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In many industrial Al-Mg-Si alloys, natural aging (NA) has a detrimental effect on the age-hardening response during artificial aging (AA), due to the formation of unfavorable nanometer-sized solute clusters during NA. In this work, we systematically studied the atomic structures of solute clusters formed in a dilute 6060 alloy and a more concentrated 6082 alloy after 1-year NA and their influences on the age hardening behavior during the following AA. In 6060, it was found that NA promotes the formation of high-density solute clusters in the form of GP-zones composed of 1–3 β″-eyes, which can act as precursors of β″ precipitates, enhancing the age-hardening kinetics during AA. In contrast, most solute clusters in 6082 after 1-year NA are 1β″-eye, binocular and square GP-zones, while GP-zones containing multiple β″-eyes are rare. As a result, NA has a strong negative effect on the age-hardening response during AA and the peak-aged strength.
Li et al. (Sat,) studied this question.