Effect of Ag and Ge on the precipitation behavior and resultant properties of AA6061 alloys

This study investigated the effects of Ag and Ge on the precipitation behavior and resultant properties of AA6061 alloys using hardness measurements, electrical conductivity tests, transmission electron microscopy (TEM), and atom probe tomography (APT). Trace addition of Ge can increase the electrical conductivity and thermal stability, but slightly deteriorates the hardness during the early- and peak-aging stages. Trace addition of Ag can enhance the hardness during aging, especially in the over-aging stage, but it deteriorates the electrical conductivity. For the Ag-added alloys, the Ag atoms provide more nucleation sites and are substantially incorporated into the clusters, suggesting the formation of various types of precipitates with increasing aging time. During the peak- and over-aging stages, the Ag atoms not only segregate but also incorporate into the precipitates, resulting in the disordering of the precipitates and suppression of the coarsening of the precipitates. For the Ge-added alloys, the formation and evolution of the clusters are suppressed by Ge addition, owing to the high binding energy between the Ge and Mg atoms. With the aging time increasing, the Ge atoms are incorporated into the precipitates and suppress the ordering process of the precipitates, resulting in better thermal stability of the Ge-added alloys in the over-aging stage. The addition of both Ag and Ge shows potential for elevated temperature component applications.