Research On Extrusion Flow Behavior And Solution Treatment Of 7055 Helical Aluminum Alloy Profile

As the core components of mechanical supercharger,screw compressor and spiral rotor flowmeter,helical rotor is widely used in automobile,machinery,chemical,metallurgy and other important fields.At present,the helical rotor is mainly manufactured on the basis of various as-cast or forged steel bars,which are formed by traditional machining(such as grinding,planer,etc.).Low processing efficiency,waste of materials and high production cost of this traditional method do not meet the developing needs of lightweight equipment.Extrusion forming can make the material form in a short time,which not only improves the utilization of raw materials,but also has higher processing efficiency and economic benefits than traditional machining.Hhigh strength 7x x x series aluminium alloys have low density,high specific strength and stiffness and can be recycled.Its extruded parts have been widely used in aircraft,ships,vehicles and other manufacturing fields.The high performance 7xxx series helical aluminium alloy profiles are hot extruded by special dies,which has great significance in reducing the weight of parts and improving production efficiency.Now the kind of extrution process has attracted great attention of scholars at home and abroad.Compared with 6xxx series aluminium alloy,7××× series aluminium alloy is more difficult to extrude because of its poor formability,so there is great challenge for the design of extrusion die and the determination of extrusion process of the helical rotor.In order to solve the above problems,the material flow behavior during extrusion of AA7055 helical profiles is systematically studied by combining numerical simulation with experimental research.The effects of different solution treatment processes on the microstructure,mechanical properties and corrosion properties of AA7055 are revealed.The main contents and conclusions are as follows:(1)The extrusion die of AA7055 helical profile is designed and the extrusion process is simulated by DEFROM 3D.Based on the FE simulation,the flow behavior during the helical extrusion process is studied.Then the extrusion die is manufactured and the extrusion experiment is successfully carried out.The AA7055 helical profile with high geometric accuracy is obtained.(2)For AA7055 helical profile,the effects of single-stage solution temperature and time on the microstructure,mechanical properties and corrosion properties of the profile are investigated.The experimental results show that when the solution temperature is 470? and the holding time is 60 minutes,the second phase dissolves reasonably and the proportion of grain boundaries with small misorientation is relatively high.The optimum mechanical properties and corrosion properties are obtained at this time.(3)Two-stage solution treatment,high temperature pre-precipitation and step solution treatment experiments are carried out for AA7055 helical profile.The experimental results show that the strength of the helical profile after double solution treatment is improved by further dissolving the second phase.The optimum comprehensive performance experimental scheme is 460?/15min+480?/15min.Its corrosion resistance is greatly improved by high temperature pre-precipitation treatment,but the mechanical properties are obviously reduced.Comparing with high temperature pre-precipitation,the similar corrosion resistance of the alloy can be obtained by step solution treatment without decreasing the mechanical properties.