Effect Of Grain Size And Residual Stress On Fatigue Properties Of2E12Aluminum Alloy

In this work, the microstructure evolution of aerostatic2E12aluminum alloy during cold deformation and annealing were studied by means of OM, SEM, TEM, XRD and EBSD. Effects of pre-deformation and quenching medium on residual stress were discussed. Besides, effects of grain sizes and residual stress on the fatigue properties of2E12aluminum alloy have been investigated by means of combining fatigue properties tests with microstructure analyses. Main conclusions were presented as followed:(1)During cold deformation,the coarse second phases were separated from the matrix, and broken down gradually. In addition, the dislocation density of the alloy increased significantly and the misorientation of sub-grains increased gradually.(2) During cold deformation, Cube texture and Goss texture reduced gradually, while Brass texture,cooper texture and S texture increased gradually. During annealing, Cube texture increased noticeably, while Brass texture and S texture reduced significantly.The formation of Cube texture obeys the orientation growth theory.(3)During quenching,the faster cooling rate,the greater surface residual compressive stress.The pre-rolling deformation after solution treatment is beneficial to increasing surface residual compressive stress, while pre-stretching after solution treatment would reduce surface residual compressive stress.(4) By changing the cold deformation and annealing process, four different grain sizes of alloys were prepared. Fatigue performance tests found that crack growth rate decreased with the increasing of grain size in the near-threshold regime.Because obvious crack deflection in the coarser grained materials leads to the roughness induced crack closure.Besides,grain refinement has a beneficial effect on prolonging the fatigue life.(5) By pre-deformation and changing quenching medium obtained two groups of alloy with different residual compressive stresses. Fatigue performance tests show that during the middle period of the crack propagation the increase of residual compressive stresses is beneficial to increase the crack propagation resistance. The crack propagation rate difference is very small in the near-threshold regime.Because on one hand the effective stress ratio decreasing in the residual stress field can lead to the crack growth rate’s decreasing.The other hand that residual compressive stress can increase the crack closure induced by wake zone plasticity, it will cause the increasing of crack propagation resistance. In addition,the increase of residual compressive stresses is beneficial to prolongthe fatigue life...