Numerical Simulation And Experimental Research Of AZ31 Mg Alloys Processed By Expansion-continuous Shear Deformation

In currently,magnesium and magnesium alloys are lightest structural metallic materials,and have broad application prospects in the automotive industry,aerospace and 3C electronics et al.However,the magnesium alloy has a close-packed hexagonal crystal structure,which leading to poor plastic deformation ability at room temperature and a low absolute strength.There is a great limitation on the deep plastic processing ability and application of the magnesium alloy.Therefore,improving the strength and toughness of magnesium alloys,room temperature formability has become the key to expanding its application.Although high-performance magnesium alloys can be obtained by traditional extrusion,the disadvantages of long processing cycle,high cost,high requirements for mold equipment,uneven strain and flow rate are also exist.It is difficult to put into practical industrial production.Therefore,on the basis of in-depth understanding of the traditional extrusion deformation process,a new extrusion technique,expansion-continuous shear deformation,was proposed to prepare the AZ31 magnesium alloy sheet,which can effectively refine the grain structure and weaken the texture,improve the comprehensive mechanical properties of magnesium alloy.The DEFORM-3D finite element simulation system was used to deeply analyse the equivalent strain,stress,metal velocity of AZ31 magnesium alloy during extrusion with different mold cavities to optimize the mold structure parameters;The microstructure was observed by optical microscope,electron backscatter diffraction and scanning electron microscope.The mechanical properties of extruded AZ31 magnesium alloy sheets were studied by tensile test.The main research contents and results of this paper are as follows:(1)The deformation behavior of magnesium alloy blank in the process of expansion-continuous shear deformation extrusion with different die structures was analyzed,including the equivalent strain,stress,metal velocity and load.When the expansion ball diameter D₁ is30 mm,the opening position length L is 8 mm,and the corner shear angles?and?are 120°,the magnesium alloy billet undergoes expansion-continuous shear can obtain a large and uniform equivalent strain,a small change of the gradient of the metal velocity change,the strong formability of sheet extrusion,and at the same time,the damage to the extrusion die can be reduced to a larger extent.(2)The effects of expansion-continuous shear deformation at different temperatures on the grain structure and mechanical properties of magnesium alloy plates were discussed.The average grain size of AZ31 magnesium alloy can be refined to?2.5?m after extrusion at 300?.With the increase of extrusion temperature,the grain size of magnesium alloy gradually grows up.The degree of unevenness of microstructure become large and texture strength gradually decreases.The magnesium alloy plates prepared at 300?show excellent comprehensive mechanical properties.The yield strength and tensile strength of the final formed plates are up to 195MPa and 310MPa,respectively,and the elongation is 19.2%.A large number of dimple emerges in the tensile fracture,which can be attributed to ductile fracture.(3)At the initial stage of expansion-continuous shear deformation,a large amount of dislocation jamming and has large stress concentration exist inside the magnesium alloy,resulting in the existence of tensile twins and double twins.The severe plastic deformation can produce a large and uniform equivalent strain in the extrusion billet,which can effectively trigger dynamic recrystallization.Moreover,the orientation of fine grains is scatter,which can effectively refine the grain and weaken the texture.