| Different from the traditional magnesium alloy sheet forming process,based on the ordinary extrusion process,this paper designs a new sheet forming process,extrusion shear process,which is used to weaken the basal texture of the sheet and change its room temperature plasticity.At the same time,the bimetallic composite sheet is prepared by magnesium / aluminum alloy cladding extrusion shear,which not only optimizes the mechanical properties of magnesium alloy The grain of magnesium alloy is refined,and the corrosion resistance of magnesium alloy is strengthened with the help of the characteristics of aluminum alloy.In this paper,the forming process of magnesium alloy sheet and magnesium / aluminum bimetallic composite sheet is simulated by using DEFORM-3D finite element simulation software,and the distribution and change of grid,velocity field,temperature field and equivalent stress in the forming process are analyzed.Through the analysis of the microstructure,microstructure,element distribution and mechanical properties of the plate,the conclusions are as follows:1?Through the numerical simulation of the sheet forming process,it can be seen that in the Extrusion-Shear process,the area with high temperature rise and large equivalent stress are mainly concentrated in Zone I(Shear region).Through the analysis of the velocity field during sheet forming,it is found that the outer aluminum billet of composite sheet lags behind the inner magnesium billet.Through the analysis of the influence of process parameters such as extrusion temperature,extrusion speed and friction factor on the Load-stroke curve of composite sheet,it is found that the higher the extrusion temperature,the slower the extrusion speed and the smaller the friction factor,the smaller the maximum extrusion force required for sheet forming.Therefore,the best process parameters for sheet metal extrusion are as follows:extrusion temperature is 410 ?,extrusion speed is 2mm / s and friction factor is 0.1.2?Through the Extrusion-Shear experiment of AZ31 magnesium alloy,the magnesium alloy sheet with relatively flat surface is obtained.Through the metallographic structure analysis of the sheet in different extrusion areas and at different extrusion temperatures,it is found that with the extrusion shear process,the grain size of the plate decreases continuously,and The grain size distribution is relatively uniform.The average grain size in different extrusion areas is 35.25?m?14.72?m?9.37?m.The increase of temperature will lead to the grain growth of the formed sheet,but the increase of temperature is conducive to the improvement of sheet plasticity.With the increase of grain size,the section hardness of magnesium alloy sheet decreases gradually.When the extrusion temperature is 330 ?,370 ?and 410 ?,the hardness is 77.59 HV,75.32 HV and 71.76 HV in turn.Higher extrusion temperature will reduce the basal texture strength and increase the dispersion of magnesium alloy plate.3?AA6063 and AZ31 were extruded to obtain composite sheets with excellent bonding properties.Through the detection of composite sheets,it was found that: The increase of temperature can promote the recrystallization of magnesium alloy grains in the composite plate,and the grain size increases evidently.The average grain size at the extrusion temperature of 410? is 14.33?m.The Electron Back Scattered Diffraction analysis of the cross section of the composite plate shows that the two metals have metallurgical bonding due to the action of shear force,and the thickness of the bonding layer increases with the increase of temperature.The thickness of the bonding layer with the extrusion temperature of 410? is 16.94?m.The section of the bonding interface between the two metal matrix is analyzed by XRD.It is found that Mg17Al12 phase and Mg2Al3 phase are produced at the bonding interface.These two phases are Brittle hard phase.Therefore,the hardness at the bonding interface is large,about 127 HV.The fracture interface is mostly fluvial pattern and tear ridge,which is determined as brittle fracture.4?When the extrusion temperature is 370 ?,the grain orientation of magnesium alloy in the composite plate changes with the Extrusion-Shear process,but the(0001)basal plane of most grains is parallel to the ED direction,and the basal plane texture of(0001)basal plane is weakened;Compared with the upsetting area,the average value of Schmidt factor increases,and the part with SF value greater than 0.2increases;The proportion of recrystallization area in the forming area has nearly doubled compared with the upsetting area,from the initial 15.9% to 31.1%.5?The effect of temperature on magnesium alloy in composite forming sheet is also obvious.Firstly,with the increase of temperature,the grain orientation of magnesium alloy deflects,and the strength of basal texture decreased significantly.When the extrusion temperature is 330 ?,370 ? and 410 ?,the maximum texture strength is 24.89,18.27 and 16.27 respectively;The increase of temperature also increases the Schmidt factor of magnesium alloy,promotes the slip of magnesium alloy and improves its plasticity;With the increase of temperature,the difficulty of dislocation climbing is reduced,and the subcrystals are easier to move and polymerize,and then develop into recrystallized nucleation core,which increases the proportion of recrystallized grains,which is 16.2%,31.1% and 50.5%. |
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