Plastic Flow Law And Mechanism Of Extrusion Forming Of High-strength Al-uminum Alloy Variablesection Structure

Lightweight is an important means for aviation equipment to save energy and reduce emissions and improve maneuvering characteristics.The technical ways to achieve lightweight include the use of high-performance light alloy materials,currently mainly aluminum,magnesium,titanium,etc.,and the use of lightweight structural forms,such as variable-section thin-walled structures.Among them,the use of variable section structure is one of the important technical ways to achieve lightweight.The variable section structure consists of a constant section part and a transition zone.According to the length of the transition zone,the variable section structure includes stage variable section and gradual change section,aluminum alloy variable section pipe usually uses extrusion forming for equal section structure,and then the cost of secondary processing is increased after extrusion,and there are multiple sets of detachable die extrusion,which is used in different molds in different constant sections,this method requires stopping and changing the mold during the extrusion process,resulting in large time consumption,low production efficiency,poor process efficiency,and seriously restricts the application of variable section structure.Therefore,this paper proposes a forming method to achieve continuous variable section extrusion by moving the perforated needle.2A12 aluminum alloy is a typical hard aluminum alloy in the Al-Cu-Mg series,which is characterized by high strength,good shaping and good heat resistance,because it has excellent processing performance,using special processes can be welded and riveted.It has been widely used in aerospace structures,rivets,hubs.Since 2A12 aluminum alloy is an unsteady process in the process of extrusion of variable cross-section,it is very important to study the influence of 2A12 aluminum alloy in the extrusion process of variable section under different process parameters.The thermal deformation behavior of 2A12 aluminum alloy at different deformation temperatures of 325 °C～450 °C and strain rate of 0.001s-1～5s-1was studied by thermal compression experiment,the flow stress change characteristics in the hot compression process were analyzed,and a constitutive model describing the flow stress change of 2A12 aluminum alloy was established based on the Arrhenius hyperbolic sinusoidal function.By analyzing the change law of strain hardening index,strain rate sensitivity index and microstructure under different deformation conditions,the mutual influence law between them is obtained.The thermal processing diagram of 2A12 aluminum alloy was established,and the evolution of microstructure under different deformation parameters was analyzed,and the mechanism of shaping and deformation was revealed,the instability zone and the better hot working area of2A12 aluminum alloy were clarified,and then the better hot working parameters were determined.In this study,Deform finite element simulation analysis software was used to carry out the preliminary design of the mold according to the principle of variable section extrusion,and the finite element simulation analysis of the variable section extrusion process of 2A12 aluminum alloy was carried out,and the influence of continuous change of extrusion ratio on the temperature distribution,stress field,strain field and material flow of the blank at the mold outlet was revealed.The changes of strain field,temperature field and stress field at different constant section outlets of different process parameters(starting temperature,extrusion belt length,mold cone angle and extrusion speed)were discussed,and the influence of different process parameters on the forming load of extrusion mold was discussed.