Microstructure Evolution Simulation And Experimental Study Of7A85Aluminum Aviation Joint Forging By Isothermal Forging Process

Abstract:The internal microstructure state of forging products is the major determinant of their macro mechanical properties. To control the microstructure and mechanical properties of the products by controlling the hot forging forming process parameters has become a popular research direction in the hot forging forming field. The dislocation density in the material grain structure is the bridge between the macroscopic deformation process and microstructure evolution. In this thesis, the present author establishes the7A85aluminum alloy dynamic recrystallization model by applying the macro and micro interaction law of "strain-dislocation density-recrystallization-flow stress" and focusing on the7A85aluminum alloy aviation joint forgings. By combining the isothermal forging process of macro-physics finite element simulation results and using Cellular Automaton(CA) method to simulate the forgings isothermal forging dynamic recrystallization microstructure evolution process. The present author has completed following research work:(1) Completing isothermal compression thermal simulation experiment by using Gleeble-1500thermal simulation machine and comparing the7A85aluminum rheological law with the behavior of dynamic recrystallization under the condition of different deformation rates and deformation temperatures. The research results have shown that7A85aluminum alloy sample tissue has gone through dynamic recrystallization. The low strain rate (0.001s-1) and high temperature (400℃～450℃) are good for the germination of dynamic recrystallization.(2) Analyzing the microstructure of isothermal compression of7A85aluminum alloy sample by using Leica-DMI5000M Metallurgical Microscope, and establishing7A85aluminum alloy flow stress model, dislocation density model and recrystallization nucleation and grain growth model based on experimental observations and the Dislocation theory. (3) Using the CA method to simulate the process of7A85aluminum alloy isothermal compression experiment of dynamic recrystallization and revising dynamic recrystallization model material parameters through metallographic observation of the sample tissue. The results show that: the low strain rate and high temperature are favorable to the occurrence of dynamic recrystallization; the CA simulation recrystallized grain morphology and recrystallization percentage are in good accordance with the experimental results; CA method and the establishment of dynamic recrystallization model can accurately describe the7A85aluminum alloy dynamic recrystallization behavior.(4) The evolution of dynamic recrystallization organization in the joint forgings’ isothermal forging process has been simulated and predicted, and verified by carrying out joint forgings isothermal forging process experiments. Results show that:the combination of coupled macroscopic deformation finite element conditions and grain topology deformation of CA method and7A85aluminum alloy dynamic recrystallization model can be helpful to predict the evolution process of grain structure in forging products. Besides, it can provide theoretical guidance for the optimization of forging process designs. Figure54, Table9, References87...