The microstructures and mechanical properties of Mg-6Zn-1Mn-4Sn-1.5Nd alloy subjected to extrusion and T5 treatment were investigated using optical microscopy（OM）, X-ray diffractometer（XRD）, scanning electron microscopy（SEM）, electron back scattered diffraction（EBSD）, transmission electron microscopy（TEM）, hardness tests and uniaxial tensile tests. The results showed that the as-cast alloy consisted of α（Mg）, Mn, Mg7Zn3, Mg2 Sn and Mg Sn Nd phases. Dynamic recrystallization has completed during the extrusion process and the average grain size was 7.2 μm. After T5 treatment, the strength increased obviously, the yield strength and ultimate tensile strength of as-extruded alloy were increased by 94 and 34 MPa, respectively. Microstructure characterization revealed that the improvement of strength was determined by the high number density of β′1 rods.
The microstructures and mechanical properties of Mg-6Zn-1Mn-4Sn and Mg-6Zn-1Mn-4Sn-0.5Y alloys under extrusion and T6 aging conditions were investigated by optical microscopy（OM）, X-ray diffraction（XRD）, scanning electron microscopy（SEM） and tensile test. The results show that Y element refines the grains and improves the comprehensive mechanical properties of ZMT614-0.5Y both in as-extruded and T6 states. The phase compositions of Mg-6Zn-1Mn-4Sn-0.5Y are α-Mg, Mg Zn2, Mn, Mg2 Sn and Mg Sn Y phases. After T6 treatment, the ultimate tensile strength（UTS） and yield strength（YS） increase while the elongation decreases severely. For both of these alloys, the theoretical results combined with the experimental values demonstrate that the grain boundary strengthening and solid solution strengthening play an important role in enhancing the YS in the as-extruded state, while the precipitation strengthening is the key factor for the enhancement of YS in the T6 state.
