Study On Deep-Drawing Mechanism Of AZ31 Wrought Magnesium Alloy

Deep-drawing is an important process for forming thin-wall voided parts under plastic deformation process.Therefore,researching on the deep drawing process of magnesium alloys has been widely concerned.In order to prepare thin-wall voided parts,research scholars have done a large number of investigations on the deep-drawing of magnesium alloy.Magnesium alloy sheets are in the state of multiaxial stress and complex strain path during the deep-drawing process.At present,the development of magnesium alloy forming process has encountered a bottleneck due to the uncertain effect of deformation mechanism on the mechanical properties and formability of magnesium alloy sheets under multiaxial load and complex strain path.By combining multi-scale simulation and experiments,this thesis investigated the deformation mechanism of blank holder areas and punch radius areas under deep-drawing process.Specifically,this thesis investigated the starting conditions,expansion rules of slips and twins during the deep-drawing process of magnesium alloy,and revealed the the deformation mechanism of magnesium alloy in deep-drawing process.The main research contents and results were shown as follows:Simufact.forming software was used for simulating of cylinder drawing experiments.By simulating different process parameters,such as forming temperature,diameters of sheets and blank holder forces,the influence of different parameters on the forming quality of magnesium alloy cylindrical parts was studied and the optimum parameters were selected for the cylindrical deep-drawing process.According to the experimental results,the thin-wall voided parts had the best forming effect when the forming temperature was 200°C,blank holder force was 6kN,sheet size was 100 mm,limit drawing ratio was 2.0.Combining with the experimental results and multi-scale simulation results,the deformation mechanisms of different areas under deep-drawing process were analyzed at room temperature.(i)The blank holder area was under triaxial stress state during the deep-drawing process.Under this stress state,the deformation mechanisms of magnesium alloy were basal slip,prismatic slip and tension twins.After the process of deep-drawing,lamellar microstructures formed in the matrix structure and the texture was deflected;(ii)The die radius area was under state of two compressive stresses and one tensile stress.Thedeformation mechanism of the die radius area was similar to the deformation mechanism of blank holder area.This deformation mechanism resulted in twin continued to expand and the content of twins area was more than that in the blank holder area.(iii)The lateral wall area was under tensile stress state.After the sheet material of die radius area flowed into the area at the round corner,the deformation mechanisms of this area were detwinning and basal slip.Then,the quantity of twins decreased and the basal texture had become the dominant texture type.The deformation mechanisms of different areas under deep-drawing process were analyzed at warm temperature.(i)Basal slip,prismatic slip and pyramidal slip were started in the blank holder area.The thickness of lamellar microstructures was thin and the content of it was less.Dynamic recrystallization grains were the major grians and the texture deflected;(ii)The dominant deformation mechanism in die entrance area was similar to that in the blank holder area.As the deformation progressing,the dynamic recrystallization grains were grew up,and most of the twins occupied the whole grain,with the texture deflecting;(iii)Due to the occurrence of detwinning in the lateral wall area,the main texture type was basal texture.By analyzing the deformation mechanism of the cylinder during deep-drawing process,the drawing die of magnesium alloy notebook shell was designed and the forming process was optimized.Finally,the notebook case which met the performance requirements was prepared at room temperature by deep-drawing process.