Effect of Sn and Cu addition on the precipitation and hardening behavior of Al-1.0Mg-0.6Si alloy

The effects of Cu and/or Sn addition on the age hardening response and microstructure of the Al-1.0Mg-0.6Si alloy were investigated using hardness test, tensile test, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and 3-D atom probe (3DAP). The results indicate that natural aging (NA) of the Al-1.0Mg-0.6Si alloy was suppressed by the addition of Sn, particularly by the addition of both Cu and Sn. The addition of Sn alone enhanced the hardening response and peak hardness of the Al-1.0Mg-0.6Si alloy artificially aged immediately after quenching, whereas the hardening response and peak hardness of those artificially aged after two weeks NA decreased, which are related to the slowing down of the precipitation kinetics. Regardless of whether the alloys were previously natural aged, the alloy with the joint addition of Cu and Sn displayed higher artificial aging (AA) hardening response and peak hardness than those of alloys with the addition of only Cu or Sn. This is related to the accelerated precipitation and high number density of the precipitates. The advantage of the joint addition of Cu and Sn is the delay of NA and the acceleration of the subsequent AA.