| As the lightest metal structural material,magnesium alloy has excellent specific strength,specific rigidity and other mechanical properties,as well as good damping performance,electromagnetic shielding performance and high recycling capacity and other physical properties,in automotive,aerospace,aviation,electronics,etc.The field has huge application prospects.Due to the close-packed hexagonal structure of magnesium alloys,the movable sliding system is limited,resulting in poor processing performance at room temperature,which restricts its application.Therefore,for magnesium alloys with different initial structures,it is of great theoretical significance to study a suitable hot processing technology to improve their hot workability and to reveal the law of change in the microstructure during hot processing.In this paper,three Mg-1.2Zn-0.2Y alloys with different initial grain sizes were prepared using as-cast Mg-1.2Zn-0.2Y alloy by hot extrusion and different heat treatment.The hot deformation behavior of Mg-1.2Zn-0.2Y alloy was explored by Gleeble hot compression experiment.The microstructure observation and analysis were combined with the constitutive equation and hot processing maps to study the hot workability characteristics and deformation mechanism of the coarse and fine grain Mg-1.2Zn-0.2Y.By comparing the microstructure of the three grain size Mg-1.2Zn-0.2Y alloys after deformation,the effect of grain size on the hot deformation behavior of Mg-1.2Zn-0.2Y alloy was analyzed.The true stress-true strain curve shows that the deformation resistance of the three grain sizes Mg-1.2Zn-0.2Y decreases with the increase of temperature and the decrease of the strain rate,and the trend of true stress with the increase of true strain is roughly the same.That is,it increases rapidly and then slowly increases to the peak,and finally decreases slightly or remains stable.The Arrhenius equation is used to describe the relationship of deformation temperature and strain rate of coarse-grained and fine-grained Mg-1.2Zn-0.2Y alloys on the flow stress.The calculated thermal deformation activation energies of coarse-grained and fine-grained Mg-1.2Zn-0.2Y alloys are 275.9 k J/mol and 142.8 k J/mol,respectively.Based on the dynamic material model,the hot working drawings of coarse-grained and fine-grained Mg-1.2Zn-0.2Y alloys were constructed.The results showed that the workability of Mg-1.2Zn-0.2Y alloys with different structures was different.The optimal processing area of coarse-grained Mg-1.2Zn-0.2Y alloy at strain 0.5 is 420-450°C,0.001-0.01 s-1,and the maximum dissipation efficiency is 56.88%;fine-grained Mg-1.2Zn-0.2Y When the strain is 0.5,the optimal processing area is 340-360°C,0.5-1 s-1,and the maximum dissipation efficiency is 61.64%.In addition,the dynamic softening mechanisms of both Mg-1.2Zn-0.2Y alloys are dynamic recovery and dynamic recrystallization..The deformation mechanism and microstructure change of Mg-1.2Zn-0.2Y alloy are closely related to grain size,deformation temperature and strain.With the increase of strain,the ratio of high kernel average misorientation area and high angle grain boundary of the three Mg-1.2Zn-0.2Y alloys increased;after the deformation,the basal texture weakened significantly,and the coarse-grained Mg-1.2Zn-0.2Y alloy has a stronger texture orientation after deformation,and the texture orientation of the fine-grained and medium-grained Mg-1.2Zn-0.2Y alloy is more uniform.As the grain size increases,the average Schmid factor of the Mg-1.2Zn-0.2Y alloy increases,confirming that the alloy undergoes non-basal slip during the deformation process;in addition,fine-grained and medium-grained Mg-1.2Zn-0.2Y alloys undergo more dynamic recrystallization and dynamic recovery.With the increase of temperature,the average Schmid factor of Mg-1.2Zn-0.2Y alloy also increases,and the dynamic recrystallization is promoted at high temperature. |
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