Optimization Design Of 7075 Aluminum Alloy Flat Extrusion Die And Research On Microstructure And Mechanical Property Of Extruded Profiles

7075 aluminum alloy is widely used in aerospace,automobile,high-speed train and other industrial fields due to its high strength,high toughness,good corrosion resistance and easy machining.The hot extrusion is the main forming process for producing aluminum alloy profiles with certain cross-section,and it also has the advantages of high production efficiency and excellent product quality.Flat extrusion die is mainly used in producing solid aluminum alloy profiles.The reasonable die design and process parameter are conducive on improving production efficiency and obtaining high performance aluminum alloy products.At present,there are relatively few reports on the flat extrusion of high strength 7075 aluminum alloy.There are still a series of technical difficulties in the die structure design,process parameter selection,microstructure and performance control,and the systematic scientific theory has not been constructed.Hence,it is difficult to provide guidance for the actual production of high strength aluminum alloy profiles.This study focused on the flat die extrusion process of 7075 aluminum alloy based on numerical simulation and experiments.The multi-objective optimization of feeder chamber was researched.The microstructure characteristics and evolution of 7075 aluminum alloy during flat extrusion was clarified.The influence of the process parameters such as extrusion temperature and extrusion speed on the microstructure and mechanical properties was studied.Moreover,the paper proposed the asymmetric feeder structure and introduced it to the flat extrusion of 7075 aluminum alloy,and obtained good application results.This study is helpful to enrich the extrusion forming theory of high-strength aluminum alloy,and realize the coordinating control of shape and property of high-strength aluminum alloy profiles,which have important theoretical significance and engineering application value.The main research contents and conclusions of this paper are listed as follows:(1)The numerical model of material flow and die strength for flat extrusion process of 7075 aluminum alloy were established.The multi-objective optimization experiment matrix was designed by regarding the key structure parameters of feeder as the design variables,and the standard deviation of the velocity field(SDV),die maximum displacement(Dis)and maximum extrusion force(F)as the optimization goal.The function relationship between the design variables and the optimization goal was constructed based on the simulation results and the optimal feeder structure was obtained by applying particle swarm optimization algorithm.After optimization,the radius of the circular arc at both ends of feeder R=16mm,the middle width W=18mm,and the center distance of the circular arc at both ends L= 60mm.Compared with the initial structure design,the SDV at the outlet of the bearing was decreased by 65.7%,the Dis of the die esd decreased by 22.0%,and the F was decreased by 36.7 tons.(2)The flat die extrusion experiment of 7075 aluminum alloy was carried out based on the optimized feeder and the horizontal extruder.The experimental results showed that the grain morphology of the extruded 7075 aluminum alloy profile presented obvious fibrous characteristics.The coarse grains were elongated along the extrusion direction(ED),and some fine equiaxed grains distributed among the deformed grains,indicating the occurrence of dynamic recovery(DRV)and partial dynamic recrystallization(DRX).The strong Brass,S and Copper textures existed in the profiles,and some Cube texture was generated due to the occurrence of DRX.The tensile properties of the profiles along 0°,45° and 90° are different,indicating the anisotropy of the extruded 7075 aluminum profiles.(3)Several groups of flat extrusion experiments of 7075 aluminum alloy were carried out under the conditions of different extrusion temperatures and speeds,and the microstructure and mechanical properties of the extruded profiles were analyzed.The results showed that DRV was the main softening mechanism during flat extrusion of 7075 aluminum alloy.However,with the increase of extrusion temperature or extrusion speed,the degree of DRX was increased gradually.A large number of fine MgZn2 phases existed in the aluminum matrix,and the deformed grains showed strong Brass and S textures,as well as some weak Cube,A,Copper and Goss textures.When the extrusion temperature increases or extrusion speed decreases,the texture strength decreased gradually.Compared with the extrusion temperature,extrusion speed had more significant effects on the mechanical properties of extruded profiles.(4)The extrusion experiment and numerical simulation of 7075 aluminum alloy were carried out using the flat die without feeder,and with symmetrical or asymmetric feeders.The results showed that the utilization of the feeder structure increased the strain on the cross-section of the profile and decreased the strain rate of the material inside die cavity.If there was no feeder,the DRX degree of the profile is higher,while the asymmetric feeder resulted higher DRV degree,and the structure of the feeder has a great influence on the second phase and texture type.The utilization of feeder was helpful to improve the elongation of profiles,and the asymmetric feeder reduced the anisotropy of profiles and improved the elongation of profiles effectively.