Achieving high strength in AA2024 alloy by natural aging and asymmetric cold rolling

The effect of natural aging followed by cold single-roll drive rolling (SRDR) on microstructural evolution, texture, hardness, tensile behavior, and fracture surface of an Al–Cu–Mg alloy was investigated. The average grain width of the cold-deformed samples was remarkably decreased from ∼ 13.2 to ∼ 6.5 µm. During the cold SRDR, the large Al7Cu2Fe particles in the as-received alloy were fragmented into smaller particles. The maximum content of deformation bands belonged to the samples after 24 h natural aging followed by 50 % SRDR. With an increase in the aging time from 0 to 24 h, shifting of the peak toward the right (higher 2θ angle) was observed due to the reduction in the coherency between precipitates and alpha-aluminum. The intensity of shear texture in all rolled samples had a high value owing to the use of the SRDR process, which causes strong shear deformation in the sample. After 24 h natural aging followed by 50 % cold SRDR, the sample indicated the peak hardness value of 217.4 HV due to the presence of semi-coherent interfaces of S’ precipitates. By increasing the natural aging duration up to 24 h, the yield strength and ultimate tensile strength were significantly increased to 642.7 and 706.1 MPa, respectively, whereas the ductility was decreased to 8.7 %. A remarkable increase in strain hardening of the 192-h sample promoted uniform elongation and retarded necking (localized deformation) and fracture. In all samples the fracture mode was ductile and in the 24- and 96-h samples there were several flat surfaces, which suggested local quasi-cleavage fracture. The fracturing of the Al7Cu2Fe particles was rarely seen in the fracture surface of the 96-h sample due to the low ductility of the aluminum matrix.