Study On The Process Of Warm Tension Forming Of U-shaped AZ31 Magnesium Alloy

With the development of science and technology,high technique and complex structures supplied to aerospace,rail transport or other industries increased a lot.As typical lightweight material,AZ31 magnesium bending profile has some weak characteristic such as passive form ability in room temperature,tradition bending forming method result in poor geometric accuracy and surface quality.Modify bending method which based on theoretical analysis,simulation tool and experiments analysis has been proposed.Warm tension-rotation bending has been investigated in extruded and U sharped AZ31 magnesium alloy profile.Theoretical analysis of bending has been achieved,stress-strain status in both side of profile has been discussed,springback rules has been analyzed.The mechanical properties,microstructure and fracture morphology of extruded AZ31 magnesium alloy profiles at different temperatures were investigated by Gleeble-3800 thermal-mechanic simulator uniaxial tension test.The warm stretching process of U-sharped AZ31 magnesium profile with thin wall was simulated by using 3D thermo-mechanically coupled finite element model.Variation of temperature filed and stress filed were simulated in different temperature model,influences of bending process parameters such as temperature and pre-stretch rates has been simulated,variation rules of process characteristics such as stress,strain,temperature,springback and geometric dimension has been summarized.Warm tension-rotation bending experiments of U sharped AZ31 magnesium alloy profile has been concluded on improved tension-rotation bending equipment.Effect of process characteristics has been analyzed and compared with simulation results.The physical experiment results about the effects of technological parameters on springback characteristics accord with the computer simulation results.The workpiece in U sharped AZ31 magnesium alloy profile can be gained,which with small springback rate and good surface quality,through the following process.The AZ31 magnesium alloy profile is heated to 170? by local heating method,at the same time,the pre-stretch rate of 0.2%is brought to end region of profile,and the pre-stretch is remained until the profile is bent up to 110°.With the increasing of temperature,the springback angel and springback rate decrease.If the temperature is higher than 170?,the forming property of AZ31 magnesium alloy profile becomes better,but the deformation is so high that the workpiece is thinned in bending position.With the increasing of pre-stretch rate,the springback angel and springback rate decrease.When the pre-stretch rate increases to some degree,with the further increasing of pre-stretch rate,the springback rate changes little.With the increasing of bending angel,the springback angel increases.When bending angel is greater than 110°,the distortions will happen at inwall of AZ31 magnesium alloy profile.