Research On The Microstructure Evolution During Processing And Fatigue Properties Of2E12Aluminum Alloy

Microstructure characteristics play a determining role in properties of alloy. In this work, the microstructure evolution of aerostatic2E12aluminum alloy during processing and heat treatment were studied by means of OM, SEM, TEM, XRD and EBSD. Besides, microstructure (grain sizes and grain orientation) effects on the fatigue properies of2E12alloy have been investigated though combining fatigue properties tests and microstructure analyses. Main research contents were presented as followed:(1) The microstructure characteristics (second phase, grain morphology, element distribution, etc.) of as-cast alloy were observed and their evolution during homogenization have been investigated. The homogenization treatment process has been studied and a optimized process has been given.(2) Two different types of precipitation-free zones (PFZs) were observed during homogenization of alloy. The formation mechanisms and morphology evolution of both PFZs were investigated. The Temperature-Gradient Zone Melting phenomenon was observed in as-cast alloy and its effects on the phase transformation and properties of alloy during homogenization have been analyzed.(3) The morphology, distribution and orientation relationships (ORs) of T phase with Al matrix have been studied. Three ORs and habit planes of T phase have been determined by employing TEM and HRTEM. These particular ORs, habit planes and morphologies of T phase were discussed through interface observation, misfit caculation and crystal symmetry analyses.(4) Three alloys with different microstructures have been prepared by adjusting heat treatment process. The hot deformation behaviors and microstructure evolution of alloy after deformation have been investigated at different deformation conditions (four deformation temperatures (340℃,390℃,440℃,490℃) and five strain rates (0.001s-1, 0.01s-1,0.1s-1,1s-1,10s-1)) by using thermal simulation experiments. By analysis and comparison, the effects of coarse precipitates and eutectics on the deformation behaviors and microstructure evolution have been discussed.(5) Through microstructure observation and mechanical performance testing, the microstructure evolution of alloy during cold rolling, annealing and solution treatment has been studied and the coarse-second-phase particle effects has also been discussed.(6) Three alloys with different grain sizes and two alloys with different strong textures have been prepared though process control. Grain size effects on fatigue crack growth rate have been studied by comparing fatigue crack behaviors of alloys with different grain sizes. Grain orientation effects on fatigue crack growth rate have also been studied by comparing strong textured alloys with those random textured ones.