The effect of Ag on the tensile strength and fracture toughness of novel Al-Mg-Zn alloys

In this study, the effect of trace addition of Ag on the microstructure, tensile strength, and fracture toughness of novel Al-Mg-Zn alloys was evaluated using transmission electron microscopy, scanning electron microscopy, electron back-scattered diffraction analysis, tensile test, and Khan tear test. The age-hardening response was improved by Ag owing to the stimulation of matrix precipitation. The type of MPts was unchanged by Ag, and the density and size of MPts were improved and refined. But the ability of matrix precipitates (MPts) to obstruct dislocation motion was weakened by Ag, thus, the Al-Mg-Zn alloys strength was not improved by Ag as expected. The addition of 0.2 wt% Ag improved the fracture toughness, while the addition of 0.4 wt% and 0.6 wt% Ag decreased the fracture toughness of Al-Mg-Zn alloys. The fracture toughness results are based on many factors such as MPts, misorientation of grain boundaries, fraction of deformed grains, and stress-strain concentration. The mechanism of the effect of microstructure on properties was also elucidated.