Research On Low-Cycle Fatigue Behavior Of Extruded MG-AL-ZN-Y Alloy

Magnesium alloys are the metallic structural materials with the practical usage value due to their low density, high specific stiffness and specific strength, high electromagnetic interference resistance, good damping and heat dispersing performances as well as excellent processing properties. Therefore, magnesium alloys have been applied in modern industries extensively. At present, AZ series cast magnesium alloys are most commonly used in industry. But such casting defects as pore, inclusion and porosity are easy to appear in cast magnesium alloys. In this investigation, as-extruded Mg-Al-Zn and Mg-Al-Zn-Y alloys were taken as the experimental materials, and through performing the tensile and low-cycle fatigue tests at room temperature and combining with the observation and analysis on both microstructure and fracture surface, the effects of rare earth element Y and T6 (solid solution plus aging) treatment on microstructures and mechanical properties of the extruded Mg-Al-Zn and Mg-Al-Zn-Y alloys.The results of tensile tests show that after adding the rare earth element Y, the ultimate tensile and yield strengths as well as elongation of the extruded Mg-Al-Zn magnesium alloy at room temperature are improved. The T6 treatment plays a significant role in improving the tensile properties of the extruded Mg-Al-Zn and Mg-Al-Zn-Y alloys at room temperature.The results of low-cycle fatigue tests reveal that at most imposed total strain amplitudes, the extruded Mg-Al-Zn(-Y) alloys subjected to T6 treatment exhibits the cyclic strain hardening during fatigue deformation. Moreover, the Mg-Al-Zn-Y alloy offers the higher cyclic stress levels than the Mg-Al-Zn alloy. For two alloys, the relationship between the plastic strain amplitudes and reversals to failure shows a linear behavior.The observations on the fracture surfaces reveal that the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly for the extruded Mg-Al-Zn and Mg-Al-Zn-Y alloys with T6 state. And the fatigue crack propagation area has the obvious quasi-cleavage fracture characteristics.