The effect of Gd and Zn additions on microstructures and mechanical properties of Mg-4Sm-3Nd-Zr alloy

The effect of gadolinium (Gd, 1 wt%) and zinc (Zn, 1 wt%) additions on microstructures and mechanical properties of Mg-4Sm-3Nd-Zr alloy have been investigated by optical microscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The additions of Gd and Zn changed the kinds of precipitates in the T6-state alloy, leading to improvement of tensile properties. The prismatic precipitated phases β′ and β″ existed in the peak-aged Mg-4Sm-3Nd-Zr alloy, while β′ phase and γ phase were dominant precipitates in peak-aged Mg-4Sm-3Nd-Gd-Zn-Zr alloy, and the strip-shaped ZrZn phase could also be observed after solution treatment at 798 K for 8 h. The peak-aged Mg-4Sm-3Nd-Gd-Zn-Zr alloy exhibited good heat resistance with ultimate tensile properties 213 MPa and elongation 8.6% at 573 K, which was attributed to β′ phase, γ phase and ZrZn phase hindering dislocation and grain boundary motions.