Research On Composite Rotary Extrusion Forming Process Of VW124A Alloy Billet

Magnesium alloy materials have unique performance characteristics and have wide application value in aerospace,transportation,electronic communications,weapons and other fields.The preparation of ultra fine grained magnesium alloy materials using large plastic DEFORMation methods and the development of new large plastic DEFORMation processes have become research hotspots in the field of material processing.Currently,sheet metal is mostly formed by rolling,but its application range is limited due to small pass DEFORMation,multiple passes,uneven DEFORMation,easy to generate edge cracks,and large anisotropy.As a new type of large plastic DEFORMation method,rotary forward extrusion has many advantages,such as no change in the cross section of the blank,high material utilization,low anisotropy,and strong grain refinement.It has unique advantages in the forming of magnesium alloy sheets.Aiming at the problems existing in plate rolling,based on normal forward extrusion,this paper proposes a method of rotary forward extrusion forming with severe plastic DEFORMation.This method forms a new type of rotary forward extrusion mold cavity through the combination of the press twist section and the press shear section.During the DEFORMation process,a series of continuous composite plastic DEFORMations occur in the blank,continuously accumulating large plastic strains,achieving the goal of uniformly refining the structure and improving material properties.On the basis of the new rotary forward extrusion process,a new composite rotary extrusion process was discovered by inserting a mandrel into the punch.This process is a combination of the rotary backward extrusion process and the rotary forward extrusion process,aiming to further change the internal properties of the material.Currently,there are no reports on the production of plates using these two new processes.In this paper,DEFORM-3D software was used to numerically simulate the composite rotary extrusion process of VW124 A rare earth magnesium alloy.The effects of mold cavity structure,DEFORMation process parameters,and different DEFORMation amounts on the forming process were systematically studied.The design of mold cavity structure is the primary issue in the research of composite rotary extrusion forming methods.Optimizing the mold cavity structure will effectively improve the uniform DEFORMation effect.In this paper,15 sets of mold cavity structures were created by creating a "cross" trapezoidal groove on the punch,a "cross" circular groove on the mandrel,and multiple "ring shaped" grooves on the curvature shear surface of the concave mold 2(with their cross-sectional openings in a ladder like shape).The simulation results were systematically compared and studied from the aspects of extrusion load,metal fluidity,equivalent stress,equivalent strain,point tracking,and organization.The results show that the mold cavity is the best choice when the convex mold trapezoidal groove and the concave mold type 2 trapezoidal groove meet the requirements of g=1.67 and k=1.5;the oblique angle is 70°;the wave peak height under the trapezoidal mold type groove is 6mm),the mandrel circular groove(radius 7.5;transition arc radius 7.5),and the concave mold type2 shear surface(curvature control flow rate is the same).DEFORMation process parameters are one of the main factors affecting DEFORMation behavior.In this paper,mixed orthogonal experiments were used for statistical analysis to clarify the range of process parameters.The effects of different extrusion temperatures,extrusion speeds,and rotational speeds on the rotary extrusion process of VW124 A rare earth magnesium alloy were studied through a numerical simulation system,and compared with composite rotary extrusion.The results show that the optimal process parameters for composite rotary extrusion are: extrusion temperature 460°C,extrusion speed 0.8mm/s,and rotation speed 0.067mm/s.The strain uniformity of the slabs formed by rotary forward extrusion is good.The composite rotary extrusion process has the ability to form slabs with large dynamic recrystallization volume fractions at low temperatures,stable loads,and large strains.Both processes can prepare ultra-fine grained materials,but there are differences in the magnitude of strain at the edges and centers of the slabs.The strain uniformity and anisotropy of composite rotary extrusion formed slabs were studied under different pressing amounts and rotation times.When the mandrel was pressed120 mm and the rotation time was 60 seconds,excellent strain uniformity and low anisotropy were obtained.It was found that good uniformity and low anisotropy can also be obtained by rotary forward extrusion when the punch is pressed for 15 mm and the rotation time is 100 s,and physical experiments have been carried out to verify this.