<p>Effects of trace elements Sn and Ag on the early stages of the natural aging process in Al–Mg–Si alloys were studied with a focus on the role of vacancies. Hardness measurements, differential scanning calorimetry, positron annihilation lifetime spectroscopy, and coincidence Doppler broadening technique were employed for this investigation. In Al–Mg–Si alloy with Sn addition, aging acceleration during natural aging and the onset of negative effects during artificial aging were both delayed compared to the base alloy. Furthermore, a positive effect was observed, with an increase in hardness after artificial aging as natural aging progressed at room temperature. This unique aging behavior is presumed to result from the release of vacancies from the vacancy-Sn atom complexes formed immediately after quenching, which occurs as natural aging progresses at room temperature. In contrast, in Al–Mg–Si alloy with Ag addition, natural aging was not delayed, and the late-stage hardening of natural aging was promoted even more than in the base alloy. This aging behavior is thought to arise from the formation of vacancy-Ag complexes immediately after quenching, which evolve into vacancy-Ag–Mg complexes as natural aging progresses at room temperature.</p>