Influence of of Sn on the precipitation and hardening response of natural aged Al-0.4Mg-1.0Si alloy artificial aged at different temperatures

The effect of trace Sn on the age hardening response and corresponding precipitation of Al-0.4Mg-1.0Si alloy were investigated by the hardness test, transmission electron microscopy (TEM) and 3-D atom probe (3DAP) to reveal the corresponding mechanism. It is shown that the natural aging (NA) is suppressed by the addition of trace Sn, which is ascribed to the suppression of the formation of clusters. The artificial aging (AA) hardening response of the natural aged alloy is slowed down by the addition of trace Sn when the aging temperature is low, i.e., 180 degrees C/195 degrees C, which is ascribed to the decreasing density of precipitates. When the natural aged alloy is artificial aged at 210 degrees C/225 degrees C, the age hardening response is accelerated due to the formation of high density precipitates. Based on the 3DAP and TEM results, a schematic model about the evolution of clusters in the Sn-free and Sn-added alloys during NA and AA is proposed to reveal the effect of Sn on the age hardening response at different aging temperatures.