Microstructure and mechanical properties of hot-extruded Mg–2Zn-xGa (x=1, 3, 5 and 7 wt.%) alloys

Abstract

The effects of Ga content on the microstructure and mechanical properties of the hot-extruded Mg–2Zn-xGa alloys (x = 1, 3, 5 and 7 wt%) were investigated. The microstructure was characterized using X-ray diffraction spectroscopy (XRD), optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron back-scattered diffractometer (EBSD). The results showed that the Mg–2Zn-xGa alloys were mainly composed of α-Mg matrix phase and Mg5Ga2 precipitates. The grains were continuously refined from 28.6 μm to 16.4 μm with increasing Ga content from 1 wt% to 7 wt%. The amount of micron-scale and nano-scale Mg5Ga2 precipitates increased with increasing Ga content and they were distributed both at the grain boundaries and inside the grain interiors. The tensile tests revealed that the addition of Ga element significantly enhanced the yield strength (YS) and ultimate tensile strength (UTS) due to the synergistic effects of refinement strengthening and precipitation strengthening. This strengthening effect was positively correlated with Ga content. The elongation (EL) firstly increased as Ga content increased from 1 wt% to 5 wt% and then decreased as Ga content further increased to 7 wt% because of the formation of excessive Mg5Ga2 precipitates.