Research On Microstructure Evolution Of AZ31 Magnesium Alloy During Bending-flattening Combined Deformation

AZ31 magnesium alloy belongs to dense hexagonal crystal structure,and its plastic forming performance is poor at room temperature,which limits the application range of deformed magnesium alloy.Therefore,improving the forming properties of magnesium alloys at room temperature is the main research content to expand the application scope of magnesium alloys.In this work,the material flow rule during the bending-flattening combined deformation of AZ31 magnesium alloy was researched by numerical simulation with experimental method,and analyzed the influence of technological parameters on the microstructure and mechanical properties.The results show that the bending-flattening combined deformation method can effectively improve the micro structure and mechanical properties of AZ31 magnesium alloy.The following research results were obtained:(1)De FORM-3D software was used to conduct numerical simulation research on the material flow rule during the bending and flattening composite deformation of AZ31 magnesium alloy,analyze the variation rule of stress field,strain field,temperature field,failure coefficient,die load force and so on,and optimize the process parameters and die structure.(2)Experimental study was carried out on the bending-flattening combined deformation of AZ31 magnesium alloy,and the influence rule of deformation process parameters on the micro structure was analyzed.The results showed that the maximum grain size refinement degree of the magnesium alloy after the bending-flattening combined deformation reached 67%.(3)The mechanical properties of magnesium alloy sheet after combined deformation were tested.The results showed that the mechanical properties of AZ31 magnesium alloy after combined deformation are significantly improved,the maximum tensile strength is increased by 15.8%,the yield strength is increased by 47.3%,and the maximum elongation is increased by 24.6%.(4)The cellular auto-ma-ta(CA)method was used to numerically simulate the evolution law of micro structure during the combined deformation of AZ31 magnesium alloy with bending and flattening,and the influence law of deformation process parameters on micro structure was analyzed.The simulation results were of certain guiding significance.(5)EBSD detection and analysis were carried out on AZ31 magnesium alloy after composite deformation.The results showed that the texture on {0001} crystal surface of AZ31 magnesium alloy was weakened after the composite deformation of bending and flattening,with the maximum weakening degree reaching 39.7%.When the composite deformation temperature is 290℃ and the tooth spacing of the die is 20 mm,the number of grains deformed after extrusion by the die is the largest,and the grain refining effect is the best.