INFLUENCE OF HEAT TREATMENT ON LOW-CYCLE FATIGUE BEHAVIOR OF EXTRUDED Mg-7%Zn-0.6%Zr-0.5%Y ALLOY

The low-cycle fatigue tests have been conducted for the Mg-7%Zn-0.6%Zr-0.5%Y alloys (mass fraction) subjected to extrusion, aging (T5) and solution plus aging (T6) treatment, respectively. The influence of heat treatment on the fatigue deformation behavior of the alloy has also been systematically investigated. The results show that T5 and T6 treatment can improve the cyclic deformation resistance of Mg-7%Zn-0.6%Zr-0.5%Y alloys. T5 treatment can reduce the fatigue life of the alloy. However, T6 treatment can improve the fatigue life at high total strain amplitudes, and reduce the fatigue life at low total strain amplitudes. The relationship between elastic strain amplitude, plastic strain amplitude and reversals to failure of the alloys can be described by Basquin and Coffin-Manson equations, respectively. For the alloys subjected to both T5 and T6 treatments, the increase in the cyclic deformation resistance is mainly due to the formation of long period stacking ordered (LPSO) phase. The twins formed during the fatigue deformation may be responsible for the decrease in the fatigue life of the alloy subjected to T5 treatment.