Study On Bauschinger Effect Of AZ31b Magnesium Plate In Straightening Process

With the development of high technology and the improvement of technical level,the demand for new material performance and quality is increasing.As a new structural material,AZ31 B magnesium alloy sheet has excellent performance features.After the plate is prepared and formed,there are often plate shape defects such as wave,ladle bend,sickle,etc.,which must be refined to meet the needs of use.In the roll straightening process,the sheet is in a reciprocating bending state,and the Bauschinger effect is significant,especially for magnesium alloy plates.However,Bauschinger effect is not considered in the traditional straightening model,which leads to a large deviation in straightening accuracy.In order to improve the straightening precision and efficiency,the Bauschinger effect of AZ31 B magnesium alloy sheet in the straightening process has become one of the key factors.In this paper,based on the mixed hardening model of Chaboche work hardening model and isotropic hardening model,combined with the calculation of equivalent plastic stress and surface strain in the traditional straightening theory,the stress calculation formula of the sheet metal in the deformation process is deduced,and the important factors affecting Bauschinger effect are analyzed systematically.Secondly,the AZ31 B magnesium alloy material model and threepoint bending model were established in this paper.By calculating the reciprocating bending process,the stress curve and BSP parameter curve of the sheet were obtained.Thirdly,use a universal testing machine to conduct a threepoint bending test to analyze the stress and BSP parameter changes of the plate during reciprocating bending deformation.Finally,metallographic experiments were used to analyze the changes of microstructure in the plates before and after deformation,and to explore the microscopic mechanism of Bauschinger effect.The results show that the Bauschinger effect and hardening phenomenon exist in the reciprocating bending process of the AZ31 B magnesium alloy sheet,and the Bauschinger effect is most obvious in the bending deformation of the first straightening unit.At the same time,the Bauschinger effect increases with plate thickness,pressure and speed,but the degree is not the same.Bauschinger effect,hardening phenomenon and material deformation mechanism are closely related to the detwinning effect.The detwinning effect in the first compression and then tension region leads to the Bauschinger effect in the material,while the dislocation slip deformation in the first tension and then compression region leads to the hardening phenomenon.