Study On The Effect Of Current On The Fracture Behavior Of AZ31B Magnesium Alloy And S32750 Duplex Stainless Steel

In the past decades,with the increasing number of research results on electro-plasticity,electrically assisted forming?EAF?became a promising forming technology.Instead of heating up the workpieces in furnaces,EAF processes heat up the workpieces directly,which raises the energy efficiency when compared to traditional hot forming.Nowadays,numbers of researches focus on applying current to processes like rolling,wire drawing,deep drawing,upsetting,and progressive forming,and has enhanced the forming limit of various alloys.However,it has been found that for some alloys,like AZ31B magnesium alloy and Ti6Al4V titanium alloy,the elongation was reduced when current was applied.With the rapid development of electric vehicles and aerospace industry,light alloy like magnesium shows its advancement in energy saving and possesses a wide application prospect.To investigate the effect of current on the forming limit of light alloys,a coupled thermo-electro-mechanical finite element model was built in the commercial FEM software ABAQUS to analyze the electrically assisted?EA?tension of AZ31B magnesium alloy.And an experiment was conducted to reveal the effect of current on the forming limit of duplex steel,S32750.The conclusions are as follows:?1?The flow stress curves of annealed AZ31B at 323K⁵73K,0.001s^-10.1s^-1 in EA tension were fitted with Hocket-Sherby model,and a flow stress model taking into account of temperature and strain rate was established,based on which the flow stress at 0.0001s^-1 and 1s^-11 was extrapolated.By putting the flow curves into FEM model,the calculated load-stroke curves anastomose the experimental ones.?2?A coupled multi-physical field analysis was performed based on the FEM software ABAQUS to simulate the EA tension of AZ31B magnesium alloy.The simulation of non-current?NC?tensile test at the same temperature and strain rate was also performed.The relationship among current,temperature and deformation distribution along the specimen's gauge during EA tension process was obtained.And the evolution of the physical fields was analyzed.It was found that during the EA tensile test,there is significant temperature non-uniformity along the length of the specimen,resulting in a non-uniform distribution of strain rate.It promotes necking of specimens and the elongation is significantly reduced.?3?By introducing the rupture strain into the finite element model,the forming limit of AZ31B magnesium alloy was discussed.The calculation result shows that although the elongation of the EA tensile specimens are50%shorter than their isothermal counterparts,they share a similar fracture strain at a given temperature and strain rate.The relationship between the fracture strain of AZ31B magnesium alloy and the Z parameter was built and the influence of temperature,strain rate and current on the fracture energy of AZ31B was calculated based on the Freudenthal fracture criterion.As the area reduction is not affected by current,it can be used to evaluate the ductility of AZ31B subjected to current.?4?EA tension and NC tension at same temperatures were conducted on S32750 duplex stainless steel.The result shows that current enhanced the elongation of S32750 by 10%compared to the NC ones without changing its flow stress.It has been proved that current has different effects on the forming limit of different alloys.