A Study Of The Dramatic Deformation Of Large-size Light Alloy Materials By Extrusion Upsetting"

Lightweighting of equipment is an everlasting theme in aerospace and defense field,and lightweighting has high requirements on materials and properties.Light alloys have the advantages of light weight and strong corrosion resistance,and the research focuses on improving the material properties.At present,to enhance the material properties mainly through solid solution strengthening,work hardening,fine grain strengthening and the second phase strengthening four kinds of strengthening methods.Fine-grain strengthening is the only way to improve strength and toughness at the same time.Severe plastic deformation has received widespread attention because of its strong grain refinement.At present,the commonly used severe plastic deformation includes high-pressure torsion,equal-channel angle extrusion,multidirectional forging,reciprocating upsetting and reciprocating extrusion,etc.However,at present,the above mentioned methods are unable to prepare large-size workpieces.In view of the above bottlenecks,the method of "extrusion heading" dramatic deformation was proposed.The extrusion and upsetting dramatic deformation method is a method to synchronize the extrusion and upsetting deformation in the same process.For the lower cavity height size is large,forming parts are easy to produce folding defects,using back pressure control axial isokinetic flow extrusion and diameter ratio unrestricted(no diameter ratio restriction near uniform)upsetting of the two large deformation way fusion,in the extrusion of the bar into the mold cavity synchronization upsetting deformation,so that large size material to produce dramatic plastic deformation,to improve the material uniform toughening.At present,there are still a lot of content for this method needs to be studied,the establishment of mechanical calculation model,for the deformation process of equipment selection to provide support;the need for the forming process of metal flow law research,to realize the process of regulation,to avoid defects.In this paper,the mentioned problems are studied.Through numerical simulation,the effect of back pressure on the metal flow in the deformation process of extrusion upsetting was investigated,the mechanism of folding defects and uneven deformation defects in the deformation process of extrusion upsetting was analyzed,and the corresponding defect suppression methods were proposed.FEM was used to study the influence of billet diameter,forming diameter and friction factor on the forming load.By analyzing the metal flow law,the boundary condition assumption of thick-walled cylinder upsetting was proposed,and the principal stress method was adopted to establish the mechanical equilibrium equations of the unit body and derived the load solving model of extrusion upsetting.AZ80 Mg alloy and VW124 A Mg alloy were used to carry out physical tests to verify the load model and provide theoretical basis for equipment selection.The effects of die slope,radius of fillet,radius of concave die and diameter of concave die on the forming load and forming quality of the dramatic deformation of "extruded header" were studied without and under back pressure,and the optimal parameter combinations were obtained.Under the optimal parameter combination,the billet diameter,extrusion fillet radius and extrusion taper angle were further optimized to get the best die parameters,which provide some guidance for the design of tooling and dies.The effects of constant backpressure,velocitydependent backpressure,area-dependent backpressure,linear loading backpressure and sectional loading backpressure on the molding quality were comparatively investigated,and the mechanism of folding in the process was studied.The optimum parameters of each process were selected and compared,and the optimum solution of the optimum loading method was obtained,which provided a certain significance for controlling the deformation process of extrusion upsetting.The influence of downward pressure speed,deformation temperature and friction factor on forming load and forming quality was studied,and the response surface method and BP neural network prediction model were established to provide guidance for production practice.AZ80 Mg alloy and VW124 A Mg alloy were used to verify the load model of the dramatic deformation of "extrusion heading".6061 Al alloy and VW124 A Mg alloy were used to verify the selected constant force and segmental loading mode.According to the simulation results,the effect of strain on the organization was studied in the corresponding area of the pick-up ring.At the same time,the high performance of the molded parts by this process was verified according to the mechanical properties.