Effects of Zn Addition on the Microstructure and Mechanical Properties of Mg-Gd-Zn Alloys

The effect of Zn additions on the microstructure and mechanical properties of Mg-11Gd-(1, 1.5, 2)Zn alloys was investigated by OM, SEM, TEM and electronic universal testing machine. The results show that the microstructure of as-cast Mg-11Gd-(1, 1.5, 2)Zn alloys are composed of alpha-Mg matrix, (Mg, Zn)(3)Gd eutectic phase and lamellar 14H-LPSO structure. With the increase of Zn additions, both the volume fractions of (Mg, Zn)(3)Gd eutectic phase and LPSO phase increase, and the thermal stability of the (Mg, Zn)(3)Gd phase is improved as well. Tensile tests at room temperature indicate that the strength of as-extruded Mg-11Gd-(1, 1.5, 2)Zn alloys decreases with the increasing Zn content. The Mg-11Gd-1Zn alloy, which contains the lowest Zn among all the alloys studied, exhibits the highest tensile strength with good ductility after T6 treatment. However, the tensile strengths of the Mg-11Gd-1.5Zn and Mg-11Gd-2Zn alloys after T6 treatment are lower than that after T5 treatment. The creep tests at 200 degrees C/80 MPa reveal that all of the alloys studied have higher creep resistance than the WE54 alloy, and the creep resistance of the alloys decreases gradually with the increase of Zn addition.