Microstructure And Mechanical Behavior Of Hot-Extruded Mg-Mn-Zn-RE Alloys

As a lightweight structural material, magnesium alloys will get more widely applied in automotive industry. It has received much more concerning how to improve mechanical properties of magnesium alloys with an increase in usage of magnesium alloys. It is obvious that to develop new wrought magnesium alloys can meet the requirement of mechanical properties for automobile structural materials and ensure magnesium alloys to be applied in automobile industry more and more. In this investigation, both microstructures and mechanical properties of hot-extruded Mg-Mn-Zn(-RE) alloys have been studied, and the influence of RE additions on microstructures and mechanical properties of hot-extruded Mg-Mn-Zn alloy has been identified in order to provide reliable theoretical reference for both engineering application of hot-extruded Mg-Mn-Zn(-RE) alloys and development of new wrought magnesium alloys containing RE elements.The results of microstructural observation reveal that the addition of RE elements can effectively refine the grains in hot-extruded Mg-Mn-Zn alloy. For hot-extruded Mg-Mn-Zn alloy, the addition of 2% Y can reduce the average grain size from 50 urn to 10 (am, while the addition of 1% Ce can decrease the average grain size from 50μm to 15μm.The results of tensile experiments reveal that both ultimate tensile strength and yield strength of hot-extruded Mg-Mn-Zn-RE alloy at elevated temperatures can get significantly enhanced due to the addition of RE elements. For example, at 150℃, when the content of either Y or Ce equals to 2%, the hot-extruded Mg-Mn-Zn-RE alloys exhibit the highest ultimate tensile strength and yield strength. At 200℃, when the content of Y or Ce reaches to 3%, the highest ultimate tensile strength and yield strength can be attained for the hot-extruded Mg-Mn-Zn-RE alloys. Moreover, the hot-extruded Mg-Mn-Zn-1 Ce alloy shows the greatest fracture elongation at room temperature and 200℃, compared with other Mg-Mn-Zn-Ce alloys. The results of low-cyclic fatigue tests show that the hot-extruded Mg-Mn-Zn alloy exhibits cyclic strain hardening at all total stain amplitudes. The hot-extruded Mg-Mn-Zn-1 Ce alloy exhibits cyclic strain hardening followed cyclic stability at the lowest total strain amplitude used in this investigation, while show cyclic strain hardening at other total strain amplitudes. For the hot-extruded Mg-Mn-Zn-2Y alloy, either cyclic strain hardening or stable cyclic stress response can be observed at the higher total strain amplitudes, and however, cyclic strain softening can be noted at the lower total strain amplitudes. For the hot-extruded Mg-Mn-Zn(-RE) alloys, the relation between elastic strain amplitude, plastic strain amplitude, and reversals to failure shows a monotonic linear behavior, and can be well described by the Basquin and Coffin-Manson equations, respectively. Moreover, a linear relation between tensile hysteresis energy and fatigue life can be also noted for hot-extruded Mg-Mn-Zn(-RE) alloys.The fractography shows that the tensile fracture surfaces of hot-extruded Mg-Mn-Zn-RE magnesium alloys exhibit typical ductile fracture feature. For the hot-extruded Mg-Mn-Zn-RE magnesium alloys, cracks initiate transgranularly at the surface of fatigue specimens and propagate in a transgranular mode under the low-cycle fatigue loading condition.