| Magnesium and its alloys,as one of the most potential lightweight materials at present,have the advantages of high specific stiffness,high specific strength,good machining performance and easy recycling and reuse,et al.They have wide application prospects in automotive,electronic 3C,aerospace and other fields.However,a strong basal texture can be formed easily due to during the traditional processing techniques,leading their poor plasticity.Especially their deformability at room temperature is seriously insufficient,which greatly limits their production and subsequent applications.Therefore,in this paper,a bimodal non-basal texture AZ31 magnesium alloy sheet with a deviation of ± 40 ° in the rolling direction(RD)was prepared through ECAR-CB-A.In the previous test,it was found that the maximum one single pass reduction of this special bimodal non-basal texture sheet during cold rolling was as high as32%,while the basal texture sheet don't exceed 22%.Therefore,the cold rolling formability of this special texture sheet has been greatly improved compared with the traditional AZ31 magnesium alloy sheet.In order to study its rolling plastic deformation behavior and deformation mechanism at room temperature,three types of 0.1m/s,0.2m/s and 0.4m/s were designed.At different rolling speeds,two kinds of plates with strong basal texture and bimodal non-basal texture are subjected to multi-pass cold rolling.Through Optical Microscope(OM),X-Ray Diffraction(XRD)and Electron Backscattered Diffraction(EBSD)and other detection methods,the effect of different initial textures and different rolling speeds on the microstructure evolution of AZ31 magnesium alloy sheets during room temperature rolling are studied,which has laid a certain theoretical foundation for the industrial production of high performance magnesium alloy sheets.The main research conclusions are as follows:(1)The effect of initial texture on the cold rolling formability and microstructure of AZ31 magnesium alloy sheet: In the cold rolling process,dislocation slip has always been the main deformation mechanism for basal-textured sheets,and twinning hardly participates in the contribution,the c-axis of the crystal grains will gradually deflect to the RD direction during the entire cold rolling process due to the higher activity of the pyramidal <c+a> slip.while for the sheet with bimodal non-basal texture,both dislocation slip and {10-12} tensile twins are involved in the early stage of deformation,{10-12}tensile twins prefers to sustaining plastic strain and its activated twinning variants mainly rotate is initial grain orientation to about ND during cold rolling process.Besides,{10-11} compression twins and {10-11}-{10-12} secondary twins begin to occur after 3rd pass of cold rolling.The former one trends to rotate its initial orientation away from ND,while the latter one prefers to rotate its initial orientation towards ND.However,as a whole,the texture of the whole cold rolling process shows a trend of converging from the double peak to the ND direction.The Schmid factor of commonly used slip systems and twin systems in the rolling force state is calculated by matlab programming.Find that the SF of the basal <a> slip and {10-12} tensile twinning of the sheet with basal texture are very low,while the value of the sheet with bimodal non-basal textures are more higher.What's more,the greater the deflection angle of the c-axis along the RD direction,the more conducive to {10-12} tensile twins,which is the main reason for the capability about sustaining plastic strain in sheet with bimodal non-basal texture is superior to that in sheet with basal texture,so as to the cold rolling performance.So in the case of a cold rolling reduction of 10% per pass,the cumulative reduction of the sheet with bimodal non-basal texture is as high as 39.2%,which is twice the cumulative reduction(18.3%)of the sheet with basal texture.(2)The effect of rolling speed on the microstructure evolution and texture of AZ31 magnesium alloy sheet during cold rolling: In the case of a single-pass reduction of 10%,three different cold rolling speeds(0.1m/s,0.2m/s and 0.4m/s)are used for multi-pass cold rolling of the sheet with bimodal non-basal texture.The three types of sheets have edge cracks at a cumulative reduction of about 40%.The rolling speed is not important for the cold rolling formability of this special bimodal non-basal texture sheet.In the early stage of cold rolling,for basal texture sheets,the number of {10-12} tensile twins increases with the increase of rolling speed,while for bimodal non-basal texture sheets,the number of{10-12} tensile twins decreases slightly with the increase of rolling speed,but their dislocation density increases greatly.In the later stage of cold rolling,{10-11}compression twins and {10-11}-{10-12} secondary twins appeared in the sheets.In the early stage of cold rolling,the c-axis of the crystal grains of the cold rolled plates at the three speeds will be rotated from the bimodal position to the ND direction.Among them,the bimodal non-basal texture sheet with the highest cold rolling speed(0.4m/s),The shrinking trend is the strongest,and the strongest point of the texture has been closed to about 15° deflection from ND to RD.This is due to the fact that the basal <a> slip will cause the c-axis rotate to the ND. |
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