Study On Electrothermal Coupled Drawing Process Of AZ31 Magnesium Alloy Cap

Cap parts are widely used in all kinds of equipment as base parts,its application range is wide and often affects the service life of mechanical equipment.Magnesium alloy,as a lightweight metal structural material,has the advantage of lightweight hat parts made of magnesium alloy,therefore,it has great application potential in aerospace,automobile transportation,electronic communication and other fields.However,due to the hexagonal crystal structure,the plastic formability of magnesium alloy is poor at room temperature,which is difficult to be processed by traditional stamping method.In recent years,it has been found that the electroplastic effect of pulse current can effectively improve the forming effect and forming quality of metal.However,when the current density is high,more energy consumption will be generated,which is difficult to be widely used.Therefore,reducing current density is one of the key points in the field of electroplasticity.In this paper,AZ31 magnesium alloy was used as the experimental material,and the electroplastic effect of pulsed low current was used to reduce energy consumption and expand the processing range of cap parts on the basis of meeting the technical requirements.In this paper,electroassisted tensile tests were carried out on magnesium alloy under different current conditions（0A-35A\0V～0.94V）to obtain the optimal process parameters,and tensile tests were carried out on magnesium alloy obtained by pulsed current pretreatment and non-electric oil bath treatment to verify the electroplastic effect,and metallographic analysis was conducted to explore the evolution of the microstructure of magnesium alloy after pulsed current treatment.Secondly,Dynaform software was used to construct a drawing die for magnesium alloy cap parts with different process parameters（die clearance,die fillet radius,die holding force）.By finite element analysis on the defects and thickness distribution of the drawing parts such as wrinkle and crack,the process combination of minimum maximum thinning rate and minimum maximum thickening rate was obtained.Finally,the influence of thermal effect and electric effect on the forming limit and quality of cap parts was explored through thermal and electrothermal coupling deep drawing tests,and the optimal process parameters were obtained.The results show that:（1）When the current density is 3A/mm^2,the twins in the magnesium alloy microstructure basically disappear and some of the microstructure recrystallizes after pulsed current treatment.When the current density is 5A/mm²,the twins in the magnesium alloy microstructure disappear completely after pulsed current treatment,the grain boundary is relatively continuous,and all the microstructure recrystallization occurs.（2）The optimal process parameters of the drawing die were obtained by Dynaform finite element simulation.The process combinations that made the maximum thinning rate of the cap part minimum and the maximum thickening rate minimum were as follows:die clearance 1.2mm,die holding force 10k N,die fillet radius 6mm.（3）The electrothermal coupling drawing process can improve the formability of AZ31 magnesium alloy sheet to a certain extent.When the temperature reaches 240℃,the ultimate drawing depth and maximum reduction rate of AZ31 magnesium alloy sheet increase.Compared with the hot drawing at the same temperature,the ultimate drawing depth increases by 0.6mm and the ultimate drawing depth increases by 7.4%.