Enhanced Mechanical and Corrosion Properties of As-Extruded Mg-12Gd-2Zn-0.4Zr Alloy by Nd Additions

The microstructures and mechanical and corrosion properties of Mg-12Gd-2Zn-xNd-0.4Zr (x = 0, 0.5, and 1.0 wt.%) alloys after hot-extrusion have been studied by scanning electron microscope (SEM), transmission electron microscope (TEM), electron back scattered diffraction (EBSD), X-ray diffractometer (XRD), electronic universal testing machine, atomic force microscope (AFM), immersion, and electrochemical tests. The results show that all the alloys consist of an α-Mg matrix, β phase, and stacking faults (SFs). Obvious texture (<1¯21¯0> parallel to the extrusion direction and the direction close to <0001>) can be found due to the introduction of the Nd element. The yield strength (YS) of the alloys with Nd additions in different testing conditions is higher than that without Nd addition. The addition of 0.5 wt.% Nd achieves the highest tensile YS at room temperature (262 MPa) and 180 °C (251 MPa), along with compression YS (246 MPa), attributable to grain refinement, stacking faults, texture, and solute atom strengthening. Moreover, the compression YS to tensile YS ratio of the as-extruded alloy increases from 0.87 to 0.98, indicating a significant improvement of tension–compression YS asymmetry. The Nd addition also plays a great role in the enhanced corrosion resistance of the alloys. Specifically, the corrosion potential of the different phases in the alloys shows the following order: β phase > SFs > α-Mg matrix. The alloy with 0.5 wt.% Nd addition exhibits the best corrosion resistance owing to its lower corrosion potential difference between the β phase and α-Mg matrix.