Investigation Of Bending Formability Of Magnesium Alloy Sheet

As the lightest metal structural material,magnesium alloy has been widely used in electronics,automotive and aerospace industries in recent years due to its high specific strength and specific stiffness and good damping properties.However,most magnesium alloys have a close packed hexagonal(HCP)crystal structure,exhibiting poor elongation and formability at room temperature,which limits the wide application of magnesium alloys to a certain extent.Therefore,it is of great significance to develop the forming technology of wrought magnesium alloys.In this paper,the mechanical properties of commonly used wrought magnesium alloy AZ31 and LAZ531(ie 5% Li in AZ31)were studied.The bending mold of magnesium alloy sheet was designed and optimized.The bending process of sheet metal was analyzed by finite element software numerical simulation and the bending was completed.Based on the microstructure,the bending forming mechanism of AZ31 and LAZ531 magnesium alloy sheets was studied.The effects of bending radius on springback and neutral layer migration were analyzed.Through the analysis and characterization techniques of metallographic microscope(OM),X-ray macro-texture and electron backscatter diffraction(EBSD),the microstructure evolution of magnesium alloy sheet during bending forming was systematically analyzed.The main conclusions were as follows:(1)A set of molds with different bending angles and different bending radii were designed.The numerical simulation analysis of different bending forming processes was carried out by finite element software.It was found that the stress-strain decreased with the increase of the bending radius,and the strain along the thickness direction of the sheet was a certain gradient distribution,the intermediate position strain is the largest;(2)When the AZ31 is bent into a V-shape,the neutral layer is displaced to the outer stretch region.There are significant differences in the microstructure of the inner and outer layers in the thickness direction of the sheet.The plastic deformation mechanism of the outer layer is mainly dominated by slip,while the plastic deformation mechanism of the inner layer is mainly represented by {10-12} tensile twinning.The deviation of the middle layer is mainly caused by the asymmetry of the plastic deformation mechanism of the inner and outer layers along the thickness direction of the magnesium alloy sheet;(3)AZ31 sheet is deflected by TD after adding Li,the texture of the base surface of the sheet is greatly weakened,and the anisotropy of the material is reduced;mechanical properties such as yield strength,tensile strength decrease,yield ratio decrease,and elongation Greatly improved,the forming performance of the sheet is greatly improved;(4)LAZ531 bending forming performance is significantly better than AZ31,the larger the inner bending radius,the larger the rebound value,and the twin crystal is gradually reduced.During the bending deformation process,the strain is mainly concentrated at the central angle ? of the bending zone.The stress strain is the largest at the geometric center of the outer surface of the bending plate with the central angle ?.The crack is first generated at the geometric center of the outer surface and grows longitudinally to both sides.