Research On Fatigue Properties Optimization Of 7XXX Aluminum Alloy

7XXX series(Al-Zn-Mg-(Cu))aluminum alloy have been widely used in aerospace,rail transit and other fields due to its high strength,low density,corrosion resistance and good extrusion deformation ability.With the increasing demand for lightweight and localization of key components,7XXX aluminum alloy have been widely used in the traction beam,pillow beam and other main structural parts of high-speed trains due to its own characteristics.Therefore,the 7XXX series aluminum alloy plays an important strategic role in the development of high-speed railway,among which A7N01 and 7B05 aluminum alloys are the most typical.Due to the increasing demands on the speed and safety of high-speed trains in practical applications,this has prompted us to make structural materials with superior performance.The fatigue properties of the components subjected to alternating loads in the long service is particularly important.It is estimated that 90% of service failures are caused by fatigue of structural materials.Therefore,how to improve the fatigue properties of materials and components is an urgent problem in industrial production and practical application.This topic is based on the service situation of main force structural components such as bolster beams and traction beams of high-speed trains.The paper mainly studies the high cycle fatigue properties of A7N01-T6 aluminum alloy with different of Si content(0.01% wt.Si,0.1% wt.Si and 0.38% wt.Si)and 7B05-T5 aluminum alloy under single aging state.The aim is to optimize the fatigue properties of aluminum alloy.In this paper,with the aid of the performance test and material microstructure characterization methods to study the different Si content of A7N01 aluminum alloy and under different ageing state of 7B05 aluminum alloy fatigue properties.According to the experimental results,the fatigue strength of these three aluminum alloys with different of Si contents were 112 MPa,115MPa and 129 MPa,respectively.The fatigue strength of 7B05 aluminum aging 30 h,120h and 576 h under 120? were 157 MPa,167MPa and 167 MPa,respectively.The main conclusions of the experiment are as follows:(1)With the increase of Si element content,the fatigue strength of A7N01 aluminum alloy increases monotonically,and the dispersion of S-N curve decreases greatly.Microstructure analysis and strength and hardness errors show that when the content of Si element increases,the microstructure homogeneity of the alloy is improved,which is proved to be the main reason for improving fatigue strength and reducing fatigue life dispersion.(2)With the increase of aging time,the fatigue strength of 7B05 aluminum alloy increases.The results show that with the increase of aging time,the average distance between grain boundary precipitate phases and the width of grain boundary precipitate band get increased,that have been responsible to the increase of fatigue strength.At the same time,it can be found from the S-N curve that the slope of the S-N curve increases monotonously with the increase of aging time.From the point of view of fatigue damage,it is beneficial to improve the fatigue properties of the alloy.