Effect of the natural aging time on the age-hardening response and precipitation behavior of the Al-0.4Mg-1.0Si-(Sn) alloy

The combined effect of adding Sn and natural aging (NA) time on the precipitation and age-hardening rate of the Al-0.4Mg-1.0Si alloy was investigated by a hardness test, electrical resistivity test, differential scanning calorimetry (DSC) analysis, 3-D atom probe (3DAP) analysis, and transmission electron microscopy (TEM). The results showed that the NA of the Al-0.4 Mg-1.0Si alloy was suppressed by adding Sn. This suppression was ascribed to the suppression of the formation of clusters. The short NA time (less than 5 days) had a positive effect on the subsequent artificial aging (AA) in the Sn-added alloys, i.e., a fast AA-hardening rate was achieved. The positive effect of the NA on the AA in the Sn-added alloys increased as the amount of Sn increased, but decreased as the NA time increased. The AA was negatively affected by the NA when the NA time was increased to 14 days. The accelerated AA precipitation of the Sn-added alloys after a short NA time was responsible for the fast AA-hardening rate. This accelerated precipitation was related to the increased amount of retained quenched-in vacancies according to their NA resistivity curves and similarity of the chemical composition between the Sn-containing clusters and β" phases.