Suppressing negative natural aging effect in automotive AlMgSiCu alloys via Sn microalloying

• Sn microalloying significantly suppresses the negative natural aging effect in Al–Mg–Si–Cu alloys, preserving peak-aged hardening capacity and early-stage hardening kinetics. • Sn addition modifies the nature of natural aging clusters, enabling a significant proportion to act as heterogeneous nucleation sites for strengthening precipitates during artificial aging. • Atomic-resolution EDS reveals that Sn atoms preferentially occupy Si atomic sites within the β′ and C/Q′ phases. • These findings provide critical theoretical insights for optimizing automotive-body aluminum alloy design to enhance paint-bake hardening response.