Study On Hot Rheologic Forming And Fatigue Strength Prediction Of7A04Aluminium Alloy Component

The present dissertation is study on the high strength aluminium alloy with the poor flowability in hot forging process which would weaken the service properity of the components. A series basic research on hot rheologic properity and fatigue properity for7A04aluminium alloy is carried out with the method of physical simulation and numerical simulation:(1) The constitutive equation of7A04aluminium alloy with different initial grain sizes was founded. The forming process of aluminium alloy part was optimized by DEFORM-3D simulation.(2) The fatigue strength of7A04aluminium alloy was predicted by ANSYS and FE-SAFE based on the measured S-N curve, the theoretical results correspond with the bench test. This work provided important guidance to raising productivity of7A04aluminum alloy forgings and predicting the component fatigue performance, this result has been successfully applied in the high-speed train key parts localization.The thermal deformation behavior of7A04aluminium alloy during300℃-450℃was studied by isothermal compression of cylindrical specimens. The steady flow stress of7A04aluminium alloy during350℃-450℃can be represented by exponential correlation with a Zener-Hollomon parameter which discribles the flow stress change with strain rate and temperature.Constitutive equation of different initial grain size of7A04high strength aluminium alloy shows that the strain rate sensitivity factor and activity energy of the flow stress increase with the decrease of the grain sizes. The DRX is the dominant softening mechanism above350℃while DRV below350℃. DRX becomes more obviously with initial grain sizes decreasing. The processing temperature of7A04aluminium alloy was optimized during360℃to430℃based on the processing map method. The die forging process of a connecting rod in friction screw press was simulated with DEFORM-3D. The optimum preheat temperature are405℃for billet,100℃for container by orthogonal experimental design. The optimum processing pranneters are appilied in practical production.S-N curve of7A04aluminium was obtained by high frequency axial loading fatigue test. The S-N curve was also describled by Basquin equation at50%survival rate. The effect of surface coarse grain on fatigue properity of7A04aluminium alloy has been studied by high frequency four-point bending fatigue test. The results show that the coarse grain reduced the fatigue crack initiation resistance and weaken the fatigue properties significantly. The accelerated life test was proposed to predict the fatigue fracture mechanism and the fatigue life. The FEM results show that the fracture would be occur at the surface hemisphere defect of the rod according to the actual defect shape under the accelerated life test loading spectrum(FMAX=27.2kN). The similar defect should be avoided in the production. The stress distribution of the connecting rod under the accelerated life testing loading was obtained by ANSYS. The stress and fatigue life distribution of the push rod was obtained and verified by bench test.Under the background of "Ministry of Science and Technology and Ministry of Railways Joint Action Plan", the7A04aluminium alloy components completed the localization and run in safe service since2010. The work is significant for the localization of the key components of bogie.