsequence ageing. Cryo-pre-straining with a higher rolling reduction of 80% introduced refined grains and high-density dislocations leveraging the uniform-distribution dislocations and increased dislocation-accumulation capability at cryogenic temperature. Apart from 1/2<1 1 0> matrix dislocations, a large number of 1/6<1 1 2> partial dislocations were unexpectedly induced in the alloy deformed under 83 K compared with that under 298 K through molecular dynamics simulation. In addition, T 1 , δ’ and θ’ phases with different width, length and density occurred in the alloy after a period of ageing at 433 K. The coordinated dissociation of a perfect 1/2<1 1 0> matrix dislocation provides the displacement necessary for the formation of a new T 1 plate or plate ledge. The diffusional glide of growth ledges composed of pre-formed 1/6<1 1 2> partial dislocations on {111} matrix planes and the migration of the growth ledges through the ledge-kink lead to the growth of T 1 plate. Compared with the pre-AR (asymmetric rolling) and pre-AHR (asymmetric hot rolling), the hardening response of the alloy processed via pre-ACR (asymmetric cryorolling) was further improved and the peak ageing time was shorter due to the highest dislocations and the dominant strengthening phase of T 1 plates. T 1 phases with the average size of 24.4 nm and the planar density of 21539.1 nm/μm 2 , originating from the high density of 1/2<1 1 0> perfect dislocations and 1/6<1 1 2> partial dislocations, further increased the ultimate tensile strength of the alloy processed by ACR-80%+433 K/20 from 513 MPa to 530 MPa with not significantly reduced fracture ductility. These findings unveil the dynamic evolution of dislocations, precipitations and their intersection, providing theoretical guidelines for microstructure design and deformation process optimization of Al–Cu–Li alloys by simple thermo-mechanical processing.