Research On Dynamic Recrystallization Behavior Of7075Aluminum Alloy During Hot Deformation

The7075alloy is a widely used high-strength aluminum alloy.7075iscommonly manufactured by hot forming process. During hot forming process, notonly does the shape vary the grain size also changes. Fine microstructure canimprove the mechanical properties of materials greatly, and ensure the qualities ofthe hot forming parts. The investigation of the dynamic recrystallization behaviorof7075aluminum alloy and the understanding of the rule of evolution of grain sizein hot deformation process can give references to the determination of theprocessing technique and grain refining procedure. Combined with finite elementanalysis techniques, the process designer can not only predict the macroscopicstress and strain fields in the forming process, but also understand the distributionof grain size of the final forming parts. These will greatly improve the ability ofquality control. In the present study, considering the initial performance of7075aluminum alloy, the evolution of grain size of hot deformation microstructure isacquired with a single-stage hot-upsetting experiments and the metallographicanalysis. Then the evolution model is applied into finite element model. Detailedinvestigations are listed below:(1) Commonly, the dynamic recrystallization of aluminum is not happenedduring hot deformation. But in fact, the microstructure of aluminum alloy aftersevere plastic deformation will change significantly. In the present study, it isconcluded that the continuous dynamic recrystallization is the dynamicrecrystallization mechanism of aluminum.(2) The composition and metallograph of a commercial7075aluminum alloyare analyzed. Hot upsetting experiments are carried out at different temperatures,strain rates and deformation strain. The evolution of grain size after upsettingexperiments is qualitatively discussed.(3) A FEM model of upsetting experiment is built and deformation parametersin metallographic observation are extracted. Based on a phenomenological theorymodel of continuous dynamic recrystallization, the effects of temperature, strainrate and deformation strain on the mean grain size are quantitatively discussed.Finally, an evolution model of grain size of hot deformation microstructure of7075 alloy is obtained.(4) The aforementioned evolution model is applied into FEM software and themulti-stage thermal upsetting of7075alloy is analyzed. The final grain size of thesample center is predicted.(5) According to the simulation parameters, a corresponding multi-stagethermal upsetting experiment is taken. The accuracy of the numerical simulation isexamined by metallographic analysis and tensile tests.