| Magnesium alloy as the lightest structural material has been used more and more in the application of engineering. The main failure form of the engineering materials is fatigue fracture, thence, the depth study on fatigue behavior of Magnesium alloy has a great significance. The plastic deformation has a great impact on fatigue behavior of Magnesium alloy. in this thesis, we study the effects of different plastic deformation impact on the rolled and extruded AZ31 magnesium alloy and further studied the plastic deformation of AZ31 magnesium alloy resulting fatigue fracture occurred in the high-cycle fatigue behavior and fracture micro-mechanism, providing an experimental evidence for the broadening of magnesium alloy which works under the conditions of high-cycle fatigue.The condition fatigue limit of rolled AZ31 is more than 100 MPa when the cycle number is 107.The Tension-Tension fatigue test of rolled AZ31 show that the compress plastic deformation reduces fatigue property significantly. SEM on fatigue fracture surface indicate that the fatigue crack initiate in the surface or sub-surface. The compress Experiment result show that it will bring in abundant twinning when the deformation more than 3%.with the increase of deformation, the number of twinning is also increase.The condition fatigue limit of extruded AZ31 is 119 MPa when the cycle number is more than 107.the cycle life is Sensitive to stress. the tension plastic deformation also reduce fatigue property, In a certain stress range, with the increase of tension deformation, the fatigue life has a Peak value. SEM on fatigue fracture surface show that fatigue crack initiate in interchange of twinning and grain boundary and propagate along the twinning boundary. TEM result show that with the increase of tension deformation ,the number of twinning is also increase, even bring in second and third twinning .It has been confirmed that twinning has important impacts on fatigue crack initiation and propagation .
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