The tension behaviors of Al-Mg alloys were tested, and the influences of deep cryogenic treatment (DCT) and grain size on their tensile properties were explored. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the evolution of the microstructure. It was concluded that the alloys with fine grain (FG) had a higher strain hardening capacity and strength, however, the alloys with coarse grain (CG) exhibited better plasticity. This can be explained by the alloy with fine grains having a higher density of grain boundary, which can hinder the motion of the dislocation; therefore, the deformation resistance was improved. For alloys with coarse grains, the dislocation has more freedom to move and is easier to rearrange, which is beneficial to the plasticity. Moreover, when given deep cryogenic treatment, the strength and plasticity of the alloys can be slightly improved, which can be attributed to the microplastic deformation that occurs during cryogenic treatment that can induce internal stress, as cold-induced internal stress is conductive in achieving a finer grain and higher density of dislocation.

The cold-rolled 2024 aluminum alloy sheets were subjected to solution treatments at different temperatures followed by artificial aging. The microstructure and mechanical properties were investigated using Vickers microhardness testing, tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that as the solution temperature increases, the coarse particles gradually dissolved into the matrix. At a solution temperature of 500 °C, the grains become nearly equiaxed with an average size of ~16.47 μm, and no significant grain growth is observed compared to the as-rolled condition. The refined microstructure contributes to excellent mechanical properties. In contrast, when the solution temperature increases to 550 °C, the microstructure shows severe grain coarsening (up to ~61.39 μm), which indicates that overburning occurs, resulting in a drastic deterioration in mechanical performance. As the aging time increases, precipitates become more uniformly and densely distributed throughout the matrix, and the hardness initially increases and reaches a peak after approximately 6 h of aging at 180 °C. The optimal mechanical performance, characterized by a favorable combination of strength and ductility, is achieved at an aging time of 6 h. In summary, the optimal heat treatment condition for the cold-rolled 2024 aluminum alloy sheet is solution treatment at 500 °C for 1 h followed by aging at 180 °C for 6 h, resulting in a hardness of 154 HV, a tensile strength of 465 MPa and an elongation of 13%.

Uniaxial tensile tests were conducted to investigate the mechanical anisotropy of rolled 2024 aluminum alloy sheets subjected to different cryogenic treatment durations along the rolling direction (0°), diagonal direction (45°), and transverse direction (90°). The experimental results indicate that the mechanical properties of the rolled 2024 aluminum alloy are strongly dependent on the treatment process and exhibit pronounced anisotropy. With increasing cryogenic treatment time, the yield strength first increases and then tends to stabilize. The optimal combination of mechanical properties is achieved after cryogenic treatment for 16 h, with the yield strength increasing to 385–390 MPa. Cryogenic treatment has no significant effect on the grain morphology of the matrix, but promotes dislocation multiplication and a more uniform distribution of precipitation features. The anisotropy analysis shows that the yield strength in the 45° direction is consistently lower than that in the 0° and 90° directions. The in-plane anisotropy parameter (IPA) decreased from 4.8% in the condition without deep cryogenic treatment to 3.0% after 4 h of cryogenic treatment, followed by an increase to 6.7% after 24 h. This result indicates that short-term cryogenic treatment can effectively reduce the in-plane anisotropy of the 2024 aluminum alloy.