Study on the effect of pre-deformation on the uniformity of residual stress and microstructure of aged 2024 aluminum alloy ultra-thin sheets

• Low pre-deformation improves the uniformity of residual stress distribution on the surface of ultra-thin 2024 aluminum alloy sheets. • The low pre-deformation of 2% enhances residual stress uniformity and mechanical properties by refining grains (23.67 ± 14.77 µm) and dispersing fine S' phase particles (8.23 ± 2.25 nm). • This study established mathematical formulas for pre-deformation and the uniformity of residual stress distribution. 2024 aluminum alloy ultra-thin sheet is an ideal material for aerospace applications such as rocket wall panels and aircraft skin structures. Uneven stress distribution caused by rapid non-uniform cooling during the quenching process of ultra-thin sheets may lead to issues such as warping and buckling. This study introduced a pre-deformation process prior to aging treatment to improve the residual stress distribution and precipitation phase distribution in 2024 aluminum ultra-thin sheets, establishing a relationship between stress and microstructural evolution. The specific mechanism of stress release was elucidated: the synergistic effect of elastic stress field on phase precipitation and dislocation obliteration. X-ray diffraction results indicate that applying 2 % pre-deformation reduces the standard deviation of stress distribution in the rolling direction and transverse direction by 49.09 % and 61.35 % (consistent with micro-indentation data), respectively, effectively enhancing distribution uniformity and lowering residual stress levels. Meanwhile, it refined grain size (23.67 ± 14.77 µm) and dispersed fine S' phase particles (8.23 ± 2.25 nm), reducing the standard deviation of grain size distribution by 12.45 %. This was accompanied by enhanced grain distribution uniformity and promoted the precipitation of finely dispersed second phases. Two mathematical fitting equations were established, revealing the relationship between pre-deformation amount, surface rolling direction, and the uniformity of transverse residual stress distribution. This study fills a research gap in regulating residual stress distribution and microstructural evolution through low pre-deformation aging in ultra-thin sheets, providing insights for producing ultra-thin high-strength aluminum alloy sheet with low residual stress and favorable stress distribution.