Study On Microstructure And Mechanical Properties Of AZ31 Magnesium Alloy Sheet With Equal Channer Angular Rolling-single Pass Bending Deformation

As the lightest metal material on the earth,magnesium alloy has the advantages of high specific strength and specific stiffness,good thermal conductivity,easy processing and easy recovery,etc.It is called "the most potential green engineering material in the21 st century".It plays an important role in more and more fields,especially in the automotive industry,aerospace and defense military fields.However,due to the characteristics of magnesium crystal structure and the formation of strong basal texture at room temperature,the plastic forming property of magnesium alloy at room temperature has become an important factor limiting the development of magnesium alloy.Aiming at the poor plastic forming properties of magnesium alloys,aiming at improving the plastic forming ability of magnesium alloy sheet,the ECAR-B process of equal channer angular rolling-single pass bending deformation(ECAR-B)is first put forward in this paper,based on the control of grain orientation and the improvement of forming ability of magnesium alloy sheet.The friction is formed between the roll and the plate,the magnesium alloy plate can pass the mold smoothly under the action of friction.Based on finite element simulation and experiment,the deformation behavior of ECAR-B magnesium alloy sheet under different die structure is analyzed systematically.Effects of different process parameters on microstructure and grain orientation of ECAR-B magnesium alloy sheet;The purpose of this study is to explore the fundamental factors of poor plastic forming of magnesium alloy sheet.the structure of the die is optimized and magnesium alloy sheet with good performance can be preparated;Study on Microstructure,Mechanics,formability and texture Evolution of magnesium Alloy sheet during the process of equal channer angular rolling-single pass bending deformation;The relationship between microstructure,texture and formability is clarified;The main contents are as follows:(1)Deformation behavior of ECAR-B magnesium alloy sheet under different die structuresThe finite element simulation shows that with the increase of the inner chamfer radius and channel clearance,the shear action of the plate at the corner gradually weakens,and the deformation behavior of magnesium alloy sheet at the corner also changes.The deformation behavior of magnesium alloy sheet at the corner changes gradually from shear deformation to twice bending deformation.After the final optimization,the die structure:the inner chamfering radius is r1=2mm,the bending radius is r2=6mm,and the gap of thedie is H=1.48 mm.(2)Analysis of microstructure and grain orientation of ECAR-B magnesium alloy sheet under various process parametersBased on the temperature,rolling speed,channel clearance and reduction experiment on process parameters showed that with the increase of speed,the surface quality of magnesium alloy sheet is good,the grain structure is more uniform,and the grain refinement effect is remarkable.The grain orientation changes from strong basal grain orientation {0001} to {10-10} non-basal grain orientation;With the increase of temperature,the grain size of magnesium alloy plate grows up,the twinning volume fraction increases obviously,the non-basal slip is activated,and the grain orientation changes from the basic grain orientation to the non-basal grain orientation.With the increase of reduction,the deformation of magnesium alloy plate increases.Under the condition of large strain,the twinning volume fraction increases obviously,and the grain orientation is changed.The non-basal grain orientation {10-10} gradually evolved into the base grain orientation {0001} with large reduction.With the increase of channel gap,the equivalent strain decreases and the grain size increases.The volume fraction of twinning decreased obviously and the grain orientation changed obviously from non-basal grain orientation to grain orientation.(3)The process parameters of equal channer angular rolling-single pass bending are optimized.According to the finite element analysis and experimental research,the optimized process is as follows: the finishing rolling press is 5%,the clearance is 1.48 mm,the plate temperature is 550 degrees,and the finishing rolling speed is 0.4m/s.(4)The deformation,shear deformation,microstructure and texture evolution of ECAR-B plate are compared and analyzed.It is found that the grain size is coarse,the dynamic recrystallization is less,and a small number of twins appear locally for the common rolled magnesium alloy sheet.The plate exhibits typical basic texture characteristics.After shear deformation,the number of twins,volume fraction and dynamic recrystallization of magnesium alloy sheet increased obviously,and the grain deflected to RD direction at a certain angle,and the basal texture strength of magnesium alloy sheet decreased.The grain size of ECAR-B plate becomes smaller,the amount of recrystallization increases at the local grain boundary and twin boundary,and the basal texture strength decreases significantly,and the columnar texture is gradually formed.After annealing,the texture of ECAR-B magnesium alloy sheet changed significantly after shearing deformation,except that the texture type of common rolled sheet did not changeobviously.Finally,a bimodal separated non-basal texture with 45 °deflection along RD was formed in ECAR-B sheet.(5)Through the cupping test,the common rolling deformation and the room temperature forming performance of ECAR-B sheet were studied.The results showed that the cupping value of the ordinary rolled deformation plate was only 5.2mm,while for the ECAR-B sheet,the cupping value could reach 7.78 mm.