Effects Of Texture And Grain Size On Yield Strength And Twinning Activation Of Magnesium Alloys

This article is committed to exploring the application of composite Schmid factor(CSF)in evaluating the anisotropy of mechanical properties and twinning activation of magnesium alloys.To this end,the commercial AZ31 hot-rolled plate and extruded rod were used as raw materials and a series of specimens with different grain sizes were obtained by heat treatment.Then the mechanical properties including uniaxial tension and compression were measured by a universal testing machine.Combined with scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD)and Schmid factor(SF)analysis,the dislocation slip and twinning mechanism under various deformation conditions were studied.The relationship between the yield strength of magnesium alloys at room temperature and the activation of slip and twinning was systematacially studied using CSF,and the mechanism of twinning activation and variant selection in magnesium alloys dominated by slip deformation wasfocally investigated.The major conclusions are summarized below:(1)For tension,the plate deformed along RD has a larger average CSF value than the rod deformed along ED,that is,the overall accommodation ability of the macro stress and local stress of the plate is better than that of the rod,so that the plate will be more likely to yield;For compression,the average CSF value of the plate is greater than that of the rod,that is,the plate compressed along RD has better overall strain accommodation ability,so the compressive yield strength of the plate is lower than that of the rod.The above results show that CSF can well explain the phenomenon of different yield strength caused by the difference in texture of the plate and rod.The greater the CSF value of the polycrystalline magnesium alloys,the lower the yield strength.(2)By setting a reasonable CRSS ratio,the normalized CSF value can be obtained,and the accommodation mode between extension twinning,basal slip and prismatic slip can be judged by this.By comparing the mechanical properties of specimens with different initial textures,it was found that CSF can basically reflect the anisotropy and the tension-compression yield asymmetry of magnesium alloys.(3)The trend of twinning activation is similar when tension and compression along the 45°from c-axis of the plate,but the effects of macro stress and local stress on the twinning activation and variant selection are different.Calculating the distribution of SF and SF rank of the twins,it was found that the SF of the twins activatedin magnesium alloys dominated by basal slip is scattered and not high,and showed distinct non-Schmid behavior.The average SF of twins in T-45° specimens is relatively higher than that in C-45° specimens.Analysis of the slip-twin interaction revealed that {10-12}twins were mainly nucleated by the stimulation of basal slip in adjacent grains,and the variant selection primarily depends on the local strain accommodation.In addition,the efficiency of slip-twin transfer in compression is better than that in tension.(4)CSF can effectively evaluate the trend of twinning activation and yield behavior of magnesium alloys dominated by slip deformation.The calculation indicates that all twins activated in tension and compression along the 45° from c-axis of the plate have CSF rank 1 or 2.Compared with SF analysis,it was revealed that CSF combining macro stress and local stress can better explain the variant selection of slip-induced twins.