Research Of High Cycle Fatigue Of ZM61 Wrought Magnesium Alloy

As one kind of lightweight structural metal material with high specific strength and high stiffness,the application of magnesium alloys in automobile,aviation and communication is increasingly wider and wider.With the expansion of application filed,the demand for magnesium alloys is correspondingly higher and more strict.Besides,many magnesium alloy components and parts of engineering structure are served under dynamic and cyclic load,such as bent axle,connecting rod,piston,undercarriage and so on.The failure mode of these components and parts is fatigue failure.Consequently,there is not only the theoretical significance but also the practical value to research the fatigue and fracture of magnesium alloys,especially the high cyclic fatigue without macroscopical plastic deformation.In this paper,the high cyclic fatigue of extruded and double-aged ZM61 magnesium alloy is systematically investigated,so as to provide the theoretical basis for anti-fatigue design and safe use.In the study,the fatigue property and mechanical property of extruded and double-aged ZM61 alloys are tested by electro-hydraulic servo fatigue testing machine(MTS)and electronic stretch test machine,respectively.Based on the results of optical microstructure(OM),X-ray diffraction(XRD),and scanning electron microscopic observation,the fatigue property and the deformation mechanism of extruded and double-aged ZM61 magnesium alloys under different types of load.Meanwhile,in order to ensure the safety of the alloy during the service duration,the safe life is estimated by the Weibull distribution.The main research contents and conclusions are as follows:? The fatigue tests were conducted on the extruded and double aged ZM61 magnesium alloys with the cyclic sine wave load type of symmetrical tension-compression.The deformation mechanisms of extruded and double aged ZM61 magnesium alloys during the fatigue test were investigate by characterizing the microstructures before and after the fatigue test.The results show that the fatigue limit of the extruded and double aged ZM61 magnesium alloys is 117 MPa and 103 Mpa,respectively.For the double aged ZM61 magnesium alloy,the main deformation mechanism is the slip during the half cycle of tension and combined action of slip,twinning and twinning during the half cycle of compression.For the extruded ZM61 magnesium alloy,the dominant deformation mechanism is slip during the half cycle of tension,and the deformation mechanism during the half cycle of compression is correlated with the stress level.During the half cycle of compression,the dominant deformation mechanisms are the slip in the fine grains and the twining and detwining in the corase grains under the high stress level,but the the dominant deformation mechanism is slip in both fine and coarse grains under the low strss level.It is noteworthy that the grains of extruded ZM61 magnesium alloy could be refined remarkblely which subjected to the fatigue test under the low stress level,and the special phenomena is attributed to the dynamic recrystallization at room temperature.? The fatigue tests were conducted on the extruded and double aged ZM61 magnesium alloys with the cyclic sine wave load type of single tension.The deformation mechanisms of extruded and double aged ZM61 magnesium alloys during the fatigue test were investigate by characterizing the microstructures before and after the fatigue test.The results show that the fatigue limit of the extruded and double aged ZM61 magnesium alloys is 169 MPa and 179 Mpa,respectively.The deformation mechanisms for both extruded and double aged ZM61 magnesium alloys are basal slip,and the {1012} tension twinning could be activated in a few coarse grains as the supplementary deformation mechanism.However,the detwinning would not occur because the cyclic loading is sigle tension.The obvious grain refinement could also be observed in the in extruded ZM61 magnesium alloy sample subjected to the fatigue test under the low stress level,and the reason is consistent with that subjected to the fatigue test with the cyclic sine wave load type of symmetrical tension-compression and interpreted as the the dynamic recrystallization at room temperature.? The data of fatigue life is analyzed and processed by graphical method and least square method of Weibull distribution to estimate the three parameters of Weibull distribution and the safe life under a certain stress level,which provides the reference frame for safe reliability of the material served under the cyclic loading.The results shows that the estimating the three parameters of Weibull distribution and the safe life by least square method of Weibull distribution is more accurate and more credible than that by graphical method.