Synergistic effect of peak aging and severe cold rolling on microstructure evolution and mechanical properties of aerospace-grade AA2014 alloy

The influence of artificial aging and severe post-aging cold deformation on microstructure evolution and mechanical properties of AA2014 alloy was systematically investigated in this work. The alloy was solution treated at 550°C for 2 h followed by artificial aging over a wide range of temperatures (75–225°C) and holding times (2–24 h) to determine the peak aging condition. Hardness measurements revealed that optimum peak aging parameters for AA2014 alloy were 175°C for 8 h. The microstructure, hardness, tensile properties and electrical conductivity of under-aged, peak-aged and over-aged conditions were evaluated using optical microscopy, SEM, tensile testing and conductivity measurements. The Young’s modulus remained relatively unaffected by aging treatment, whereas yield strength, ultimate tensile strength, ductility, hardness and electrical conductivity changed due to their strong dependence on aging temperature. The maximum ultimate tensile strength and elongation of 460 MPa and 35%, respectively, were obtained for the specimen aged at 150°C for 8 h, while the peak hardness of 168 HV 5 and maximum electrical conductivity of 41% IACS were achieved at 175°C for 8 h. Further improvement in hardness, reaching approximately 192 HV 5 was achieved when peak-aged alloy was subsequently subjected to severe cold rolling up to 93% thickness reduction without intermediate annealing treatment due to deformation-induced strain hardening. The combined strengthening response was further clarified by microstructural evidence using both the TEM and XRD techniques, which shows the evolution of θ′ precipitates, increased lattice strain, refined crystallites, and a high dislocation density after severe cold deformation, resulting in strong mechanical and electrical properties in severely cold-rolled AA2014 alloy.