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

While Sn has been established as an effective microalloying element for suppressing the negative natural aging (NA) effect in Al-Mg-Si alloys, its potential to mitigate the negative NA effect in Al-Mg-Si-Cu alloys remains to be confirmed. The present study systematically investigates Sn's role in the NA effect of Al-Mg-Si-Cu alloys through hardness measurements, differential scanning calorimetry, and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. Our results demonstrate that the addition of Sn completely suppresses the adverse NA impact on the peak-aged hardening capacity during subsequent artificial aging while substantially alleviating early-stage hardening kinetics degradation. Our findings suggest Sn modifies the nature of NA clusters in Al-Mg-Si-Cu alloys. A significant proportion of NA clusters in the Sn-added alloy effectively serve as heterogeneous nucleation sites for strengthening precipitates during artificial aging, thereby preserving precipitate nucleation rates and preventing coarsening at the peak-aging stage. Atomic-resolution energy-dispersive X-ray spectroscopy reveals preferential occupation of Si atomic sites by Sn atoms within the β′ phase and C/Q′ phases. This investigation provides critical theoretical insights for alloy design optimization in automotive body aluminum applications.