Hardening and precipitation behavior of as-quenched Al–0.4Mg–1.0Si alloy with minor Sn addition at different aging temperatures

The effect of Sn on the hardening and corresponding precipitation behavior of as-quenched Al–0.4Mg–1.0Si alloy at different aging temperatures was investigated with hardness tests, differential scanning calorimetry analysis, and transmission electron microscopy. The hardness of the Sn-free alloy was higher than that of the Sn-added alloys during under-aging, but the tendency is reversed during over-aging. The effect of Sn on the hardening behavior of these alloys is not substantially affected by the aging temperature, i.e., the addition of Sn can improve resistance to over-aging softening at different aging temperatures. The reason for the resistance to over-aging softening by the addition of Sn is related to the increase in the number density of precipitates during under-aging and the decrease in precipitates size during over-aging. •The hardness of Sn-free alloy aged at different temperatures during under-aging and over-aging are higher and lower than that of the Sn-added alloys.•The advantage of the addition of Sn can improve the resistance to over-aging softening.•The higher hardening response of Sn-free alloy than that of Sn-added alloys during under-aging is attributed to large precipitate size and the fast precipitation of β".•The higher hardness of Sn-added than that of Sn-free alloys during over-aging is due to higher number density of precipitates.