Investigations Of The Correlation Between Twinning And Mechanical Behavior Of AZ31 Magnesium Alloys

Twinning plays a critical role in plastic deformation of magnesium alloys.Twinning not only provides strainning along the c-axis to help satisfy the Von Mises criterion,but also alters the orientation of original grains and influences the activation of slip systems,which plays a great role in improving the plasticity and anisotropy of magnesium alloys at room temperature.In this paper,the twinning behavior and texture evolution of magnesium alloys during plastic deformation have been studied by electron backscatter diffraction(EBSD)and optical microscope(OM).DEFORM 3D is used to simulate the effective stress and strain of magnesium alloys during room temperature compression and bending,while viscoplastic self-consistent(VPSC)is used to simulate twinning and slips activities of magnesium alloys during uniaxial compression.Based on the observation and simulation results,the relationship between twinning and mechanical behavior of magnesium alloys was analyzed.The main research results are summarized as follows:For room temperature compression experiments,DEFORM 3D simulated point tracking results show that the equivalent stress and strain in the center region of specimen are smaller than those in the corner region.EBSD analysis show that a large number of {10-12} tensile twins,a small amount of {10-11} compression twins and{10-11?-{10-12} secondary twins are observed during uniaxial compression of extruded AZ31 magnesium alloys.With the increase of deformation,twins begin to thickening and coalescence,twin boundaries disappears,and dislocation slip leads to the formation of low-angle grain boundaries.VPSC simulation results show that in addition to the activation of tensile twins,basal slips and non-basal slips also contribute to the plastic deformation of magnesium alloys during uniaxial compression.Under loading perpendicular to ED,basal slips dominate the plastic deformation process,and the activity of basal slips and non-basal slip increase with the increase of deformation.When loading along ED,tensile twins dominate the plastic deformation before strain reaches 5%,and basal slips dominate the plastic deformation when the strain is higher than 5%.For repeated bending experiments,DEFORM 3D simulated results indicate that the stress states along Y axis of upper region in the process of bending,restoring and reverse bending are compression,tension,tension,respectively.The stress values of middle region along Y axis fluctuates around OMPa during repeated bending.In the process of repeated bending,the stress state of the lower region along Y axis changes from tension to compression,which is completely opposite to the stress state of upper region.EBSD analysis shows the twin types of repeated bending under different deformation are mainly {10-12} tensile twins.The upper region P1 undergoes same plastic deformation mechanism,twinning?detwinning?twinning and detwinning,in a bending?restoring?reverse bending process with different deformation amounts.When deformation is 2.5%,middle region P2 undergoes twinning?detwinning?detwinning in the third bending process;middle region P2 undergoes twinning?detwinning?twinning and detwinning at 5%.The increase of {10-12} extension twins at middle region P2 in the third bending process depends not only on the stress state,but also on the strain.The lower region P3 undergoes a small amount of twinning,a large number of twinning and detwinning in the three bending processes with different deformation.