Microstructure Evolution Of 7075 Aluminum Alloy By Rotating Reverse Extrusion

Among the various 7xxx series aluminum alloys,7075 aluminum alloy is widely used in structural parts manufacturing due to its high strength,high specific stiffness and fracture toughness.However,7075 aluminum alloy has poor plasticity at room temperature,it is difficult to deform when manufacturing complex parts,and only a small range of plastic processing can be performed.As a new method of large plastic deformation,the rotary reverse extrusion process increases the shear deformation through rotation,which makes the microstructure refine and the mechanical properties become stronger.And performance changes are unclear.Therefore,this paper takes 7075 aluminum alloy as the research object and uses the Deform-3D simulation software to explore the cup-shaped parts with a feed speed of 0.1mm/s and a feed speed of 0.5mm/s at 400 °C and 480 °C.At the same time,through metallographic microscope,electron backscatter diffraction technology,Vickers microhardness and other analysis and characterization methods,it is revealed that under different feed speeds at 400 °C and 480 ° C.The deformation mode,as well as the texture transformation and mechanical properties of the cup-shaped parts,provide experimental data and theoretical support for the preparation of high-performance 7075 aluminum alloy cup-shaped parts.The main conclusions obtained are as follows:Deform-3D simulation shows that the equivalent strain of the 7075 aluminum alloy rotary backward extrusion(RBE)cup is much higher than that of the conventional backward extrusion(CBE)in the two feed rates at 400 °C and the three deformations at 480 °C with a feed speed of 0.1 mm/s pressure,almost three times the original equivalent strain.When the feed rate is 0.1mm/s,the equivalent strain at 480°C is slightly higher than the equivalent strain at 400°C,but according to the SD value of the equivalent stress,the equivalent stress of the cup at 400°C can be obtained The distribution is more uniform than the equivalent stress distribution at 480°C.Compared with the cup with a feed rate of 0.5mm/s,the equivalent strain of the cup with a feed rate of 0.1mm/s not only does not increase,but also decreases.This is because the feed rate is too large.The alloy is deformed before it has time to flow,so the equivalent strain of the cup with a feed rate of 0.5 mm/s is reduced.In traditional reverse extrusion,the metal flow law at the bottom mainly flows from the center of the billet to the surrounding in the radial direction,and the wall only performs rigid translational motion,while in the rotational reverse extrusion deformation,the bottom area performs a circular motion under the rotation of the die.,due to the addition of shear deformation to the rotational anti-extrusion deformation,the accumulated strain of the metal is increased,the deformation dead zone is eliminated,and the structure is more uniform.In addition,the inner cup wall of the traditional reverse extrusion cup has an inclination of 30° to the ED direction,and the rotating reverse extrusion has no similar phenomenon due to centrifugal force.In the process of rotary back extrusion,the bottom area(equiaxed area,elliptical area and corner area)is combined by two recrystallization mechanisms of discontinuous dynamic recrystallization and continuous dynamic recrystallization,while in the wall area(inner wall,outer wall)Only discontinuous dynamic recrystallization is formed,which is due to the fact that the stress state at the bottom of the cup promotes the initiation of the intragranular slip system.In the process of rotary back extrusion deformation,the grains can be refined and the dynamic recrystallization ratio can be increased.The microhardness of different areas of the rotary reverse extrusion cup is higher than that of the traditional reverse extrusion,which is mainly due to the fine grain strengthening;the hardness value under the two deformation methods at 480 °C is lower than the hardness value at 400 °C,which is Since more dynamic recrystallization occurs at 480 °C,the dynamic recrystallization consumes dislocations,and the dislocation density decreases,which reduces the hardness.However,the cup with a feed rate of 0.5mm/s increases the dynamic recrystallization ratio and weakens the texture due to the high feed rate,resulting in a decrease in hardness compared with the cup with a hardness of 0.1mm/s.