| As the lightest metal structure material,the development of magnesium and its alloys industry becomes much faster since the 1990s,occupying a important position in the non-ferrous metals industry.Since it exhibits the advantages of specific strength,specific stiffness,shock absorption,casting and machining performance,Magnesium alloys have broad application prospects and market demand in the national defense,transportation,electrical and electronic equipment and other industries.But magnesium alloy is in HPC structure,causing its poor mechanical properties,which restricts its development.As a modern technique for developing ultrafine grain structures with the method of top-down approach,constrained groove pressing accumulates strain to break the original grain and refine metal materials so as to improve the plasticity and superplasticity.Constrained groove pressing is a method of severe plastic deformation,which does not change the appearance of the material shape and size.but introduces large amount of stain in deformation process to make grain internal dislocation density increases,forming dislocation walls and eventually turning them into high angle grain boundary,so as to achieve the goal of refining grains.The technology has applied in low carbon steel,aluminum,pure copper metal and achieved good results.In this paper,through the numerical simulation and experiment method,The thesis studied constrained groove pressing of AZ31 magnesium alloy plate,analyzed the influence of CGP on mechanical properties and microstructure and revealed the changes of mechanical properties after post deformation annealing.The main research contents are as follows:With finite element simulation technology,the magnesium alloy CGP deformation process is built based on Deform software.According to the changes of the loading,the grid deformation,the material flow and the distribution of the strain field in the deformation process,The change of mold and plate was analyzed,the deformation mechanism and strain distribution of the plate were studied.The basis of molds and experiments designing were established.The CGP experiments of AZ31 magnesium alloy were carried out.By adjusting the deformation temperature,deformation rate,different times and patterns of CGP,The influence of different CGP deformation parameters on the magnesium alloy sheet was analyzed,and the optimal conditions of the CGP deformation of the magnesium alloy were discussed.The tensile test of the CGPed sheets were carried out to analyze the influence of CGP on the mechanical properties in different directions.The influence of CGP deformation on the grain structure of the sheets was revealed by metallographic observation.The post deformation annealing experiment were carried out to analyze the influence of mechanical properties and grain size under different annealing process through to the annealing temperature and annealing time adjustment and discuss the the optimal annealing conditions.The heat tensile experiment and microstructure observation were carried out to research the changes of macro properties and microstructure in the post deformation annealing. |
