Research On Fatigue Behavior Of2A12Alloy In Low Temperature And Vacuum Environment

The fatigue behaviors of2A12alloy at83k in vacuum (10-6torr) with the loadratio R=-1and R=0has been studied, respectively, by using fatigue testing machine,optical microscope, scanning electron microscope and transmission electronmicroscopy.The results show that the fatigue life of2A12alloy increases when stressamplitude reduced gradually. The fatigue life of2A12alloy with R=-1is longerthan that with R=0under the same stress amplitude. The fatigue limits of2A12alloy with R=-1and R=0are200~240MPa and175~225MPa respectively, whichare about34%and28%of yield strength of the alloy at83k in air respectively.Fatigue steps and pores appear in the fatigue crack initiation region of2A12alloy, while secondary cracks and slip traces are observed in sequence with theincreasing of the stress amplitude. The fatigue striations and pores appear in thefatigue crack propagation region, while the fatigue steps and tyre patterns areobserved in sequence with the stress amplitude increasing. The pores and the tearridges distribute mainly in the transient breaking region.The dislocations distribute evenly in cellular substructure of the original2A12alloy and near to the fatigue fracture of the alloy with R=-1, while the cellularsubstructure composed by the high density dislocation forming the wall and lowdensity intracellular dislocation near to the fatigue fracture of the alloy with R=0.Compare to the original alloy, the density of the dislocation near to the fatiguefracture of the alloy. With the same load ratios, the dislocation density of the alloywith the low stress amplitude is higher than that with high stress amplitude. Thedislocation density of the alloy with R=-1is higher than that with R=0although thefatigue lives are the same.