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Graphical Abstract
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Abstract
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.
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