Effect of Ag Content on Microstructure and Mechanical Properties of Mg-Gd Binary Alloys

This study systematically investigates the influence of Ag content on the microstructure and mechanical properties of Mg-8Gd-0.5Zr-xAg（x%=0，0.5%，2%，5%） alloys fabricated via high-temperature extrusion with a large extrusion ratio， employing scanning electron microscopy （SEM）， transmission electron microscopy （TEM）， and tensile testing. The results demonstrate that the yield strength increases markedly with Ag addition， showing a remarkable improvement of 142 MPa in the Mg-8Gd-0.5Zr-5Ag alloy compared to the Ag-free counterpart. Microstructural analyses reveal that Ag not only refines grain size but also fundamentally alters the types of precipitates formed during extrusion. Electron backscatter diffraction （EBSD） indicates that the Mg-8Gd-0.5Zr-0Ag and Mg-8Gd-0.5Zr-0.5Ag alloys consist of partially recrystallized microstructures with elongated grains， whereas the Mg-8Gd-0.5Zr-2Ag and 5Ag alloys exhibit fully recrystallized structures， with the Mg-8Gd-0.5Zr-5Ag alloy achieving the smallest average grain size （1.3 μm）. SEM-EDS analyses confirm an increase in the volume fraction of dynamic precipitates with higher Ag content. While the secondary phases in Mg-8Gd-0.5Zr-0Ag and Mg-8Gd-0.5Zr-0.5Ag alloys are identified as Mg5Gd （via TEM）， the Mg-8Gd-0.5Zr-2Ag and Mg-8Gd-0.5Zr-5Ag alloys form Mg12Gd2Ag ternary phases. The superior yield strength of the 5%Ag alloy is attributed to the synergistic effects of precipitation strengthening and grain refinement.